Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

JoeFaeGlesga wrote:
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

The right way to do this is to drill holes in the centers of the joists,
and route all the cables through them.
However, barring a rewire, this probably isn't possible.

The trivial way is to take some wood of the same width as the joist, and
1/2" thick or so, and apply over the existing joists, not covering where
you want the cables.
This can be bits of the flooring chipboard or whatever.

The better way is to do this with 2" thick (or more - depending on the
thickness of your existing beams) of the same width as your joists, the
full width of the attic (removing a couple of tiles may make it easy to
get these in).

Take these beams, notch the bottom of them where the cables are needed
to pass through, then glue and screw to the existing beams.
This gives extra space for insulation, and makes the beams much firmer.

"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to accommodate
the recommended depth of insulation. What I'm planning to do with mine is
fit 8"x2" (8" side vertical) at right angles to the existing joists, 370mm
apart. This conveniently allows the lighting electrics to be left as-is.
There's enough slack to allow it to be moved aside where necessary. I'll
then fit insulation, then put chipboard over it. That'll give me 11" of
insulation (270mm is recommended, this is a little more) and all the storage
I need.

If you want to re-wire, allow 1-3 weekends (depending on house size), a reel
of 1mm sq T&E and maybe some junction boxes. It's not hard assuming you
understand a) how a lighting circuit is set up, b) how your particular house
has been done & c) are competent!

Mark

MarkK wrote:
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of
cables crossing the beams. Obviously whoever rewired the house
didn't really use the loft so just threw the cables wherever to get
to their destination. IS it a difficult job to reroute these along
joists etc. Was maybe going to get a spark into do it but no idea
the complexity of th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate the recommended depth of insulation. What I'm planning to
do with mine is fit 8"x2" (8" side vertical) at right angles to the
existing joists, 370mm apart. This conveniently allows the lighting
electrics to be left as-is. There's enough slack to allow it to be
moved aside where necessary. I'll then fit insulation, then put
chipboard over it. That'll give me 11" of insulation (270mm is
recommended, this is a little more) and all the storage I need.

8 X 2??????????

Why are you cutting your loft space down, adding a load of extra weight,
creating lots more work and generally making a complete hash of it? - why
not just use 2X2? - all the weight is going onto the bedroom ceiling joists
anyway, adding all this extra weight will cause cracking of the
ceilings....your ideas WRT insulation aren't good neither, putting
insulation over the cables is bad...if you do go ahead with the 8X2's, just
leave the gap underneath as it is....if you want more insulation up there,
just thread it under each cable prior to putting cross joists in.


To the OP: just use 2X2 or 3X2's at right angles to the existing joists, lay
chipboard on it, enjoy.

"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine is
fit 8"x2" (8" side vertical) at right angles to the existing joists, 370mm
apart. This conveniently allows the lighting electrics to be left as-is.
There's enough slack to allow it to be moved aside where necessary. I'll
then fit insulation, then put chipboard over it. That'll give me 11" of
insulation (270mm is recommended, this is a little more) and all the
storage
I need.

If you want to re-wire, allow 1-3 weekends (depending on house size), a
reel
of 1mm sq T&E and maybe some junction boxes. It's not hard assuming you
understand a) how a lighting circuit is set up, b) how your particular
house
has been done & c) are competent!

Mark


Mark,

Is there a reason you're choosing 8" deep, aside from making your total
depth 11"??
I'm kinda doing the same thing, but wasn't planning on doing it at right
angles to the existing joists (which are 4" deep and only 1.5" wide :S).
Are there advantages to strengthening rafters at right angles?? I was only
going to add an extra 2" in height to cope with about 5 pipes from the CH
system that run through mine. I guess I'm kind of worried about losing head
room!! (I'm tall.. there's not a lot to start with!!)
Now I'm thinking upping the insulation from 4" to 6" isn't really good
enough!!

Regards,
_____________________________
The Christmas Grimch

The Grim Reaper wrote:
"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine is
fit 8"x2" (8" side vertical) at right angles to the existing joists, 370mm
snip

Is there a reason you're choosing 8" deep, aside from making your total
depth 11"??

I suspect lack of payback calculations.
Taking as am example my loft, it's got 6" of rockwool, with 6*2" beams at
24" centers, what's the average power leaving through the ceiling?

Let's call the roof area 100m^2 of rockwool, and 8m^2 of wood.
Assuming 10C difference, the rockwool loses around 2.6W/m^2, and the
wood about 8W/m^2, or 260W + 64W.

(Average U value of 3.2)

Call it 320W.

My initial suggestion was to add 2" along the beams.
This will drop the heating requirements by a third, to 200W, and will
use around (assumign timber is 300 quid per cubic meter) 120 quid of
timber, and 100 pounds of rockwool.

Putting the 2" beams crosswise is better than this, but not a whole lot,
as the rockwool dominates the heat loss by a factor of 4:1, so if you
put the second layer crosswise, you gain relatively little.
I did not do the exact numbers, but they will be around 180W.

Adding another whopping 8" of rockwool and wood will cost around 800
quid, and save another 90W.

90W, assuming it's on-peak electricity used to heat it will cost about
25p/day to heat, and will payback in 10 years, neglecting interest.

With interest, or with off-peak electricity, or gas heating, it will
almost certainly not pay back ever.

I'm kinda doing the same thing, but wasn't planning on doing it at right
angles to the existing joists (which are 4" deep and only 1.5" wide :S).
Are there advantages to strengthening rafters at right angles?? I was only

No. It is almost always worse to do this, unless the only load up there
ever will be sparse point loads.

If the loading is 'stuff spread at random', then adding a ton of wood up
there which does not add strength is not going to help with ceiling
cracking from the load of stuff up there.
It will help with ceiling cracking from people moving around.

It adds no strength in the short direction, only spreads the load.

going to add an extra 2" in height to cope with about 5 pipes from the CH
system that run through mine. I guess I'm kind of worried about losing head
room!! (I'm tall.. there's not a lot to start with!!)
Now I'm thinking upping the insulation from 4" to 6" isn't really good
enough!!

4" to 6" is a worthwhile upgrade.
6" to 8" is quite debatable, but probably worth it if it's very cheap.
8" - unless you are going to be on electric heating forever, probably
not.

If you are doing the gluing + screwing thing, then for best results,
support the joist you are doing in the middle, with a hoist, to push it
upwards with a force of 50Kg or so, then work from the adjacent beam to
attach the 2*2 - lots of screws and enough glue. This pretensions the
beam, so that the new composite beam has a long way to sag before cracks
appear.

A nice plane, to plane the top of the joists smooth is probably a good
idea, as it will mean you need lots less glue, and get a better stronger
joint.

Ian Stirling wrote:
The Grim Reaper wrote:

"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
groups.com...

Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine is
fit 8"x2" (8" side vertical) at right angles to the existing joists, 370mm

snip

Is there a reason you're choosing 8" deep, aside from making your total
depth 11"??


I suspect lack of payback calculations.
Taking as am example my loft, it's got 6" of rockwool, with 6*2" beams at
24" centers, what's the average power leaving through the ceiling?

Let's call the roof area 100m^2 of rockwool, and 8m^2 of wood.
Assuming 10C difference, the rockwool loses around 2.6W/m^2, and the
wood about 8W/m^2, or 260W + 64W.

(Average U value of 3.2)

Call it 320W.

My initial suggestion was to add 2" along the beams.
This will drop the heating requirements by a third, to 200W, and will
use around (assumign timber is 300 quid per cubic meter) 120 quid of
timber, and 100 pounds of rockwool.

Putting the 2" beams crosswise is better than this, but not a whole lot,
as the rockwool dominates the heat loss by a factor of 4:1, so if you
put the second layer crosswise, you gain relatively little.
I did not do the exact numbers, but they will be around 180W.

Adding another whopping 8" of rockwool and wood will cost around 800
quid, and save another 90W.

90W, assuming it's on-peak electricity used to heat it will cost about
25p/day to heat, and will payback in 10 years, neglecting interest.

With interest, or with off-peak electricity, or gas heating, it will
almost certainly not pay back ever.


I'm kinda doing the same thing, but wasn't planning on doing it at right
angles to the existing joists (which are 4" deep and only 1.5" wide :S).
Are there advantages to strengthening rafters at right angles?? I was only


No. It is almost always worse to do this, unless the only load up there
ever will be sparse point loads.

If the loading is 'stuff spread at random', then adding a ton of wood up
there which does not add strength is not going to help with ceiling
cracking from the load of stuff up there.
It will help with ceiling cracking from people moving around.

It adds no strength in the short direction, only spreads the load.


going to add an extra 2" in height to cope with about 5 pipes from the CH
system that run through mine. I guess I'm kind of worried about losing head
room!! (I'm tall.. there's not a lot to start with!!)
Now I'm thinking upping the insulation from 4" to 6" isn't really good
enough!!


4" to 6" is a worthwhile upgrade.
6" to 8" is quite debatable, but probably worth it if it's very cheap.

8" - unless you are going to be on electric heating forever, probably
not.


If you are doing the gluing + screwing thing, then for best results,
support the joist you are doing in the middle, with a hoist, to push it
upwards with a force of 50Kg or so, then work from the adjacent beam to
attach the 2*2 - lots of screws and enough glue. This pretensions the
beam, so that the new composite beam has a long way to sag before cracks
appear.

A nice plane, to plane the top of the joists smooth is probably a good
idea, as it will mean you need lots less glue, and get a better stronger
joint.

Ian, I have been absolutely fascinated by this thread (we are hopefully
moving to a 1920s house with poor loft insulation/ boarding, amongst
other slight problems) and it is clear that you know what you are
talking about.

Can I ask you how you work out these values of heat loss? Please don't
think that I am trying to find fault but rather that I would like to do
calculations like yours for our new property.

OK, I can google but if you can provide a trusted link or reference that
would give me the necessary information to do the calculations myself
that would be even better.

It seems that there is clearly a diminishing law of returns here, as in
most things to do with physics - once we are in the new place it would
be nice to put some numbers into the equation.

Thanks

Steve.

Ian Stirling wrote:

The right way to do this is to drill holes in the centers of the joists,
and route all the cables through them.

Ceiling joists in lofts are often only 100 mm deep, so you can't do that
and comply with wiring regs. Where an unprotected cable passes thro' a
drilled hole in a joist it must be at least 50 mm above the bottom (if
there is a ceiling below) and below the top (if there is a floor above).

You're OK if the joists are 125 mm or more, or if the cable is protected
in earthed steel conduit, or if you can use those protection plates that
TLC sell:
http://www.tlc-direct.co.uk/Main_Ind...ion/index.html

--
Andy

Steve wrote:
snip
Ian, I have been absolutely fascinated by this thread (we are hopefully
moving to a 1920s house with poor loft insulation/ boarding, amongst
other slight problems) and it is clear that you know what you are
talking about.

Can I ask you how you work out these values of heat loss? Please don't
think that I am trying to find fault but rather that I would like to do
calculations like yours for our new property.

Unfortunately, the hard way.

OK, I can google but if you can provide a trusted link or reference that
would give me the necessary information to do the calculations myself
that would be even better.

It seems that there is clearly a diminishing law of returns here, as in
most things to do with physics - once we are in the new place it would
be nice to put some numbers into the equation.


Unfortunately, I have not found a 'nice' solution that works for me -
say javascript/java, pick your construction, specify depths, ...

I did it the hard way.
google for
BS EN ISO 6946:1997 examples

http://www.thenbs.com/BuildingRegs/k...DOMEST_6_6_0_1

looked interesting.

and that will turn up examples of how to calculate the U value, to the
1997 BS standard - which is slightly out of date, but nothing much has
changed, and is fine for indicative purposes.

Basically.
Thermal conductances - measured in w/m/k give the number of watts that
a cube one meter in dimension will pass, per kelvin (or centigrade)
difference across the opposite faces.

For example, stone is about 1.2, rockwool and many other insulators
(polystyrene, compressed straw, wool) about 0.04, kingspan 0.02, wood
0.15.

If you have a tenth of a square meter, it passes a tenth as much heat.
If the wall is a tenth of a square meter thick, then it passes 10 times
the heat.

U value - the number of watts per square meter that a structural element
will pass given a 1C difference.

For monolithic structures, this is just the conductance divided by the
thickness (in meters) - for example 50mm of kingspan has a thermal
conductance of .02 w/w/m / 0.05m = 0.4W/m^2/k

(Or 4 watts per meter square, at a temperature difference of 10C)

For stone, with a conductance of 1.2, you need 3 whole meters (1.2 / 3 =
0.4) to get a U value similarly.

Stone sucks (heat).


Now, it gets more complex.

You can't simply add U values of multiple elements in a wall - as that
would mean that adding another identical element onto the side of this
one would double the heat loss, which is obviously wrong.

You've got to convert into R values, which are the inverse of U values
(R value = 1/U value), then add these, then convert back to U values by
the same manner.

This all works find for homogenous walls.

It gets complex when you consider plasterboard + lath, with insulation
between.

A simple way is to consider these as two seperate structures - in the
last post I made, I used the example of 100m^2 of rockwool, and 8m^2 of
wood - as 1/12th of the area of my example ceiling was wood.

So, simply
((U value of rockwool) * rockwool area ) * ((U value of wood) * wood area)

--------------------------------------------------------------------
total area

= composite U value.


R values can be thought of as the area that will pass one watt, with a
difference of 1C across the structure.

Hope this helps.

Ian Stirling wrote:
Steve wrote:
snip

Can I ask you how you work out these values of heat loss? Please don't
think that I am trying to find fault but rather that I would like to do
calculations like yours for our new property.


Unfortunately, the hard way.


OK, I can google but if you can provide a trusted link or reference that
would give me the necessary information to do the calculations myself
that would be even better.

It seems that there is clearly a diminishing law of returns here, as in
most things to do with physics - once we are in the new place it would
be nice to put some numbers into the equation.



Unfortunately, I have not found a 'nice' solution that works for me -
say javascript/java, pick your construction, specify depths, ...

I did it the hard way.
google for
BS EN ISO 6946:1997 examples

http://www.thenbs.com/BuildingRegs/k...DOMEST_6_6_0_1

looked interesting.

and that will turn up examples of how to calculate the U value, to the
1997 BS standard - which is slightly out of date, but nothing much has
changed, and is fine for indicative purposes.

Basically.
Thermal conductances - measured in w/m/k give the number of watts that
a cube one meter in dimension will pass, per kelvin (or centigrade)
difference across the opposite faces.

For example, stone is about 1.2, rockwool and many other insulators
(polystyrene, compressed straw, wool) about 0.04, kingspan 0.02, wood
0.15.

If you have a tenth of a square meter, it passes a tenth as much heat.
If the wall is a tenth of a square meter thick, then it passes 10 times
the heat.

U value - the number of watts per square meter that a structural element
will pass given a 1C difference.

For monolithic structures, this is just the conductance divided by the
thickness (in meters) - for example 50mm of kingspan has a thermal
conductance of .02 w/w/m / 0.05m = 0.4W/m^2/k

(Or 4 watts per meter square, at a temperature difference of 10C)

For stone, with a conductance of 1.2, you need 3 whole meters (1.2 / 3 =
0.4) to get a U value similarly.

Stone sucks (heat).


Now, it gets more complex.

You can't simply add U values of multiple elements in a wall - as that
would mean that adding another identical element onto the side of this
one would double the heat loss, which is obviously wrong.

You've got to convert into R values, which are the inverse of U values
(R value = 1/U value), then add these, then convert back to U values by
the same manner.

This all works find for homogenous walls.

It gets complex when you consider plasterboard + lath, with insulation
between.

A simple way is to consider these as two seperate structures - in the
last post I made, I used the example of 100m^2 of rockwool, and 8m^2 of
wood - as 1/12th of the area of my example ceiling was wood.

So, simply
((U value of rockwool) * rockwool area ) * ((U value of wood) * wood area)

--------------------------------------------------------------------
total area

= composite U value.


R values can be thought of as the area that will pass one watt, with a
difference of 1C across the structure.

Hope this helps.


Thanks very much for the information and the web link Ian.

I have saved this and bookmarked the page for future use.

The explanation you give has helped me to understand the principle as
well as the actual calculations.

I am now looking forward to spending some time (when I have some :-( )
putting some numbers in...

Cheers

Steve

"Ian Stirling" wrote in message
...
The Grim Reaper wrote:
"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of
cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity
of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine
is
fit 8"x2" (8" side vertical) at right angles to the existing joists,
370mm
snip

Is there a reason you're choosing 8" deep, aside from making your total
depth 11"??

No.

I suspect lack of payback calculations.

Correct. I have relied on the advice of the energy savings trust, which
recommends 270mm:
http://www.est.org.uk/myhome/insulation/loft/. I simply haven't considered
the payback period and don't think it's relevant. You don't question
building regs when you build something that has to comply, and I have taken
270mm as a standard that I wish to comply with.

Taking as am example my loft, it's got 6" of rockwool, with 6*2" beams at
24" centers, what's the average power leaving through the ceiling?

Let's call the roof area 100m^2 of rockwool, and 8m^2 of wood.
Assuming 10C difference, the rockwool loses around 2.6W/m^2, and the
wood about 8W/m^2, or 260W + 64W.

(Average U value of 3.2)

Call it 320W.

I've already bought Knauf Space Blanket, the 200mm version, so payback
calculations are somewhat academic as the cost (£300 for 60 rolls, or 108m
sq) has been sunk. Its R-value is 4.50m sq. K/W and thermal conductivity is
0.044 W/MK.

In your calculations you've made a number of assumptions. A 10 degree
difference is probably relevant for Oct, Nov, Mar, Apr. 5 degrees Sept &
May. 15 degrees Dec, Jan, Feb. Roughly.

Significantly more energy is required to keep a house warm in the coldest
months, which is probably why the EST recommends 270mm and why your 10
degree assumption has led you to something different. However, without your
workings it's hard to be sure.

You don't say whether you've allowed for the efficiency of the heating
system in terms of the cost per kWh. A condensing boiler like mine can get
up to about 90%, but it won't be at that level all the time. Shall we assume
75%? And that all 75% warms the house, i.e. that once the energy is
transferred to the water it is then transferred to the house without waste?
Any inefficiency will effectively increase the effective cost per kWh and
therefore reduce the payback period.

You can reduce the wood area you used significantly, as the whole point of
fitting it at 90 degrees is to minimise the area where heat can flow through
wood, which is a poor insulator.

Would you like to recalculate and show your workings?

My initial suggestion was to add 2" along the beams.
This will drop the heating requirements by a third, to 200W, and will
use around (assumign timber is 300 quid per cubic meter) 120 quid of
timber, and 100 pounds of rockwool.

Putting the 2" beams crosswise is better than this, but not a whole lot,
as the rockwool dominates the heat loss by a factor of 4:1, so if you
put the second layer crosswise, you gain relatively little.
I did not do the exact numbers, but they will be around 180W.

Adding another whopping 8" of rockwool and wood will cost around 800
quid, and save another 90W.

£800? £300 for insulation plus about £70 per room area. I'll do up to 4 of
these areas, so total spend will be about £580. However, I consider this to
be £300 on insulation and £280 on providing storage. Yes, storage would be a
little cheaper with less depth, but not hugely.

90W, assuming it's on-peak electricity used to heat it will cost about
25p/day to heat, and will payback in 10 years, neglecting interest.

With interest, or with off-peak electricity, or gas heating, it will
almost certainly not pay back ever.

Presumably invalid conclusions in my case due to wrong assumptions.

I'm kinda doing the same thing, but wasn't planning on doing it at right
angles to the existing joists (which are 4" deep and only 1.5" wide :S).
Are there advantages to strengthening rafters at right angles?? I was
only

No. It is almost always worse to do this, unless the only load up there
ever will be sparse point loads.

I've been worried about the weight, and considered spanning the structural
walls and supporting the timbers on them rather than just the ceiling
joists. This would be tricky, and I don't believe it is necessary as each
existing joist can support 75kg at its centre without detectable flex - they
feel very, very strong under foot. I'm therefore confident that I don't need
to do this. I have also discussed it with my neighbour who's a structural
engineer. Note that this is a 1950s house, so it's quite possible that the
timber used will be stronger than today's size equivalent. Loads of people
say that today's fast-grown softwoods aren't as good and they certainly rot
faster.

If the loading is 'stuff spread at random', then adding a ton of wood up
there which does not add strength is not going to help with ceiling
cracking from the load of stuff up there.
It will help with ceiling cracking from people moving around.

It adds no strength in the short direction, only spreads the load.

It'll add to the load, but spread it very effectively, particularly with 8"
joists! For logistical reasons, I'm doing above one room at a time, so can
monitor the effect and any downsides, like cracks in the ceilings. I doubt
I'll need the whole 100m sq for storage.

going to add an extra 2" in height to cope with about 5 pipes from the
CH
system that run through mine. I guess I'm kind of worried about losing
head
room!! (I'm tall.. there's not a lot to start with!!)
Now I'm thinking upping the insulation from 4" to 6" isn't really good
enough!!

4" to 6" is a worthwhile upgrade.
6" to 8" is quite debatable, but probably worth it if it's very cheap.
8" - unless you are going to be on electric heating forever, probably
not.

So the EST is wrong?

If you are doing the gluing + screwing thing, then for best results,
support the joist you are doing in the middle, with a hoist, to push it
upwards with a force of 50Kg or so, then work from the adjacent beam to
attach the 2*2 - lots of screws and enough glue. This pretensions the
beam, so that the new composite beam has a long way to sag before cracks
appear.

Makes sense in theory, but overkill unless you're going to turn it into a
habitable space. I also doubt that 50kg of upwards tension would introduce
more than a miniscule amount of flex, and hence would not make a difference
once released after glueing & screwing. Have you tested this theory at all?

A nice plane, to plane the top of the joists smooth is probably a good
idea, as it will mean you need lots less glue, and get a better stronger
joint.

Double overkill! A really nice way to do it if you need the strength, but
think about the time involved. How do you value your time, what's the
opportunity cost (e.g. other jobs delayed) and what's the payback period?
;-)

Mark

MarkK wrote:

big snipola

The EST are frequently worng, when I started installing insulation about 16
years ago, they reccomended 80mm,then it went to 100mm then after a few
years it went to 150mm, then 200mm, then 250mm now it's actually 300mm
according to building regs and cross laid, IE 150mm between joists and 150mm
crossways, covering the joists.

and another point to note - you don't need 200mm joists to fit in 200mm
insulation - it has a very similar U-value if compressed down to 100mm.

On Mon, 04 Dec 2006 14:10:38 GMT Phil L wrote :
and another point to note - you don't need 200mm joists to fit in
200mm insulation - it has a very similar U-value if compressed down
to 100mm.

Given that the insulant is the air trapped between the fibres, I find
this a somewhat doubtful suggestion.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

Tony Bryer wrote:
On Mon, 04 Dec 2006 14:10:38 GMT Phil L wrote :
and another point to note - you don't need 200mm joists to fit in
200mm insulation - it has a very similar U-value if compressed down
to 100mm.

Given that the insulant is the air trapped between the fibres, I find
this a somewhat doubtful suggestion.

Me too, until I visited Owens Corning and saw 1 inch fibreboard being made
from 300mm fibreglass and was told that the u-value was of 250mm
fibreglass.....they are used in oven manufacture

"Phil L" wrote in message
.uk...
Tony Bryer wrote:
On Mon, 04 Dec 2006 14:10:38 GMT Phil L wrote :
and another point to note - you don't need 200mm joists to fit in
200mm insulation - it has a very similar U-value if compressed down
to 100mm.

Given that the insulant is the air trapped between the fibres, I find
this a somewhat doubtful suggestion.

Me too, until I visited Owens Corning and saw 1 inch fibreboard being made
from 300mm fibreglass and was told that the u-value was of 250mm
fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

"Andy Wade" wrote in message
...
Ian Stirling wrote:

The right way to do this is to drill holes in the centers of the joists,
and route all the cables through them.

Ceiling joists in lofts are often only 100 mm deep, so you can't do that
and comply with wiring regs. Where an unprotected cable passes thro' a
drilled hole in a joist it must be at least 50 mm above the bottom (if
there is a ceiling below) and below the top (if there is a floor above).

What he is doing is increasing the depth of the joist by laminating another
joist on top by gluing screwing. Cutting out a small notch in the bottom of
the top joist will not (in most cases) infringe the figures you gave as this
hole will be in the centre of the new laminated beam.

"Ian Stirling" wrote in message
...
The Grim Reaper wrote:
"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine
is
fit 8"x2" (8" side vertical) at right angles to the existing joists,
370mm
snip

Is there a reason you're choosing 8" deep, aside from making your total
depth 11"??

I suspect lack of payback calculations.
Taking as am example my loft, it's got 6" of rockwool, with 6*2" beams at
24" centers, what's the average power leaving through the ceiling?

Let's call the roof area 100m^2 of rockwool, and 8m^2 of wood.
Assuming 10C difference, the rockwool loses around 2.6W/m^2, and the
wood about 8W/m^2, or 260W + 64W.

(Average U value of 3.2)

Call it 320W.

My initial suggestion was to add 2" along the beams.
This will drop the heating requirements by a third, to 200W, and will
use around (assumign timber is 300 quid per cubic meter) 120 quid of
timber, and 100 pounds of rockwool.

Putting the 2" beams crosswise is better than this, but not a whole lot,
as the rockwool dominates the heat loss by a factor of 4:1, so if you
put the second layer crosswise, you gain relatively little.

The reason insulation is counter laid is to cover the joists, which creates
a thermal bridge if not covered. The wood can amount to 10% of the loft
floor area - significant.

I did not do the exact numbers, but they will be around 180W.

Adding another whopping 8" of rockwool and wood will cost around 800
quid, and save another 90W.

90W, assuming it's on-peak electricity used to heat it will cost about
25p/day to heat, and will payback in 10 years, neglecting interest.

With interest, or with off-peak electricity, or gas heating, it will
almost certainly not pay back ever.

I'm kinda doing the same thing, but wasn't planning on doing it at right
angles to the existing joists (which are 4" deep and only 1.5" wide :S).
Are there advantages to strengthening rafters at right angles?? I was
only

No. It is almost always worse to do this, unless the only load up there
ever will be sparse point loads.

If the loading is 'stuff spread at random', then adding a ton of wood up
there which does not add strength is not going to help with ceiling
cracking from the load of stuff up there.
It will help with ceiling cracking from people moving around.

It adds no strength in the short direction, only spreads the load.

going to add an extra 2" in height to cope with about 5 pipes from the CH
system that run through mine. I guess I'm kind of worried about losing
head
room!! (I'm tall.. there's not a lot to start with!!)
Now I'm thinking upping the insulation from 4" to 6" isn't really good
enough!!

4" to 6" is a worthwhile upgrade.
6" to 8" is quite debatable, but probably worth it if it's very cheap.
8" - unless you are going to be on electric heating forever, probably
not.

If you are doing the gluing + screwing thing, then for best results,
support the joist you are doing in the middle, with a hoist, to push it
upwards with a force of 50Kg or so, then work from the adjacent beam to
attach the 2*2 - lots of screws and enough glue. This pretensions the
beam, so that the new composite beam has a long way to sag before cracks
appear.

A nice plane, to plane the top of the joists smooth is probably a good
idea, as it will mean you need lots less glue, and get a better stronger
joint.

Laminating the joists to create a thicker stronger joist is only necessary
if the joist are not supported beneath. Even Paramount walls have batons
floor to ceiling every 100mm which will support the joists of trusses above
to some degree.

Counter fixing joists above the existing joists at 90 degrees, that are
"well" screwed down, with chipboard over, which is "well" screwed down,
creates a pretty firm floor and unlikely that the older joists under would
sag - you create a sort of box girder out of the whole structure. The
counter joists and the chipboard creates racking and tightens the floor
right up. Best secure the ends of the counter joists into the gable if
possible.

On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:
http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034
http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to acheive a
U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use 200mm
joists in a case like this.

On Mon, 04 Dec 2006 17:54:52 GMT Phil L wrote :
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034

Those are the k values, the amount of heat W that will pass through
a 1m thickness for a 1C/1K temperature difference.

If you look at the resistance values 200mm of loft insulation has a
thermal resistance of 5.00, 25mm slabs 0.70/0.75

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:
http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034
http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to acheive
a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use 200mm
joists in a case like this.

What is the price? Cellotex has low U value and thin but look at the price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.

"Doctor Drivel" wrote in message
reenews.net...

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:

http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034

http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to
acheive
a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use
200mm
joists in a case like this.

What is the price? Cellotex has low U value and thin but look at the
price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.


Never thought I'd say this, but you talk much sense, Drivel. I don't think
anyone credible has come up with a valid reason for not doing what I
propose. The only question is whether 270mm is really necessary, which is
academic having spent the money, but I wouldn't mind seeing Ian's revised
calculations for curiosity if nothing else.

Mark

MarkK wrote:
"Doctor Drivel" wrote in message
reenews.net...

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as
250mm of fibreglass would be a dream product for loft converters
and the like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or
been bought out by) Knauff insulation has data sheets:

http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034

http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to
acheive a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use
200mm joists in a case like this.

What is the price? Cellotex has low U value and thin but look at
the price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.


Never thought I'd say this, but you talk much sense, Drivel. I don't
think anyone credible has come up with a valid reason for not doing
what I propose. The only question is whether 270mm is really
necessary, which is academic having spent the money, but I wouldn't
mind seeing Ian's revised calculations for curiosity if nothing else.

Mark

by all means use the insulation which you have already purchased, but a
valid reason is that there's way too much weight in 8 X 2 timbers, hence my
suggestion to compress the fibreglass

"MarkK" wrote in message
news
"JoeFaeGlesga" wrote in message
ups.com...
Hi all,

I was planning on flooring my loft but there seem to be a lot of cables
crossing the beams. Obviously whoever rewired the house didn't really
use the loft so just threw the cables wherever to get to their
destination. IS it a difficult job to reroute these along joists etc.
Was maybe going to get a spark into do it but no idea the complexity of
th job....

Any advice appreciated.

Joe.

If you just board over the existing joists you won't be able to
accommodate
the recommended depth of insulation. What I'm planning to do with mine is
fit 8"x2" (8" side vertical) at right angles to the existing joists, 370mm
apart. This conveniently allows the lighting electrics to be left as-is.
There's enough slack to allow it to be moved aside where necessary. I'll
then fit insulation, then put chipboard over it. That'll give me 11" of
insulation (270mm is recommended, this is a little more) and all the
storage
I need.

If you want to re-wire, allow 1-3 weekends (depending on house size), a
reel
of 1mm sq T&E and maybe some junction boxes. It's not hard assuming you
understand a) how a lighting circuit is set up, b) how your particular
house
has been done & c) are competent!

Use 1.5mm. Oversize because of being covered in insulation. It is called
derating.

"MarkK" wrote in message
news
"Doctor Drivel" wrote in message
reenews.net...

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:

http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034

http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to
acheive
a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use
200mm
joists in a case like this.

What is the price? Cellotex has low U value and thin but look at the
price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.


Never thought I'd say this, but you talk much sense, Drivel. I don't think
anyone credible has come up with a valid reason for not doing what I
propose. The only question is whether 270mm is really necessary, which is
academic having spent the money, but I wouldn't mind seeing Ian's revised
calculations for curiosity if nothing else.

There is no such thing as too much insulation. Fuel is not going to get
cheaper.

In article ews.net,
"Doctor Drivel" writes:

Use 1.5mm. Oversize because of being covered in insulation. It is called
derating.

1mm is already oversized in domestic lighting situations.

--
Andrew Gabriel

"Doctor Drivel" wrote in message
reenews.net...
anyone credible has come up with a valid reason for not doing what I
propose. The only question is whether 270mm is really necessary, which is
academic having spent the money, but I wouldn't mind seeing Ian's revised
calculations for curiosity if nothing else.

There is no such thing as too much insulation. Fuel is not going to get
cheaper.
Tell me about it...
We helped BP pump up an extra 70,000 barrels from the North Sea in the last
year... did they put the price per barrel down when they sold it??
Did they fu....
_________________________
Grim

"Doctor Drivel" wrote in message
reenews.net...

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:
http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034
http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to
acheive a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use 200mm
joists in a case like this.

What is the price? Cellotex has low U value and thin but look at the
price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.

I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not putting my
second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the height -
to work round water pipes (with their foamy insulation thingamybobs).
Would the addition of the chipboard over the top of the lot not help with
the insulation of the entire area as a whole?
______________________________
The Grimch Reaper

"The Grim Reaper" wrote in message
...
"Doctor Drivel" wrote in message
reenews.net...

"Phil L" wrote in message
. uk...
Tony Bryer wrote:
On Mon, 4 Dec 2006 15:09:15 -0000 Doctor Drivel wrote :
Me too, until I visited Owens Corning and saw 1 inch fibreboard
being made from 300mm fibreglass and was told that the u-value
was of 250mm fibreglass.....they are used in oven manufacture

There is a loss of 50mm there.

Yes, but a 25mm thick slab that had the same insulation value as 250mm
of fibreglass would be a dream product for loft converters and the
like. If it were so - I remain sceptical.

Owens Corning, who I used to work for have changed their name (or been
bought out by) Knauff insulation has data sheets:
http://www.knaufinsulation.co.uk/cgi...%20CD67306.pdf
shows that 200mm of loft insulation has a w/mk u-value of 0.040.

While their compressed slabs at 25mm have a value of 0.034
http://www.knaufinsulation.co.uk/cgi...%20CD56706.pdf

Both pages have this to say:

"Complies with the requirements of the new Building Regulations to
acheive a U-value of 0.13 W/m2K"

I did say that the u-values were similar...I certainly wouldn't use
200mm joists in a case like this.

What is the price? Cellotex has low U value and thin but look at the
price.

I would be inclined to look into laying this stuff over the joints
(eliminate thermal bridging) and put chipboard over.

I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not putting
my second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the
height - to work round water pipes (with their foamy insulation
thingamybobs).
Would the addition of the chipboard over the top of the lot not help with
the insulation of the entire area as a whole?

2" in total? I would get 1"x1" baton and counter these to the joists. If a
1" gap then 2"x1" batons Over this put the thick chipboard. I think there is
22mm thick chipboard. Put the 1x1 batons at 200mm centres counter to the
joists. Screw the chipboard to the 1x1 batons - well, prob every 6 inches.
The batons at 200mm and the thick chipboard will stiffen it up. As it is
only for storage and the occasional walking upon, the thick chipboard will
be good enough. The gap between the joist and the batons now can hold the
25mm insulation slabs covering the joists. Or foam Kingspan or Cellotex,
which is high performance for the thickness - but costs. You only have 6"
for insulation so getting high performance insulation is the way.

"Phil L" wrote in message
k...


by all means use the insulation which you have already purchased, but a
valid reason is that there's way too much weight in 8 X 2 timbers, hence
my
suggestion to compress the fibreglass

I doubt it'll be too heavy - it'll be spread out and form a strong
structure. If I detect any flex or ceiling problems I'll strip it all out.
I'm more concerned about the weight of the 18mm chipboard flooring than the
8x2...

Compressing the fibre will reduce its insulative properties. It's not the
weight of fibre that does the insulating, it's the volume of trapped air. So
it doesn't make sense. If it did we'd all be insulating our homes with 10mm
solid fibreglass! Anyone know what boats are like in the winter?

Mark

The Grim Reaper wrote:

I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not putting my
second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the height -
to work round water pipes (with their foamy insulation thingamybobs).
Would the addition of the chipboard over the top of the lot not help with
the insulation of the entire area as a whole?

You could fill the space between the joists with rockwool / fibreglass.
Then lay a foil covered PIR foam ridgid board (i.e. the stuff celotex /
kingspan is made from - but find another brand for half the price!) over
the top and screw your chipboard down through the PIR into the joists.

The ridgid foam is plenty dense enough that it will not crush under the
distributed load of the chipboard and anything on it.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Doctor Drivel" wrote in message
reenews.net...

"The Grim Reaper" wrote in message
...


I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not
putting
my second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the
height - to work round water pipes (with their foamy insulation
thingamybobs).

If you're covering the pipes you won't need the foam insulation on them, but
there may be no advantage to removing it. I saved money by not buying pipe
insulation for my plumbing in the loft at floor level, as I knew it would be
covered by my new floor & insulation.

Would the addition of the chipboard over the top of the lot not help
with
the insulation of the entire area as a whole?

Yes, although chipboard is not good insulator itself, the fact that you're
sealing over the fibre will mean reduced airflow and hence convection, so
should help.

2" in total? I would get 1"x1" baton and counter these to the joists. If
a
1" gap then 2"x1" batons Over this put the thick chipboard. I think there
is
22mm thick chipboard. Put the 1x1 batons at 200mm centres counter to the
joists. Screw the chipboard to the 1x1 batons - well, prob every 6
inches.

I think I get the gist, but what you say isn't 100% clear. I think we need a
diagram.

You can get 22mm chipboard, buy 18mm is pretty heavy and surely strong
enough. The thicker stuff is for joists that are further apart.

The batons at 200mm and the thick chipboard will stiffen it up. As it is
only for storage and the occasional walking upon, the thick chipboard will
be good enough. The gap between the joist and the batons now can hold the
25mm insulation slabs covering the joists. Or foam Kingspan or Cellotex,
which is high performance for the thickness - but costs. You only have 6"
for insulation so getting high performance insulation is the way.

If you really can't add more than 2" why not just fit 2x2 at 90 degrees? 6"
is the minimum level recommended by NEF, so you'd have a reasonable level of
insulation. See http://www.nef.org.uk/energyadvice/insulation.htm But why
not go for an extra 4" as a compromise and have a total of 8"? You say
you're tall, so you must be used to ducking ;-). It's only for storage after
all.

Mark

"MarkK" wrote in message
...
"Doctor Drivel" wrote in message
reenews.net...

"The Grim Reaper" wrote in message
...


I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not
putting
my second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the
height - to work round water pipes (with their foamy insulation
thingamybobs).

If you're covering the pipes you won't need the foam insulation on them,
but
there may be no advantage to removing it. I saved money by not buying pipe
insulation for my plumbing in the loft at floor level, as I knew it would
be
covered by my new floor & insulation.

Would the addition of the chipboard over the top of the lot not help
with
the insulation of the entire area as a whole?

Yes, although chipboard is not good insulator itself, the fact that
you're
sealing over the fibre will mean reduced airflow and hence convection, so
should help.

2" in total? I would get 1"x1" baton and counter these to the joists. If
a
1" gap then 2"x1" batons Over this put the thick chipboard. I think there
is
22mm thick chipboard. Put the 1x1 batons at 200mm centres counter to the
joists. Screw the chipboard to the 1x1 batons - well, prob every 6
inches.

I think I get the gist, but what you say isn't 100% clear. I think we need
a
diagram.

Counter means at 90 degrees.

You can get 22mm chipboard, buy 18mm is pretty heavy and surely strong
enough. The thicker stuff is for joists that are further apart.

22mm chipboard on 1x1 or 2x1 batons will make the floor more rigid.

The batons at 200mm and the thick chipboard will stiffen it up. As it is
only for storage and the occasional walking upon, the thick chipboard
will
be good enough. The gap between the joist and the batons now can hold
the
25mm insulation slabs covering the joists. Or foam Kingspan or Cellotex,
which is high performance for the thickness - but costs. You only have
6"
for insulation so getting high performance insulation is the way.

If you really can't add more than 2" why not just fit 2x2 at 90 degrees?
6"
is the minimum level recommended by NEF, so you'd have a reasonable level
of
insulation. See http://www.nef.org.uk/energyadvice/insulation.htm But why
not go for an extra 4" as a compromise and have a total of 8"? You say
you're tall, so you must be used to ducking ;-). It's only for storage
after
all.

If he can't go above 2 inches then he is better off buying high performance
insulation. He has no option and to do all this work an not improve the
insulation value is pretty dumb.

"John Rumm" wrote in message
...
The Grim Reaper wrote:

I realise your advice was meant for Mark's particular case, however...
How could I go about laying insulation over the joists if I'm not putting
my second layer of joist at right angles to the first??
As I mentioned before, I'm only planning on adding 2 inches to the
height - to work round water pipes (with their foamy insulation
thingamybobs).
Would the addition of the chipboard over the top of the lot not help with
the insulation of the entire area as a whole?

You could fill the space between the joists with rockwool / fibreglass.
Then lay a foil covered PIR foam ridgid board (i.e. the stuff celotex /
kingspan is made from - but find another brand for half the price!) over
the top and screw your chipboard down through the PIR into the joists.

The ridgid foam is plenty dense enough that it will not crush under the
distributed load of the chipboard and anything on it.

I would check with the makers first.

Doctor Drivel wrote:

You could fill the space between the joists with rockwool /
fibreglass. Then lay a foil covered PIR foam ridgid board (i.e. the
stuff celotex / kingspan is made from - but find another brand for
half the price!) over the top and screw your chipboard down through
the PIR into the joists.

The ridgid foam is plenty dense enough that it will not crush under
the distributed load of the chipboard and anything on it.


I would check with the makers first.

You will find this is a solution they suggest. It is commonly used for
construction of warm deck roofs as well. Some of the insulation
manufacturers also make a board which consists of insulation bonded to
ply for just this purpose (Tuf R Deck, Temp Check Deck etc). Having said
that, the ply they use is usually too thin for construction of a flat
roof that will last.

--
Cheers,

John.

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"John Rumm" wrote in message
...
Doctor Drivel wrote:

You could fill the space between the joists with rockwool / fibreglass.
Then lay a foil covered PIR foam ridgid board (i.e. the stuff celotex /
kingspan is made from - but find another brand for half the price!) over
the top and screw your chipboard down through the PIR into the joists.

The ridgid foam is plenty dense enough that it will not crush under the
distributed load of the chipboard and anything on it.


I would check with the makers first.

You will find this is a solution they suggest. It is commonly used for
construction of warm deck roofs as well. Some of the insulation
manufacturers also make a board which consists of insulation bonded to ply
for just this purpose (Tuf R Deck, Temp Check Deck etc). Having said that,
the ply they use is usually too thin for construction of a flat roof that
will last.

The problem is the insulation foam resting on joist 2" thick. I have seen
cheap ply run across joist and foam insulation board over then chipboard. A
ply-insulation-chipboard sandwich. The ply spreads the load.

This method is the best as thermal bridging is 99% reduced. Only the screws
act as a bridge.

Doctor Drivel wrote:

The problem is the insulation foam resting on joist 2" thick. I have

It is not a problem in practice. PIR foam is more than rigid enough to
support this load. If you place PIR foam on the ground and stand on it,
it does not crush - and that is just with a foot sized area.

I built the flat roof on my loft with 80mm PIR foam boards laid directly
onto the firrings, and then 18mm WBP ply over that. Even driving 5 1/2"
screws through the deck into the firrings/joists, to the point where
they were pulled right into the ply there was no noticeable deformation
in the foam.

seen cheap ply run across joist and foam insulation board over then
chipboard. A ply-insulation-chipboard sandwich. The ply spreads the load.

The celotex Tempchek deck product is made like that - although it only
has 12mm ply on the top surface. With the thicker board on top there is
no need for a board under unless you need it for fixing into (not much
of an issue on a floor)

This method is the best as thermal bridging is 99% reduced. Only the
screws act as a bridge.

It is also much easier to do than extending the joist heights.

--
Cheers,

John.

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"MarkK" wrote in message
...

I've been worried about the weight, and considered spanning the structural
walls and supporting the timbers on them rather than just the ceiling
joists. This would be tricky, and I don't believe it is necessary as each
existing joist can support 75kg at its centre without detectable flex -
they
feel very, very strong under foot. I'm therefore confident that I don't
need
to do this.

Humble pie time - discussed it properly with my structural engineer
neighbour. Conclusion is that I do need to span the structural walls and
ensure the weight is supported properly by the walls and not the ceiling
joists. The good news is that using 8x2 means they'll be strong enough for
the span.

Mark

"MarkK" wrote in message
...
"MarkK" wrote in message
...

I've been worried about the weight, and considered spanning the
structural
walls and supporting the timbers on them rather than just the ceiling
joists. This would be tricky, and I don't believe it is necessary as each
existing joist can support 75kg at its centre without detectable flex -
they
feel very, very strong under foot. I'm therefore confident that I don't
need
to do this.

Humble pie time - discussed it properly with my structural engineer
neighbour. Conclusion is that I do need to span the structural walls and
ensure the weight is supported properly by the walls and not the ceiling
joists. The good news is that using 8x2 means they'll be strong enough for
the span.

Mark

As I said. Support the 8" joists on the gable ends. Joist hangers are
available for this

MarkK wrote:


Humble pie time - discussed it properly with my structural engineer
neighbour. Conclusion is that I do need to span the structural walls and
ensure the weight is supported properly by the walls and not the ceiling
joists. The good news is that using 8x2 means they'll be strong enough for
the span.

If you are going to the hassle of increasing joist size to that extent,
you may as well do the structural calcs to show they meet the
requirements for a floor in a habitable room, and do the work on a
building notice. Then you have the foundation work for a complete loft
conversion in place should you need it later.


--
Cheers,

John.

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