Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi. I
may add some extra joists at 90 degrees to add another 4" of insulation. As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying the
thickest pack of insulation around and squash it into 4", rather get one
which is closest to the thickess I require. Should be cheaper (per m^2) and
provide similar insulation to a thicker one squashed to 4". Or am I wrong?

Thanks

D

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To send email to me - remove references to NoSpam, and Spammer from my email
address.

In message , David Hearn
writes
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi. I
may add some extra joists at 90 degrees to add another 4" of insulation. As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying the
thickest pack of insulation around and squash it into 4", rather get one
which is closest to the thickess I require. Should be cheaper (per m^2) and
provide similar insulation to a thicker one squashed to 4". Or am I wrong?

No you are correct.

In theory the thicker one compressed down should provide poorer
insulation.
--
Chris French, Leeds

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's
semi. I
may add some extra joists at 90 degrees to add another 4" of
insulation. As
I understand it, its the air that gets trapped in the insulation
that
provides the insulating effect. Therefore, there's no point in
buying the
thickest pack of insulation around and squash it into 4", rather get
one
which is closest to the thickess I require. Should be cheaper (per
m^2) and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?


I have just added another 4" of insulation, (roll type), and just laid
it on top of the existing insulation, running on top of the joists,
with the lengthwise joins actually on the joists. This way, I know
where the joists are if I need to walk in the loft. Total cost about
£30.00, for a two bedroomed semi.
--
Gavin Gillespie
Giltbrook
Nottingham UK

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi. I
may add some extra joists at 90 degrees to add another 4" of insulation.
As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying the
thickest pack of insulation around and squash it into 4", rather get one
which is closest to the thickess I require. Should be cheaper (per m^2)
and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?

Thanks

D


Why are you going to lay another layer of joists ? Why not just roll your
new insulation at 90 degrees across the top of the existing stuff that's
already there ? The insulation doesn't need to be between joist to be
effective, in fact the looser and thicker it is, the better it works. The
fibre insulation is very cheap to buy on its own, so please don't go to
expense of laying joists on top of joists just to be able to squeeze
insulation between them. It's just not worth it.


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"BigWallop" wrote in message
...

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi.
I
may add some extra joists at 90 degrees to add another 4" of insulation.
As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying
the
thickest pack of insulation around and squash it into 4", rather get one
which is closest to the thickess I require. Should be cheaper (per m^2)
and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?

Thanks

D


Why are you going to lay another layer of joists ? Why not just roll your
new insulation at 90 degrees across the top of the existing stuff that's
already there ? The insulation doesn't need to be between joist to be
effective, in fact the looser and thicker it is, the better it works. The
fibre insulation is very cheap to buy on its own, so please don't go to
expense of laying joists on top of joists just to be able to squeeze
insulation between them. It's just not worth it.

I guess I assumed everyone would remember my other posts! I'm planning on
boarding out the loft, and therefore need the extra joists to add height for
additional insulation whilst hopefully providing a little extra strength.

D

"David Hearn" wrote in message
...


I guess I assumed everyone would remember my other posts! I'm planning on
boarding out the loft, and therefore need the extra joists to add height
for
additional insulation whilst hopefully providing a little extra strength.

D


Unless they're firmly supported by supporting walls at both ends, they'll
simply add weight to the existing potentially overloaded joists - but not
strength!

Roger

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's
semi.
I
may add some extra joists at 90 degrees to add another 4" of
insulation.
As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying
the
thickest pack of insulation around and squash it into 4", rather get
one
which is closest to the thickess I require. Should be cheaper (per
m^2)
and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?

Thanks

D


Why are you going to lay another layer of joists ? Why not just roll
your
new insulation at 90 degrees across the top of the existing stuff that's
already there ? The insulation doesn't need to be between joist to be
effective, in fact the looser and thicker it is, the better it works.
The
fibre insulation is very cheap to buy on its own, so please don't go to
expense of laying joists on top of joists just to be able to squeeze
insulation between them. It's just not worth it.

I guess I assumed everyone would remember my other posts! I'm planning on
boarding out the loft, and therefore need the extra joists to add height
for
additional insulation whilst hopefully providing a little extra strength.

D



The only way to gain extra strength is to make the existing joist thicker in
both surfaces. Adding joists on top of joist is only adding more weight to
the joists underneath the new ones, so that is a definite no, no. The whole
purpose of joists it take the load they are designed for, and because you've
put thicker ones on top, doesn't mean you've made anything stronger. Try
putting the ends of a matchstick across two points and pressing down on it
until it snaps. Then try putting another matchstick at ninety degrees
across the lower one and press down on them both where the meet. I think
you'll find that lower matchstick still breaks at about the same pressure.

After reading your other post, I think you find that when you take away the
joists that are already running at 90 degrees across the top of the joists
and then lay your new boards at 90 degrees to the existing joists, you're
actually doing the same job as the timber that is already there. Once
you've boarded over the joist you should actually see an increase in the
insulation properties of the ceiling because you've created a sealed unit
with the existing fibre wool that's there. So you shouldn't really need to
lay another layer of insulation on top.

If the area of the loft is boarded over right up to the edges with the new
chipboard flooring systems that are currently on the market, then they to
add some insulation properties to the ceiling because of their construction.

Try to make the job as simple and as cheap as you can. You won't gain
anything hugely different from what you already have, unless you intend to
increase the size of the existing joists and make them deep enough to able
to take two layers of insulation between them. A loft area must be allowed
to breath and move with different weather conditions, so the space must be
ventilated properly to prevent moisture from gathering and then dripping
through. So to seal the loft space to tight will mean you are actually
going to create more problems for yourself in the future.

Try doing a web search for roofing construction and get some tips on what a
roof and loft space actually do for a house. I think you'll be amazed at
what you find out.

Good luck with it all.


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"Roger Mills" wrote in message
...

"David Hearn" wrote in message
...


I guess I assumed everyone would remember my other posts! I'm planning
on
boarding out the loft, and therefore need the extra joists to add height
for
additional insulation whilst hopefully providing a little extra
strength.

D


Unless they're firmly supported by supporting walls at both ends, they'll
simply add weight to the existing potentially overloaded joists - but not
strength!

I was aware of that (hence I think I've generally said 'possibly at 90
degrees'...) - I did expect though that it would spread the load more.
Whereas I could put a box down which may sit on a single joist, if the cross
joists were screwed together, then that joist is not going to move down
without bending the joist on top, which would also require the joist next to
it to bend... which would spread the weight over two joists. The question
is though is whether the boarding itself would do that anyway (though
chipboard is possibly not great at resisting being bent compared to 4x2's)
and whether the additional weight added by the joists would outweigh the
benefit added by spreading the load....

D

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's
semi.
I
may add some extra joists at 90 degrees to add another 4" of
insulation.
As
I understand it, its the air that gets trapped in the insulation
that
provides the insulating effect. Therefore, there's no point in
buying
the
thickest pack of insulation around and squash it into 4", rather get
one
which is closest to the thickess I require. Should be cheaper (per
m^2)
and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?

Thanks

D


Why are you going to lay another layer of joists ? Why not just roll
your
new insulation at 90 degrees across the top of the existing stuff
that's
already there ? The insulation doesn't need to be between joist to be
effective, in fact the looser and thicker it is, the better it works.
The
fibre insulation is very cheap to buy on its own, so please don't go
to
expense of laying joists on top of joists just to be able to squeeze
insulation between them. It's just not worth it.

I guess I assumed everyone would remember my other posts! I'm planning
on
boarding out the loft, and therefore need the extra joists to add height
for
additional insulation whilst hopefully providing a little extra
strength.

D



The only way to gain extra strength is to make the existing joist thicker
in
both surfaces. Adding joists on top of joist is only adding more weight
to
the joists underneath the new ones, so that is a definite no, no. The
whole
purpose of joists it take the load they are designed for, and because
you've
put thicker ones on top, doesn't mean you've made anything stronger. Try
putting the ends of a matchstick across two points and pressing down on it
until it snaps. Then try putting another matchstick at ninety degrees
across the lower one and press down on them both where the meet. I think
you'll find that lower matchstick still breaks at about the same pressure.

After reading your other post, I think you find that when you take away
the
joists that are already running at 90 degrees across the top of the joists
and then lay your new boards at 90 degrees to the existing joists, you're
actually doing the same job as the timber that is already there. Once
you've boarded over the joist you should actually see an increase in the
insulation properties of the ceiling because you've created a sealed unit
with the existing fibre wool that's there. So you shouldn't really need
to
lay another layer of insulation on top.

If the area of the loft is boarded over right up to the edges with the new
chipboard flooring systems that are currently on the market, then they to
add some insulation properties to the ceiling because of their
construction.

Try to make the job as simple and as cheap as you can. You won't gain
anything hugely different from what you already have, unless you intend to
increase the size of the existing joists and make them deep enough to able
to take two layers of insulation between them. A loft area must be
allowed
to breath and move with different weather conditions, so the space must be
ventilated properly to prevent moisture from gathering and then dripping
through. So to seal the loft space to tight will mean you are actually
going to create more problems for yourself in the future.

So if I was boarding out 4" insulation, it may not be worth trying to add
extra insulation (which would require adding extra timber to give the
height, either cross or on top of existing joists) as it would seal the
joists off.

I doubt I'll board it out right to the edges (its pitched on 3 sides, which
limits access, plus these sides tend to be in the middle of joist spans,
which would be weakest). At the edges then I can just lay extra insulation
on top.

Thanks

D

Air is the insulator used in loft insulation. The thicker it is the more air
is trapped and the better insulation.

By boarding the loft, you automatically trap air under the boards, and
provided that air doesn't circulate, I would think that there is no
advantage in providing a thicker layer below the boards. In fact if you
sealed the gap between ceiling and board completely, you wouldn't need any
fibreglass, the air would act as the insulator as in double glazing.

The fibreglass you have there will impede the air circulating and so I would
just go ahead and board over, paying attention to general loft ventilation,
especially over the bathroom, as discussed.

Colin

PS Don't forget to box in any halogen downlighters if fitted

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
ventilated properly to prevent moisture from gathering and then dripping
through. So to seal the loft space to tight will mean you are actually
going to create more problems for yourself in the future.

So if I was boarding out 4" insulation, it may not be worth trying to add
extra insulation (which would require adding extra timber to give the
height, either cross or on top of existing joists) as it would seal the
joists off.

I doubt I'll board it out right to the edges (its pitched on 3 sides,
which
limits access, plus these sides tend to be in the middle of joist spans,
which would be weakest). At the edges then I can just lay extra
insulation
on top.

Thanks

D



But access to the edges doesn't have to be any thicker than the thickness of
the boards, because you'd slide the boards in to the edges of the space.
Then just fix them down where it is most convenient to do so. If you go
with a flooring grade chipboard system, then the tongue and groove around
the edges of the boards will be enough to hold them together in the short
distances you can't reach right under the eaves. So you'll still literally
be able to board the loft right out to the edges and make the space between
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.


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"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
ventilated properly to prevent moisture from gathering and then
dripping
through. So to seal the loft space to tight will mean you are
actually
going to create more problems for yourself in the future.

So if I was boarding out 4" insulation, it may not be worth trying to
add
extra insulation (which would require adding extra timber to give the
height, either cross or on top of existing joists) as it would seal the
joists off.

I doubt I'll board it out right to the edges (its pitched on 3 sides,
which
limits access, plus these sides tend to be in the middle of joist spans,
which would be weakest). At the edges then I can just lay extra
insulation
on top.

Thanks

D



But access to the edges doesn't have to be any thicker than the thickness
of
the boards, because you'd slide the boards in to the edges of the space.
Then just fix them down where it is most convenient to do so. If you go
with a flooring grade chipboard system, then the tongue and groove around
the edges of the boards will be enough to hold them together in the short
distances you can't reach right under the eaves. So you'll still
literally
be able to board the loft right out to the edges and make the space
between
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.

The reasoning for not boarding right to the edges is two fold. The boarding
is mainly for storage, and storage at the edges would be difficult to access
(plus loading may be an issue when its in the middle of the spans - not
boarding saves me thinking I can put things on it!). The edges form a
significant proportion of the loft area, which means I could do it quite
cheaply if I just boarded the area I would store in. Of course, if the area
I'm boarding is a small proportion, then the insulation benefits from it
wouldn't be so great.

Depending on the cost of the boarding, I may well board it all (or the vast
majority).

The small packs I have already (2 packs of 3) say they're designed for 45cm
spacings. As I've got 30cm gaps (which should work out to be 35cm centre
spacing), these would probably have to have a proportion trimmed off of
each, which would be wasted. I'm hoping to go for large boards and cut them
to an appropriate size for my spacing. This should be cheaper than using
pre-cut boards - shouldn't it? Any idea of the normal size of these boards,
and their relevant costs (18mm thickness - unless I can get away with less
as I'm using 35mm spacings rather than 45?)? I'll look at our new "The
Timber Store" which has recently opened in Guildford - hopefully that'll be
cheaper than B&Q etc.

I've got a jigsaw which I expect I could use to cut down these sheets
(probably using a bar to aid as a straight edge). The other option I have
is to invest in a circular saw - though I'd prefer to keep costs as low as
possible. Do you think a jigsaw would be up to it?

Thanks for everyone's advice - its been very useful!

D

snip

I've got a jigsaw which I expect I could use to cut down these sheets
(probably using a bar to aid as a straight edge). The other option I have
is to invest in a circular saw - though I'd prefer to keep costs as low as
possible. Do you think a jigsaw would be up to it?


I've done a couple, one where the joist spacing matched the board length
( i.e. a fairly new property )
and another on an older ( approx. 35 yrs old ) property where the joist
spacing was incompatible.

In both cases many boards needed cutting to fit round fittings, e.g.
chimneys, water tanks etc.

I used a jigsaw for all the cuts and found it perfectly adequate to cope,
but get a couple of *good* blades.

Another point worth mentioning is that cutting the boards with a jigsaw
makes a large amount of dust.
A solution is to mark them up a few at a time and then take them outside or
into a workshop to cut,
either that or get a good mask for protection and be prepared to suffer a
berating from the misses for all the dust that blows out the hatch into the
landing or bedroom underneath.

In message , David Hearn
writes

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi.
I
may add some extra joists at 90 degrees to add another 4" of insulation.

Why are you going to lay another layer of joists ?

I guess I assumed everyone would remember my other posts!

a poor assumption, not only do I not remember you other posts, I didn't
even read them - I maybe read 10% of the thread in uk-d-i-y at the
moment.

I'm planning on
boarding out the loft, and therefore need the extra joists to add height for
additional insulation whilst hopefully providing a little extra strength.
I just boarded over the central part of my loft with 4 inches of
insulation below, and then put thicker insulation over the -parts.
--
Chris French, Leeds

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.

The reasoning for not boarding right to the edges is two fold. The
boarding
is mainly for storage, and storage at the edges would be difficult to
access
(plus loading may be an issue when its in the middle of the spans - not
boarding saves me thinking I can put things on it!). The edges form a
significant proportion of the loft area, which means I could do it quite
cheaply if I just boarded the area I would store in. Of course, if the
area
I'm boarding is a small proportion, then the insulation benefits from it
wouldn't be so great.

Depending on the cost of the boarding, I may well board it all (or the
vast
majority).

The small packs I have already (2 packs of 3) say they're designed for
45cm
spacings. As I've got 30cm gaps (which should work out to be 35cm centre
spacing), these would probably have to have a proportion trimmed off of
each, which would be wasted. I'm hoping to go for large boards and cut
them
to an appropriate size for my spacing. This should be cheaper than using
pre-cut boards - shouldn't it? Any idea of the normal size of these
boards,
and their relevant costs (18mm thickness - unless I can get away with less
as I'm using 35mm spacings rather than 45?)? I'll look at our new "The
Timber Store" which has recently opened in Guildford - hopefully that'll
be
cheaper than B&Q etc.

I've got a jigsaw which I expect I could use to cut down these sheets
(probably using a bar to aid as a straight edge). The other option I have
is to invest in a circular saw - though I'd prefer to keep costs as low as
possible. Do you think a jigsaw would be up to it?

Thanks for everyone's advice - its been very useful!

D



But if you use flooring grade blockboard, then the spacing in the joists
doesn't matter because the tongue and groove style means they fit together
anyway. As long as the tongue is in the groove of the other board next to
it, then the boards will take the wait of someone walking on them. So all
you're really cutting off is the end of a full row of boards. That's the
beauty of this type flooring system.

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
the ceiling and the new loft floor into a sealed unit with the
existing
insulation still between it.

The reasoning for not boarding right to the edges is two fold. The
boarding
is mainly for storage, and storage at the edges would be difficult to
access
(plus loading may be an issue when its in the middle of the spans - not
boarding saves me thinking I can put things on it!). The edges form a
significant proportion of the loft area, which means I could do it quite
cheaply if I just boarded the area I would store in. Of course, if the
area
I'm boarding is a small proportion, then the insulation benefits from it
wouldn't be so great.

Depending on the cost of the boarding, I may well board it all (or the
vast
majority).

The small packs I have already (2 packs of 3) say they're designed for
45cm
spacings. As I've got 30cm gaps (which should work out to be 35cm
centre
spacing), these would probably have to have a proportion trimmed off of
each, which would be wasted. I'm hoping to go for large boards and cut
them
to an appropriate size for my spacing. This should be cheaper than
using
pre-cut boards - shouldn't it? Any idea of the normal size of these
boards,
and their relevant costs (18mm thickness - unless I can get away with
less
as I'm using 35mm spacings rather than 45?)? I'll look at our new "The
Timber Store" which has recently opened in Guildford - hopefully that'll
be
cheaper than B&Q etc.

I've got a jigsaw which I expect I could use to cut down these sheets
(probably using a bar to aid as a straight edge). The other option I
have
is to invest in a circular saw - though I'd prefer to keep costs as low
as
possible. Do you think a jigsaw would be up to it?

Thanks for everyone's advice - its been very useful!

But if you use flooring grade blockboard, then the spacing in the joists
doesn't matter because the tongue and groove style means they fit together
anyway. As long as the tongue is in the groove of the other board next to
it, then the boards will take the wait of someone walking on them. So all
you're really cutting off is the end of a full row of boards. That's the
beauty of this type flooring system.

I take it that flooring grade blockboard is not the same as flooring grade
chipboard? From what I've read about the chipboard, the boards must join
over a joist? This would require cutting 27cm off a 8' board. Is this
actually the case with 18mm chipboard T&G flooring? If so, that would be
great. The flooring does have T&G on the short edge, not just the long
edge.

Thanks

D

In article ,
says...


But access to the edges doesn't have to be any thicker than the thickness of
the boards, because you'd slide the boards in to the edges of the space.
Then just fix them down where it is most convenient to do so. If you go
with a flooring grade chipboard system, then the tongue and groove around
the edges of the boards will be enough to hold them together in the short
distances you can't reach right under the eaves. So you'll still literally
be able to board the loft right out to the edges and make the space between
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.

I've been following this thread with interest as I'm in much the same
position as David. My house has 4x2 joists (not measured the spacing
yet) and I'd like to board at least the centre section but probably a
bit into the eaves as well. My original plan was the same as David's -
Put cross joist across the existong one to give extra height to allow
for more insulation and ventilation but I take your point about extra
loading.

I'm a bit confused about your previous advice here though - If I lay 4
inches of insulation between the joists and then board over am I likely
to run into condensation problems due to lack of ventilation to the
insulation? Is it generally OK if I were to not board over the bathroom
but to add extra insulation here instead?

I take your point about the boarding preventing air circulation and
acting as insulation but how does this compare with more fibre? The
current suggested minimum is 200mm (and I note that some people have
gone upto 450mm - Surely there's a law of diminishing returns here!)
The suggested solution would only have 100mm insulation, and boards?

Thanks,

Peter

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
the ceiling and the new loft floor into a sealed unit with the
existing
insulation still between it.

The reasoning for not boarding right to the edges is two fold. The
boarding
is mainly for storage, and storage at the edges would be difficult to
access
(plus loading may be an issue when its in the middle of the spans -
not
boarding saves me thinking I can put things on it!). The edges form a
significant proportion of the loft area, which means I could do it
quite
cheaply if I just boarded the area I would store in. Of course, if
the
area
I'm boarding is a small proportion, then the insulation benefits from
it
wouldn't be so great.

Depending on the cost of the boarding, I may well board it all (or the
vast
majority).

The small packs I have already (2 packs of 3) say they're designed for
45cm
spacings. As I've got 30cm gaps (which should work out to be 35cm
centre
spacing), these would probably have to have a proportion trimmed off
of
each, which would be wasted. I'm hoping to go for large boards and
cut
them
to an appropriate size for my spacing. This should be cheaper than
using
pre-cut boards - shouldn't it? Any idea of the normal size of these
boards,
and their relevant costs (18mm thickness - unless I can get away with
less
as I'm using 35mm spacings rather than 45?)? I'll look at our new
"The
Timber Store" which has recently opened in Guildford - hopefully
that'll
be
cheaper than B&Q etc.

I've got a jigsaw which I expect I could use to cut down these sheets
(probably using a bar to aid as a straight edge). The other option I
have
is to invest in a circular saw - though I'd prefer to keep costs as
low
as
possible. Do you think a jigsaw would be up to it?

Thanks for everyone's advice - its been very useful!

But if you use flooring grade blockboard, then the spacing in the joists
doesn't matter because the tongue and groove style means they fit
together
anyway. As long as the tongue is in the groove of the other board next
to
it, then the boards will take the wait of someone walking on them. So
all
you're really cutting off is the end of a full row of boards. That's
the
beauty of this type flooring system.

I take it that flooring grade blockboard is not the same as flooring grade
chipboard? From what I've read about the chipboard, the boards must join
over a joist? This would require cutting 27cm off a 8' board. Is this
actually the case with 18mm chipboard T&G flooring? If so, that would be
great. The flooring does have T&G on the short edge, not just the long
edge.

Thanks

D



And if you cut to the length of the spacing of the joists, how much of each
board do you loose ? Quite a bit I'd imagine. So if you keep all the
tongue and grooves together, no matter where the joint ends up, you be able
to board out the whole loft, right up to edges, and it should all be strong
enough for you to use as storage space.

When one board ends up with an overlap on one joist, then the other board is
banged in against the edge of it, it will still have enough strength to take
the weight of an average bloke, even if the joint ends up in the middle of
the gap in the joists, because of the construction of the boards.

Try placing a board between a couple of bricks on the ground and then stand
on it in the middle. You should find that the board will quite happily take
your weight, not jumping up and down on it of course, but it should be able
to bend to a hell of a lot before you can break it.

Sorry. Flooring grade blockboard and flooring grade chipboard are one in
the same item.

On Fri, 7 Nov 2003 21:55:36 -0000, Peter Watson
wrote:



I take your point about the boarding preventing air circulation and
acting as insulation but how does this compare with more fibre? The
current suggested minimum is 200mm (and I note that some people have
gone upto 450mm - Surely there's a law of diminishing returns here!)
The suggested solution would only have 100mm insulation, and boards?

Thanks,

Peter


There certainly is a law of diminishing returns. If you look at the
U value of a roof with 100mm of insulation and work out the heat loss
for the area of a typical house it is generally a great deal less than
that which is lost through the walls and windows.

Doubling it to 200mm reduces that heat loss of course, but generally
to the tune of tens of watts. One can argue that the insulating
material is cheap enough so that the ROI on doing this is short but it
is rather like changing a 100W bulb for a 40W bulb while all the time
there is a 10kW heater running.

If the job can be done easily, then fine, but otherwise, if there is a
bunch of cost to install it such as timber etc. and that is not
otherwise useful, then going mad with roof insulation is not the most
cost effective way to deal with energy cost reduction.



..andy

To email, substitute .nospam with .gl

"Peter Watson" wrote in message
...
In article ,
says...


But access to the edges doesn't have to be any thicker than the
thickness of
the boards, because you'd slide the boards in to the edges of the space.
Then just fix them down where it is most convenient to do so. If you go
with a flooring grade chipboard system, then the tongue and groove
around
the edges of the boards will be enough to hold them together in the
short
distances you can't reach right under the eaves. So you'll still
literally
be able to board the loft right out to the edges and make the space
between
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.

I've been following this thread with interest as I'm in much the same
position as David. My house has 4x2 joists (not measured the spacing
yet) and I'd like to board at least the centre section but probably a
bit into the eaves as well. My original plan was the same as David's -
Put cross joist across the existong one to give extra height to allow
for more insulation and ventilation but I take your point about extra
loading.

I'm a bit confused about your previous advice here though - If I lay 4
inches of insulation between the joists and then board over am I likely
to run into condensation problems due to lack of ventilation to the
insulation? Is it generally OK if I were to not board over the bathroom
but to add extra insulation here instead?

I take your point about the boarding preventing air circulation and
acting as insulation but how does this compare with more fibre? The
current suggested minimum is 200mm (and I note that some people have
gone upto 450mm - Surely there's a law of diminishing returns here!)
The suggested solution would only have 100mm insulation, and boards?

Thanks,

Peter

As Andy Hall says, there is not a huge difference in the effect of laying
extra insulation when the same can be done by trapping the air between the
existing material with boards on top. The insulation works by stopping air
movement through the space between the boards and the ceiling, hence not
allowing colder air to travel through and cool the space down. The trapped
air is then heated by the very slow convection through from the room below
and has to stay where it is.

So by increasing the thickness of the insulation your actually just slowing
the air lose a very minuscule bit more than one layer does. But then your
giving yourself more work to try and increase the height of the space you
need before you can lay boards as a storage platform. Doing the math shows
that it is really not worth that kind of expense to gain so very little
more.

In article ,
says...


As Andy Hall says, there is not a huge difference in the effect of laying
extra insulation when the same can be done by trapping the air between the
existing material with boards on top. The insulation works by stopping air
movement through the space between the boards and the ceiling, hence not
allowing colder air to travel through and cool the space down. The trapped
air is then heated by the very slow convection through from the room below
and has to stay where it is.

So by increasing the thickness of the insulation your actually just slowing
the air lose a very minuscule bit more than one layer does. But then your
giving yourself more work to try and increase the height of the space you
need before you can lay boards as a storage platform. Doing the math shows
that it is really not worth that kind of expense to gain so very little
more.


Fair enough - What about the ventilaition issue though? My loft
curently is fairly sealed so I'm intending to fit ventilated soffits (in
the future) and not insulate to the very edge etc. Is boarding laid
directly over insulation with very little air gap likely to lead to
problems (condensation etc) later? If I lay less insulation to give an
air gap then I will lose any insulation properties that the boards give
as the air will no longer be trapped?

I don't really want to go the whole hog of laying plastic sheet (as a
vapour barrier) if I can avoid it hence my thought that the greatest
amount of 'damp' air is in the bathroom so I won't boasrd over that...

Thanks for the advice so far...

Peter

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

"David Hearn" wrote in message
...

"BigWallop" wrote in message
...

snipped
the ceiling and the new loft floor into a sealed unit with the
existing
insulation still between it.

The reasoning for not boarding right to the edges is two fold. The
boarding
is mainly for storage, and storage at the edges would be difficult
to
access
(plus loading may be an issue when its in the middle of the spans -
not
boarding saves me thinking I can put things on it!). The edges form
a
significant proportion of the loft area, which means I could do it
quite
cheaply if I just boarded the area I would store in. Of course, if
the
area
I'm boarding is a small proportion, then the insulation benefits
from
it
wouldn't be so great.

Depending on the cost of the boarding, I may well board it all (or
the
vast
majority).

The small packs I have already (2 packs of 3) say they're designed
for
45cm
spacings. As I've got 30cm gaps (which should work out to be 35cm
centre
spacing), these would probably have to have a proportion trimmed off
of
each, which would be wasted. I'm hoping to go for large boards and
cut
them
to an appropriate size for my spacing. This should be cheaper than
using
pre-cut boards - shouldn't it? Any idea of the normal size of these
boards,
and their relevant costs (18mm thickness - unless I can get away
with
less
as I'm using 35mm spacings rather than 45?)? I'll look at our new
"The
Timber Store" which has recently opened in Guildford - hopefully
that'll
be
cheaper than B&Q etc.

I've got a jigsaw which I expect I could use to cut down these
sheets
(probably using a bar to aid as a straight edge). The other option
I
have
is to invest in a circular saw - though I'd prefer to keep costs as
low
as
possible. Do you think a jigsaw would be up to it?

Thanks for everyone's advice - its been very useful!

But if you use flooring grade blockboard, then the spacing in the
joists
doesn't matter because the tongue and groove style means they fit
together
anyway. As long as the tongue is in the groove of the other board
next
to
it, then the boards will take the wait of someone walking on them. So
all
you're really cutting off is the end of a full row of boards. That's
the
beauty of this type flooring system.

I take it that flooring grade blockboard is not the same as flooring
grade
chipboard? From what I've read about the chipboard, the boards must
join
over a joist? This would require cutting 27cm off a 8' board. Is this
actually the case with 18mm chipboard T&G flooring? If so, that would
be
great. The flooring does have T&G on the short edge, not just the long
edge.

Thanks

D



And if you cut to the length of the spacing of the joists, how much of
each
board do you loose ? Quite a bit I'd imagine. So if you keep all the
tongue and grooves together, no matter where the joint ends up, you be
able
to board out the whole loft, right up to edges, and it should all be
strong
enough for you to use as storage space.

When one board ends up with an overlap on one joist, then the other board
is
banged in against the edge of it, it will still have enough strength to
take
the weight of an average bloke, even if the joint ends up in the middle of
the gap in the joists, because of the construction of the boards.

Try placing a board between a couple of bricks on the ground and then
stand
on it in the middle. You should find that the board will quite happily
take
your weight, not jumping up and down on it of course, but it should be
able
to bend to a hell of a lot before you can break it.

Sorry. Flooring grade blockboard and flooring grade chipboard are one in
the same item.

Thanks - your explanation has made things a lot easier (and cheaper).
Cheers!

D

"Peter Watson" wrote in message
...
In article ,
says...


As Andy Hall says, there is not a huge difference in the effect of
laying
extra insulation when the same can be done by trapping the air between
the
existing material with boards on top. The insulation works by stopping
air
movement through the space between the boards and the ceiling, hence not
allowing colder air to travel through and cool the space down. The
trapped
air is then heated by the very slow convection through from the room
below
and has to stay where it is.

So by increasing the thickness of the insulation your actually just
slowing
the air lose a very minuscule bit more than one layer does. But then
your
giving yourself more work to try and increase the height of the space
you
need before you can lay boards as a storage platform. Doing the math
shows
that it is really not worth that kind of expense to gain so very little
more.


Fair enough - What about the ventilaition issue though? My loft
curently is fairly sealed so I'm intending to fit ventilated soffits (in
the future) and not insulate to the very edge etc. Is boarding laid
directly over insulation with very little air gap likely to lead to
problems (condensation etc) later? If I lay less insulation to give an
air gap then I will lose any insulation properties that the boards give
as the air will no longer be trapped?

I don't really want to go the whole hog of laying plastic sheet (as a
vapour barrier) if I can avoid it hence my thought that the greatest
amount of 'damp' air is in the bathroom so I won't boasrd over that...

Thanks for the advice so far...

Peter

If your bathroom has a window or a fan extraction system, then why worry
about damp air escaping through the plasterboard ceiling ? You can insulate
and board over the whole area in the loft of you want, unless that is, you
have holes up through the bathroom ceiling into the loft space.

No one is stopping the ventilation into the loft, you're only lagging the
space directly above the room ceilings to trap air so it doesn't escape as
quickly as it otherwise would. If that makes sense. :-))

Hi Folks,

"BigWallop" wrote in message
...
And if you cut to the length of the spacing of the joists, how much of
each
board do you loose ? Quite a bit I'd imagine. So if you keep all the
tongue and grooves together, no matter where the joint ends up, you be
able
to board out the whole loft, right up to edges, and it should all be
strong
enough for you to use as storage space.

When one board ends up with an overlap on one joist, then the other board
is
banged in against the edge of it, it will still have enough strength to
take
the weight of an average bloke, even if the joint ends up in the middle of
the gap in the joists, because of the construction of the boards.

I'm probably too cautious but I always make sure that any joint is supported
with
a noggin if it doesn't always work out to be over a joist.
True, the chances of someone jumping up and down on it are slim, until my 15
year old
lad ran along our upstairs corridor and jumped and landed on a joint with
such force
that he broke the tongue&groove! He then reported the fact that "the carpet
gave way"
which I always find amusing!

Simplifying for ascii-art, the tongue is like a "TTT" and the groove like a
"GGG". With
any downward pressure the weight must be on the lower edge of the groove's
"" ?
Therefore half the wood thickness is supporting the 15 year old landing on
it... snap.

If you are going to board an area for walking on, methinks it won't be that
much extra
effort to put (say) four by two noggings to support some part of a tongue
and groove
joint.
If it were to snap, consider how far the person may fall when they slip down
through the
crumbling plasterboard. In my house the worst drop would be through the
ceiling above
the stairwell... about 3 metres.

Just my opinion.

Mungo

"Mungo Henning" wrote in message
...
Hi Folks,

"BigWallop" wrote in message
...
And if you cut to the length of the spacing of the joists, how much of
each
snipped

If you are going to board an area for walking on, methinks it won't be
that
much extra
effort to put (say) four by two noggings to support some part of a tongue
and groove
joint.
If it were to snap, consider how far the person may fall when they slip
down
through the
crumbling plasterboard. In my house the worst drop would be through the
ceiling above
the stairwell... about 3 metres.

Just my opinion.

Mungo



You mean that every builder and joiner using the chipboard flooring in new
builds, has to put dwangs (noggins to you southerners) on the edge of each
and every board they lay and fix. I think you should get on to new building
sites a bit more. :-))

"BigWallop" wrote in message
...

You mean that every builder and joiner using the chipboard flooring in new
builds, has to put dwangs (noggins to you southerners) on the edge of each
and every board they lay and fix. I think you should get on to new
building
sites a bit more. :-))



"Southerner" indeed ... I'm from Ayrshire! :-)

What happens in "new builds" is not my concern. Squeaky floors and
15-year-old
kids dislodging chipboard flooring IS my concern, but only in my house.

Having replaced the floor of a friend's porch we had one extra 8' by 2'
length of flooring
grade chipboard left over. I suggested to the friend that they install the
surplus board in
their loft - they might as well use it somewhere.
The plan was to take the hand circular saw and cut the board so that each
half would
be easier to fit through the loft hatch.
"Ah but no" says I "I'll need to see the spacing so that the end of the
board sits on top of
a joist.
"But I haven't done that" says the householder. As it turns out the sparse
boards that the
householder did install were nailed down. Imagine a 13-stone bloke standing
on the overhang
of such a board, relying on the nails to hold it down!

So the final decision was that I could keep the surplus board myself.

Mungo

"Mungo Henning" wrote in message
...

"BigWallop" wrote in message
...

You mean that every builder and joiner using the chipboard flooring in
new
builds, has to put dwangs (noggins to you southerners) on the edge of
each
and every board they lay and fix. I think you should get on to new
building
sites a bit more. :-))



"Southerner" indeed ... I'm from Ayrshire! :-)

What happens in "new builds" is not my concern. Squeaky floors and
15-year-old
kids dislodging chipboard flooring IS my concern, but only in my house.

Having replaced the floor of a friend's porch we had one extra 8' by 2'
length of flooring
grade chipboard left over. I suggested to the friend that they install the
surplus board in
their loft - they might as well use it somewhere.
The plan was to take the hand circular saw and cut the board so that each
half would
be easier to fit through the loft hatch.
"Ah but no" says I "I'll need to see the spacing so that the end of the
board sits on top of
a joist.
"But I haven't done that" says the householder. As it turns out the sparse
boards that the
householder did install were nailed down. Imagine a 13-stone bloke
standing
on the overhang
of such a board, relying on the nails to hold it down!

So the final decision was that I could keep the surplus board myself.

Mungo



Now that is asking for trouble. :-)) I said, only if the other boards
around it were fitted into the tongue and groove of the other boards. That
way, any overhangs are left out at the edges which you can't stand on. But
the design of these boards is meant to take the weight of normal use on the
tongue and groove sections.