Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

Yes.

If you've correctly calculated the U value.
You do know that you can't add U values to get the value of the composite
wall, but have to add the R values to get a composite R value, then
convert that to a U value (R=1/U)


My thoughts right now are to save the money, and use it to put extra
into the roofspace.

U value gives you the number of watts per square meter at a 1K (1C)
difference.

To get the number of average watts you'll need to overcome the heat lost
from the walls, you take the average temperature difference (in C), multiply
by the area of the walls, multiply this by the U value, and you'r there.

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly. For heat loss purposes, the stone wall inner face will
have an averaging effect on the temperature as seen by the outside of
the insulation

Assuming that you can accomodate the extra thickness of Rockwool and
don't mind working with it

I would do the same heat loss calculations for the roof and compare
the overall figures. Normally the roof space and the totality of the
windows have about the same heat losses as one another and account
together for approximately the other half vis-a-vis the walls. It
does all depend on sizes of course.




..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly.

Not that quickly as he has block on the inside. He should use normal
plaster on the block to give access to the thermal mass of the blocks.

On Fri, 20 Aug 2004 20:24:48 GMT, Rick Dipper
wrote:

On Fri, 20 Aug 2004 19:19:22 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly. For heat loss purposes, the stone wall inner face will
have an averaging effect on the temperature as seen by the outside of
the insulation

Assuming that you can accomodate the extra thickness of Rockwool and
don't mind working with it

I would do the same heat loss calculations for the roof and compare
the overall figures. Normally the roof space and the totality of the
windows have about the same heat losses as one another and account
together for approximately the other half vis-a-vis the walls. It
does all depend on sizes of course.



Thanks Andy, I am not sure I understand what you are saying, the stone
wall is on the outside, I think you think its on the inside.

No, sorry. I did mean that the wall is on the outside as you describe
but did not describe it as well as I should have done.

What I meant was that if you treated the outside wall as not existing
as you were for insulation calculation, you have outside temperature.
If you add the wall back in, you have not only its U value (which will
make things better), but more importantly a huge thermal mass. The
effect of that will be to stabilise the temperature to some extent at
the point where the insulation meets the outer wall.
Therefore, looking at your model of effectively ignoring the wall, the
effect will be to give a much more stable "outside" temperature - in
other words you won't need to account for the extremities of
temperature unless they last a long time.
It is hard to say whether this has a big overall effect on energy use
averaged over time, but if the temperature can be maintained in a more
stable way inside, you are less likely to want to reach for the
thermostat.



Doing the figure for the roof sort of imples that we have designed it,
we have some sketches and strength caculations but have not got much
further, thats for a cold winters night.


There are tables of U values for roof structures in the building
regulations. To a first approximation, you can simply factor in
the U value of the insulation. By comparing the relative areas and
losses of the walls roof and windows, you can then figure out where
the cost/benefit comes.





.andy

To email, substitute .nospam with .gl

..andy

To email, substitute .nospam with .gl

On Fri, 20 Aug 2004 19:09:49 +0100, "IMM" wrote:


"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish


Sir IMM

Even at 2.55 the insulation is costing more than the
blocks/sand/cement. My outside wall has a lean on it, I intend to fill
the whole space with insulation, giving some 8 - 10 inches of the
stuff at the top of the wall. 8-10 inches of celotex is mind blowingly
expensive.

200mm Rockwall at 0.037 = 5.54
+ blocks .6666

Comes out at 0.16, getting down to 0.1 is gonna make for some very
expensive walls.

The idea of more insulation at the top of the walls feels good, heat
rises, so the tempertaure difference is bigger at the top. My room
will be 3 meters high of walls, with 2 more meters to the top of the
pointed roof.

Thanks
Rick

"IMM" wrote in message
...

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

No he shouldn't ! The L regs require 0.35. Of course doing better than
this is a good thing but you are better off spending the money improving
other heat losses - windows and doors for example.

"Andy Hall" wrote in message
...
What I meant was that if you treated the outside wall as not existing
as you were for insulation calculation, you have outside temperature.
If you add the wall back in, you have not only its U value

but not much - even 2 feet of stone has a very poor insulation value.


but more importantly a huge thermal mass.

This is more important though. However one has to be careful not to end up
with a thermal lag so bad that south facing living rooms stay cold all day
and need more heat than expected to keep them warm until evening when they
suddenly warm up dramatically.

On 20 Aug 2004 17:39:33 GMT, Ian Stirling
wrote:

Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

Yes.

If you've correctly calculated the U value.
You do know that you can't add U values to get the value of the composite
wall, but have to add the R values to get a composite R value, then
convert that to a U value (R=1/U)


My thoughts right now are to save the money, and use it to put extra
into the roofspace.

U value gives you the number of watts per square meter at a 1K (1C)
difference.

To get the number of average watts you'll need to overcome the heat lost
from the walls, you take the average temperature difference (in C), multiply
by the area of the walls, multiply this by the U value, and you'r there.

Thanks

I got U values by doing
100mm blocks / 0.15 (from makers website) = .6666
50mm celotex / 0.023 = 2.1739
60mm rockwall / 0.037 = 1.6216
All those up = 4.4621
1/4.4621 = 0.224

on a cold winters day, 24 degress difference, 75 square meters of wall

75*24*0.224 = 40.32 watts required of heat input to maintain stable
temperature assuming no loss from other means.

That does not sound very much to me, the coolong from wind will be
close to zero, the house is well sheltered desined so the windy side
has no doors/windws at all, and the insulation is protected with some
600mm of stone walls.

Any idea of the values for a slate/lime mortar stone/rubble wall ?

Thanks
Rick

On Fri, 20 Aug 2004 19:19:22 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly. For heat loss purposes, the stone wall inner face will
have an averaging effect on the temperature as seen by the outside of
the insulation

Assuming that you can accomodate the extra thickness of Rockwool and
don't mind working with it

I would do the same heat loss calculations for the roof and compare
the overall figures. Normally the roof space and the totality of the
windows have about the same heat losses as one another and account
together for approximately the other half vis-a-vis the walls. It
does all depend on sizes of course.



Thanks Andy, I am not sure I understand what you are saying, the stone
wall is on the outside, I think you think its on the inside.

Doing the figure for the roof sort of imples that we have designed it,
we have some sketches and strength caculations but have not got much
further, thats for a cold winters night.


.andy

To email, substitute .nospam with .gl

IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling) result in overheating
most of the time except in sub-zero temps from the ambient electrical load,
and human inhabitents, not to mention solar gain.

If going from 0.25 to 0.1 costs around 1500 quid extra (and incidentally
knocks 50 cubic meters off the habitable space), saving me no money,
unless it goes below 10C outside (heating set to 20C now) and vanishingly
small amounts if it does. (currently I reckon the overall insulation is
about 900W/K, with the walls having a U of about 2.4)

Rick Dipper wrote:
On 20 Aug 2004 17:39:33 GMT, Ian Stirling
wrote:

Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

Yes.

If you've correctly calculated the U value.
You do know that you can't add U values to get the value of the composite
wall, but have to add the R values to get a composite R value, then
convert that to a U value (R=1/U)


My thoughts right now are to save the money, and use it to put extra
into the roofspace.

U value gives you the number of watts per square meter at a 1K (1C)
difference.

To get the number of average watts you'll need to overcome the heat lost
from the walls, you take the average temperature difference (in C), multiply
by the area of the walls, multiply this by the U value, and you'r there.

Thanks

I got U values by doing
100mm blocks / 0.15 (from makers website) = .6666
50mm celotex / 0.023 = 2.1739
60mm rockwall / 0.037 = 1.6216
All those up = 4.4621
1/4.4621 = 0.224

Assuming you've got the above numbers correct (and they look ballpark)
then that's right.

on a cold winters day, 24 degress difference, 75 square meters of wall

75*24*0.224 = 40.32 watts required of heat input to maintain stable
temperature assuming no loss from other means.

Sounds about right.

That does not sound very much to me, the coolong from wind will be
close to zero, the house is well sheltered desined so the windy side
has no doors/windws at all, and the insulation is protected with some
600mm of stone walls.

Any idea of the values for a slate/lime mortar stone/rubble wall ?

A 1m sandstone wall has a U of about 2.4.
In other words, it's slightly worse than 50mm of celotex.
(rather higher thermal mass though)

Rick Dipper wrote:

- Also the money saved can be better spent insulating the 2 rooms that
we have not rebuilt, that simply have stone walls.

Having just had to buy loads of foil faced PIR foam, one thing worth
doing is shopping around. I saved over 1500 quid on the price of celotex
as quoted by a builders merchant! It is still not cheap (about 12 quid
for a 8x4 50mm sheet) but a factor of two to three times variation in
price between suppliers is not uncommon it seems.

--
Cheers,

John.

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

On Fri, 20 Aug 2004 21:06:11 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 20:24:48 GMT, Rick Dipper
wrote:

On Fri, 20 Aug 2004 19:19:22 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly. For heat loss purposes, the stone wall inner face will
have an averaging effect on the temperature as seen by the outside of
the insulation

Assuming that you can accomodate the extra thickness of Rockwool and
don't mind working with it

I would do the same heat loss calculations for the roof and compare
the overall figures. Normally the roof space and the totality of the
windows have about the same heat losses as one another and account
together for approximately the other half vis-a-vis the walls. It
does all depend on sizes of course.



Thanks Andy, I am not sure I understand what you are saying, the stone
wall is on the outside, I think you think its on the inside.

No, sorry. I did mean that the wall is on the outside as you describe
but did not describe it as well as I should have done.

What I meant was that if you treated the outside wall as not existing
as you were for insulation calculation, you have outside temperature.
If you add the wall back in, you have not only its U value (which will
make things better), but more importantly a huge thermal mass. The
effect of that will be to stabilise the temperature to some extent at
the point where the insulation meets the outer wall.
Therefore, looking at your model of effectively ignoring the wall, the
effect will be to give a much more stable "outside" temperature - in
other words you won't need to account for the extremities of
temperature unless they last a long time.
It is hard to say whether this has a big overall effect on energy use
averaged over time, but if the temperature can be maintained in a more
stable way inside, you are less likely to want to reach for the
thermostat.



Doing the figure for the roof sort of imples that we have designed it,
we have some sketches and strength caculations but have not got much
further, thats for a cold winters night.


There are tables of U values for roof structures in the building
regulations. To a first approximation, you can simply factor in
the U value of the insulation. By comparing the relative areas and
losses of the walls roof and windows, you can then figure out where
the cost/benefit comes.



Thanks Andy, now I understand. The building your own house is a good
way to learn how this stuff works. Experience in the bit of the house
we live in now suggest that once its hot inside it stays hot, but
getting it up from cold is a real nightmare.

At a guess,

- the underfloor heating needs massive insulation below it, as its the
hottest place, the area being much smaller than the walls its also
quite cheep to do.

- The windows need to be good, especially the one in the point of the
roof where all the heat rises too. and the sliding door in the master
bedroom. This one needs some thinking about, windows can eat up *LOTS*
of money.

- The roof itsself will need pleanty, not only to stop loss in winter,
but to stop gain in summer. The ammount of money I can save on the
extra 12% in the wall, will double the insulation in the roof.

- Also the money saved can be better spent insulating the 2 rooms that
we have not rebuilt, that simply have stone walls.

Thanks for all your advice, I feel much happier now. I really did not
want to save a pile of cash now so I could regret it for 25 years to
come.

Rick




.andy

To email, substitute .nospam with .gl

.andy

To email, substitute .nospam with .gl

On 20 Aug 2004 20:34:13 GMT, Ian Stirling
wrote:

IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling) result in overheating
most of the time except in sub-zero temps from the ambient electrical load,
and human inhabitents, not to mention solar gain.

If going from 0.25 to 0.1 costs around 1500 quid extra (and incidentally
knocks 50 cubic meters off the habitable space), saving me no money,
unless it goes below 10C outside (heating set to 20C now) and vanishingly
small amounts if it does. (currently I reckon the overall insulation is
about 900W/K, with the walls having a U of about 2.4)

Which works out at about 10 pence of elcetric an hour, that sounds
good to me, especailly if we go geo-thermal and get it down to 2.5
pence an hour.

Thanks Ian, I now see a second problem of overinsulation, overheating.

Rick

"Ian Stirling" wrote in message
...
IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling)
result in overheating most of the time except
in sub-zero temps from the ambient electrical load,
and human inhabitents, not to mention solar gain.

You install adequate ventilation.

If going from 0.25 to 0.1 costs around
1500 quid extra (and incidentally
knocks 50 cubic meters off the habitable
space), saving me no money,
unless it goes below 10C outside
(heating set to 20C now) and vanishingly
small amounts if it does. (currently I reckon
the overall insulation is
about 900W/K, with the walls having a U of about 2.4)

0.1ish is the point where a 2000 squ foot house does not require a full
heating system. So this extra £1500 is clawed back by not installing a full
heating system. As oil is not getting cheaper, it is a worthwhile investment
for the future. Also the insulation will keep out heat in the summer. All
makes sense.

"Rick Dipper" wrote in message
...

More is always better.

"G&M" wrote in message
...

"Andy Hall" wrote in message
...
What I meant was that if you treated the outside wall as not existing
as you were for insulation calculation, you have outside temperature.
If you add the wall back in, you have not only its U value

but not much - even 2 feet of stone has a very poor insulation value.

but more importantly a huge thermal mass.

This is more important though. However one has to be careful not to end
up
with a thermal lag so bad that south facing living rooms stay cold all day
and need more heat than expected to keep them warm until evening when they
suddenly warm up dramatically.

If south facing you enlarge windows and use passive solar gain.

"G&M" wrote in message
...

"IMM" wrote in message
...

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

No he shouldn't !

He should.

The L regs require 0.35.

Which is pathetic and is going to be increased over the next 4 years.

Of course doing better than
this is a good thing

Sense at last.

but you are
better off spending the money improving
other heat losses - windows and doors
for example.

He is probably doing that already. He is better off getting the walls to
0.1ish, as once done it is difficult, and very expensive, to uprate.

It is common simple logic.

"Rick Dipper" wrote in message
...
On 20 Aug 2004 20:34:13 GMT, Ian Stirling
wrote:

IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling) result in overheating
most of the time except in sub-zero temps from the ambient electrical
load,
and human inhabitents, not to mention solar gain.

If going from 0.25 to 0.1 costs around 1500 quid extra (and incidentally
knocks 50 cubic meters off the habitable space), saving me no money,
unless it goes below 10C outside (heating set to 20C now) and vanishingly
small amounts if it does. (currently I reckon the overall insulation is
about 900W/K, with the walls having a U of about 2.4)

Which works out at about 10 pence of elcetric an hour, that sounds
good to me, especailly if we go geo-thermal and get it down to 2.5
pence an hour.

Thanks Ian, I now see a second problem of overinsulation, overheating.

There is no problem of overheating. Where do they come from?

IMM wrote:

"Rick Dipper" wrote in message
...

More is always better.

No, it's not.
If you end up living in a 2m*2m*1m box, and having to constantly actively
cool, then you've probably put too much on.

"Rick Dipper" wrote in message
...
On Fri, 20 Aug 2004 21:06:11 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 20:24:48 GMT, Rick Dipper
wrote:

On Fri, 20 Aug 2004 19:19:22 +0100, Andy Hall
wrote:

On Fri, 20 Aug 2004 17:43:23 GMT, Rick Dipper
wrote:


I have worked out the U values of the insulation I intend to use in my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

I did not take account of the external wall, plaster, mortar or wall
ties in working out these figures. The external walls are 600mm stone
walls.

Normally I would go for option 1, but its arround twice the cost of
option 2, a whole lot more difficult to install (I am building the
inner wall second) and there is not a big difference in the insulation
values.

Any ideas on how I work out if its worth it ?

Is it as simple as working out the temperature difference, the surface
area of the wall, to work out the loss via the wall, and then mutiply
by the cost of a watt of heat ?

My thoughts right now are to save the money, and use it to put extra
into the roofspace.

Thanks
Rick

taking Ian's point that you have to add the reciprocals of the U
values of the different insulations and then the reciprocal of that to
combine them, and assuming the figures you have above are right, then
the discussion is about the second decimal place and in effect a 12%
difference. This is not significant.. You also have the effect
of the stone. By insulating, you are altering the thermal time
constant of the inside of the house. It will heat up and cool down
quickly. For heat loss purposes, the stone wall inner face will
have an averaging effect on the temperature as seen by the outside of
the insulation

Assuming that you can accomodate the extra thickness of Rockwool and
don't mind working with it

I would do the same heat loss calculations for the roof and compare
the overall figures. Normally the roof space and the totality of the
windows have about the same heat losses as one another and account
together for approximately the other half vis-a-vis the walls. It
does all depend on sizes of course.



Thanks Andy, I am not sure I understand what you are saying, the stone
wall is on the outside, I think you think its on the inside.

No, sorry. I did mean that the wall is on the outside as you describe
but did not describe it as well as I should have done.

What I meant was that if you treated the outside wall as not existing
as you were for insulation calculation, you have outside temperature.
If you add the wall back in, you have not only its U value (which will
make things better), but more importantly a huge thermal mass. The
effect of that will be to stabilise the temperature to some extent at
the point where the insulation meets the outer wall.
Therefore, looking at your model of effectively ignoring the wall, the
effect will be to give a much more stable "outside" temperature - in
other words you won't need to account for the extremities of
temperature unless they last a long time.
It is hard to say whether this has a big overall effect on energy use
averaged over time, but if the temperature can be maintained in a more
stable way inside, you are less likely to want to reach for the
thermostat.



Doing the figure for the roof sort of imples that we have designed it,
we have some sketches and strength caculations but have not got much
further, thats for a cold winters night.


There are tables of U values for roof structures in the building
regulations. To a first approximation, you can simply factor in
the U value of the insulation. By comparing the relative areas and
losses of the walls roof and windows, you can then figure out where
the cost/benefit comes.



Thanks Andy, now I understand. The building your own house is a good
way to learn how this stuff works. Experience in the bit of the house
we live in now suggest that once its hot inside it stays hot, but
getting it up from cold is a real nightmare.

At a guess,

- the underfloor heating needs massive insulation below it, as its the
hottest place, the area being much smaller than the walls its also
quite cheep to do.

- The windows need to be good, especially the one in the point of the
roof where all the heat rises too.

You can fit a duct that is built into the wall that fans this hot air back
to ground level.

and the sliding door in the master
bedroom. This one needs some thinking
about, windows can eat up *LOTS*
of money.

- The roof itsself will need pleanty, not only to stop loss in winter,
but to stop gain in summer. The ammount of money I can save on the
extra 12% in the wall, will double the insulation in the roof.

It is not a matter of robbing Peter to pay Paul. You insulate properly,
0.1ish for the walls. Buy the book, The Whole House Book, all is there, all
the figures. Don't rely on the advise of inexperienced people making it up.

- Also the money saved can be better
spent insulating the 2 rooms that
we have not rebuilt, that simply have stone walls.

Thanks for all your advice, I feel much happier now. I really did not
want to save a pile of cash now so I could regret it for 25 years to
come.

Spend more on insulation and eliminate a full hearting system.

IMM wrote:

"Rick Dipper" wrote in message
...
On 20 Aug 2004 20:34:13 GMT, Ian Stirling
wrote:

IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling) result in overheating
most of the time except in sub-zero temps from the ambient electrical
load,
and human inhabitents, not to mention solar gain.
snip
There is no problem of overheating. Where do they come from?

Unless you are insane, there is no point in insulating better
than where the minimum solar gain plus energy emitted by the house
equipment and householders causes a temperature rise high enough over
ambient that it'll be warm enough even on the coldest blizzard.

Adding more just reduces habitable volume, and adds cost.
You've also got to consider on whether you want to hit this level.

At what point does the income of just sticking the money in the bank of
a portion of your insulation at base-rate exceed the savings on possibly
rising energy costs.

"Ian Stirling" wrote in message
...
IMM wrote:

"Rick Dipper" wrote in message
...
On 20 Aug 2004 20:34:13 GMT, Ian Stirling
wrote:

IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use
in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling) result in
overheating
most of the time except in sub-zero temps from the ambient electrical
load,
and human inhabitents, not to mention solar gain.
snip
There is no problem of overheating. Where do they come from?

Unless you are insane, there is no point in insulating better
than where the minimum solar gain plus energy emitted by the house
equipment and householders causes a temperature rise high enough over
ambient that it'll be warm enough even on the coldest blizzard.

Adding more just reduces habitable volume, and adds cost.
You've also got to consider on whether you want to hit this level.

At what point does the income of just sticking the money in the bank of
a portion of your insulation at base-rate exceed the savings on possibly
rising energy costs.

It is obvious you don't know enough about this subject. Do a Google on
"superinsulation" and a raft of information comes up. Read it all.

On Fri, 20 Aug 2004 23:26:11 +0100, IMM wrote:


"Rick Dipper" wrote in message
...

More is always better.

Surely the rule of diminishing returns applies here.

Dave

--

Some people use windows, others have a life.

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

"Tom" wrote in message
...

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

???

"IMM" wrote in message
...

"Tom" wrote in message
...

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

???
Sorry, I was just making the point that whereas increasing the insulation on
a plane surface is always additive hence your supposition "more is better",
on a pipe it is not so.
Sorry to butt in.
Cheers
Tom

Tom wrote:

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

Even around a pipe, but to a much, much lower degree.

"Tom" wrote in message
...

"IMM" wrote in message
...

"Tom" wrote in message
...

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

???
Sorry, I was just making the point that whereas increasing the insulation
on
a plane surface is always additive hence your supposition "more is
better",
on a pipe it is not so.

It depends on what you want to do with the insulation around the pipe. If
you want to prevent heat from a pipe heating up say a cupboard, then more is
better.

"IMM" wrote in message
...

If south facing you enlarge windows and use passive solar gain.

Not in a conservation area you don't. I would love to as my windows are
under 12% of the wall area.

"Rick Dipper" wrote in message
...

Thanks Ian, I now see a second problem of overinsulation, overheating.

This can happen in some very modern highly insulated houses but for most of
us doing up existing houses it ain't going to happen. There will always be
thermal bridges and so on leaking heat.

And if it does happen all one has to do is use low energy lighting and so
on.

"Ian Stirling" wrote in message
...

A 1m sandstone wall has a U of about 2.4.

Yes

In other words, it's slightly worse than 50mm of celotex.

Nope. 50mm of Celotex has a U value of 0.46

G&M wrote:

"Ian Stirling" wrote in message
...

A 1m sandstone wall has a U of about 2.4.

Yes

In other words, it's slightly worse than 50mm of celotex.

Nope. 50mm of Celotex has a U value of 0.46

For large values of slightly

I think I meant to type 10mm, but got confused.

"G&M" wrote in message
...

"Rick Dipper" wrote in message
...

Thanks Ian, I now see a second problem of overinsulation, overheating.

This can happen in some very modern highly insulated houses but for most
of
us doing up existing houses it ain't going to happen. There will always
be
thermal bridges and so on leaking heat.

And if it does happen all one has to do is use low energy lighting and so
on.

or open a window

In article , Ian
Stirling wrote:
If going from 0.25 to 0.1 costs around 1500 quid extra (and
incidentally knocks 50 cubic meters off the habitable space)
^^^^^^^^^^^^

Given that more than a few buildings are constrained by having to be x
from the boundary or some other limitation, increasing the wall
insulation thickness reduces the internal floor area. This is more
than just 'incidental' IMO.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm

"G&M" wrote in message
...

"IMM" wrote in message
...

If south facing you enlarge windows and use passive solar gain.

Not in a conservation area you don't. I would love to as my windows are
under 12% of the wall area.

Well move and get a proper house.

"Ian Stirling" wrote in message
...
Tom wrote:

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

Even around a pipe, but to a much, much lower degree.

On a pipe, I assume the surface area of the insulation increases by a factor
of approx 6.3 times the thickness of the insulation, I'm afraid my maths is
not good enough to work out at which point it starts to be non effective.
Perhaps there are some mathematicians out there that can help on this one.?
Tom

Tom wrote:

"Ian Stirling" wrote in message
...
Tom wrote:

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

Even around a pipe, but to a much, much lower degree.

On a pipe, I assume the surface area of the insulation increases by a factor
of approx 6.3 times the thickness of the insulation, I'm afraid my maths is
not good enough to work out at which point it starts to be non effective.
Perhaps there are some mathematicians out there that can help on this one.?

It never starts to be non-effective, it's always better than air.
It rapidly starts to have a vanishingly small effect.
Consider the heat flow.

The heat flow from the surface of the pipe is the same as the heat flow from
the surface of the insulation. (once it's all reached steady temps)
This means that the temperature difference across the last little bit
of insulation depends on its area.
So, at ten times the pipe diameter, the insulation is only doing
1/10th as good a job as that just next to the pipe.
If you need a very well insulated pipe (or worse, tank that's small
compared to the insulation) then it usually pays to buy some really
expensive insulation to put next to the pipe,

For example, considering the insulation at various numbers of times
the pipe diameter from the surface of the pipe. (1 is next to the pipe)

Distance from pipe Relative insulation
1 1
2 1/2
3 1/3
4 1/4
5 1/5

Total=2.28 (this is inaccurate, finer and finer graduations would give a
more accurate idea, but this is ballpark)


So the last fifth has contributed about a tenth.
But it's a third of the total volume.