The cavity wall insulation in my house...

[Al Ackroyd]

My house has solid stone walls, about 18" thick. Onto the house, an extension was built in the 1990s. It has cavity walls, into which polystyrene sheets, about 30mm thick were inserted into the cavity. I have some questions:

Is the polystyrene board going to have any significant heat- conserving effect (considering that ther is a good bit of empty airspace on each side of it?

Does the presence of the polystyrene sheet preclude me from adding more insulation to the cavity such as expanding foam or whatever?

What is the best type of insulation to add?

What is the heat-insulating property of a 18" stone wall? Is it better or worse than a regular cavity wall?

Many thanks,

Al

[dom]

Yes.

It would have to be injection, which I think is usually polyurethane or polyisocyanurate - although it may not increase the insulation value by much, it may help seal off heat loss due to air leakage. See manufacturers data for compatibility info.

Much worse than a cavity wall - solid masonry will be responsible for a truly dreadful heat loss.

It's so bad that double-glazing is near-pointless until you've sorted out the walls.

I've added 50-100mm celotex/kingspan throughout my solid-wall property

- and the transformation is incredible - I'm getting lower heating bills than my neighbour in a high-spec recent-build bungalow.

[The Natural Philosopher]

yes.

no

anything that reduces air movement without adding conductivity will do. avoid things that cam fill with water though. .

Slightly worse I would say., I do recall calculating that a 3 meter thick stone castle wall would meet modern insulation regulations.

Hmm sandstone as a k value of 2.4, so the U value of 18" is ..ahem ..

5.2 or so.

That's about the same as a poor double glazed widow or a good single glazed one, or a thick wooden door.

My regs book indicates that an otherwise uninsulated cavity wall is about 2.6, so twice as good really.

Target wall U values are ten times that or better, to modern standards, about 0.2-0.5 being where you are getting more heatloss from ventilation than from the walls themselves.

To get your wall to say 0.5 or so, you need to line it with material of a U value of about 0.55 I would say..essentially at that sort of conductivity and target U values the wall of stone might as well not be there, heatloss wise..35 mm of celotex will give you that. Ten times better (less) heatloss than the bare stone.

Of course., building control will insist that you go for 75mm to bring it up to spec, but maybe don't tell them.

[The Natural Philosopher]

Double glazing is nearly always pointless anyway. windows are not the biggest areas or anything like it, in a house, and the gains from double glazing are not great.

I would think you should at that sort of thickness!

[spamlet]

That was an interesting little tour of rocks and thermodynamics and building materials your question has sent me on. In general it seems that stone is more conductive, the harder and denser it is, but you also have the heat storing effects to consider as well so a thick solid stone wall like yours will be less subject to daily outdoor temp fluctuations than one with thin stone walls, but still will lose heat faster overall than modern methods and materials (you can do a certain amount of 'passive' heating say, by putting a big block of dark stone indoors in front of a south facing window - then it keeps the room warm over night). However, what you may find useful is this table:

the 'engineering toolbox' looks like a goldmine of useful info of diyers of all kinds!

If your 18" is chalk you might be in luck!

S

[Al Ackroyd]

Thanks to all for the helpful replies. It sounds like Celotex or similar might be a good investment then. Nevertheless, it would be a pricey job, so I'll look into what grants might be available. I like the idea because my exterior walls have a slight damp issue too, wich would also be sealed in by the Celotex board.

Interesting comment about double glazing. I'll cross that off my to-do list then, and save £££'s Thank you.

Am I right in thinking that when improving the insulation of one's house, the biggest benefit-to-cost ratio is to be had by improving loft insulation? (my loft has virtually none, and it's drafty up there too, as felt is missing in places etc.)

Al

[John Rumm]

To be fair, they are usually pragmatic if you are making some improvement...

You may find this handy:

solid walls you have the choice of whether to insulate inside or outside. There are pros and cons to both.

There is more to DG than just energy saving though. Reducing noise, or condensation, or increasing security may also be factors.

Generally a principle of going for the low hanging fruit pays off. So an uninsulated loft will lose vast amounts of heat, and is very easy to upgrade - so that is a good first choice. If you already had say 100mmm of loft insulation, then adding cavity wall insulation (or dry lining etc) would give a bigger overall reduction than say adding an extra

100mm of loft insulation - although doing both would be better still.

If you play with the heat loss spreadsheet you can soon see what relative differences you get.

[Tim Streater]

Indeed. There is the fact that the windows fit and close properly, and so don't leak cold air. Like some in this house that we moved to just before the big freeze last Dec. Any hint of East or North wind, and freezing draughts around the house.

Also, in our bedroom - the first time I've seen ice on the inside of the window since I was a kid - 50 years ago. Our new DG will fix all that.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Al Ackroyd" saying something like:

It's about as bad as a single-skin brick wall. It usually comes as a great surprise to owners of such walls, but the heat just keeps on keeping on - out the way.

[Al Ackroyd]

Excellent help - thank you,

Al

[Al Ackero]

"spamlet" wrote in news:NYnAn.315323$ [e-mail]:

Yes, I had wondered about that.

but still will lose heat faster

Food for thought! I'm short of South-facing windows unfortunately...

Thanks, it was interesting. It seems that my 18" Portland stone walls would be about 1.33 (i.e., limestone), except that they consist of about 25% lime mortar. One thing I keep noticing is that the part of the house built with modern cavity walls seems to get colder than the stone part, so perhaps the stone and lime mortar combo isn't so bad after all.

Al

[The Natural Philosopher]

If they are vented, they will be wiorse ..

[spamlet]

I was discussing the stone wall problem yesterday with my brother in law who has a thick stone walled cottage in Cornwall. Much of the appeal of the building is in the very thick and irregularly surfaced walls, so getting an insulating coating on the inside would rather spoil the effect, but, on the other hand if the building is allowed to cool down, there is a lot of condensation until the stone warms up again. Originally there would probably have been a turf fire going all year round to prevent this, but the modern best they could come up with was storage heaters...

Mind you, if someone had a very very big angle grinder that could put a slot down the middle of those walls... The roof would fall in...

:-)