DIY Conservatory Cavity wall insulation


4 Aug 2003
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United Kingdom
The glazing part of the conservatory has come to the end of its life, but the base and the dwarf walls are fine. We are therefore having the conservatory roof and windows only replaced.

The company has taken down the roof and windows which has revealed - as expected - the walls cavities are not insulated. The cavity is pretty narrow (approx 60mm between the bricks) so the total volume of the cavity for all walls is about 40cuft.

Although I have some 50mm celotex, I can't use that because of the ties which stop me sliding the celtex down. So I was thinking of using EPS beads which I could pour in from the top and gently rod to ensure no voids.

I know these wont be glued like a professional blower, but as they are mainly dwarf wallsthey are unlikely to be drilled or cut into so no real risk of a snow storm for later changes :)

Any comments - like dont do it, or seems like the best solution
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The difference will be tiny. I'm sure you won't notice it, but if you heat this conservatory it might reduce the proportion of the bill relating to the connie by 2-3%.

Do it if you wish, but if you have to pay for the beads, don't expect any payback.
If the cavity is open & you have a few quid to spare you might as well put something in there as not but, as stated, the difference it's going to make will be tiny compared to the heat loss through the roof & windows. Can you get cavity bats in there? Are you having a new roof as well?
Roof will be aluminium with Pilkington active glass. Walls will be UPVC with Pilkington K glass, so a massive improvement on the broken and thin panes previously there. Heat loss from the glass will always be an issue with conservatories, but we have gone for about the best we can.

The conservatory has low level heating, but we never intended to be sitting in there in the depth of winter just to look at the stars so it's not hot. Our bougenvilla generally manges to keep most of it's leaves through the winter in the conservatory so it can't bee freezing.

Cavities are open at the moment (protected by some tarps I have put over them) so access from the top is easy.

Richard, thanks for the suggestion. I don't really want to use mineral wool, and anyway, I have the same issue with batts as I do with the celotex - the wall ties are in the way. If I can solve that problem then as I already have enough Celeotex, I'd use that.

The beads seemed a way of overcoming the ties issue.

Looking on the web (admitedly from packaging or bean bag refill suppliers) I can get 40cuft of beads for under £100. Yes I know that's not exactly cheap and I doubt we will save that in heating during my lifetime (in the house at lest :) ), but if for the same heating cost as now the ambient temperature is higher and more comfortable, then it might be worth it.

I'm more concerned about problems we might get by doing it, and alternative suggestions on how to do it.

The other thing is that we do have one wall (bordering our neighbours) that is about 2m high and which has a balanced flue gas fire in it. What are the implcations of beads around that?
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I don't know the regulatory position on this, but I see no real risk.

A balanced-flue has two concentric pipes. The inner one exhausts the flue gases and the outer one sucks in air for combustion. The outer skin is therefore in contact with air drawn in at ambient temperature .

My b-f is only warm to the touch and that is exhausting gases from a 25kW boiler. I think it highly unlikely your gas-fire will create any problem.

If you still have any concerns , just wrap it in glass-wool/Rockwool this will both serve to keep the pellets off the flue and also insulate with fire-proof material.
Thanks for the replies.

Since I'm not likely to get much gain, and I have already paid for celotex that I wont be able to use for some time due to the the dry rot delaying finishing one room and the missus banning me from ripping any other part of the house apart this year, I'm thinking I might use the celotex.

If I cut it into smaller pieces and work it around the ties I can get it in the cavity. Obviously there will be a lot more joins and they wont be taped and probably not even very tight joins, so there will be "holes" in the coverage.

But the money is already spent on the celotex so no additional outlay, getting it out of the spare room will get me brownie points and as both Richard C and Mountainwalker say, something is better than nothing.

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