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Cavity wall insulation and damp

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Editor:
We had a bloke round the other day to assess our house for cavity wall insulation. It's a 1930s detached. 

He took one look and said he wouldn't touch it because he said it would likely cause damp. We have never had a problem with damp, but he said that cavity wall insulation would create damp because of the age of the house and the way they were built.

He then told us that we are probably losing 40% of our heat through the walls. He suggested the answer might be a new treatment coming out in the autumn where you attach panels to the outside of the house and render over.

Anyone else had cavity wall insulation conversations like this?

Alfred the Great:
If your outside wall is in sound order, there's no reason why cavity insulation should cause damp. However, if your house is rendered then you would need to be sure that there were no cracks through which damp could penetrate.

But I'm wondering if you actually have cavity walls Dave because if it was built in the 30s it will almost certainly be 9" solid brick. This might also be why he suggested applying a coating to the outside and rendering over. Many council houses of pre war build have been upgraded in this way, but it doesn't always improve the appearance as they use horrible looking fine stone render finish to save putting a hard outer surface on.

If you are 9" solid brick with render on the outside then your heat losses will be like ours were (with identical build), ie, horrendous. So do you want good appearance or low heating bills?

Do you have any bare brickwork in the roof space? If so, you could prove whether or not you have a solid wall by looking at the bonding. Or you could just measure the wall thickness by an original opening, adding on about 2" for the internal plaster and external render.

BrookyP:
hi david.

we had loft insulation and it caused huge problems in the loft with condensation as it was tucked to close to the eaves and blocked airflow. now sorted thankfully.

we have had cavity done  in an 80s build house with no issues at all.

i guess you have to find out if its damp or condensation he's talking about.

with cavity wall installs they will put a vent in to your wall  to prevent condensation. This is a compulsory building regs thing.
My vent is now blocked up as it was too cold in the winter and all is fine after 2 years.

dont forget cavity is free/reduced from the council contractors.

ta bp

Ferdie:
David, No and I have had mine done, but my house is 1950's built and (so far) no issues at all.

The following information on Which? website may be of interest http://www.which.co.uk/energy/saving-money/guides/how-to-buy-wall-insulation/

I wonder if the person making this suggestion has a vested interest in this new method and is trying to buy time so he can offer that when the time comes? I believed this was being introduced for houses without cavity walls. By the sound of it, this new method will be considerably more expensive and therefore potentially more lucrative for installers. I also remember the horror stories of its predecessor the 'dreaded stone cladding brigade' that so blighted victims in the 1970's. The new insulation method will involve changing the appearance of houses and some are expressing concern about the affect that will have on the overall appearance of towns and villages. Of course many properties have already had successful external cladding, this can be seen in some Council houses in Welham Green which have solid walls and were clad many years ago and re-rendered. It is noticible against properties that were bought under the 'right to buy' and were not clad in the terrace.

The plan is the energy companies will be expected to subsidise the cost of this new external insulation, but I guess that will mean we'll all end up paying even more for our energy bills.

epiphany:
I have always felt that the cavity is there for good reason and to bridge the gap could
potentially lead to moisture penetration from the outer skin or interstitial condensation
due to reduced ventilation and/or subsequent change of temperature making dew point more probable.

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