My Mum has a timber frame bungalow with a brick skin. The wall is an insulated 4"x2" timber frame with about a 3" cavity in between that and the brick skin. There is a vapour barrier behind the plasterboard internally but no service void. Standard 1980s contruction when they first started with timber frame.

I turned up today to find a neighbouring house (same construction) having its cavity filled with White Wool. Apparently this is now thought to be OK (according to the installer I spoke to) and was attracting grant funding. I noticed they were also pointing up the weep holes at the bottom of the brick wall.

Is this is a good or bad idea?

Sounds like a recipe for disaster. The purpose of the brick is to act as a rainscreen and allow moisture/water to run down the inside rather than get through to the wood frame. If there's a breathable air barrier (such as tyvek) outside the timber frame, it won't work as designed if it's touching insulation through which moisture can pass from the brick. And if the weep holes are sealed up, if will be even worse!!!

Paul in Montreal

The membrane is blue polythene just under the plasterboard. Nothing on the other side of the insulation I don't think (had to remove an old boiler flue a couple of years back so I could see inside the wall construction), certainly not Tyvek.

In theory, if the vapour barrier was intact there should be no problem with interstitial condensation and if the pointing was in good order then no moisture penetration from outside. However, I do agree it seems dodgy. They're issuing 25 year CIGA guarantees on the work though....

I think there is a interstitial condensation risk with block and brick filled cavity construction where no vapour barrier is used on the inside (e.g. foil backed plasterboard). Why don't we worry abut this?

Posted By: StuartBSo is it ok to fill cavities in brick built homes but not wooden framed ones whatever the membranes used?

Sometimes it is not OK to fill brick built cavity walls either.[IMO]

Depends on several factors:
The level of exposure to bad weather.
The porosity of the external brick/stone/block/render etc.
Whether there are inbuilt timbers such as floor joists.
etc

Filling external wall cavities with insulation on a timber frame is asking for trouble.

DO NOT DO IT.

I don't give a monkies what anyone says, be it installer, manufacturer or 'expert' (excluding me of course ;) ) It should never be done retrospectively.

There are designs that allow no external wall cavity with insulaiton or some form of insulation on the outside of the frame, but just banging insulation into the external wall cavtiy willy nilly is wrong wrong wrong.

And pointing up the weep holes has just banged the last nail into that houses coffin.

Depending on circumstances, I suspect big problems for that house within the next 10 years. Within a few more years i suspect that the house will be a total loss or require major major repair work.

People just don't understand and really should learn not to medal with stuff they don'y understand.

*rant over* Timber

The limit on the guarantee is £10k, which is bit light if you need to rebuild a rotten house. I've emailed the insulation manufacturer to see what their take on it is.

For our 1970s timber frame we were advised very strongly (by a number of experts) not to fill the cavity between the brick and the frame. Instead we had Warmcel blown behind the plasterboard - very messy all that plaster dust in the house, but its certainkly made a difference.