cavity walls

lkmc01

Hi

We bought a 1930's terrace in August and moved in with British gas standard being the utility provider. We spent about 6 weeks switching to edf on their fixed tarrif.

Whilst with British Gas we booked in for their cavity wall and loft insultation survey. We have a flat roof kitchen extention on the back of the house. They said that we couldnt have cavity wall insulation as there are 'blockages in the cavity' that will cause damp. We couldnt have loft insulation as the loft hatch was too small.

We have since made the loft hatch bigger. We booked in for edf's assessment for cavity wall and loft insulation and they have been today. They will do the loft and.... will also do the cavity around the kitchen, the back of the house and the front of the house which is all of it.

They have seen the blockages also seen by British gas and say that they are not a problem and take up alot of customers that British gas will not do. They also have a 25 year guarentee so if their cavity wall cause damp we are covered.

But they will not be able to do it until February. So, shall I wait? Shall I have cavity wall done at all?

What do you think?

Scania_Man

Is your wall plastered or dashed etc or is it just bare bricks?

Reason I ask is rendering the outside of the wall offers it some waterproofing properties and would reduce the risk - definately the case in new builds so i'd assume the same in an older narrower cavity wall construction too.

I'd have thought the risk of dampness was the same if there are already blockages which i assume are bridging the cavity, as if you filled the wall with insulation, but again i suppose this depends on your wall being just brick etc.

Unfortunately i can't remember back far enough but there is a thing called interstitial condensation, maybe that is linked to their decision.

Sorry i've probably raised more questions than answers for you, but the 25yr guarantee is reassuring.

lkmc01

thanks. We have rendering on the outside upstairs and brick underneath. It is plastered inside. Its also the rockwool type that edf want to use.

whasup

The fact that you have a blockage in the cavity does not necessarily mean you will get a dampness issue after cavity insulation is installed. It just means there is a slightly increased risk. Blockages in cavity walls (regardless of cavity insulation) actually rarely cause a dampness problem. They do sometimes but it is not common. And if a blockage was likely to cause a problem you would almost certainly be getting a problem allready. So the risk is actually very small. My advice is have a good look around your walls - particularly the ones exposed to prevailing wind - and see if there are any dampness patches. If all seems well it is unlikely cavity insulation will change anything. PS. the type of insulation is also a factor - and blown mineral wool presents the least risk.