cavity wall insulation...

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OP
OP
Maz

Maz

Guru
Your house is cavity - you tell by looking at the stretcher bond to the gable end wall in the loft (not the shared wall with the other semi). The age of the property may mean that your wall ties are on the way out. The first sign will be horizontal cracking to the external leaf of brickwork. The cracking is normally about 18 inches apart, and usually most obvious on the elevation which is most exposed to the prevailing winds and rain. There are plenty of companies that will do boroscope surveys but beware the ones that do it for "free" because they make their money by selling you wall tie replacement. D

Re cavity wall insulation - this is great in new houses where it is built into the construction - but NB there is almost always some form of cavity left. Retro fitting CWI is not an ideal solution as it fills the cavity. The cavity is there for a reason - air is not a bad insulator and the cavity also prevents transmission of damp from the outer leaf of the walls to the inner leaf. If you fill the cavity you have bridged this gap making it far easier for damp to penetrate to the inner leaf.

There are many instances where CWI works fine - but there is a risk involved. The risk increases if you are in an elevated or exposed position.
Thanks.
What is the risk in an exposed or elevated position?
 

Night Train

Maker of Things
Thanks.
What is the risk in an exposed or elevated position?
Driving rain and weather causes the outer, protective, skin of brick work to get wet. Normally that moisture stays in the outer skin and evaporates off. Having rubble, or insulation, in the cavity means that moisture can get across the otherwise dry airspace and wet the inner skin of brickwork which both supports the house and provided the dry inner walls to the rooms.
Exposed locations allows the walls to remain wetter for longer giving a greater risk of moisture being able to brige the cavity.

This is also why wall ties have to be correctly installed to drip condensation towards the outer skin of bricks and cavity trays over windows and doors channel moisture to drips on the outside instead of on the window/door frames wetting the inner skin of bricks.
 

summerdays

Cycling in the sun
Location
Bristol
The original CWI that I had put in 20 odd years ago had an exposed West facing wall - ok urban but I could see several miles in that direction, due to being on a hill. We have never had damp problems but it was only recently that I learnt about the potential problems.

Once you have had CWI could the wall ties carry on deteriorating ... or could it make the situation worse?
 

summerdays

Cycling in the sun
Location
Bristol
That's a bit of an eye-opener.
I'm now having serious doubts about getting CWI.
Thanks, everyone.

I think when we had it done it did make a difference to the house. Friends have often commented on how warm our house is and we don't usually put the heating on until November. But we also get good passive solar as well.

But it is weighing it up against the possible problems as well.
 

asterix

Comrade Member
Location
Limoges or York
air is not a bad insulator

That is true so long as the air can be trapped in small cells. e.g. fibre insulation. Moving air is not a good insulator and the air in an open cavity is going to be moving.

I suspect that cavity wall insulation is not a good idea if you have porous bricks exposed to driving rain. Non-porous bricks - less of a problem.

We had insulation added, in common with many other similarly built houses (30's style built post-war) and there are no reported problems locally. After over 10 years we have no damp or other signs of deterioration, however the bricks are very dense and we are in a sheltered position. Not only that but the quality of the brickwork is good, better than houses built nearby in the 70's many of which are showing their age far more.
 
OP
OP
Maz

Maz

Guru
I think when we had it done it did make a difference to the house. Friends have often commented on how warm our house is and we don't usually put the heating on until November. But we also get good passive solar as well.

But it is weighing it up against the possible problems as well.
Hm, I don't know how 'exposed' my wall is (and it is West-facing). I need to take a look at that wall when the rains lashing it down - see what it looks like then.
 
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