h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When my parents had it done, it was all done from outside. It was VERY NOISY.

You have to make sure to keep airbricks clear, vents etc. And in this weather they get very cold draughts. Drafts? Blowing through. It's tempting to block them up, but damp is WAY more nasty for your health than a chilly wind.

Only other cons I can think of is that there may be an environmental impact? But can't think what and don't have time to do research. I'm sure there was something I was thinking of recently that made me think the insulation was annoying, but as I watched the snow melting on house roofs around me and mine stayed put I was glad my heat was staying in the house!

Oh, insulation is nearly always a good idea. The question is whether cavity wall insulation is the right choice.

The other obvious point is to make sure you've actually got a damp course...

Quite a few older houses were either built without one or it's long since deteriorated...

Don't know how much it costs to have done, but cavity wall insulation _without_ a damp course seems, to me, to be a _very_ bad idea.

We qualify for a grant towards having the work done but when the surveyor came around to check the house we decided against it pretty smartish. We have a multi-fuel burner in the living room which provides the central heating and hot water and so we have a vent in the front wall. This is very draughty!! In the dining room we have an open fire which we only usually light on Christmas day, the rest of the year the hearth is full of orange, red and black paper flowers. Because it's there, and we do use it (even once a year) we would have to have another vent installed.

Seemed self defeating to us.

Well, I've decided to get the loft done and leave the walls alone.
We've just had the coldest winter for 30 years, and it wasn't too bad.

A house has to breathe. Don't want our house getting all mouldy.

Don't go by what some internet weirdoes tell you (even if this one happens to be an archi-). Get a consultation with someone who really knows what they're doing and can tell you what, for your specific house, is the most sensible investment where saving energy is concerned.

And thanks for not simply turning up the heater instead

Best insulation is to be in a mid-terrace house with neighbours who are home all day, as their house will keep yours warmer.

That's what I do, and boy does one of them moan at me for not having my heating on! Still, I'd swap for her end of terrace and therefore side access to the back garden any day.

I believe there is a massive con that needs considerable thought.

A cavity wall is there to allow fresh air to pass through.
As part of my City and Guilds Gasfitting this subject was covered.
It was then considered imperative not to block the access and egress of fresh air to pass through the cavity via internal and external air bricks.
Further more, when knocking a hole through a cavity wall it was important not to allow bricks/rubble to fall in to the cavity because it would allow moisture to transfer from the outside wall to the inside via the resulting brick/rubble bridge.

Having been taught the importance of the above it always puzzled me why it was now considered OK to fill the cavity.

What I believe is the con.
My brother had cavity wall insulation done to his house about 4 years ago.
Every winter since then the surface of some of the external bricks have splintered off and fallen to the floor.
It had never happened before.
I can only presume that the recent abnormally cold winters have frozen the water that has been absorbed in to the external surface of the bricks.
Water that would have been significantly less had there been fresh, dry and slightly warmer air circulating through the cavity, therefore, drying the bricks out.
I am convinced the expansion of the frozen water absorbed in to the external surface of the bricks is the cause of the splintering, after all, frozen water does the same thing to the surface of mountains.

His house does have quite a high, exposed location which leaves it exposed to a significant chill factor.

Think before you have cavity wall insulation. Think of the cost of rebuilding external walls.

My brother now has no chance of selling his house, particularly in this current, economic climate.

Some interesting comments.

We had cavity wall insulation installed in two houses in the UK - one in Berkshire & the other in Northumberland. No problems with either.

We researched it and were told that, properly done, there is a slow drift of air to keep the cavity dry - but choose your installer.

In both cases we selected long established firms to do the work. Both were noticeably more expensive than others - and both did the job properly.


Here (NZ) it's different, though I can't comment on older houses. Ours is wood framed with a brick outer veneer that doesn't contribute much to the construction. Insulation is fibreglass batts, through which again, I'm told, there is a slow drift.


So - you pays your money and you takes your choice?

The tops of cavity walls should allow rising, moist, warm air
to pass out of the building through gable ends and ridge vents.
This is helped by the convection from air entering the eves along
the space below the outer rafters which must be covered with
vented soffets. These are indicated by the arrow in this illustration:

http://www.totalcanada.ca/prod12.jpg

Note that an air and water-tight 'vapour barrier' is installed
on the inside of the cavities.


~jwf~

we had it done a few years ago and have had a notable problem with black mould
we made the mistake of closing the vents at the top of the windows dont do that

Oops!.
my post 29, 1st line: please amend to read:

There have been some interesting comments. I shall attempt to add to them:

My only problem is that I keep reading the thread title, and thinking that it must have something with dental work and root canals to do.

Just to ans jwf.

That's right but, cavity foam fills the lot..no breathing in a lot of cases.

Modern insulation in new build is probably OK but, some older houses suffered with certain methods.