Cavity wall insulation?

[David J]

Not quite diy, but does anyone have a view (positive or negative) on modern cavity wall insulation with foam or granules.

I had a previous house done with insulation foam in the 1970s and I had no problems at all - apart from giving myself a problem later when trying to drop a TV cable between floors via the cavity. The foam insulation reduced my annual heating bill by 25%, and soon paid for itself.

At the time I remember a brief cancer scare in the newspapers about homes treated with this foam - but that ultimately came to nothing.

I had assumed that my current house, built in 1997, would have had the wall cavities filled with insulation slabs at the time of building - but some recent drilling through the exterior walls confirms that I was wrong about that. Maybe the current building regulations for insulation were not in place in 1997.

David

[Invisible Man]

Ours was done a couple of years back with some sort of blown fibre.

Previously had a house with granules that fell out all over the place. Believe some now used stick together.

Foam did have a bad press because it did give off fumes which did cause difficulties for some people. No idea whether this is still the case.

Choice may be affected by where you live. We are in a very dry part of the country. If you live somewhere wetter the choice may be more restricted.

Grants used to be available from councils or your power supplier. Probably still the case.

Googling found me a lot of information.

[Doctor Drivel]

The regs at the time it was enough to fit insulated light-weight blocks. Not now. Worth getting done.

In the loft fit rockwool between the joists and rigid foam over the joists. Boards on top and screws right through the two into the joists. Make sure all cables and pipe running through the ceiling are sealed with silicon. Do not forget the loft hatch and make it is insulated and sealed.

[Tim W]

Invisible Man wibbled on Saturday 07 November 2009 09:52

Our bungalow has blown fibre. According to the neighbours, it may have been done as much as 20 years ago.

Having bashed holes through the walls (new doorway) and having seen the top of the cavity I would say that fibre is pretty good stuff. It all seemed to still be in place, not slumped.

Yes - a decent version *should* use sticky balls to stop that "swiss mountain avalanche" effect when knocking holes through.

Definately worth investigating the grants options.

[Tim W]

Doctor Drivel wibbled on Saturday 07 November 2009 10:04

I noticed in T Wells B&Q the other day some sandwich loft boarding - two sheets of chip (or similar crap) with foam bonded in between, in loft chip sized pieces. Cannot remember the price. Think it was about 75mm thick, might have been 100mm.

[OG]

You may have partial insulation that doesn't completely fill the cavity - but it leaves too narrow a cavity to allow the CWI to be blown in.

Our house (built 1983) had CWI installed about 12 months ago (and like you, we've saved about 25% on gas heating, despite 2009 starting with a much colder winter than 2008). A friend living in a similar house (same builder, same design) built in the early 90's couldn't get a quote for CWI because the cavity was too narrow.

[Phil L]

houses are still being built today without CWI - it's not required if the u value of the walls can be achieved without it, that is to say, thermal blocks can be used, coupled with internal drylining can be as efficient as cavity insulation.

I'd get it insulated if it were mine - I used to install CWI for many years and I can tell you that they use fibreglass now, and very occasionally, polystyrene beads, but these have many drawbacks, not least when the house comes to be demolished as they never disintegrate and also knocking holes through creates huge voids higher up the wall, fibreglass tends to 'stick' better on the rough surfaces of both brick and block.

There's grants available via energy suppliers and also it can be installed for free if you or your spouse recieves any benefits

[David J]

Thanks for that info Phil. It probably explains a lot, since my house exterior wall construction is as you stated:

standard facing brick + air cavity + 100mm thermal block + drywall plasterboard. I have not seen the mu value for this construction, but I presume it can only be improved the CWI.

I checked the 'free' CWI deals available, and it looks as if it restricted to buildings constructed between 1924 and 1982. I'll check further.

David

[george]

i bought a thermometer gun from maplins, you point it at a wall and it tells you the temperature. useful for showing where insulation is worth doing, in my case the top few feet of the walls seems to leak heat through the edge of the roof.

And the air leaks

[g]

[Doctor Drivel]

The most common point of cold bridging - where walls meet each other, roofs and the ground.

[David J]

Brilliant suggestion! Why didn't I use such lateral thinking..?

Of course, the surface temperature of the inner wall is all I need to know. You can forget all this mu value nonsense.

They have one for £29.99 that would do the trick I reckon.

David

[Jim]

Might be worth investigating how your cavity walls are closed at the top: originally this was done with brick which creates a cold bridge that is difficult to elimate. You sometimes can see this from outside as a course of brick "ends" just below the soffits.

[<me9]

In my case, (1970s house) the wall plate is on the inner leaf, and the outer leaf just stops at the soffits, resulting in 3 bricks and wall plate of inner leaf above the outer leaf. The foam insulation stops about 3 bricks below this, resulting in the top 18" off the upstairs walls being cold (as measured with IR thermometer from CPC).

I plan to install kingsan or celotex to fill the gap once I get round to replacing the "roofline".

The bottom foot or so of he downstairs walls are similarly lacking in insulation due to the mortar debris allowed to drop down during construction.

The bonus system in operation at the time (with lack of adequate supervision and enforcement) is the cause.