Cavity wall insulation

There has never been a requirement to install CWI on any building - the only requirement is that the wall must meet certain levels of heat retention, this can be acheived by using thicker thermalite blocks and having them dry lined.

I'll wager that the walls in your house are about 350mm wide - 100mm outside brick, 75mm cavity and 150mm inside block...the reamaining 25mm will be drylining.

Why housebuilders go down this route is beyond me - the cost of the thicker blocks far outweighs the price of having regular blocks and CWI

Looking on the good side, you can now upgrade the insulation further with CWI, where as, if they had just put this in, and not used the thicker thermalite blocks, then upgrading the insulation would have been more expensive and more disruptive, so really they have done you a favor :-)

Toby...

I have a 10 yr old Rerow home , again without cavity wall insulation. The construction is, as you say, themalite block but also with dry lining. This was apparently good enough for the regs at the time. As an aside, if you hve small bore heating, the pipes come down the wall between the plasterboard and the blocks, sometimes in the corner of the room.

Malcolm

IIRC the NHBC do not allow CWI in some exposed areas

How can you tell if a house has CWI? I have a 2001 build (Permisson, I think) house. How would one tell if it has CWI?

drill a hole in the cement joint and have a poke around. The hole only needs to be about 5mm diameter, but obviously 100mm deep, and poke in a piece of wire, a straightened coathanger preferably, and if there's any sponginess, it's insulated with yellow fibreglass batts, if there isn't, it may still be insulated with loose fill fibreglass, and to check for this, add a bit of gob oil to the end of the wire and have another poke, fibreglass will be white, rockwool will be cement coloured. If it's insulated with polystyrene or celotex type rigid foam, you should be able to push the wire into it and you can 'feel' the sqeakiness of it as the wire goes through, if that makes sense.

I'll wager a pound to a piece of dogturd that it's done with white blowing wool - I used to do Persimmon homes every Saturday morning for years, and we used white fibre,.

Thanks for the reply. Actually I was wrong with Persimmon, it was built by Alfted McAlpine. Have you any experience of these?

No. McAlpine, and Barratt come to think of it, were never on our list of new build sites. This doesn't mean it isn't insulated though.

No: Walls have to meet the thermal resistance standard specified in the building regs. There are many ways to achieve that.

We are now planning to have the insulation installed,

I'd be very wary of doing that. It may last a few years but you might end up with a different problem or 2. Cavity walls need an air gap in the cavity of at least 25mm against the outside wall. Water vapour from the atmosphere inevitably percolates through the outside brick skin & the air gap allows this to run down the inner surface of the wall. Without it the insulating rockwool or fibre in the cavity will get wet & become ineffective. Other types of filling have their own problems. Also shaling may occur on the outside brick face.

but what were

Much the same as now except required level of thermal resistance has been upped + some options verboten. You need to check the building regs for exact info or if you are lucky someone else will be along this way soon with chapter & verse :-)

and should Redrow have been allowed to get away

IMHO they didn't 'get away' with anything: they made the best engineering decision.

underrated CH boiler? under-rated rads not heating up fast enough?

You might do better to concentrate your efforts on upping attic insulation & look at ways of minimising heat loss in exposed sections of your house - curtains, carpets etc can all help. Can you mask a wall exposed to the full force of cold winds so that they are deflected, eg by repositioning a shed? Consider putting rockwool insulation between ceiling joists over living rooms. We found that made quite a difference to comfort in our sitting room.

HTH

replying to chudford, Steve Scott wrote: Hi I'm in a persimmon Hatfield house. The house is 18 months old. When sold I asked the cwi question and was told they are a traditional builder and as such didn't supply any form of cwi just brick and a thermal block. So what I'm saying is some builders only do the bare minimum.

Blown in cavity wall fibres are silicon coated to make them water repellent. As are the cavity wall bats.

Perhaps it's quicker to build. The cost of the materials might not be a major factor.

Robert

That wasn't always so. Newcastle has a problem with rogue cavity wall installations from about 10 years ago that are still just about under guarantee failing in large numbers because the fibre method used has bridged the outer and inner wall causing widespread penetrating damp.

I happened to meet one of the insurance assessors when he was looking at my brother in law's house. It has wrong method of insulation but so far doesn't have any obvious signs of water ingress. The guy suggested moving any furniture backed up against outside walls and taking a look since the deadline for making a claim was fast approaching. -- Regards, Martin Brown