Cavity Wall Insulation - some advice, please?

[ExThornHeating]

I'm really hoping that there's someone on here with knowledge of installing cavity wall insulation - I have asked as many questions as I can, but I just don't have the building knowledge to proceed further.

I've moved into a traditional 1930s semi. It's got recent double glazing and a double thickness of (new) roof insulation - but when the wind blows, it's so draughty! I am desperate to have cavity wall insulation - but have run up against problems.

I have had the survey done, and there is a cavity wide enough to support insulation being inserted. However, the survey found some rubble in the cavity - I looked through the fibre optic, and it seems to be building debris/ small pieces of wood, which have fallen to the bottom of the cavity when the house was built. However, because of this, the company who surveyed say that they cannot insulate. They use the cotton-woolly type of insulation that is blown in at high pressure; and they say that any debris in the cavity will cause uneven 'filling', which in turn will cause damp patches.

But my house is cold! Please, can someone tell me: is the problem insurmountable? Is there another form of cavity insulation, e.g. polystyrene, that would work better? And where can I get it? I have repeatedly tried the energy saving trust for information, but they only refer to their approved suppliers.

Thank you very much if you can help!

Before proceeding on this bandwagon, you need an independent building surveyor. But, as the insulation firm you selected seem highly professional, further pursuit is likely a waste of time as the vented cavity is there to stop dampness rotting your timber floors. Try all other remedies first, such as overlaying your floos with laminate flooring underlain with UF foam matting. Good luck.

 

[anobium]

The average house loses approx 35% of its heat through the cavity walls, and cavity wall insulation is after roof insulation, the most cost effective method of insulation.
On average you will recoup the cost of the insulation within 7 years in reduced heating bills, probably less now at the rate they are increasing.
Cavity walls were designed purely to stop the transmission of moisture and modern wall insulants as previously described cannot hold water.
Basically due the size of the fibre strands.
Double glazing comes way down on the list for reducing heat loss and would take in the region of 20+ years for you to recoup the costs, unless of course you have exceptionally large windows, ie curtain walling.

 

[renov8fun]

Hi. I know this thread dates back 15 years but am hoping the person who originally posed the question is still on here.

I have a similar issue. 1930s house with cold walls with both rising and pentrating damp. I've had a cavity survey and been told the insulation is wet where there is penetrating damp and one wall which is the worst affected has no insulation but is filled with debris which is wet. I've been advised to have the debris and insulation removed.

My understanding from recent research is that certain property types and certain locations should not have cavity wall insulation. It seems mine is one of those. My neighbour had CWI installed 7-8 years ago and has had damp and cold walls ever since.

I'd love to find out what the original poster did and what helped the most. Are you still here?

 

[noseall]

When you open up a typical wall that has been, so called filled with blown insulation, you find large gaps have formed on the blind side of wall ties. So the filling is useless as an insulation as heat always goes to cold and all that happens is you block the movement of heat in one place and it moves to the next weak link.
Cavity walls were re-designed in the late 18 hundreds as many houses of that time had wind blown rain coming through the walls. This still happens today!
If you fill a cavity with this yellow string, it merely transmits the damp across the cavity making the inner wall damp.
Damp walls equal a good transmission path for heat to cold so, the problem is made worse and your heating bill goes up.
A better idea is to follow the lead of modern office blocks and factories, where they have a water proof skin, either glass or steel to stop the wind and rain with polystyrene or similar underneath.

Wind blown rain (total) saturation is rare, sporadic and affects usually one exposed wall. When it does occur, it only affects masonry that is susceptible. Nonsense argument against CWI.

 

[cdbe]

You need to get the cavities cleared. I'm not convinced about the "rising damp" as a 1930s house should have an effective dpc.

If your internal walls are universally damp then the cwi probably needs to go (if you have any paperwork from the original install you may be able to reclaim the costs of this) - if it's localised and/or concentrated at ground floor level you could see how clearing the cavity goes in the first instance. It goes without saying that your pointing and rainwater goods should be in tiptop condition.

A note of caution - personally I would imagine the CWI removal "industry" is probably as dodgy as those who inappropriately sprayed the stuff in the first place.