Cavity Wall Insulation

  JYPX 17:33 14 Oct 2010

A little bit of internet research seems to reveal lots of people saying Yes, go for it, and a lot of other people saying No - the cavity is there for a reason.
What do the wise heads on the forum think? The house in question is a bungalow - approx 1960. When I am told that a heavily subsidised price is on offer "while funds are available" I would usually see that as a sales tactic but, with council budgets getting the squeeze, maybe it is a good time to get it done.

  jakimo 17:40 14 Oct 2010

The Government recommends cavity insulation, even making grants available in order to help keep down heating costs..Thats a good enough reason for having it installed

  Woolwell 17:48 14 Oct 2010

Just because the government recommends it doesn't necessarily make it a good reason for having it installed. For an opposite view see click here.

It really depends on the house structure and how good the cavity is. If the cavity has rubbish in it (and some do) then cavity wall insulation may be a bad idea. A very recent house should not need cavity wall insulation because of the method of building. I think that the installers should do a survey of the cavity before installing but few do.

  birdface 18:08 14 Oct 2010

I would go for it and get the loft insulated as well.
You can tell lofts that have not been insulated.
All the other houses have snow on the roofs the uninsulated one will not.

  Forum Editor 18:32 14 Oct 2010

Originally, cavities provided an effective way of keeping internal wall surfaces dry - moisture couldn't migrate from the outer (brick) leaf of the wall to the inner (building block) leaf. There were all kinds of issues in the past, mainly caused by twisted galvanised metal wall ties having mortar droppings on them, so they 'wicked' water across to the inner leaf, and in lots of cases the galvanised ties rusted and failed, compromising the structural stability of the wall.

Nowadays good builders use stainless steel wire 'butterfly' ties, and all cavities must be filled with special cavity insulation bats to comply with building regulations. Cavity widths have altered, too - modern cavities are far wider than their predecessors' to allow for thicker insulation.

Insulating an existing cavity is commonly done by blowing small polystyrene beads into it. The beads are mixed with a binder so they don't cascade out of the wall if you replace a window, or make a hole for some other purpose, like a tumble dryer vent, or a boiler flue.

You can't over-insulate a house, so go for the cavity fill, and while you're about it why not beef up the loft insulation to 200mm?

  the hick 19:12 14 Oct 2010

I have never really understood why cavity insulation is needed, as the air, which is the insulating medium, can surely not be susceptible to draughts and therefore constantly changing as air in a loft does.

From the link, 'homes with cavity wall insulation are put on the market. Homes most at risk of wall tie corrosion are those built with wrought-iron "fish-tail" ties prior to 1920, and those built with galvanised steel "butterfly" ties between 1964 and 1981.' Does anyone know, whatwere ties made of between 1920 and 1964?

  jakimo 19:23 14 Oct 2010

'Insulating an existing cavity is commonly done by blowing small polystyrene beads into it. The beads are mixed with a binder so they don't cascade out of the wall if you replace a window, or make a hole for some other purpose'

Precisely the type I have in my cavity outer cavity walls,,but apparently without a binder as I found out when a hole was made to install a French window,there were polystyrene beads everywhere

  VCR97 19:30 14 Oct 2010

In my house the air bricks open into the cavity. Isn't that normal? In any case there will be convection currents in the cavity.

  johndrew 19:51 14 Oct 2010

Many new homes are built with the inner walls constructed with 'Thermalite' type blocks which (apparently) negates any need for cavity wall insulation - this according to our local council building inspectors.

Even so I am aware of residents in such properties who still install the insulation material.

  the hick 20:58 14 Oct 2010

VCR97, there are no air-bricks in my 1964 house. I think it depended on the regulations of local authorities at that time.

johndrew, I would have thought, if a house has Thermalite-type blocks on the inner leaf, then it would have insulation from new, since these type of blocks are relatively recent.

  Forum Editor 23:16 14 Oct 2010

All new cavity walls have the inner leaf constructed with lightweight building blocks, and they certainly do not negate the need for cavity wall insulation. You will not meet the building regulations criteria for cavity wall energy performance without cavity insulation bats.

Frankly it would be a very silly builder/property owner who tried to build a new home without insulating the cavity - it would not meet the current regulation standards.

I think your local authority building inspectors need to do some homework.

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