Internal cavity wall insulation

[Robert Rickey]

A recent air tightness test at my house highlighted a major air path through a cavity wall that was “captured” by a first floor extension built about 12 years ago. I dithered about treating this wall, and now must address it. In addition to the infiltration, there is also the thermal bypass issue. I have been advised against using expanding foam, since would be difficult to verify that the foam has joined up between injection points. I am favouring EPS beads with adhesive – good insulation and some reduction in infiltration.

Has anyone studied the airtightness of cavity fill insulation? All brilliant answers to this problem welcome!

[Mark Siddall]

Rob,
The EPS beads will address closed loop bypass but not airtightness. Depending upon exposure (check in BRE Insulation Avoiding the Risks) then carefully installed PU foam may the way to treat the airtightness issue.

Mark

[Paul Buckingham]

I have a cavity in my party wall with next door and the draught whistling through this is staggering. I think this is potentially a major problem with old housing stock and also potentially very difficult to address. It can more than likely be found in most new builds aswell!

[Mark Siddall]

Paul, when was your house built?
Traditionally party walls used to be solid. I understand that it is only recently (since 1960s?) that cavity party walls have come into play (acoustics.)

It is thanks to Leeds Met that party wall is now on the radar. Unfortunately building regs does not go far enough as dry lining (on dabs) still predominates and this facilitates other open loop thermal bypass mechanisms.

[Paul Buckingham]

Hi Mark, it was built in around 1963 and is probably about 30mm wide with a gale force 9 whistling through!

I do thermal imaging and I have seen cold air penetrating behind dry lining in a number of new builds. In this day and age with building regulations supposedly tightening up why are these things not being addressed. I think a full survey of a new property should be carried out by someone who knows what they are looking for, including air tightness and thermal imaging, before a building can be signed off and it should be either a pass or a fail instead of “that will do”. If it is a fail the builder should be forced to strip out the building, rectify all the identified issues and pay for a second survey to be carried out. They would only have to do this once because the first fail would be so costly that they would never want another!

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