cavity wall U values error

[DIYedboy]

A figure of 1.6 is thrown about for a cavity wall and 2.2 for a solid wall, however that cavity wall figure is wrong.

I've just drilled 2" holes in my 70's cavity walls to fit polystyrene beads n the draught flying out of them blows the beads back out!! prior to doing this, I could feel the draught flying out the gaps in the wall around the cables going up the cavity from the fusebox (all those cables have now been removed) The cavity walls are closed at the top but not at the gable ends or the air bricks. So if we imagine it's zero degrees outside, it's gonna be zero degrees up me cavities. I therefore have only a 4" wall between my living area and the outside temperature.

That equates to a U value far worse than a solid wall n probably a figure more like 4!!!..............give me your thoughts

 

[^woody^]

There shouldn't be any significant draughts in a cavity wall. Calculations can factor this in.

 

[DIYedboy]

I wonder who supplied these figures initially n were they theoretical or a 'real life' study?

 

[^woody^]

You can't blame the person that did calculations that specify how the wall should perform, if someone does not build a cavity wall correctly in the first place.

 

[tony1851]

Houses with timber floors should have 9x6 airbricks ducted through the cavity. But some builders would also put narrower 9x3 airbricks near ground level, open to the cavity, in an attempt to keep the cavity aired and dry in case any rain penetrated the outer skin.
This reduces the insulation value of the wall.

However, it's important to remember that the original purpose of cavity walls when they were introduced into mass housing after WW1 was to prevent rain penetration through the traditional 9" wall. The thermal insulation given by cavity walls was not originally considered on its own right and has only become more significant since the mid-1970s.

 

[DIYedboy]

Right on Tone! insulation didn't get invented until the 70's, further to this,any house that has had urea formaldehyde foam cavity insulation fitted probably aint insulated anymore cos the stuff disintegrates over time