Historic retrofilled foam cavity insulation - U value?

[PeteTheSwede]

Hi all

 

My 1930s detached house has walls made of brick then a 50mm filled cavity and then brick again. The cavity has been filled with foam at some time in the past (don't know when or what with). I'm trying to work out the U value of the wall currently, so I can calculate the impact of adding external wall insulation.

 

I've used various online calculators, but don't know what to choose for the foam. Can anyone suggest what the foam might actually be, assuming it was done some years ago? Extra points for suggesting an R or U value for 50mm ?

 

Thanks all

 

Peter

[ADLIan]

Expect U=0.43 at best, perhaps 0.45.

 

[PeteTheSwede]

Thanks - is that just for the 50mm of foam or the whole brick - foam -brick wall?

 

I had read that pre-1970's retrofilled walls were unlikely to be better than 0.5 for the whole wall.

 

Thanks again

 

Peter

[ADLIan]

U-vals are always for the whole wall (or other element). Old cfc blown pur had lambda of approx 0.020 W/ mK but expect this to degrade considerably in this application to nearer 0.03 W/mK. 

[gravelld]

And that's assuming it was installed properly in the first place.

 

Might be a good idea to hire an IR camera as part of your project.

[A_L]

5 hours ago, PeteTheSwede said:

 

I've used various online calculators, but don't know what to choose for the foam. Can anyone suggest what the foam might actually be, assuming it was done some years ago? Extra points for suggesting an R or U value for 50mm ?

 

 

@PeteTheSwede If it is t least 30yrears old then it is most likely Urea Formaldehyde foam. It will probably be white and if you squeeze it will crumble as it has become brittle with age. How much this would affect its insulation qualities I do not know.

Assuming a lambda value of 0.029W/m.K it gives a U value of 0.44W/m².K in the build up below.