9" Cavity Block u-value ??

Hopefully this helps

I believe S.R.54 has concrete cavity blocks as 2.09 W/m^2K as a baseline value. I'm not sure where post 3 replies come from, interested as it looks like its from an official document, that makes its R value 0.48 m^2k/W. That said, I found a few values, and it may depend on the density of the block? I think Part L TDG may give a different value though.

Depending on how accurate you want it, I'd say the most accurate way would be to calculate the R-value of the section of of block thats concrete through and then the R value for the sections that are concrete+air+concrete inside to out. That could be calculated by getting the depth of a section and dividing by the thermal conductivity (lambda or K value, units of W/m.K). ie R=L/lambda, then add the percentage of the different R values and derive the U value? or just use the 2.09 or if there is something available in Part L?

I have found lambda values for concrete at 0.9-1.0 W/m.K

I should say to clear something up, S.R.54 says the baseline U-value for a hollow block is 2.09 so the R-value would be 0.478.

The value from the DEAP manual says for age A-E, a U-value for a hollow block is

2.4 so the R-value would be 0.41

Not much of a difference, and as its given as the U-value, that has to be the complete path for heat to cross including the air space.

I realise different blocks will have different values, but you would think the DEAP manual and the NSAI document (S.R.54) would be aligned, ie that DEAP would take its values from NSAI??? Who wrote or controls DEAP? I'll go and see if I can download the manual??

S.R.54 mentions a baseline value, DEAP has a range of values

BUT, I am wondering, why the older age categories show the U-value reducing in the DEAP extract, i.e lower thermal transmittance, therefore supposedly improving in thermal performance??? am I missing something here? or it's because it's an extract?

It looks like an error???