How much Insulated Plasterboard for Cavity Block wall

little_monty

I'm trying to decide the thickness of insulated plasterboard for external walls of 20 year old 3 bed Semi.

The walls are 9" Cavity Block so have insulation.

I've came across the following rule of thumb on other threads :

"internal insulation DOES NOT exceed 0.5 times the cavity insulation"

I believe this is to avoid condensation buildup on the walls.
So any opinions on how thick i can go with the insulation / what u value without risking condensation issues ?
(plasterboards will likely be attached directly to wall without battens)

A secondary question is whether its ok to leave the area between floors uninsulated ? (im not sure whether there is or should be insulation there now !!)

kodak

Hi,

I'm looking for the same answers!

This is a very good document showing all details you will encounter but it doesn't state max mm of plasterboard. http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18756,en.pdf

However, I have seen details with the size of 82.5mm attached to the cavity block and the u-values are very good, sub 0.30 w/m2 k