Cavity wall on a extension minimum size

[markblue777]

Hi all,
I know that it differs in region but basically we are looking to extend our house we have an area of 2.5 meters to the side (right up to the boundary which we can go to) What I was wanting to to know is the minimum thickness of cavity wall we can get away with.

It will be brick on the outside then breeze block on the inside, I read somewhere that it is 225mm does that sound right. We are under broxbourne council if that helps with a more acuate answer.

Im just trying to design the extension and want to get a feel for how much room we would have inside (we want to sound proof one of the rooms down stairs which will be a hobby come workshop room so want to see how much floor space there would be once the sound proofing is in).

Cheers
Mark

 

[rdesign]

depends on how you want to insulate. if you our insulating it in the cavity the insulation thickness plus 50 mm is the standard if doing internal or external a 50mm cavity is all thats needed. hope that helps.

regards richard

 

[RobinBHM]

The building regs 2010 part L1b require a u value for walls of 0.28.

In practice I think thisgenerally translates into a 300mm wall overall (brick - cavity -lightweight block+plaster). Plaster thickness needs to be added to this as well, say 15mm if wet plaster

The cavity may be part fill with 50 celetex or 100mm full fill rockwall.

You may able to reduce the cavity thickness slightly, say to 75mm, (I think with Knauf Dritherm 32), but I cant see any further reductions.

cheers Robin

 

[markblue777]

ah thanks for the explanation. I was running with 300mm and the 20mm for plaster so i think it should give us an internal space of 2 to 2.1m in the end