oversite

[selfbuildextension]

Hi,

My extension will have a suspended timber floor. There is a sleeper wall but it has its own foundation same as normal walls.

the spec for the over site is

150mm hardcore
25mm sand
1200 qauge visqueen
50mm concrete

Seems excessive just so covert he soil and stop vegetation?

I mentioned it to the BC and he said "yeah that's what is needed"

I'll do it, but it seems like a lot of wasted money, can any one fill me in on why this is required?

 

[^woody^]

You dont need the harcore or the sand, and not the DPM - unless your scottish regulations are different to English ones.

The idea is to remove topsoil and then form a barrier to stop any vegetation growing. So just concrete, or a barrier and gravel will do this.

 

[tony1851]

You don't need concrete; 50mm of inert material such as sand or gravel would do, but IIRC the Approved Document recommends covering the ground first with 1200 g dpm.