Finished floor level same as ground level

[pattieG]

Hello.

I am designing my extension and I have come up against a problem. It appears my FFL is the same as ground level outside. Incidentally I've also noticed that on the plans for other houses built at the same time on my road that they show the FFL as 150mm above ground level. I know this is a requirement for current building regulations but I don't see how this will work unless I put a step from the existing house into the extension.

Is there a workaround for this or are my measurements wrong?

[Equus]

It is a requirement that the DPC is at least 150mm above ground level... the floor can be wherever you want it (obviously even well below ground level, in the case of basements) so long as it is there is a suitable DPM, linked to the DPC (and if below ground, that DPM will need to be able to resist hydrostatic pressure... tanking. in other words). Refer to the NHBC 'Standards' for further guidance.

But the obvious question is: if the mountain won't come to Mohammad... can you not simply lower the external ground level?

[pattieG]

Would the 1200g membrane for the concrete floor be placed up the inside wall leaf and then lapped over the DPC in the wall?

Edited by pattieG on Wednesday 7th February 13:15

[Equus]

It depends on the ground level difference; if the external ground is the same or a little lower than the SFL, then most BCO's will accept that, yes. If not, then refer to the NHBC Standards (section 5.4).

[pattieG]

Magenta line is the Membrane going up the wall and lapped with the DPC three courses above ground level.

Or if BCO don't like that then a type A waterproofing barrier.

Edited by pattieG on Wednesday 7th February 13:54

[barryrs]

This is the detail I generally use for a raised ground level.

[Equus]

^^^ Yes, that sort of detail: DPM lapped up the cavity face of the inner leaf is better.

It would be prone to damage if on the inner (exposed) face of the inner leaf, as you'd shown (and also means that your plaster wouldn't bond to the wall if you're wet plastering... though of course most people dry line these days, in which case the dry lining protects the DPM better and most BCO's would tolerate the detail as you'd drawn it, albeit it's not ideal).

[magooagain]

Attention to the skirting installation. Probably stuck onto the plaster finish.