Floor type for extension

[PaulB]

We're planning a side extension for our 1970's house. The existing house has a suspended wooden floorboard ground floor, and I'm wondering what to do for the extension?

I'm assuming we're allowed under BR to have a suspended wooden floor for the extension too? However, it seems most houses/extensions are built with a solid concrete/screed floor now - I guess this is more energy efficient (and less squeaky!) - so my questions are:

1) Am I right to assume we could do a suspended wooden floor in the extension if we wanted to? 2) Is there likely to be a big difference in cost (it's around 30m2 at ground floor level) between the two methods of construction? 3) If we went for a solid ground floor, what do we do with the below- floor air vents from the existing house which abut the extension? 4) Are there any other good reasons to choose one method over the other?

TIA for advice.

Paul.

[sm_jamieson]

Yes it is quite permissible.

Not sure, but more weight bearing on the foundations, so could possibly affect them.

I've just done this. The vents must be carried under the new floor slab. Usual method is to use underground drainage componenets (brown

110mm pipe), and offset cavity wall vents to connect the piping below the slab up through the cavity to an airbrick above the DPC. There is an adapter to connect the piping to the cavity vent. I got mine from buildbase (manufacturer timloc I think). See near the bottom of this page (this is an excellent site by the way

- [nothing to do with me]). The parts look identical to the bits I used :-

4) Are there any other good reasons to choose one method over the > other? Less squeaky floor. Room usage might be a factor. e.g. kitchen as usually solid floor (originally so they could be hosed down !), but a washing machine on a suspended floor makes an awful racket.

[Tournifreak]

g a side extension for our 1970's house. The existing

More choice of floor coverings with a concrete floor. (eg tiles) Underfloor heating then also becomes a sensible option. Jon.

[Hugo Nebula]

On Mon, 7 Jul 2008 00:58:31 -0700 (PDT), a particular chimpanzee, PaulB randomly hit the keyboard and produced:

It depends on how far above ground level your floor will be. You need to provide a minimum of 150mm clear airgap between the bottom of your joists and the top of the concrete oversite. This oversite must be no lower than the adjoining ground on at least one side of the building. Therefore the finished floor level must be at least (25mm floorboards

• 100mm joists + 150mm airgap) 275mm-300mm above the ground.

If you haven't got this height, then timber floors are not practical. That's not to say they can't be installed, but you're then looking at something akin to a basement. Another option is to have a concrete slab but lay floorboards on battens over.

[Andrew Gabriel]

Two houses were built near me about 5 years ago. At one point, I looked in and they had the ground floor joists there, except they were concrete lintels ("T" profile IIRC). Next time I looked in, there was a screeded floor there - I didn't see what went between that and the lintels. There are air bricks around the houses under the floor level, so I presume there's an air space under the floor. Wouldn't be very easy cutting a trap door to gain access to it though.

[dennis]

> --

[Andrew Gabriel]

Looks very unfriendly for any later DIY work though.

[sm_jamieson]

Beam and block. Concrete beams infilled with concrete blocks and screeded over. Simon.