Possible to pour a concrete floor when extending

vallo

I live in a 1930s two-storey semi-d with floor-boards over a cavity. I'm planning an extension out the back to put in a good sized kitchen/living area and I am thinking of getting a solid poured concrete floor in this part.
Thing is, the rest of the house is quite chilly and I know that some of this (not all) is attributable to cold air coming up from the cavity under the house.
So what I'm wondering is, can you pour concrete into the cavity, making the entire ground floor essentially one big concrete slab? If I thought it would work I'd have no problem redoing all the heating, plumbing, flooring and skirting afterward.
Has anybody done anything like this?
Thanks in advance for any advice.

brendankelly

We do a lot of work on old houses and this can be done but it is not as simple as just pouring concrete. I do not know the details but if it is not done properly you will have dampness. I can PM the details of someone that does this work and knows all about French drains etc if you wish. This man is based in the mid lands but he travels all over doing this type of work.

DOCARCH

What the OP is asking is quite straight forward. Yes you can put a poured concrete floor into an existing house where there is/was a suspended timber floor (after removing the suspended timber floor - but it's not quite as simple as simply pouring concrete into the 'cvaity'). The new concrete floor (as with an extension) will require a full damp proof membrane/radon barrier and insulation.

As alternative is that you can upgarde your existing suspended timber floor by taking up the floor boards, insulating between the floor joists, put down an airtight membrane and plywood/flooring on top. This will both insulate the floor and eliminate drafts.

If you do keep the existing floor to the main house and build a new extension to the back, with a concrete floor, bear in mind the 'cavity' under the floor of the main house is probably or should be vented. This ventiltaion needs to be maintained.

vallo

Thanks folks! That is very helpful. The more I think about it, I'm tending toward the idea of just insulating between the joists and reflooring as you described DOCARCH.
The only thing that would sway me back to the concrete floor is if there was a difference when it comes to flooding. My house is on quite low ground and a nearby river has flooded this general area (but never this road) in the past. Would having a concrete slab foundation be an advantage in the case of a flood?

FesterBeatty

If you want a concrete floor then why not go for a beam and block solution? No major advantage if it floods however...but at least you won't have rotten joists. It would be prudent to look into drainage solutions first, which will at least provide you with some level of protection in the event of a flood.

ayeboy

Doing a renovation project. Im still undecided whether to insulate between joists of my suspended floor or remove them and pour concrete. But my query is... if i pour concrete what is the best way to damproof a solid external wall? Its hardly the same procedure as damproofing up a cavity wall? Can anyone tell me what procedure is used in this circumstance? Thanks.

brendankelly

I was at a presentation on limes and gatecrashed a presentation on this subject. It is somewhat complicated and for some reason I did not grasp will cause dampness to go up the walls if not done properly. I will PM you the contact details of a guy that knows about this if you wish.

ayeboy

Hi Brendankelly, please pm me!