Sub floor on extension - concrete or floorboards?
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Practical.
Simple.
Economical.
Solid.
Efficient.
Simple.
Economical.
Solid.
Efficient.
Thanks.
Lets say you were building a new extension that joined onto an existing room that had a timber suspended floor (with about 4 foot head height under the floor)
Would you still make it from concrete with ducts to maintain ventilation to the original floor?
Thanks
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No.
Maximum depth of infill should not exceed 600mm otherwise a suspended floor should be specified.
Otherwise yes we would and do as you say extending the existing vents to the new outside walls via ducting and air-bricks.
Noseall, I'm not sure what you mean.
My kitchen has this sort of suspended floor (ie about 4 foot head room underneath)
6 years ago I had a rear extension built that comes straight off this kitchen (ie almost open plan) and this extension has a solid floor.
The new extension will be extending the kitchen to the side.
Are you saying that my rear extension should have had a suspended floor?
Thanks
How thick is this existing slab, and how much lower than the current internal floor level is it?
There is a cheat
Internally, the existing slab is at the same level as the timber subfloor. The existing slab is about 15-20cm off the ground (comparing to the level outside the house). As it is uninsulated, I believe I have two options - 1) to break it out and then to have a concrete subfloor done where the existing concrete slab was and where the extension will be. or 2) have a timber subfloor.
Bit confused.
So you have an existing concrete floor internally, as well as a timber floor. Both of which will be incorporated into the new kitchen, which will also extend outside. The outside level being 20cm below current internal floor.
?
If that's the case then get your builder to advise, and get a quote for both options, chances are the concrete will work out cheaper.
There are a few good threads on here regarding ventilation of subfloor. Search.
So you have an existing concrete floor internally, as well as a timber floor. Both of which will be incorporated into the new kitchen, which will also extend outside. The outside level being 20cm below current internal floor.
?
If that's the case then get your builder to advise, and get a quote for both options, chances are the concrete will work out cheaper.
There are a few good threads on here regarding ventilation of subfloor. Search.
Nothing to do today, and as Indus has stuck his beak in, and there is a possibility of screwing him for a couple of more notes for the heroes fund ,will add a little more to this post.
The Rt Hon Nose is correct in everything he has said.
The 600 max fill regulation came in more than 40 odd years ago. Prior to this we would think nothing of tipping 100 tons of loose brick hardcore direct from LBC straight into the over site.
To over come this reg we then started filling over site up with excavated spoil from foundations and any thing we could lay hands on, scaffold board down cavity as shutter board, DPM and C35 150 concrete slab with A252 mesh RE. Then later, came the introduction of block and beam.
So Indy, technically if you have a metre of loose fill under your slab, then you have a suspect floor. It may never move, but is still suspect.
OP,. There are a lot of implications not mentioned but need considering. On suspended timber floors, even if you do not suspend your joists on sleeper walls, but you increase depth of joists and suspend joists on hangers you still need a sub base and concrete sub over site to comply with BRs and 150 clear air space between underside of joists and concrete sub site. . Min excavated depth below FFL will be 600.
With block and beam floors, you do not need a concrete sub base, a poly membrane and 30mm of pea shingle will suffice as weed suppression, and including insulation and screed you will need an excavation of 575 below FFL. Concrete over site including insulation and screed excavation depth below FFL to be 350.
Some quick approx labour and material figures based on 16m2 footprint.. Excluding any excavation. Inclusive of VAT on materials, but exclusive of VAT on labour.
Concrete slab. 100 fill, 100 con, insulation and 75 screed
Approx £81.00 m2.
Suspended timber. Sub base concrete as above, two course sleeper walls, 47x100 joists and plates, insulation tween joists 22 floor decking
Approx £107.00 m2
Block and Beam, including delivery and crane of load, insulation and screed.
Approx £102.00 m2
If you then talk UFH, this then does drastically increase the cost of suspended timber, but that is another story.
Regards oldun
The Rt Hon Nose is correct in everything he has said.
The 600 max fill regulation came in more than 40 odd years ago. Prior to this we would think nothing of tipping 100 tons of loose brick hardcore direct from LBC straight into the over site.
To over come this reg we then started filling over site up with excavated spoil from foundations and any thing we could lay hands on, scaffold board down cavity as shutter board, DPM and C35 150 concrete slab with A252 mesh RE. Then later, came the introduction of block and beam.
So Indy, technically if you have a metre of loose fill under your slab, then you have a suspect floor. It may never move, but is still suspect.
OP,. There are a lot of implications not mentioned but need considering. On suspended timber floors, even if you do not suspend your joists on sleeper walls, but you increase depth of joists and suspend joists on hangers you still need a sub base and concrete sub over site to comply with BRs and 150 clear air space between underside of joists and concrete sub site. . Min excavated depth below FFL will be 600.
With block and beam floors, you do not need a concrete sub base, a poly membrane and 30mm of pea shingle will suffice as weed suppression, and including insulation and screed you will need an excavation of 575 below FFL. Concrete over site including insulation and screed excavation depth below FFL to be 350.
Some quick approx labour and material figures based on 16m2 footprint.. Excluding any excavation. Inclusive of VAT on materials, but exclusive of VAT on labour.
Concrete slab. 100 fill, 100 con, insulation and 75 screed
Approx £81.00 m2.
Suspended timber. Sub base concrete as above, two course sleeper walls, 47x100 joists and plates, insulation tween joists 22 floor decking
Approx £107.00 m2
Block and Beam, including delivery and crane of load, insulation and screed.
Approx £102.00 m2
If you then talk UFH, this then does drastically increase the cost of suspended timber, but that is another story.
Regards oldun
Hi Oldun, I might as well set up a direct debit for hth!
However, either I have misunderstood or not explained myself properly. I can't believe I have a suspect floor as it was designed by a decent agent, built by a good builder and inspected by the local BR dept.
Basically my kitchen was at the rear of the house and the extension was built outwards from there. The kitchen (like all of the ground floor) has a suspended floor with a 3-4 feet of void underneath. The extension has a solid floor.
I'm sure the builder did a proper job, just not sure how!
However, either I have misunderstood or not explained myself properly. I can't believe I have a suspect floor as it was designed by a decent agent, built by a good builder and inspected by the local BR dept.
Basically my kitchen was at the rear of the house and the extension was built outwards from there. The kitchen (like all of the ground floor) has a suspended floor with a 3-4 feet of void underneath. The extension has a solid floor.
I'm sure the builder did a proper job, just not sure how!
aah geddit now.
So long as the new extension did not require above 600mm of infill then a concrete floor in this area will be fine as long as the builder has extended the existing vents to the new outside wall.
You would not for example automatically use a suspended floor for the new just because the existing has it. There would need to be a legitimate reason and one of those being excessively deep (600mm plus) infill.
Indy,
The Rt Hon nose has a hole in one. His description is poetry.
We read your post wrong and assumed you had a metre of fill. You can now safely remove a wall and park your car inside.
Suggest you donate to the favourite charity of nose. The Old P*ssy Home. And we don’t mean cats.
Regards oldun
The Rt Hon nose has a hole in one. His description is poetry.
We read your post wrong and assumed you had a metre of fill. You can now safely remove a wall and park your car inside.
Suggest you donate to the favourite charity of nose. The Old P*ssy Home. And we don’t mean cats.
Regards oldun
Thanks, that makes me feel better.
The rear extension doesn't seem to have air bricks so ventilation has not been extended under it.
HOWEVER, the kitchen has three external wall ie left, right and the previous rear. Both the left and right walls have their original airbricks to provide cross ventilation.
Whether it is just good luck or whether the builder calculated that the two remaining bricks would suffice I don't know.
Should I be ok with just these two remaining airbricks??
Thanks again.
The rear extension doesn't seem to have air bricks so ventilation has not been extended under it.
HOWEVER, the kitchen has three external wall ie left, right and the previous rear. Both the left and right walls have their original airbricks to provide cross ventilation.
Whether it is just good luck or whether the builder calculated that the two remaining bricks would suffice I don't know.
Should I be ok with just these two remaining airbricks??
Thanks again.
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