Sub floor on extension - concrete or floorboards?

[ssharrow]

Hi All, we are going to do a ground floor extension to the house next year - side and rear. We have already received planning permission. Architect finalising drawings for building regs now. On the current draft architect has drawn in timber subfloor. A few people I know (e.g. neighbours) have extended their house with a concrete subfloor. I'd like an independent opinion on what the better alternative is? concrete or floorboards? Part of the existing area that will be part of the new kitchen has a concrete subfloor (not insulated) - the remaining exiting house has timber subfloor. Is there a cost difference between going down the concrete route? Thanks

 

[freddiemercurystwin]

Others can answer the cost difference, note that any existing ventilation in your existing floor will need to be extended out to your new external wall line, a suspended timber floor makes this easier. Otherwise you're into silly ducts under the slab to retain the crossflow. But this may not be applicable, not very clear tbh.

 

[ssharrow]

hi thanks, yes we will make sure the existing sub floor is ventilated with ducts to the outside. Do most home extensions use a concrete sub floor or timber sub floor?

 

[freddiemercurystwin]

I generally only spec timber suspended where there is a need over the other eg to maintain existing ventilation or where the floor is above ground level. Otherwise ground bearing concrete. Either is OK though really if done correctly.

 

[ssharrow]

thanks, I should also mention that we are considering having underfloor heating in most of the extension - does this change your opinion?

 

[freddiemercurystwin]

TBh I've not had much experience of UFH but there are plenty of systems that will work in either/or. I recall reading some techy report sometime that concrete is always best as the timber floor systems rely on having to heat the air surrounding the pipes before it heats the floor boards and wastes energy and of course the screed will retain more heat better.

 

[ssharrow]

Thanks, what about a) cost and b) speed of building work when it comes to deciding whether to go for timber suspended sub floor or concrete subfloor?

 

[tony1851]

FMT - you should be charging the OP a consultation fee!

 

[freddiemercurystwin]

Its all about the love Tony!

 

[jabuzzard]

TBh I've not had much experience of UFH but there are plenty of systems that will work in either/or. I recall reading some techy report sometime that concrete is always best as the timber floor systems rely on having to heat the air surrounding the pipes before it heats the floor boards and wastes energy and of course the screed will retain more heat better.

In Scotland suspended timber floors must now be insulated to 100mm of fibreglass equivalent. No idea if this applies to England and Wales however.

 

[freddiemercurystwin]

TBh I've not had much experience of UFH but there are plenty of systems that will work in either/or. I recall reading some techy report sometime that concrete is always best as the timber floor systems rely on having to heat the air surrounding the pipes before it heats the floor boards and wastes energy and of course the screed will retain more heat better.

In Scotland suspended timber floors must now be insulated to 100mm of fibreglass equivalent. No idea if this applies to England and Wales however.

Err, 100mm fibreglass in a floor won't get you anywhere near compliance. Its not a suitable insulation for a floor anyway.

 

[noseall]

Provided there is no risk of clay heave etc, then concrete every time.

 

[^woody^]

Timber ground floors are so 1920's.

For UFH, you really need the mass and thermal store of concrete

Kitchens should have concrete floors too due to noise and leaks

 

[ssharrow]

Thanks so it seems that its best to go for concrete subfloor overall? at least we'll be able to break out the existing concrete subfloor at the back of the house (which will be part of the new kitchen) and then insulate it along with the new concrete subfloor. What I need to know is also whether there is a cost difference between going for concrete sub floor and timber? Any answers on that? Many thanks

 

[Deluks]

at least we'll be able to break out the existing concrete subfloor at the back of the house

How thick is this existing slab, and how much lower than the current internal floor level is it?
There is a cheat