Sub floor options

FP Peking Duck

I am going with underfloor heating. My question is what to build the subfloor underneath from.

The construction will be: sub-floor, radon barrier, insulation, screed with UFH pipes in.

This is an old stone house. The floors were suspended timber, which I removed. I then dug out all the debris that had accumulated, down to a firm footing. All the walls are standing and roof on...just the inside floors removed.

I had been advised to pour a concrete sub floor and then put my barrier and insulation on top.

I have seen another house where they put down 804 and whacked it. Then put a dusting of sand to level it, and then the barrier and insulation directly on top of this.

I will need about 8 inches of sub floor to get me to the required height (insulation and screed on top of this to get to finished floor level). So the cost diffrence between concrete and 804 will be big (approx 40 mtres by 5 metres floo area).

My question is: Does the sub floor need to be concrete? Will whacked 804 do instead? Are ther any advantages to usng concrete instaed? Thermal properties, no movement etc etc.

Thanks in advance.

RKQ

FP Peking Duck wrote: »

My question is: Does the sub floor need to be concrete? Will whacked 804 do instead? Are ther any advantages to usng concrete instaed? Thermal properties, no movement etc etc.

804 whacked could be seen as hardcore for a ground supported floor slab. So whacking in layers of 225mm is possible - provided you have removed all soft soil material. Can you whack hardcore 804 tight to existing walls?

Every ground supported floor slab must be 150mm thick - TGD A Structure. A sand / cement screed is not a structural element.

Underfloor heating requires a good thickness of floor insulation.

It might be more practical to pour a conc sub floor - handy for installing radon and insulation etc. o a level firm surface.

Carlow52

FP Peking Duck wrote: »

I am going with underfloor heating. My question is what to build the subfloor underneath from.

The construction will be: sub-floor, radon barrier, insulation, screed with UFH pipes in.

This is an old stone house. The floors were suspended timber, which I removed. I then dug out all the debris that had accumulated, down to a firm footing. All the walls are standing and roof on...just the inside floors removed.

I had been advised to pour a concrete sub floor and then put my barrier and insulation on top.

I have seen another house where they put down 804 and whacked it. Then put a dusting of sand to level it, and then the barrier and insulation directly on top of this.

I will need about 8 inches of sub floor to get me to the required height (insulation and screed on top of this to get to finished floor level). So the cost diffrence between concrete and 804 will be big (approx 40 mtres by 5 metres floo area).

My question is: Does the sub floor need to be concrete? Will whacked 804 do instead? Are ther any advantages to usng concrete instaed? Thermal properties, no movement etc etc.

Thanks in advance.

200 sq m is a lot of floor:)

See http://www.environ.ie/en/TGD/ how the different floors are detailed, in particular look at provision for a radon sump and piping in the 804

If it were my gaff I would line the floor with the radon barrier now, bringing it up beyond the dpc in the walls and taping all joints and then pump in a lean concrete sub-floor, followed by loads of insulation.

ps the layer of sand is to stop the 804 from perforating the radon barrier

.

AckwelFoley

OP. You need both.

You need to have a solid compacted hardcore a subfloor with steel and insulation of min 120mm polyiso but there is a narrower equlivent, and a finish floor of no more than 80mm due to the use of ufh. Laying insulation o top of "whacked" hardcore and putting an 80mm screed on top is not sufficent. Some may do it, but i certainly wouldnt