Underfloor heating on suspended floor

[tmf786]

I'm planning to fit a wet system underfloor heating on my ground floor. So need some advice please:

The floor is timber suspended as shown below. The height of the gap below the joists is about 500mm. The joists themselves are 4'x2' (100mmx50mm).

I plan to:
- use battens on either side of the joist
- then fit PIR insulation in-between joists
- then ufh pipes on top of insulation (notch the joist on one end to fit below the top of the joist
- then dry pug mix
- floor leveling screed
- vinyl glue down planks

Question:
- should I fill the void below with hardcore then concrete?
- Do I need damp proof membrane? Where should this go?
- will a notch on 4x2 be ok?

Any other considerations?

 

[motorbiking]

You can't fill the void, it looks like a vented space, so you will need air flow to avoid rot. Unless you fully insulate the floor, you will be wasting a lot of energy. You don't need DPM as the PIR has a built in vapour barrier. You don't need battens, a couple of nails in each side will "catch" the PIR and you will foam it into place to avoid any gaps.

 

[tmf786]

You can't fill the void, it looks like a vented space, so you will need air flow to avoid rot.

Thanks, understood.

Unless you fully insulate the floor, you will be wasting a lot of energy.

Does this mean I shouldn't put UFH at all?

You don't need DPM as the PIR has a built in vapour barrier.

Thanks, understood.

You don't need battens, a couple of nails in each side will "catch" the PIR and you will foam it into place to avoid any gaps.

Will this be strong enough for the UFH, screed, vinyl planks?

 

[motorbiking]

You are insulating between the joists, then you have floor boards, then the UFH matting etc.

I would say no it’s going to cost a lot of money and waste a lot of energy. There is a risk of very expensive repairs if you get any rot or movement in the joists.

For me I would insulate between the joists, foam any gaps and lay floor boards as normal and maybe spend the money on som nice designer radiators with pipes all insulated when in the void.