Routed foam plastic with underfloor heating on top of the concrete slab in the conservatory

[S-hills]

Planning to build a 40 sqm conservatory with a 34 mm multi-wall polycarbonate roof and sliding panels with a U-value of 1.3. Will pour a slab on grade with integrated 16 mm tubing (underfloor heating) containing glycol. The loop or loops will then be heated by our air-to-water heat pump via a heat exchanger. The conservatory is attached to the house and measures 11.1x3.6 meters. The idea is to heat the conservatory only on special occasions (Christmas, New Year, etc.). Normally, as I mentioned earlier, I would lay out polystyrene insulation and then embed underfloor heating in the slab with some form of flooring on top. But now to my consideration, wouldn't it be better to pour the slab directly on durable plastic (with a supporting layer underneath) and then lay polystyrene insulation with grooves for underfloor heating on top of the slab? Heating up an entire concrete slab takes more than 2 days and will retain heat for 2 days afterward. The conservatory will never be heated more than one day at a time. Does anyone have experience with a similar construction? Additionally, the slab would not freeze in the same way since it gets some help from the ground heat. Keeping the heat on all the time would be like heating for the birds.

 

[jonaserik]

Do as you think with the loops, no point in heating an entire concrete slab, something to consider is having one or double layers of construction plastic on top of the concrete. Prevents condensation moisture from the slab upwards.

 

[S-hills]

Do as you think with the loops, no point in heating a whole concrete slab. What to consider is having one or double sheets of construction plastic on top of the concrete. Prevents condensation moisture from rising from the slab.

Exactly, it's important for the slab to dry out properly. But it should dry quite quickly when the sun is out in spring (direct south facing).

 

[Plupp 405730]

Yes, you get a much more responsive heat by having it on top of the concrete. However, lay at least 50mm of cellplast under the plate so it doesn't freeze or preferably more, it's not a huge cost.

 

[S-hills]

Yes, you will get a much more responsive heat with it on top of the concrete..
But lay at least 50mm of foam insulation under the slab so it doesn't freeze, or preferably more, it's not a huge cost..

Shouldn't the slab become colder with foam insulation underneath? If it's -20 degrees outside, the slab doesn't get any help from the ground heat below if there's foam insulation there, but on the other hand, the slab is protected by the foam insulation from above. Or should I think differently?

 

[Plupp 405730]

Shouldn't the slab become colder with foam underneath? If it's -20 degrees outside, the slab doesn't get any help from ground heat below if there's foam there, but the slab is protected by the foam from above. Or should I think differently?

No, you always insulate on the outside; if you have macadam underneath, the cold will reach far below the slab..

 

[S-hills]

No, you always insulate on the outside. If you have gravel underneath, the cold will find its way far under the slab.

You definitely have a point there. However, I think you can bypass that problem if you lay foam on the ground around the conservatory. I was planning to lay self-cast concrete slabs 240x120cm.
Then, if I lay age-resistant plastic under the concrete, I'll avoid moisture migration from below.

 

[Plupp 405730]

You absolutely have a point there. However, I believe one can circumvent that problem by placing foam plastic on the ground around the conservatory. I was planning to lay self-cast concrete slabs 240x120cm.
As long as I lay age-resistant plastic under the concrete, I can avoid moisture migration from below.

You can do as you wish, but it's not a used and proven method.

 

[S-hills]

You can do as you please, but it's not a useful and proven method..

Sorry, I was a bit unclear, the concrete slabs 240x120 are to be cast in expanding concrete and be outside the conservatory. Above the foam blocks. My experience with all the concrete slabs we cast at work, e.g., unheated garages, etc., would be warmer without foam underneath. But you might be right. 5 cm of foam underneath might not be such a bad idea.