2 Q about insulation in joists above concrete slab

[dare]

Hello,

we have a 70s house that stands on an uninsulated concrete slab on the ground. The slab extends under the house and under the garage that is built together with the house. The floor on the lower level rests on a wooden joist on top of the slab. On the slab, there are blocks and on these the joist itself, which is insulated with mineral wool.

I am now going to extend and will have access to this joist from two directions as I demolish the walls.

Question 1: Is it appropriate to spray insulation into this joist to improve the insulation against the slab? I have installed hydronic floor heating and I don't want to unnecessarily heat the slab. Will I create moisture problems by filling with insulation?

Question 2: I am going to extend the house into the garage in a certain area, where I also plan to have a wooden joist, how should I insulate against the slab? Can I use foam directly against the slab and then joist with mineral wool, or...??

Thanks in advance Dare

 

[ByggIng]

Oh no, you're about to make things difficult for yourself. As most people know, an uninsulated slab on the ground with a raised floor is a risky construction. I'm sorry to have to tell you, but the underfloor heating doesn't make it any better.

First and foremost, remove any organic material from the slab. It should be spotlessly clean! Then plastic film so the diffusion stops as early as possible. On that, a floating floor with something like foam plastic as insulation. The surface layer must be able to breathe, so tiles or wooden flooring. Then you've done what you can.
If you don't want to remove the beams, still make sure the slab is clean, that you have a plastic film, and not too much insulation. However, you can probably increase it slightly since the underfloor heating will raise the temperature of the floor, but you'll likely have to settle for 95mm of mineral wool.

This underfloor heating that needs to go in everywhere...