Installing radiant heat on an existing basement slab

paroo

I'm doing a DIY radiant floor heat install in my in finished basement. I've got the base plate down for my walls and I was going to wait until I had the heating installed before I finish the walls. My main question is how are you guys doing this type of install?

There's a lot of talk about having proper insulating under a new slab, but I see very little out there about overpouring existing slabs. I'm in a very dry zone 5 (almost 6) with winters averaging in the 30-40s F. My basement has a 4" slab and is almost entirely below ground (about 7'). My ceilings are already under 8', so I was wanting to keep the total retrofit height to a minimum, and I'll have r-19 walls.

My current plan is laying down 1/2" rigid foam (r-3 value), wire mesh (cheaper than the rails), 1/2" PEX, then 1-1.5" of concrete or gypcrete. In a perfect budget free world, I'd get some Roth board, or warm board, but I'm already way over budget.

Is an r-3 thermal break worth the time and money? In my situation with fairly mild winters, and r-19 walls would skipping the insulation be that big of a deal? If efficiency went down by $5/month during the winter then it'd take me 20 years to equal the cost of the insulation and supplies. I'd also have more head room.

Your thoughts and experience are greatly appreciated.

the_donut

Depends if you want to pay for heating the ground outside your foundation. Money saved on skimping insulation now is money spent later on fuel.

Ironman

I would put at LEAST 1" board down; another 1/2" of lost ceiling height is not gonna be noticed.

The federal energy code now requires 3".

cloves

I put down 2 inches of xps plus 1/2 inch pex and used the metal inserts and then 3/8 cement board and then tile (used ditra on top of cb). I grooved my xps with a router and made all the pex channels then inserted the metal plates. The basement is the fastest heating room in my place.

Dave H_2

I have to ask one question:

Why do want a radiant floor in your basement? What is the goal other than heating the space?

The reason I ask is I did a radiant basement retrofit in my house. The install consisted of a plywood base on the concrete and then quik-trak. What I never really experienced was a warm floor. The space was heating just fine but because of the low heat loss of the basement, it just never ran long enough to feel it.

If I had the chance to do it again, I would have installed a radiant wall or ceiling. It would have been easier to install and not add too much height to the floor.

Dave H.