piping between floor and slab

Matt_21

on top of the insulation right beneath the floor you will still be in the conditioned space of the room. the heating from the room penetrates your floor and is stopped by the insulation. if you had a 2" gap between the floor and the top of the insulation, that 2" space would be conditioned. there isn't much r value in the flooring material.

tom_75

I have hot water baseboard heat.
I have a room connected to my house that used to be a porch and is built on a concrete slab. The floor is 6" lower than the house floors. It is 2x4's with 3/4 plywood over the slab. I am going to add another set of 2x4's 16" on center, add another plywood layer, then finished floor boards to get me even with my joining house floors. I thought that I would sandwhich fibergass insulation between the old floor and the new floor. Question:
Can I run my 3/4 piping from the basement through this space between the floors if I use pipe insulation in addition to the fiberglass that would surround the pipes? If I can do this, then I can get my baseboard along the outside wall which is ideal in more ways than one.Thanks in advance for any help.

Matt_21

i think

you would be taking a chance of freezing by doing that. what you may want to do is open up the existing 2x4 space where the pipes would be running above and insulate that space as well as the new 2x4 space where the pipe would be running. now you could lay an r-25 insulation in the space. you should try to keep the 3/4" pipe between the floor and the top of the insulation this way the pipe is in the conditioned area.

hr

I wonder

about the condition of the current framing over the slab? Maybe it would be better to remove that and build a new floor system, at the correct elevation, with joist and treated lumber at any concrete connection points.

You would be able to get a higher R-value in a deeper joist bay than in 2X4's.

Then you could also get the piping up above the insulation.

hot rod

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tom_75

thanks mattr, if I insulate the existing space too, then the insulation would be resting directly on the concrete slab - I was not sure if this was a good idea or not.

tom_75

hot rod,
thanks - I was thinking of that. I wripped up one piece of plywood and the existing 2x4's look fine - no moisture and no termite signs. Do I really need to use treated lumber in this case? How about if I were wrip out the plywood and build a new joist system with 2x6 douglas fir? This would leave a couple of inches between the slab and the bottom of the 2x6's with no direct contact. Still not sure if I should let the insulation contact the concrete??

hr

Really

any wood in direct contact with the slab should be treated, or redwood.

I see contractos around here have switched to TimberStrand products for bottom plates. They tell me it is rated for direct contact and get's them away from using stainless steel nails that are required with the newer treated woods.

I would suggest a layer of 25psi foamboard between the slab and framing, then the fiberglass batts in the joist. You don't want the fiberglass in contact with the concrete, due to potential moisture issues.

Hard to say without seing what you have, but the idea of 2X4 floor joist scares me Not much of a span allowed with 2X4. Nothing worse than a springy, squeaky floor caused by joist undersizing.

Might be best to start fresh from the slab up with properly sized framing material?

hot rod

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tom_75

I like hot rod's last bit of advice. I think I should rebuild with 2x6's and use foamboard against the concrete. The room is only 7' wide so 2x6's are plenty. I guess my only question is - if I keep my piping towards the top, will I be protected from freezing? I would have the foamboard and about 4"s of fiberglass beneath my copper.

tom_75

That makes sence. I am definately going to keep the pipes on top of the vapor barrier paper side of the fiberglass. I was worried that the heated room would not penetrate the 2 layers of wood flooring to protect the pipes. Would I still want pipe insulation or better without it??

tom_75

Would a 6 mil plastic sheeting be a good idea to use directly on the concrete pad 1st, before the foamboard and then fiberglass?