Blow cellulose into air space between 4″ gap from floor to slab? Other options?
Hi, love this place, it has answered so many of my questions but this one I’m stumped on.
I’m in a 1960 split level, half of which is slab on grade. But, the slab section of the house is built where there are 2×4 sleepers keeping the floor off of the slab. Pretty nice, it does offer some insulation value I guess. But i’m looking to install radiant floor heating to this area of my house. I have absolutely no moisture issues in my house, but still I’m not sure if i can blow in insulation into the floor. It would be awesome if I could drill some large holes between the sleeper joists and just blow in insulation. My other option would be to remove the subfloor in 2 rooms and a hallway and lay some sort of insulation down. But that would take 100 times more work/money than just blowing in insulation.
The floor consists of 1/2″ plywood topped with 3/4″ plywood. So I could just router out the grooves for the radiant floor in the 3/4 and put in my sandwhich plates and install new flooring above (it was carpet before, loooking to do some sort of wood flooring).
Here’s a shot of my bathroom floor where I already installed the radiant.
http://i.imgur.com/Db87zDA.jpg
I took up the floor completely here. This section was done with the sleepers laying flat to accommodate the pipes I think. The rest of the house they are installed like joists from what I can tell. Here I put in rigid insulation, but this was a tiny bathroom. The area I want to do now is much larger,
here’s my house plans, cool that I actually have them. I’ll be doing the hallway, playroom, and laundry room. The wall between the laundry and play room were removed by the previous owner but I’m putting it back, a room that shape is just strange.
http://i.imgur.com/K5GFbiG.jpg
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Replies
Only if you KNOW that you have a ground vapor barrier under the slab should you risk blowing cellulose in there! Cellulose is hygroscopic, and can wick copious amounts of moisture before becoming noticeably damp. It would probably be fine during the heating season with the radiant floor heating it, but during the summer it could potentially reach mold levels in the bottom layers, even when you don't have apparent risk of bulk water / flood.
Luke,
The best way to address this type of floor is to remove the existing subfloor and sleepers. Install several inches of rigid foam on top of the existing slab, followed by a layer of 3/4-inch plywood, secured to the slab with TapCon screws.
+1 on that!
With 3.5-4" of EPS under the subfloor you'd have about R14-R16, under the radiant, but with far less thermal bridging. than with the 2x4 sleepers 16" o.c.(which would come in about R9-10 average, after factoring in the thermal bridging.) And the floor would be at about the same level that it is now.
Like any other heating system, calculating the actual heat load would be an important first step, and WILL affect the cost and methods use in the radiant design.