Best fix for cold slab-on-grade family room floor
geoffhazel
| Posted in Energy, Heating & Insulation on
Client has a family room that was slab-on-grade with nothing between the concrete and dirt. They had a berber carpet over cheap pad, but they like to walk around the house barefoot and the floor feels cold to their feet, esp. compared to the wood floor of the rest of the house that is over an insulated crawl space. What would you recommend to warm up the floor, esp, something that doesn’t send half its heat down into the slab, or add a lot of thickness. This room has a slider patio door leading to an outside patio.
Replies
Nothing. Not much you can do, at all. Can't insulate it w/out adding thickness. Radiant heat would be awkward ... even the electric warm mat (forget what it's called). Any heat you apply would be sucked into the ground, although it would warm the slab and make it more comfortable. I suggest a set of slippers at the entrance to the room that are easy to slip on/off.
Possibly a thin layer of foam and a small diam. radiant tubing and a layer of concrete slurry, but I don't know. You're talking a minimum of a couple inches anyway. Not sure if that can be done.
I had the same concerns here about sending heat into the earth with a pex radiant solution, so will describe the situation:
Original condition:
- elevated mono slab 2-season sunroom, off kitchen, 13x15; no insulation below. 4-inch slab.
- indoor/outdoor carpet, 2-season windows and uninsulated porch door
Conversion:
2x4 framing with R13 insulation
11 Andersen 200 t/w windows (wall-to-wall)
Cheap slider door
Flooring:
1 layer foil-backed bubble wrap (forget what this is called, but purchased at local lumber yard in 2' width.)(tape each row with aluminum tape)
1 layer 1/2 inch ACQ plywood, shot and screwed into slab.
Upinor Quik-Trak radiant flooring
1/4 inch Hardi-backer
3/8-1/2 inch slate tile
Results:
Ambient temp fine apart from three days in a row last Feb. when afternoon temps did not reach 10 degrees (F). I attribute that to the R13 in the walls, and wall-to-wall glass, and the fact that the slider faces north. At that point, the best temp I could get out of the pex radiant was about 62 degrees.
The upinor Quik Trak has an aluminum stamped back, which helps. With the added foil-backed bubble wrap below, (above a vapor barrier) I believe this was a good investment. I can say that our heat bills have not increased whatsoever since the installation. However, I can't tell you whether the bubble wrap helped one bit. No way to tell, but I know it didn't hurt.
Issues: - Shooting ACQ over the foil-backed bubble wrap is no fun. You will need pressure on the boards if they are not dead flat. I used a hydraulic car jack against the ceiling joists to push the ACQ into the slab. Worked well, but took some time to figure out that solution. Wasted many screws and shots.
Happy to help with any questions.
Your heat bills for your entire house have not increased since you added heat to your sunporch? That's sweet. You must have greatly improved (i.e. reduced) your heat loss w/ the walls, ceiling and windows over what the old wall was (i.e. between the sunporch and house).
Course only able to hold 62 in the space is pretty marginal. I'm guessing though an increased heat load of the sunporch somehow was off set by something else somewhere. I doubt that you actually decreased your heat load, so somehow, somewhere there was a compensating factor that went unnoticed to the lay person.
Thicker carpet, thicker pad.
We have installed Thermosoft's electric heat mats under all of our floating engineered wood floors (Pergo) and absolutely love them. Our house is slab on grade with no insulation under the slab. The mats are only 1/8" thick, the same thickness as the underlay felt that normally goes under the floating floors. As long as the engineered floor is rated for radiant heat, you shouldn't have a problem. Highly recommend the mats for a remodel situation where traditional radiant systems would be impractical.
Submitted by geoffhazel on Wed, 12/16/2009 - 18:49
in Energy, Heating & Insulation
What would you recommend to warm up the floor, esp, something that doesn't send half its heat down into the slab, or add a lot of thickness. This room has a slider patio door leading to an outside patio.
In a "3-season" room w/uninsulated slab on grade we added 1/2" Homasote under the carpet and pad. Goal was the same as you, un-cool the floor. Heat came from main house by leaving a sliding patio door open between rooms. This works well down to highs in the high teens in NW Oh. Half glass 2 sides S&E. Insulated "patio roof".
Ran 1/2" ply strip around perimeter as base for tack strip.
You must leave an expansion gap between sheets of the Homasote. I would be hesitant if slab is not at least moderately dry, as Homasote is pretty much compressed paper. We did not put a visqueen layer between the slab and Homasote, as the slab was divorced from grade outside by the poured foundation on all exposed sides and remained dry.
I went to the trouble of gluing and tap-conning the sheeting to the concrete. If using a visqeen barrier of course you couldn't do that. Hoever, this stuff lays flat (unless it sucks up moisture-then you'll probably wish you had PL Premiumed it down.
But, with a vis. barrier and dry perimeter, I would expect it to lay flat. All you're doing now is "holding" it in position. I believe you can use a PAD with furring nails, and shoot it down. I may have done that instead of Tapcons, it's been awhile. So say a dozen pins or screws per sheet-plenty. Shooting it down would save a boatload of time.
At any rate, the Homasote worked as planned, divorcing the direct cold from the slab. It'd be nice if you could use a dense foam panel similar to Dow Bluebd, but I don't think it would hold up to direct pressure spots like couch, etc.
Hope that diatribe gives you more information to decide from. Best of luck.
geoff,
Our family room is slab on grade just like the one you describe. We have a high quality wall to wall carpet over a very dense, thick pad and it is just as warm as any other part of the house. Barefoot is no problem.
Now the ceramic tile I put down in the kitchen is another story :(