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Insulating Basement Floor

 
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Old 01-25-2010, 12:46 AM   #1
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Insulating Basement Floor


i'm renovating a basement and the customer wants a heated floor. if we install radiant floor heating directly onto the existing slab without insulating it somehow, would that make it totally useless? i am just looking for some ideas on what to do here. open to anything. we are not totally sure on the floor finish yet. i think a finished concrete floor might be cool. the other thing is i don't want to build up the floor too much. we are already at 7 feet from subfloor to underside of joist. any ideas would be appreciated .
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Old 01-25-2010, 01:23 AM   #2
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Re: Insulating Basement Floor


i think radiant actually relies on thermal mass and most of the heat wants to go upwards

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Old 01-25-2010, 01:33 AM   #3
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Re: Insulating Basement Floor


i hope so. i would hate to skip the insulating and wind up heating the earth instead of my customers toesies.
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Old 01-25-2010, 01:56 AM   #4
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Re: Insulating Basement Floor


Assuming nothing else is out of the ordinary, it will work fine. Just less efficient than an insulated slab. Warm air rises but "heat" moves to cold.

Gypcrete with tile would be ideal and around 2" thick. Some type of warmboard with a wood floor or carpet could work. The right mix of concrete, reinforced and cured properly, can be poured pretty thin.
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Old 01-25-2010, 08:42 AM   #5
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Re: Insulating Basement Floor


You can do it without any problems. Best thing for that is electric
ultra-thin heating mat, they have them on the market today, they can be embedded in a thin set. They also great to use, if you need radiant heat flooring and the height is a concern,they will not raise the floor by much.
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Old 01-26-2010, 11:38 AM   #6
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Re: Insulating Basement Floor


Quote:
Originally Posted by Bencouver View Post
i'm renovating a basement and the customer wants a heated floor. if we install radiant floor heating directly onto the existing slab without insulating it somehow, would that make it totally useless? i am just looking for some ideas on what to do here. open to anything. we are not totally sure on the floor finish yet. i think a finished concrete floor might be cool. the other thing is i don't want to build up the floor too much. we are already at 7 feet from subfloor to underside of joist. any ideas would be appreciated .
Absolutely it will work without insulation.

Unfortunately, it will be about as inefficient a heating system as can be designed. Hot air rises, but heat travels from hot to cold, in any direction.

The subsoil below the slab generally holds a relatively consistent temperature, say about 50 deg F (depending on location, depth, etc.). Given that the slab is in direct contact with the subsoil, heat transfer occurs very efficiently, via conduction. Given that the subsoil is the biggest thermal mass available (i.e. the Earth), your boiler, electric coils, etc are going to be working very hard.

Heat transfer in the other direction, on the other hand, is either through radiant heat transfer, or through convective heat transfer, neither of which are particularly efficient in these conditions. There is a small bit of conductive heat transfer, from floor to feet, which is the part that feels great, but doesn't really have an effect on efficiency.

Just to make matters even better, lay carpet on the floor - 3/4" of insulating pad and carpet between heat source and desired direction of heat flow.

I'm not an expert; surely one will chime in here. A system like this will work, as proven by some of the 'better' builders here (sarcasm factor of quote marks are insufficient). But it will be energy-expensive.
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Old 01-26-2010, 12:12 PM   #7
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Re: Insulating Basement Floor


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Originally Posted by greg24k View Post
You can do it without any problems. Best thing for that is electric
ultra-thin heating mat, they have them on the market today, they can be embedded in a thin set. They also great to use, if you need radiant heat flooring and the height is a concern,they will not raise the floor by much.
YES, this does work!
Another thing is, we have actually created a "floating" insulated floor, we stripped it all out with 1x's and 3/4" foam styrene in between. Then installed sub floor and floating laminate, carpet etc. Just a thought. Takes some time to do but turned out very slick!
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Old 01-28-2010, 10:29 PM   #8
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Re: Insulating Basement Floor


thank you all for the ideas. i like the idea the idea of using the 1x material and 3/4 rigid foam. that was one of the first ideas i had. my only concern there was the labour cost of installing everything compared to pouring gypcrete. did you use treated 1x or did you put tar paper down to stop it from rotting? did you fasten the 1x down? i would think that would be necessary for a solid floor. i would probably just use nail and tie-wire for that. one of the home owners ideas was to use linoleaum(however the fk you spell it)for the floor and i think this idea would be perfect for that.
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Old 01-29-2010, 03:59 PM   #9
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Re: Insulating Basement Floor


Hello, The last one we did was about 4 years ago. The customers basement floor was already sealed and very dry. They had a perimeter french drain around it as well, but they wanted to put some laminate in a couple rooms and carpet in the others. All we did was place a vapor barrier down on the floor to stop any moisture from wicking up then 1x4's fastened together, 3/4" foam styrene then another vapor barrier with just a few holes here and there to allow it to all breathe. Created a large floating floor. Each room was done separately. Then we used 3/8 plywood as a subfloor then did our finishing floor in each room. The weight of each subfloor and framing was enough to hold it down and firm. We did one bedroom first to see just how sound it was. Customer gave us the go and did the rest. This way if the slab did expand or contract it would not raise or lift the finished floor. It turned out very nice and very sure. No problems so far. Customer loves how warm the floor is now with the 3/4 foam styrene below. All in all we did a large game room, 3 bedrooms a bath, closets and an office.
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Old 01-30-2010, 06:41 PM   #10
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Re: Insulating Basement Floor


after compacting the earth

pour 6 to 12 inches of pea gravel the deeper the better

rake it out level compact it

place brand new concrete blankets down, silver side up, two layers = more r factor, but two layers is alot of mush

duct tape the joints

place your mesh, tie your tube to the mesh, pour and enjoy the warmth

done it plenty of times

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