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Old 02-21-2010, 08:42 PM   #1
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Insulating for radiant heat


I'm building a new 1500 sq feet house in the spring and have a question about insulation. I will have in-floor heat in the basement the garage and on the main floor. In the garage I know I need to insulate under the slab. In the basement since the slab is 8ft under ground do I still need to insulate under the slab. What about the main floor since there will be the warm basement underneath do I still need to insulate. If so what is the method to insulate the main floor. Do I insulate between the joist or over the plywood before the concrete gets poured. Thanks in advance.

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Old 02-21-2010, 09:12 PM   #2
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Insulating for radiant heat


You MUST insulate the basement floor if you want it to work. And not cost more to heat then a 5,000 sq ft house.

What type of flooring will you have on the first floor.

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Old 02-21-2010, 09:17 PM   #3
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Insulating for radiant heat


Ceramic tiles
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Old 02-22-2010, 11:49 AM   #4
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Insulating for radiant heat


If you are putting the tubes in gypcrete or light weight concrete on the main floor (over a wood subfloor) I believe the usual practice is to insulate from underneath between the joists.
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Old 02-22-2010, 02:40 PM   #5
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Insulating for radiant heat


Quote:
Originally Posted by jogr View Post
If you are putting the tubes in gypcrete or light weight concrete on the main floor (over a wood subfloor) I believe the usual practice is to insulate from underneath between the joists.
Yes, that is the easiest way, and doesn't lose you height in your home.
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Old 02-22-2010, 02:57 PM   #6
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Insulating for radiant heat


INSULATE!! INSULATE!! INSULATE!!

And if I forgot to mention it......INSULATE

Under the concrete (Basement and Garage) WBBF (White-Bubble-Bubble-Foil) or 1 1/2" foil faced BlueBoard (like you can buy at the home center).

As to the rest of the house, you will want to insulate up in the joist spaces with the foil facing up toward the tubing.

Oh yeah, one more thing......INSULATE!!!
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Old 02-22-2010, 03:36 PM   #7
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Insulating for radiant heat


Are you talking about this stuff:

http://www.buyfoilinsulation.com/All...ble-Insulation

In my detached garage I built a few years ago I used that 1 1/2" blue rigid foam insulation. I the WBBF as good or better than the foam.
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Old 02-22-2010, 03:48 PM   #8
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Insulating for radiant heat


Yes, you should insulate under the concrete slab in the basement.

However, foil faced products are of very limited benefit under a concrete slab. The reflective foil when used properly is for reflecting "radiant" energy not "conductive" energy. But when the foil is sitting under a concrete slab the reflective properties of the foil are useless. In this situation the insulation is operating in a "conductive" environment. The best for this situation is rigid foam (blue or Pink).

Foil products require an air gap to function properly. This is what you would typically find between floor joists. The foil then has the ability to work as designed, reflecting. If used under a slab the only thing providing insulation are the bubbles themselves. About a R-1.

Google search a variety of things starting with Slab Insulation and foil insulation under concrete slab.

Here is just one result: http://www.naturalspacesdomes.com/be...st_results.htm

After reading several sites you will quickly determine that rigid foam is best. Don't believe the sales pitch hype on those foil bubble wrap insulation for underslab insulation. Read the details from many sites and you should start getting a consistent picture.

Here is a quote from Wikipedia:

"The effectiveness of aluminum foil or metallised film radiant barrier in preventing heat loss is negated if it abuts any material with high thermal conductivity. Reflective foil needs an air gap to function as a conduction insulation material. A radiant barrier system is defined as a reflective material facing an air space. When the radiant barrier faces an enclosed air space it becomes a reflective insulation with a measurable R-value."

Quote from above is from here:
http://en.wikipedia.org/wiki/Thermal_insulation

Here is another: http://www.rimainternational.org/myths/index.html


Those Foil faced Bubble wrap insulation products have their place; it is just not as an insulation under a concrete slab.

Generally 2 inches of rigid foam seems to be a good compromise between cost and performance. This is especially critical in cold weather climates.

Last edited by Dragon; 02-22-2010 at 03:57 PM.
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Old 02-22-2010, 03:56 PM   #9
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Insulating for radiant heat


For slabs. The more insulation you put down, the better.
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Old 02-22-2010, 10:01 PM   #10
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Insulating for radiant heat


So would I use the WBBF for the main floor. Or should I use foam insulation since I will be doing all my walls with it.
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Old 02-22-2010, 10:06 PM   #11
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Insulating for radiant heat


Since your heating the basement. You don't need to use spray foam for the floors.

Unless your not going to heat the basement 24/7.

Have you ran your ducts for your ERV/HRV since your foaming.

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