How much underslab insulation should I put in my new basement floor radiant heat system. Is 2" overkill, 1-1/2, or 1" sufficient, the basement isbelow frost, I don't think we are really tryingto stop cold coming up, more lossing heat down, so do we need a lot. Was considering "The Barrier" insulating tarp, but my research shows it to be a scam. I can't find anything good abt. it unless it's coming from a vendor or mfg.
Underslab Insulation? How Much is too much. too little??
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Where do you live? I'm a builder in northern VT and we generally use 2" blue Dow below all radiant slabs. It's also important to install at least 1" between the slab and the foundation wall, or you'll lose heat into the wall.
Don't bother with any of those tarp type systems.
Reggie
Don't bother with any of those tarp type systems.
Reggie
Nofossil
Moderator Emeritus
mtnxtreme said:
I don't know your climate, but I think 2" is a minimum. I'd consider 4" if it were mine, especially near the edges. Make sure that you get a thermal break around the edges of the slab as well.
2 is my vote also. Consider Crete Heat. it is a foam, vapor barrier and tube holding product all in one.
I agree on the edge insulation detail. Walk out basements are a particularly tough detail to handle, while being a big loss detail. Energy Edge is a new product to handle exposed edge details like slab to walk out or garage slab to drive way.
Upgrading insulation under a slab isn't a good option. Spend the extra to do it right and. Be sure to use 25 psi foam rated for ground contact, underslab use. Some of the "box store" stuff is not suitable
hr
I agree on the edge insulation detail. Walk out basements are a particularly tough detail to handle, while being a big loss detail. Energy Edge is a new product to handle exposed edge details like slab to walk out or garage slab to drive way.
Upgrading insulation under a slab isn't a good option. Spend the extra to do it right and. Be sure to use 25 psi foam rated for ground contact, underslab use. Some of the "box store" stuff is not suitable
hr
lawandorder
Member
What is Energy Edge, I am pouring a slab for a garage w/radiant floor and plan on 2inch blue ridid under and also for the sides but would look into different options if possible. Thanks
2" gets my vote as well. Insulation is your friend. We just did a lab test conducted by a test engineer I know. He tested how effective the "bubble foil" is in comparison to 2" insulation. I will spare you the details but the "Bubble wrap" is best suited for packaging your wifes china dishes and not under your floor. Use the Foam.
The rep at Schluter that I talked to said that their office in NY has 4" under slab. He said it is a requirement in Germany where Schluter is based. Think of the earth as a giant heat sink just waiting to gobble your hard earned BTU's.
Will
Will
heaterman
Minister of Fire
Actually when you think about it, all you need to do is make it more difficult for the heat to travel downward than upward. Concrete has an R-value of about 1 per inch so if you can get something around an R-6 under 4" of crete you'll force most of the heat into the slab/room. Of equally great if not greater importance is the edge insulation and how it's done. You can lose more from an exposed edge than you can downward through the center of the floor. We usually use 1-1/2" under a 4" slab and 2" if the cement is 5-6". Always a minimum of 1-1/2" around the perimeter with good contact between the slab and edge insulation. No gaps for heat to leech out into the sides. Concrete basement walls are best insulated on the exterior to eliminate condensation issues inside a basement stud wall. Nasty stuff can grow in that environment.
Now....... if you're in an area where the frost line goes to six or seven feet.......that's a whole 'nuther can of worms.
Now....... if you're in an area where the frost line goes to six or seven feet.......that's a whole 'nuther can of worms.
Ok, More questions than answers. I have read that any type foil under slab is not effective. It seems that foil needs air space to work properly. Bubble foil bubble is what I installed under 4" slab with 1/2 pex at 1'0" centers.I used 2 inch blue foam (r-10?) on all sides of concrete. Concrete poured 6/08 900 sf. 3 circuits of less than 300 feet.I have read that bubble wrap if you will. is as good as 2" styrofoam. I will direct you to the web page- naturalspacedomes.com radiant floor tests. This seems a little crazy however if the test is accurate and I know of no reason to deny it I would go with bubble wrap. It is easy to install and you can walk on it with out rupturing it like foam. The grade is not as fussy, I chose to overlap about 3" and not tape with duct tape. foil does not go well with concrete (DIRECT CONTACT) but if it is encapsulated (bubble, foil,bubble)it is ok. I believe you want to go for 10x insulating power under the slab.As to concrete think of it this way 3.5: fiberglass insulation is r-11 7.51 FEET thick is r-11. Concrete is a great conductor of heat. This is my 1st post.
heaterman
Minister of Fire
sizzle said:
RE bubble foil insulation; I don't know of any product in the heating industry , other than Outdoor wood burners, about which so much false propaganda is perpetrated. It falls in the same category as the paint with a supposed R-value of 70 that was on the internet. That company had all sorts of test data to back up their claim also.
The sellers of this product make wild eyed claims of R-values beyond any stretch of common sense and I can show you installation after installation where its use has resulted in extremely disappointing results. A logging company just a couple miles from me put up a 10,000 sq ft repair shop and used the double bubble stuff under the slab and on the edges. They have the largest OWB made by Central boiler and they fire it non stop in order to keep the building above 40*. In mid February there is no snow within 6 feet of the perimeter of that building, which by the way is itself very well insulated.
One of my friends at heatinghelp.com did a real world experiment using different types of insulation under a slab. He had insul-tarp, foam of varying thickness, bubble/foil/bubble, double bubble/foil/double, and a couple other types IIRC. All the slabs were tubed the same and fed the same temp water. The control was an uninsulated slab. After he put heat to them, he took pictures of the slabs with an infrared camera and measured the surface temp. The bubble foil slabs were nearly the same temp as the control (uninsulated) except for a 3" wide band above each tube. The ridgid foam slabs performed best, coming up to temperature far faster and distributing the heat evenly through the width of the slab with far less "striping" being noticed. If you go there and search through the archives you can probably find it. The stuff has been banned in Canada for use not only under slabs but also in buildings IIRC.
heaterman said:sizzle said:
RE bubble foil insulation; I don't know of any product in the heating industry , other than Outdoor wood burners, about which so much false propaganda is perpetrated. It falls in the same category as the paint with a supposed R-value of 70 that was on the internet. That company had all sorts of test data to back up their claim also.
The sellers of this product make wild eyed claims of R-values beyond any stretch of common sense and I can show you installation after installation where its use has resulted in extremely disappointing results. A logging company just a couple miles from me put up a 10,000 sq ft repair shop and used the double bubble stuff under the slab and on the edges. They have the largest OWB made by Central boiler and they fire it non stop in order to keep the building above 40*. In mid February there is no snow within 6 feet of the perimeter of that building, which by the way is itself very well insulated.
One of my friends at heatinghelp.com did a real world experiment using different types of insulation under a slab. He had insul-tarp, foam of varying thickness, bubble/foil/bubble, double bubble/foil/double, and a couple other types IIRC. All the slabs were tubed the same and fed the same temp water. The control was an uninsulated slab. After he put heat to them, he took pictures of the slabs with an infrared camera and measured the surface temp. The bubble foil slabs were nearly the same temp as the control (uninsulated) except for a 3" wide band above each tube. The ridgid foam slabs performed best, coming up to temperature far faster and distributing the heat evenly through the width of the slab with far less "striping" being noticed. If you go there and search through the archives you can probably find it. The stuff has been banned in Canada for use not only under slabs but also in buildings IIRC.
As to conflicting resulats and propaganda I agree their is a ton of that out there. Do you know of anyone using a spray foam insulation (polyethylene) under a slab? Seems to me other than cost it may be a good bet, with its air seal quality and a noted r value of 7 per inch, I think you can walk on it also.
heaterman
Minister of Fire
I've never seen or heard of anyone spraying under a slab. I don't think there would be any noticeable advantage over 4x8 sheets of regular EPS foam that would justify the cost. The only minor thing I could envision would be the function of the spray application as a vapor barrier in a high water table environment. Frankly, if the water table is that high the grade should be changed or the building located somewhere else. The sheets of foam make a very nice even platform to attach the tubing to also.
Here are the results of the test we conducted. This test was done by a test engineer using calibrated testing equipment. I have heard of a test conducted by the Canadian government that basically said the stuff was worthless as well. Bubble wrap is better than nothing but, again, bubble wrap is for packaging the dishes.
Test Procedure:
1) Verify block, water, and container were all at desired temperatures.
2) Start data logger (channels were as follows)
- 1. Air Temperature
- 2. Water Temperature
- 3. Insulation temperature at contact surface with aluminum block
- 4. Aluminum Block core temperature
3) Pour 2 gallons of hot water into test container
4) Record data for 20 minutes or until a measurable temperature change occurs.
Tests Performed:
1 – Baseline (double layer of poly between water and block)
2 – Reflector Shield between poly and block
3 – 2” Rigid foam between poly and block
BTUs/hour Lost:
1 - 138 (No insulation, basline)
2 - 27.9 (5 times better than no insulation)
3 - 7.7 (18 times better than no insulation)
Test Procedure:
1) Verify block, water, and container were all at desired temperatures.
2) Start data logger (channels were as follows)
- 1. Air Temperature
- 2. Water Temperature
- 3. Insulation temperature at contact surface with aluminum block
- 4. Aluminum Block core temperature
3) Pour 2 gallons of hot water into test container
4) Record data for 20 minutes or until a measurable temperature change occurs.
Tests Performed:
1 – Baseline (double layer of poly between water and block)
2 – Reflector Shield between poly and block
3 – 2” Rigid foam between poly and block
BTUs/hour Lost:
1 - 138 (No insulation, basline)
2 - 27.9 (5 times better than no insulation)
3 - 7.7 (18 times better than no insulation)
I forgot, in our test we did not account for when the bubbles pop and you loose the air space under your slab.
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