ICF home - insulating roof and radiant floor heating

jodainsDecember 4, 2009

My wife and I are about half way completed with our ICF home in Southwestern PA. Here is a link so you can get an idea of what we are building.


Now for the questions.

ROOF INSULATION. Since the home is made using ICF, there is no issue in insulating the walls, only the roof. The home has some 9 foot ceilings and some vaulted ceilings. The builder is recommending cellulose insulation. I am leaning toward spray foam insulation. The builder states that the attic area must "breathe". Everything I read about spray foam says that it will create an air-tight space. Is it important for an attic to breate? I want to have the spray foam insulation blown in just under the roof throughout the entire home and the builder wants to use cellulose just above the ceiling and leave the attic area to breathe.

HEATING - The entire home is being heated by radiant floor heat. The HVA contractor is installing the radiant floor heat as the only source for providing heat to the home. I do not doubt that it will be enough to heat the home in the coldest of weather. My concern is that I may need heat in the fall or spring just in the evening or mornings. Will the radiant floor heating be good for the days when you just need heat for a part of the day?

Thanks for helping out.

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An unvented roof will work just fine, though the initial cost of foam will exceed using cellulose in a vented roof. See Link.

Radiant heating takes time to heat up the floor and to cool down, so there may be a concern. You should be able to get referrals to existing customers in your area from the installer. Ask them.

Here is a link that might be useful: Unvented roof assemblies for all climates.

    Bookmark   December 4, 2009 at 10:46PM
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I just built my house the same way. Unvented is fine (I hope you have some sort of air exchange system, though, for your health!) With ICF the temperature is incredibly stable, so the radiant shouldn't have to work that hard. It will take days for a house to get cold in mild weather, so I doubt you'll need spot heating.

    Bookmark   December 5, 2009 at 2:43PM
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that is what i did. used a Munchkin boiler for the radiant heat. unvented attic with sprayed foam under the roof. my utilities are significantly less than the neighbors. also used the most efficient Trane A/C units at the time.

    Bookmark   December 5, 2009 at 11:40PM
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The OP probably needs to confirm with his town's building inspector that an unvented attic would pass with him/her, though. Regardless of what code may say, the local inspector wields the final say.

FWIW, I wish we'd used SIPs for the roof deck, and an unvented attic.


    Bookmark   December 6, 2009 at 9:19AM
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My reccomendation was going to be sips also.
for a house to need to 'breathe' it needs to be
less than .25 air changes per hour. a lot of work
has to be done to achieve this performance.
foam spray for unvented attics is not always
air tight.
I test homes with a blower door, in most cases
the attic is not air tight..total encapsulation
takes attention to all the details..vaulted ceilings
are almost always a problem ..in my experience.
if it is not too late go sips..unvented.
www.buildingscience,com has excellent info
search for unvented attics and make sure that
you review info for your climate.

If I were to build a house..knowing what I know now..
I would build sips total package.

best of luck.

    Bookmark   December 6, 2009 at 7:33PM
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House looks great! I'm planning my ICF house build also in southwestern pa (Latrobe). Who was your builder? I've learned there aren't too many qualified/experienced builders in our area. Oh, and I too am planning on the radiant floor heat, cellulose underside of roof, sealed attic, HRV in attic. Any info on builders would be greatly appreciated. Thanks.

    Bookmark   December 20, 2012 at 1:12PM
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I lived in Germany for 6 years, with all radiant floor heating. The temp remained completely stable, each room had individual controls dial 1-6. So when it started to get cold, we turned the dial from 0 to 2....then 3....then up to 4. That's about as high as we went. At 5, the dog was leapfrogging from area rug to area rug and refused to walk on the hot tiles.

    Bookmark   December 29, 2012 at 1:49PM
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