ICF home - insulating roof and radiant floor heating

14 years ago

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.

http://www.tracksidesoftware.com/dainshouse/house.htm

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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Comments (7)

worthy
14 years ago
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.
shouts
14 years ago
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.
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Thanks for all the input; it's been really helpful. Shanghaimom, I did a 'step test' with a 12x12 marble sample I had on hand, and you're right; it is so much colder than the tile. That has convinced me to install floor heat, even if it's only a secondary source. I had no idea that hydronic toekick heaters existed; the quotes I got all mentioned 'electric fan toekick heaters', and I didn't want to go that route. When discussing with my contractor last evening, he was very supportive of the hydronic solution; now I just have to make sure that the unit will fit under the 'door' side of my vanity (will need to access it for service, so it really shouldn't creep into the drawer side of the cabinet.) Fingers crossed! Mongo, thanks! I'll do my homework on the BTU calculations; thanks for pointing out what to look for. Lynneblack, thanks for the vent/fan/light combo idea. I've read on the boards that the Panasonic is a great unit, but one of the two items I'm keeping from the current bathroom is my Nutone melon vent fan/dimmable light.
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>> Tdegen, Im curious through your readings if they addressed on tankless water heater installs, where the incoming water is extremely cold even in the warmer months, how that effects performance. I know it was a problem in the early tankless days, wondering if it still is. Thanks! Everything that I read indicated that the gpm (gallons per minute) decreased proportionally with how much you wanted to raise the temperature of the water. Assuming that most water coming into the house is around 50 degrees and you want a hot shower (about 105 degrees), you want to raise the temp about 55 degrees. This would give you a flow rate of 5.5 gpm. On the other hand, if you have really cold intake water and you want *really* hot water - and want to raise the temperature by 80 degrees, your gpm would drop to 2.2. Every tank is different, the more you pay for the tank, the less gpm is affected. All tankless heaters are rated in this fashion and you should be able to get the exact figures of the model you are looking at buying. The best thing that you can do for yourself is to try to figure out how many gallons per minute you would like to use on average and how important it is for you to be at a certain temperature with a certain water pressure. That is, I like my showers hot, and I like the water pressure high. So all of my calculations will be based on my shower. If my washing machine takes a little longer to fill up, I don't really care. For things like radiant floor heating or maybe a jacuzzi... that's something out of my purview. On a side note: unless you want to be cleaning the heater every month, you will probably want to buy slightly larger heater than what you need. No matter how clean your water is, you'll still get some calcium build-up on the heating elements. This will lower your gpm slightly. I'd suggest buying about 10% over what you expect to use.
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both ICF and the staggered studs are far more $$ but want to know if they payout in the end from people who have done either way You need to tell us how long you intend to live there. Is this your intended "final house"? If so, I'd definitely spend the extra to get a more efficient & comfortable home. I expect energy costs to be volatile in the future, but with a general upwards trend. But if you tend to move around every 5-7 years, maybe not. Personally, we built with ICF walls from basement to roof. I don't regret it, because the house is quiet and cheaper to heat. But we do intend to live here "forever", so the cost will almost certainly pay off for us. A side-benefit of thicker walls, aside from the quiet, is that you get deep window sills. Our cats certainly thank us for that , and it allows us to get multiple window treatments (double-wall cellular blinds plus curtains) well within the 11" deep window openings, if we choose to put curtains inside the opening rather than overlapping the outside. --Steve
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Thanks again for all of your comments and ideas - the give and take of your posts provide us with great insights and ideas which will help us eventually choose the right system for our situation. Hubby found the DYI attachment interesting, but as an overworked aerospace engineer he just doesn't have the heart to tackle a DYI project of this size. (Over 1000 hours of overtime last year, similar amounts for the previous five years, and no end in sight! We joke this is our dream house money.) We did a major remodel of our own master bath four years ago, which included installing electric radiant heat, and it took two years, partially due to hubby's lack of time and partially due to the fact his engineer training meant every thing had to be perfect! Slows everything way down! :-) (Our current plan is to have the shell of the home, plumbing, and wiring done for us, and then we'll tackle as much of the interior work as we can ourselves, over time.) The JAGA site has some beautiful options (I love the scrolled radiator), but had my heart set on in-floor heat since this will be a small home with small rooms and would prefer to keep our wall space open. Just out of curiosity why is clay soil considered not good for geothermal? (I can't remember where I had read clay soils were preferred over dry, sandy soils.) I want to make sure I'm fairly well informed if and when we start to talk to geothermal installers. We may rule that option out entirely if it appears to be a problematic option for our property. Right now I'm really leaning towards the soapstone/masonry fireplace idea, and a combination of electric radiant in-floor heat (in tiled places where we might like heat year round, like the bathrooms) and hydronic radiant heat in rooms with wood flooring. Just need to figure out what will be the best way for us to heat and circulate that water. (If we use the fireplace to partially heat the water will we need a boiler or could a tankless or regular water heater handle the load?)
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msm859
14 years ago
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.
foolyap
14 years ago
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.

--Steve
energy_rater_la
14 years ago
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.
batista14
11 years ago
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.
ashley97
11 years ago
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.

ICF home - insulating roof and radiant floor heating

Comments (7)

worthy

shouts

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