In need of insulation facts

[rcp612]

My house is on a slab, and all mechanicals are in the attic. The attic only has approximately 8" of insulation and a very, very low head space.
Since I live in north-central Ohio, I've been told I need about an R-54 in the attic. If I install this over the exsisting, there would be no way to maneuver in the attic.
Does anyone know if it's possible to use a spray foam insulation product directly on the under side of the roof? And would that even be a good idea? There is a whole house fan mounted in the roof that's both temperature and humidity controlled and the soffets are all open and vented.
Am I thinking in the right direction?
There is no insulation contractors I've been able to find in my area to give me "real" information, just sales pitches.
Also, there are not any building codes to adhere to in my area so, I'm trying to be overly cautious.
Any advice from any one in the trades would be appreciated.

[jking]

By "all mechanicals are in the attic", does this include the plumbing? If so, 8" of insulation will be asking for burst water pipes. Generally, running water lines through unheated spaces is not a good idea.

How much room do you have in the attic? It sounds like you have an 8" deep member framing the ceiling of the house & a raftered roof? How far from the top of ceiling joists to bottom of rafters at the peak?

[Ed62]

I think you'll find the information you need here. I don't think it's a good idea to put insulation right up against the roof sheathing. You need ventilation. http://www.owenscorning.com/around/i...ducts/pfgi.asp

Ed

[MilDoc]

Insulation sprayed on to the under side of the roof is very common in England, and seems to be catching on here. Just be certain to use open cell foam (not closed cell that can trap a leak between it and the roof) and be sure there is adequate ventilation.

Check the internet. Lots of sites there.

[jackellis]

What you need is insulation on top of the ceiling. Since the attic is ventilated (open soffets), the attic is at the same temperature as the outside air in winter and it's hotter than the outside air during the day in summer.

If mechanicals that require periodic maintenance are not installed in the ceiling joist bays, you might consider removing the existing insulation and then installing spray foam in its place. You'll get about R-32 and less air leakage. You could also install about 4 inches of rigid foam panels on top of the existing insulation but I'm not sure that would solve your headroom problem or give you R-50.

You should also do what you can to seal drafts around plugs and light switches, doors, windows, etc. I don't suppose you have an opportunity to insulate the walls, do you?

[Uncle Cracker]

You would not need to add R-54, as you already have some insulation in place. You would only need to add as much insulation as necessary to arrive at a combined rating of R-54. And I have a hard time believing that there are no relevant building codes where you live.

[JimD]

I would try to suspend the mechanicals off the roof rafters and put insulation under them. If you both ventilate your attic and insulate the roof sheathing, all you will accomplish is making your shingles get hot and deteriorate faster. Heat transfer by convection is much quicker than conduction. You get convection from ventilation, you slow down conduction by insulation. You also slow down convection with weatherstripping.

Jim

[rcp612]

And I have a hard time believing that there are no relevant building codes where you live.

Sure enough, the HOA has inspections of foundations only(??). Whatever goes up from there can be built by anyone, inspected by no one, as long as the end results are aesthetically accepted by, again, the HOA.
Looks are most important in this community.

[krogers]

"Just be certain to use open cell foam (not closed cell that can trap a leak between it and the roof)."- Milldoc

Do you have any more information on this? Closed cell poly gives you a much higher R value. A contractor I spoke to prefers closed cell. He says that when applied closed cell actually prevents leaks. I seal every crack and crevice. I can see both sides of that arguement. It will prevent a leak from entering the living space and staining/ruining the drywall. But if water is getting under the shingles to the sheathing, then the sheathing will never get a chance to dry out.

Can anyone point me toward more information on this subject?

Thanks - Kevin