I know that alot of guys believe that foaming an unvented roof is the best way, and or using SIPS as your roof is the best way. Im using standard truss roof on top of ICF home, what can i do to ENSURE a best case scenario?

What is the center-to-center spacing on your roof trusses?

I dont have the trusses yet, they were just ordered, will have them in a few weeks. I just want to be prepared.

If you have ordered the trusses, you should know the spacing, it should be speced on the order. Typically, residential trusses are 16 or 24 inches on center. It really doesn't matter, if the order was with a professional truss mfgr, then the loading will be correct for your particular circumstances.
As to your insulation, DON'T ventilate the attic, DO use spray foam on the underside of your roof sheathing, sealing your attic space. It really does work.

My builder just took the plans to the truss maker...

Is spray foam something a DIY can do? There are no spray foam guys around here, I would have to haul someone up here for a 3-4 hours away.

You think NOT venting the attic it s good solution for northern maine? Ive read how it reduces the life of shingles ?

Non Vented is better even if you have a couple feet of insulation there?

The reason I asked about truss spacing was my recommendation to use blown cellulose for ceiling insulation. But due to its mass, you are limited to how much your ceiling board can hold up without bowing, particularly if you are on 24" spacing. 16" spacing and 5/8" sheetrock on the ceiling and you can put a bunch of cellulose up there.

Around here, you get more R for your $ with cellulose in the ceiling than with spray foam on the rafters.

If you are not using foam I hope the truss manufacturer is providing an energy heel. This will provide you with more insulation at the edge of the roof on top of the wall where insulation is the biggest problem, this area gets neglected and becomes the cold spot and largest heat loss (next to a skylight).

Unvented attics are now a standard thing in Fire Zones here in California, spray foam is taking off like crazy.

So to do a cost comparison, cost out cellulose, ridge vents, soffit vents, baffles, vapor barrier (I assume it's needed in Maine) and compare to spray foam, no venting or ancillary products needed. Can your heat loss calculation person give you a energy comparison? The additional cost of spray foam may have a short payback period.

You can do spray foam yourself, I don't recommend it.

Has anyone has the chance to use and evaluate this type of product?

http://www.sprayfoamdirect.com/?gclid=CJ2Ott_21JoCFQKaFQod_E4k2Q

I considered a DIY foam kit once.  Then I got the estimate on having someone else do it for me.  The price was actually cheaper to have it done.  They charged a dollar a board foot to do it.  That is cheaper than the product you linked.  Perhaps if you had a really small job, those kits would be good.  However, my job was about 500 feet and there was no savings in the DIY method. 

So I guess the next logical question if going to go for unvented attic with spray foam on the entire underside of roof is ...

OPEN cell or CLOSED cell and why...

What type of RValue should I be striving for in this install with a ICF home?

Open or closed - you will not get a consensus on that issue. If you haven't already read the thread in the general forum, residential, on spray foam on the underside of the roof. It's 5 pages long with 95 responses!!! You'll get a lot of good explanations there as to the benefits and drawbacks of both.

R value gets a lot of differing opinions also. I say, at a minimum go with what the Energy Star requirement is for your area. That could be upwards of R 40 or more. You may limited by what the contractor can do in one or two passes. In my case the contractor was able to apply ~ 10" of Icynene in one pass, but not without problems. That gives me about an R 40. Keep in mind that the true R value at the end of the job will be an estimate because the surface of the foam is about as flat as the foam on a latte.

Here is what I received for a quote for the roof job...


Thanks for contacting ASF. I just left you a voice mail on the phone number you left on the website. We are certainly interested in the job you have available. That is certainly a big roof. Could you tell me the pitch? Also, what is your time frame?

We quote our prices by each job and the specifications required. We bill out by the board foot, which is the square foot x the amount of inches applied. We can usually rough quote $1.00 per board foot. I have only seen the company exceed this once, and that was a very small job many hours away on the other side of Maine.

I look forward to hearing from you. Thank you.


$1 per foot per inch it appears. roughly 59x36ft exterior dimensions

1$ a foot was about what I was charged.  That was for a closed cell foam.  The open cell foam should be cheaper.  Of course the R value per inch is less, too.

closed cell is around R6 per inch, open cell is around R3.5 per inch. Even though closed cell is more money you almost need half the amount to reach the specified R value.

Why spray foam the roof deck in a trussed roof? Unless its an attic truss, you will not be using that space, but you will be heating it, and yes a hot roof does shorten shingle life. Don't get me wrong i love hot roof systems, but why the heck would anyone hot roof a trussed roof?  As for truss load you can configure interior partitions to support your trusses if they are actually not rated to support the weight of cellulose. If they are not I would not use them. I would strap and sheetrock the bottom of the truss cord, after installing a vapor/air barrier, air seal all penetrations athrough the attic floor, including chimney, interior walls, top plate of exterior walls, plumbing and electrical, and attic hatch. Calculate and install necessary ventilation for your attic space. Insulated with loose fill cellulose, at least 11" R-40.7

A house loses heat through conduction, radiation, and air leakage. The area of a roof is not a whole lot greater than the ceiling area so loss by conduction and radiation is not significantly increased by insulating the roof deck. One of the main benefits of foam is you create a pretty good air tight seal around the building envelope, whether that foam is on the ceiling or roof deck. Now that brings us to the heat load created by the volume of air in the house, which stays in the house except as changed out by ventilation, which will stay the same whether or not you heat the attic air. If you look at how many pounds of air are in a house it's not much. It takes very few Btus to heat a pound of air. Therefore, the added volume of the attic adds very few pounds of air to the heated volume, hence adds very few Btus of heat load.

Think for little bit how much air is moved by a conventional furnace to transport heat from the fire to the living space. Compare that the volume of air in an attic space. Big difference!!

Can you cite a study that unequivocally shows that? There have been several comments in these forums about studies that show that isn't the case.

There used to be a sign where I worked for several years. "In God we trust. All others please bring data!"