It's a concern when venting is required in your area. Venting/non-venting requirements is a regional issue,so it depends on where you live. The foam is an envelope utilizing rafter spaces rather than attic/ceiling insulation. If you have the rafter cavties foamed w/o venting when required in your area, you will have the moisture/freezing issues in the winter as well as condensing in the summer.Your best bet is to check out what is required in your area outside of taking the foam companies word, as the only outfit servicing our area steered us wrong stating no venting was necessary when it is required by our county.The county would have made us rip it out and vent, which would have been extremely costly. The foam cannot be re-used.

I would only consider an unvented attic if I were in a hot or hot-humid climate, as unvented systems have been proven to work in those climates by the Building Science Consortium.

Otherwise I would use blown cellulose. It's a high R product with no formaldehyde made from recycled materials; compared to fiberglass, it provides more resistance to air leaks and handles water better.

Hi Worthy, My response has nothing to do with the qualities of foam. From research on the building sciences site, and from several foam companies, my conclusion is that no venting is needed with solid foam in the cavaties. Millions of folks have coleman/igloo ice chests in their trucks/r.v's and i dont know about you, but i've never noticed one condensing on the outside. They are solid foam walls and lid. Pretty simple parrable there.

Unfortunately in our county, there is an obvious lack of research on their part concerning foam and venting. Because continous run ridge/soffit venting is a requirement with any insulation type, they have included foam with that code.

I will always have a sore spot for not having our build with a foam envelope as i'll always believe that it is the best out there and venting isn't necessary regardless of geographical location. I just put our experience out there as a warning for people to double check should there area have an inept ruling on venting. It would have run us over 12k to completely foam in our build. To tear that out and see it go to the landfill was not appealing, so maybe a heads up will save some others similar to the heads up we got that saved us major dinero.

Good point on the rigidity of Codes that preclude unvented attics.

I see the advantage of unvented attics in hot and humid climates mainly for slab-built homes that put the air handling systems in the attic; and that may also be able to use the attic space as living space.

Where I build, in a cold climate where finished basements are the norm, I don't see the benefit. The insulation has to be at least R40 (our Code requirement anyway). Plus another layer of sheathing has to be added to the roof for the shingles to be nailed to, so they don't disrupt the insulation.

You should also check out this company to do your rim joists in crawl space or basement for you DIY'ers.

Most people these days hire a contractor to do Cathedrals,Tray or difficult ceiling applications. You really have to know what you are doing there not to waste product. plus everything has to be covered well, including the installer in a Tyvek suit & face/respiratory protection.

Here is a link that might be useful: tiger foam

I read an article from the Journal of Light Construction last week that states the following:

'You  and your building code inspectors  may be
unaware that the 2006 version of the IRC for one- and
two-family dwellings permits attic construction with no
ventilation of the attic cavity. This new provision,
R806.4, is largely due to the efforts of Joseph Lstiburek,
Armin Rudd, and their colleagues. In brief, unvented
conditioned attic assemblies are permitted when an airimpermeable
insulation such as rigid foam is applied in
direct contact to the underside/interior of the structural
roof deck, with sufficient thickness  given the climate
 to prevent condensation on the underside.'

Perhaps mentioning the specific code with documentation to your local building department would convince them that venting the attic is not necessary?

Thanks, Embie. We presented them with not only the foam company's research and findings that serviced our area, but other foam outfits as well from all around the country,different companies,etc and they would not budge on their current insulation codes.We mentioned the building sciences website as a suggested research on their part and they only smiled. It strikes me funny on items such as gas fireplaces, they go strickly by the mfgr's specs on clearances, venting, install procedures, but because the foam falls into the realm of their insulation codes, they wont take a listen to what the mfg'r has to say about proper installation/ methods. Kinda backwards i would say and maybe causing more harm than good for those who are going ahead with foam including the venting. Thanks again for the article from jlc!