I would appreciate the communities input regarding vented versus unvented attics for ICF. I've also included a design we used here in Texas a few years ago that has worked really well (only a couple of implementations though). This design attempts to address conduction, radiation and convection. I don't know if it would be a valid design in another climate or not. Regards.

This is pretty well covered here.

I think it's helpful to talk in terms of vented vs unvented and insulation at roof vs ceiling plane. Ie, your drawing is vented, but insulated at the roof.

For your design, I'd review here and also think about how many perms you have between you and the outdoors and what that does to latent AC load.

That is interesting, basically a big foam arched tunnel spanning from ICF to ICF. I am assuming you build a stud wall(vented) at the gable ends and tarp and spray-foam it as well? How much does the foam weigh? That heavy cloth(and the way it is attached to the joists) supports it without any additional re-enforcement? Do you actively exchange/condition that attic air space?

It would make for a good place to run duct work, but might be more difficult to impliment with seismic zone out of plane wall bracing requirements...

Texas thats the one we have been doing for awhile, unvented and unconditioned attic space, it works great, its like an air buffer for the conditioned finished space below - there is still alot of debate going on about it by the talking heads but the first one we did was almost 15 years ago and its been performing excellent no issues at all, been checking decking etc, its a perfect match for ICF!

One thing I remember from back in 2008 when I was designing my house was heat loss/gain through the ceiling vs the roof. The programs I used all showed that for the same R value on the ceiling vs underneath the roof sheathing the heat loss/gain was almost identical. So, when I looked at the benefits of the insulated roof vs insulated ceiling this is what I determined.

I could use the attic for storage without having to contend with walking through or planking over insulation.

I did not have to mitigate air leakage around ceiling fixtures.

Stuff stored in the attic doesn't deteriorate due to excess heat or cold.

I did not have to provide for air flow from the eaves into the attic space.

And, probably best of all, I was able to use the attic as the return plenum for my heating/cooling system.

I got all these benefits at little, if any, additional cost over ceiling insulation.

I've done it many times, only you show open cell, we used closed cell spray foam and had to spray a fire retardant paint over it when finished

I did one 5000' house in Toronto with a heating bill of $ 45.00 per month in the dead of winter, 2 story plus full basement, ICF to the roof, 2" under slab insulation, 8" closed cell to the u/s of roof sheeting, radiant infloor heating and high velocity A/C.

jonr- thanks very helpful and you also picked up on the fact that this design is a little different.
ronmar - we almost always run our gables all the way up with ICF and do not vent gables. As currently designed space is not actively cooled or heated but could be. I would think very minimal just to control humidity.
Bill- this is probably not the same as what you been doing for a while - as jonr observed it's a bit different. It is vented but not to the attic space so allows for convective cooling of roof. It includes a protected radiation barrier for solar radiation. The foam is continuous -- no studs to short circuit it for optimum protection from conduction.
dmaceld -- nice! but I think this is a little different and does not include plenum approach as this would add to overall A/C tonnage.
Chris -- I believe those numbers -- but not sure if this is similar design or not. Did you spray between the studs? This design does not since the studs will short circuit the foam -- hope you put up your 8" in phases.

regards.

i don't know it looks pretty darn close to me, see attachment this is back when we were still hand drawing, but what DMACELD says is a home run! we have since added more SPF to meet the new code requirements but it is a great design feature. the same design works with our concrete sloped roof systems as well.

attachment?

Bill - I don't see your attachment. FYI it has to be very small to put in this site - like 100 kb, so you may need to resize it.

Bill - I don't see your attachment. FYI it has to be very small to put in this site - like 100 kb, so you may need to resize it.

yeah i apologize for some reason i cant get it to send - it loads but when i send it - its not there- trying again

trying one more time?

I tried to pm you but it didn't work either. If you go futurestone site and contacts us you can mail it to me and I'll post it for you. Regards.

I tried to pm you but it didn't work either. If you go futurestone site and contacts us you can mail it to me and I'll post it for you. Regards.

I tried to pm you but it didn't work either. If you go futurestone site and contacts us you can mail it to me and I'll post it for you. Regards.

Here's my worry. You are introducing moist air into the uninsulated roof space. The canvass will soak that up over time. We used to have a straw doll wall decoration hanging by a patio door. When we would leave that door open on cool nights, the doll would be dripping wet next morning. The moisture will eventually rust, rot or otherwise corrode whatever attachment method you used to attach the canvass, and long term, the canvass itself. In my thinking, at least