Non-Vented Attic Concept

[OffshoreDreamer]

I will be building a home about 30 miles north of Gulf Shores, Alabama in about a year. I have done a lot of research on new concepts in home building. Just wondering if any of you experts are familiar with the apparently new concept of using closed cell foam insulation in the attic (2") on the underside of the roofing deck and no insulation in the ceiling. The attic is non vented and becomes semi-conditioned air. Tempertures are suppose to not increase more than 10 degrees above the the temperture of the living space. Other benefits are suppose to be - greater strength to the roof due to the spray foam between the rafters, attic HVAC duct work would be more efficient due to the semi conditioned attic, no roof vents to blow off during hurricanes and heating and cooling bills are lower. I talked with the local building inspector and he was familiar with the idea and said it was acceptable provided it was indicated on my plans and that the HVAC system would have an "Air Exchanger" installed. Seems that the only down side is that the foam insulation cost more. Some of this information came from the Building Science Corporation and some from one of the foam companies.

Just wondering if any of you guys have had any experience with this and what your opinions are. Thanks.

[little dude]

How much attic space are looking to have? I live in a older home in North Georgia which has no vents at all in the roof, it gets really d@mn hot in the summer upstairs. It gets just as hot or hotter in southern Alabama.

[Big Builder]

We live in a completely different climate in Ontario but we frequently use
styrofoam ( blue or spray in place urethane foam in attics and it does not require ventilation.

I have never had a call back.

That being said I have to admit that I think ventilation is a good idea.

[oceaneering]

I used spray foam when I built my home in 2004.
Benifits for me: It strengthened up the walls, (racking strength). LOw energy cost $120 a month total electric over 3000 square feet.
Disadvantages: It's exspenssive In the winter it shrank and seperated from the 2x4's slightly, creating small gaps reducing the concept of a complete shell from the outside air. My energy efficiency rater said moist air would penetrate the minor gaps and get trapped in the attic and eventually cause mold. (This is what scares me most).
Things I would verify: I like the closed cellfoam over the soft. Its stiffins the cavities between studs. Its more efficient, I think it's just better. My installer quoted me closed foam and then tried to spray in open ( soft) foam.
All things considered I really like the product. Right now I'm seriously considering concrete walls, metal rafters and galvalume. I will still spray foam in the attic. By the way my attic wasnt much hotter than the rest of the house I hope this info helps, let me know what you go with.

[tooltroll]

We're putting 2" of foam board on the old roof deck, radiant barrier, (1x2 battens 12" oc, ½" ply deck, new roofing. Rafters (2x4s, 1911 built house) thickened to 2x8, and the cavities stuffed with fiberglass.

The airspace between the RB and ply will be vented at the soffit and peak, since I'm in a cold climate and don't want ice dams. (I've also got a third story in the attic (knee walls, etc.) so I'll be able to add storage nooks in the triangular spaces that'll be heated.) In your climate, the worst that I can imagine would happen is you'd gain heat through the attic insulation and get condensation on your roof. God, NO! Not water on the roof! Hehe. :D

Oceaneering, was yours sprayed in the summer or winter? Does anybody know if it makes a difference? I've read docs on the stuff that state that the tanks need to be heated during cold applications, but the substrate and hoses don't have to be. I've been thinking of using the stuff instead of fiberglass, but not if it's going to shrink. I'm hoping if applied in winter, it won't shrink the following winters.

[David]

In your climate, the worst that I can imagine would happen is you'd gain heat through the attic insulation and get condensation on your roof. God, NO! Not water on the roof!

Troll -- Actually, if you lived in the humid south, I gaurantee you wouldn't be laughing for long. ;)

OE -- I don't know where Gulf Shores, Alabama, is, but if it is in a humid climate, you have to be careful. As Troll mentioned, you'll be susceptible to moisture on the roof, only on the underside of the shingles. Where will this moisture go? The moisture will be pushed into the roof decking via a solar heat gradient, and then thru it the decking. So here's where it gets tricky.

CLOSED cell does not allow moisture to pass, so it would be trapped and will rot your osb/ply decking. OPEN cell does allow moisture to pass, so it would get pushed thru the insulation and will dry into your attick.

Read the BSC details carefully. If you are in the humid part of Bama, which I'm guessing you are, then I think you need OPEN cell. If you can't get consistent info from pros, then call BSC.

[tooltroll]

Aha! This is why we always take the climate into consideration! Thanks, David! I wouldn't have thought the cond. would form under the shingles. . . I sit corrected.

[oceaneering]

My spray foam was sprayed in more climate. 2 months later when we had a cold front all the closed cell in the walls shrak, just enough to create a small gap. At least in the wall area,s I could still see, mainly from the second floor attic. I neglected to mention that I did Have open cell foam in the rafters. This was at the installers advice. I didnot know why. All the specs I saw was that closed cell was basically impermiable by air & moisture, and that open was almost as good. Blocking virtually all or most air and moisture (80% if my memorie serves me correctly, at 3" thick. To the best of my memorie my open foam in the rafters did not have a shrinking problem. Also I have seen a lot of little companies startup advertising sprayfoam with 100% guarantee against shrinkage. Of course they could be planning on using or at least advertising the oped cell. Even though my closed cell shrank I would still use it in the walls. Hey anybody know anything about concrete walls icf wall framing.

[Big Builder]

We used closed cell.

I have never seen it shrink at all.

Perhaps the installers mix was wrong. Could be too hot or too cold when they sprayed?

[David]

In Cold to Very Cold climates one should use closed cell.
In Alabama, one should NOT use it.

[Don_P]

Not sure if you've run across this from FEMA with regards to your area;
http://www.fema.gov/library/viewRecord.do?id=

My inlaws used to live in Orange Beach, I'll be missing that place in a few months.

I've used ICF's a couple of times, they worked well. Around here I'm leery of what carpenter ants could do but have not heard of problems. They moved into the foam in my motorhome and had a large party underway before I knew it.

[David]

Just curious Don, where is "around here" for you?

[Don_P]

I'm in the southern Blue Ridge in VA. Just up the hill from Mayberry. First frost for us last night. Colors are just beginning to turn.

[David]

My folks in Iowa just had a frost a few nights ago. We still have highs in the 80's. Maybe you could add Blue Ridge, VA to your profile? :)

[energy rater La.]

Offshore dreamer..
just tossing you a few more options..

what about a radiant barrier roof decking,
to reflect heat out. (see www.fsec.ucf.edu)

Unvented attic (www.buildingscience.com)

upgrade ducts (installed in attic in your build?)
to R-8 instead of R-4.2 mastic sealed, not duct taped.

install insulation (R-30 to 38) on attic floor
conventional insulation, not foam.

Walls outside to inside 1" foil faced sheathing boards
(think reflect heat out)

R-15 insulation (again conventional insulation) &
Air tight drywall approach interior of home.

Low e windows, high efficiency hvac..sized
with manuel J load calculations.

I find that the cost of the foam will lengthen the payback
to excess of 20 years, and longer when roofline is foam insulated
depending on roof pitch.

On a conventional build with conventional insulation & upgrades
suggested above payback on upgrades are usually in the 6 to 10
year range.
Much more cost efficient.

I ran this by Joe of building science as a more affordable
option and got a very positive reply.

just food for thought..

(and hello david & richard..)

[David]

Nice to see you Deb. Why didn't you go with ERLA as a name?

Also, just for clarity, I believe you are recommending LowE2 windows, not LowE. Correct?

[energy rater La.]

erla was just for bahrr -for fun.
just shortened from other forums.

I gotta tell you I don't see much difference when
testing low e & low e 2 with my light meter.

I am open to what I may have missed -
care to clarify??

btw pretty cool forum you guys have going on here!
I have gotten several links connecting me here
& wanted to follow up & see what I was missing.

[rabadger]

You can learn a lot here. Just the other week I had the pleasure of running load calcs for someone that has a design temp of 104 degrees. They are using SIP construction with standard roofing materials and radiant barrier only. The attic installation added 17% to the A/C load.
Another way of reducing energy costs is through the use of soffits in the conditioned areas.

[David]

Deb, I'm just gonna quote our friend and window expert Oberon.

"All LowE coatings block IR energy. Hardcoat or single-silver LowE coatings block primarily long wave IR while allowing short wave IR to pass thru the coating and glass.


LowE2, or dual-silver coatings, block both long wave and short wave IR from passing thru the coating and the glass...and it blocks both better than the HSHG products. Again - although the HSHG coatings block long wave radiation - thus keeping that heat in your home - the LowE2 or Low Solar Heat Gain product blocks more long wave IR energy as well as short wave IR energy."

[energy rater La.]

And I thought I read all of Oberon's posts!!


I did an energy rating on a sips house
that had 4" sips walls & 6" sips floors & ceilings.
Talk about an efficient house.
2 ton 16 SEER dual stage heat pump on 1800 sq ft.
His highest utility bill was in August & was $65.00
I love it when it comes together like that!