Bluestone, I am interested in hearing how you do the air core. Do you have a double set of roof decking, with an air space between them?
Thank you -- Pstu
One aspect not mentioed here is comfort, in my experience ( over 25yrs building with sips, and nearly 10 with spray applied closed cell polyurethane) there is no comparison to a home with fiberglass and one with foam. Energy is what it is all about, there are so many problems with fiberglass I wont go into here, but a couple are mold, and formaldehide, glass sucks in my opinion.
Tightness of the envelope, sound deadening, and enhanced structural integrity are but a few of the positives of foam.
As to the roofing issue, air core roofs can be constructed to allow thermosiponing of air between the sheathing and insulation.
Most top brand foams have waivers that allow foam application directly to sheathing from roofing manufacturers, but I still use an air core.
Icenene R 3 p/in Most urethanes R 7 p/in, Icenene is less expensive p/ applied inch. Really depends on your use
Bluestone, I am interested in hearing how you do the air core. Do you have a double set of roof decking, with an air space between them?
Thank you -- Pstu
OK I haven't read all the replys here so forgive me if I am repeating something...
To make a long story short, I have been envolved with this extensively for over 6 month. I live on the Gulf Coast and we know about humidity problems first hand! One of my good customers had a large home damaged by Katrina. He is a fairly big roofing contractor and has inhearted a contacting business. We got his house A/C system(S) half installed and he then decided to BUY a foam company. I got dragged to all the factory BS and to the power company REGIONAL school on this stuff.
Here is the scoop as I see it.
Flame Spread or fire rating = Don't worry about it. All foam today have fire retardents and you cannot set it afire, it will only melt.
The Bad - A totally foamed home will build up heat way faster because of the insluating factor and the home will have a HOTTER fire. I come from a FD family and that means more things will get destroyed!
Close cell foam is more expensive! It will not absord mosture (as dunked in a pale of water) if it is put into a flood prone wall. This is why FEMA is pushing it. Open cell foam is just fine for other applications.
My friend the roofing contractor contacted roofing Mgf. and was sorta told that cheap shingles will have a problem anyway, bur quality (i.e 30 yr. ) shingles will not have a problem.
If you foam the attic, the underside of the roof rafters. The attic becomes just another room of the house with a 0 wall height. Even tho this cuts down on the A/C load infiltration factor, you have to have a "vent" in the attic with X CFM to condition the attic. You will not need ceiling insluation and will need a return air somehow back to the unit.
And bvecause of the above this will help your ducts sweating. Now having a "tightly" (as of foam) insluated attic and a regular possible loose home may have other problems.
You really need to get with an A/C guy who knows his stuff to check your house before plunking down big bucks....
Life is too short, Behappy!
TFMM
OOOpps ... Oh Well.
Life is too short, Behappy!
TFMM
One way to do this is strap the roof vertically (some may call it furring) and apply a second roof deck. I cant go into all the details regarding valleys and such, here, but you get the idea. Just make air flow from bottom to top, soffit vents, and I use coravent for the ridge. I don't use roll type ridge vent as I fell they don't have enough free area.
Another way is from the inside with prefab plastic or EPS foam insulation chutes, stapled up, this is a good choice for retrofits. cheaper by factors and slightly to moderately less effective but I would still highly recommend it.
My house is done with the chute method, only with custom , site fabbed, chutes made from fan fold insulation normally used for vynil siding. I saw an ad in Fine Homebuilding for rafter clips to hold ridged insulation to form air cores recently, another way to go
Does anybody have any experiance with homes spray foamed on the exterior? There was one in Fine Homes a while back. I've been looking into it but haven't found any info on what to coat the foam with.
Any advice/links would be appreciated. The local foam contractor doesn't know either but he's interested.
Closed cell foam is sprayed on the exterior and a coating is sprayed on it. My friend owns a foam company he uses a titan airless spray gun. The product he uses to spray over the foam he buys from foam enterprise not sure what it is called.
I know from past experience he does not like to do roofs with it because of problems in the past.
The louisiana Superdome has a foam roof.
"Football Season again finally"
Could you put me in contact with your friend. I would like to pick his brain a little if he's willing. Could you ask him what the product is that he uses to coat foam on verticle applications. The house in Fine Homes had kind of a stucco look. I've also seen SPF homes that had an adobe look.
Maybe what you are asking is not sprayed foam, but sheet styrofoam panels on the exterior of buildings. This is very common on commerical buildings.
Styrofoam sheets are attached to the outside of the building and stucco is floated on the outside of that?????
I am not real crazy about this on a home, because the hurrican showed us how stable this construction was.
Life is too short, Behappy!
TFMM
Nope, it was 2 1/2 lb density spray foam over sheeting with a coating that had a stucco look. Sept or Oct issue 2006. I've been trying to find more info about the coating. Spray foam is differant than board insul. I found several products that are used with ICF's and something called Grancrete. These do not stick to spray foam as well as they do insul board. The rep said something about the coatings sticking but not bonding to Spray foam as spray foam is actually a plastic of sorts.
I have been looking into spraying the underside of the deck with open cell Icynene and was told by the two contractors who do most of that work in the Dallas area not to use closed cell. The cc is more energy efficient but if the roof leaks you end up with a big problem. Open cell will let the leak through so it can be observed and fixed. I was close to pulling the trigger when I found out that my new propane water heater would have to be framed off separately from the attic so it could have its own air supply and exhaust. Also, all my vents that duct into the attic (I know, not good) would have to be run outside.
I had a manual J done and my house is very tight, actually better than an Energy Star spec. It is passive solar with 2x6 walls, low "e" windows and R38 in the ceiling. I wanted to go to the next level of technology with the foam but the logistics are killing me. I'm having a 16 SEER Amana heat pump installed in my all electric house next week which should get me substantial savings.
I still like foam but I think the best application for the attic would be in new homes.