Spray foam:closed cell

A.Pierce

Any input appreciated.Thanks.My house is entirely cathedral ceiling.No attic space.Can I spray foam in between my rafters a few inches thick and avoid having to vent my soffits and ridge?If so should I fill the remaining cavity with fiberglass batts?Faced or unfaced?The rafters are 2x12's.The roof has osb with felt paper and metal panels.Thanks for any advice.

Big Bob

Is this a remodel? are the ceilings down?

A.Pierce

Thanks BIG BOB.My house is newly framed.The only thing between the rafters are the pink owens-corning vent thingys which can be quickly removed.I would love not having to vent the ridge or soffits if possible.Ive just read a few articles saying if you use foam that venting was unnecessary.I live near Richmond Va.so its humid most of the summer.Thanks again.

Kingfisher

I think what you are asking is all true, atleast here in FL. I would call the insulation company to make sure that for your weather conditions that is OK and get it in writing. Again I think you can use the foam and then you do not need vent but there are other things that change too, again here in FL. You may have to down size you AC system so that it will run longer to help keep the humidity controled and add a freash air intake. Are you the conractor too? If not ask his/her opinion, he may have done this before.

A.Pierce

Thanks Kingfisher.No Im not a contractor but Im contracting out the work on my house.All of my units have humidifiers on them because the entire house inside is gonna be finished with wood.No sheetrock anywhere.I hope I figured this right.Im just a little confused about vapor barriers.I think the foam companies are saying with foam I dont need to vent my ridge or have intake air at the soffits.But if I spray two inches or so that still leaves nine or so inches of air space in between the rafters.So if I add fiberglass batts does this now create a double vapor barrrier?The finished wood is about six inches wide by three quarters thick.It is tongue and groove so it wont be exactly "air tight".I just dont want water dripping from the ceiling.This would really,really suck.Thats why I needd all the advice I can get! Thanks a lot once again.

Kingfisher

Spary 4" and no fiberglass insulation, the air intake is for the AC not the soffits. If you seal a house to well you need freash air If you have too large of and AC with foam it well cool the space quickly, seems good but this is bad it needs to runs some to get the humidity out of the air, so you go with a smaller AC. This causes it to run longer fixing the proble and it cost less Those are specs for FL, not sure where you are and the local condition make a diff in this case. Call three diff insulation companies for bids and advise. You will get three diff answers, LOL, but it should point you in the right direction. Congrats on being your own contractor on your home but if you are unsure on something find an expert in that feild, thats what I do and I'm a pro

Randell Tarin

Long Long Ago in a youth far away, I used to install Foam insulation. Back then, you needed an enclosed cavity, which was then flled with foam. This worked fine in older homes that were built without insulation. The foam would expand and fill every little crack and hole in the wall. It was funny to see it ooze out of cracks. Once it cured, you simply cut and sanded it.

30 years later, foam insulation has improved. You should have a commercial firm apply it for you. What they will do is spray the underside of your roof deck all the way down to the rafters. After the foam has cured, they come back and scrape off the excess. You are now living in a beer cooler. You won't need roof vents if you do this, because there will be no air flow whatsoever.

I would also recommend that before this step that you have the underside of the roof deck sprayed with a radiant energy paint. This is a metallic based paint that reflects the summer heat away from your living space and keeps the winter heat in. I put this in my new home and swear by it. It's a little pricey, but you'll re-coop your money quickly with energy savings. It's available at Sherwin Williams in 5 gal. cans or I think I've seen it at Home Depot in 1 gal.

Personally, I wouldn't leave an air space below the foam. The foam itself provides a vapor barrier. I agree with the previous poster. Don't hermetically seal you home. If you don't have a way to remove the moisture from your home, you could have problems later. Also, fumes from carpets, drapes and other pollutants exist in you home so the inside air needs to be replaced regularly with fresh air. Good luck.

A.Pierce

Thanks for all the info Kingfisher and Randell.

Earnie

I hope this is ok. There are some good posts at This Old House forum regarding foam insulation:

http://advice.thisoldhouse.com/forumdisplay.php?f=158


I picked up a good magazine called "The Best of Fine Home Building: Energy Smart Homes", winter issue, that is full of great information.


Also, here is an article on foam though a bit dated:

http://www.rlcengineering.com/sprayfoam.htm


One more:

http://www.buildingscienceconsulting.../homeowner.htm


Hope these help.

Big Bob

Take some of the foam outside and light it on fire... then decide...

Randell Tarin

Foam poses a danger when it's left exposed. It is my understanding that the Op will probably cover the insulation with another material.

If we built our homes only out of inflammable materials they'd all be made of brick, steel or stone.

A.Pierce

Thanks for the sites Earnie.Hey BigBob Ive got great insurance and a back-up mobile home.lol.
Hey Randall,I investigated the radiant heat block paint and from what the manufactures say I need to leave at least a 1 inch air gap off of the painted osb.Therefore I would be back to venting the ridge and soffits.I want to spray foam in between the rafters so I dont have to vent.

Girla

What about if you have metal roof panels? Will this foam work for that on a hip roof with no ridge and no soffits? I am trying to figure out how to vent this roof. maybe this is the answer.

A.Pierce

I do have panels,Girla but Im not sure of your question?

Girla

my question is, what is the best way to vent this new hip metal roof when I have exposed rafter tails and no soffits and only about 3 feet of ridge? As you were talking about in a previous post, you dont have to vent if you have sprayed on foam, correct? I still dont understand where the humidity goes in that case, or how the heat gets out with no venting.