Need second opinion on open cell Post New Topic | Post Reply
Posted: Mar 17, 2013 08:24 AM
Need second opinion on open cellGreetings foamers. I'm in the process of framing an addition on my house and very interested in SPF for it. Typical 2x6 walls and 2x10 cathedral ceiling rafrers, Tyvak Housewrap. I'm in upstate New York, climate zone boarder 5-6. Due to my budget I'm only concidering OC.
There are three foam contractors in my area that I've talked to,however only one of them sprays OC. His recommendation is 3.5" in walls, and 5.5" in cathedral ceiling. From what I've read on this site this sounds like minimal coverage for my climate zone. Will the 3.5" in walls provide enough protection for vapor barrier??
Also what are your thoughts on installing 6 mil polly sheets for vapor barrier with OC, will this cause a double barrier traping moisture?
My Building Inspector LOVES SPF and is not hung-up on "R" value.
As usual the concern is budget, budget, budget. However I understand there's one chance to get this right and if the kids have to go without food and shoes for a couple mounths, in lieu of extra inches, so be it. Your thoughts and suggestions will be greatly appreciated.
Posted: Mar 17, 2013 12:32 PM
|Definitely not nearly enough foam. Check out Roger Morrison's article on Determining insulation thickness. I can send you a copy if you can't find it online. firstname.lastname@example.org Also check my website for Learning the Difference Between 1/2 lb and 2 lb density foam. masonknowles.com|
Posted: Mar 18, 2013 06:18 PM
joe,,what you got here is a guy sellin a job..he heard you had budget constraints and he threw you a cheap number,,
cheap number wins usually and thats what he is throwin...so he gets the job,,,is it the right thing for your project??who knows..you decide...
my take,,,not a chance...maybe if he was tellin you 3.5" closed cell in the sides and 5.5" closed cell in the cathedral,,maybe...
...think about it..yes foam is wonderful
yes foam works great,,yes foam creates a marvelous air barrier in the first inch if closed cell or ~2.5 inch if open cell,,but then physics is physic,,hot travels to cold..and lets not forget that when hot meets cold condensation occurs...
oh yes,,,and lets not forget that the DOE tells us that in your zone five that cathedral ceiling requires a minimum of r19 air impermiable insulation to not see condensation in the assembly..minimum,,and that 5.5" of open cell has you teterin on the edge of the cliff,,
sell the trolls for slave labor in china...fill the sidewall to +/-1" and the cathedral the same..you wont regret,,either decision..
yes on the poly on the sidewall,,imho...
Posted: Mar 21, 2013 12:12 PM
I agree with dude!
Some of the open cell manufactures have ESS reports that approve as little as 3.5inches for walls and 5.5inches for ceilings. And that will perform as well as the R-19 and R-40 that you would get with a good fiberglass job.
But why pay more for foam if you are only getting fiberglass performance? Don’t you want to save money on your energy bills?
To save money you want as much insulation as is practical that is as close to an R-40 as possible with the roof being the largest heat gain/heat loss surface. As we all know all buildings are a compromise when it comes to energy savings and costs.
What we recommend here in Indiana and your weather is very similar is at least R-19 to 20 in the walls (5-5.5inches open cell) and R-30 to 40 on the underside of the roof depending on space and budget, if you can we like to get 10 inches of open cell under the roof.