conflicting spray foam insulation warnings
Intended for use as a great room with vaulted ceilings, we are remodeling our attic in CT (hot, humid summers and cold winters). The attic is actually four stories high, counting the walk out basement. We were told that this amount of rising air is an important component to consider.
We replaced the worn roof with new decking and added one side raised full dormer. The shell: (original 2x4" sides, new const. 2x6 walls, Half the roof has the original 2x6s, new dormer roof 9 1/2" I-joists. Lots of windows and fixed skylights.
Since the spacing between rafters is ALL OVER THE PLACE, and the busy street belo is extremely noisy, we are thinking about ruling out bats and baffles.
I have talked with open and closed spray foam contractors.
They each sternly warn against using the others' type of foam.
OPEN CELL Concerns:
will absorb house moisture and freeze, defeating efficiency or worse. Also, potentially seriously large interior voids (caves) in insulation compromising eficiency.
Closed CELL Concerns:
will trap moisture or roof leaks, which will then be undetectable and thus, rot the roof deck and/or outside walls. Also, unable to match environmental movement of decking, leaving hairline pathways for air/moisture leaks. Also, potentially seriously large interior voids (caves) in insulation compromising eficiency.
Then, the discussion about adding vapor and thermal barriers gets really convoluted.
While these concerns "sound" palusible, we cannot find any evidence to confirm these claims. We would appreciate any advice available.
BuildingScience.com has alot of articles about this. Closed cell is more expensive per R value but has some advantages. My opinion is that unless you are in Climate Zone 6 save yourself some money and go with open cell. Just follow the guidelines for vapor control for regular insulation. If you are in a zone that heating perdominates, tyvek, well sealed on the outside and painted drywall, no plastic on the inside. I don't know where you got your concerns but they appear unfounded.
conflicting spray foam insulation warnings
Thank you, Perpetual,for taking the time to comment.
The renovated attic space will retain vaulted ceilings.
Respectfully, I chuckled at your belief that my concerns about contractor wordsmithing are unfounded. Not trying to be a wise guy, but here's why I say this:
Today, I visited my Building Inspector here in Connecticut.
I was shocked when he said that he would reject any open cell foam contractor proposal or work that did not first establish an eave/soffitt -to-ridge vent system to achieve a ventillated airspace, thus creating air movement between the open cell foam and the roof deck.
This completely challenges two open cell contractors' proposals to spray directly to the roof deck, and in addition, seal off all eave/soffitt/ridge vents completely.
I don't know who to believe, the contractors or the town! Furthermore, once sprayed, I don't know how he would inspect to even determine the existence of deck ventillation. My hunch is that no-one in my town must be taking out permits, because I know for a fact that open cell guys are spraying directly to the roof deck all over the place.
He did confirmed that Vapor barrier is required over open cell, followed by 20 second block such as 1/2" sheetrock. I was delighted to hear him state that it was ok to also use architectural hardwood veneer panels using 1/2" mdf, or even some mteallic radiant wrap materials.
Now, I never intended to spring for a total closed cell job.
To offset the cost of closed cell, I was investigating flash & batt, using just 1 or 2" of closed cell, followed by fiberglass. The inspector recommended this approach and indicated that a vapor barrier would then be unnecessary because it was already achieved by the closed cell attached directly to the roof deck.
Furthermore, he stated that concerns about closed cell "shrinking", "not-adhering" or "breaking free" can happen, due poor applicator skill (not deficient product) and that it mostly affect the rafters and studs, not the roof deck. He concluded that these problems always show up at inspection.....not down the road. 'Not sure I buy that one either.
Since the plan calls for vaulted ceilings, I was told that meeting the required R-18 overall forces me to complete a REScheck Compliannce Certificate from www.Energycodes.gov. I plan to throw that one at the contractors.
So, is Mass similar to CT in these regards?
I would not put spray foam against the deck, that's just me
Many shingle Mfg's specify that you must have deck venting
That heat if not vented builds up & can cause shingles to fail earlier
I'm just not sold on the spray foam
I prefer to have that plywood deck able to dry out & water/vapor vented
We have to meet the Energy check here too
I usually surpass the requirements by 20%
Ceiling I use R38, walls are R19 or 21
At least in my area the issue with shingle life is ice dams. According to Cold Region Research Labs you need R40 with vented roofs to prevent ice dams and R50 with unvented. I just ran a thermal model and with my very long cathedral ceilings and found I need to vent even with R50. So I am spraying foam from the roof to create air channels with foam.
Creating air channels with foam insulation is out of the ordinary. If I had a choice in a cathedral ceiling between spraying foam on the roof deck and using fiberglass insulation held off with the styrofoam channels, I would pick the spraying on the roof deck. Air works its way around styrofoam channels and kills the R value of the fiberglass.
If its new construction, then over cathedral ceilings Tyvek's AtticWrap using the furring strip method is a good choice. It allows you to use low cost fiberglass insulation, it provides a vapor barrior, a radiation barrior and a drainage plane in case the roof leaks.
vaulted ceilings R50????
Not sure how I would achieve cathredral ceilings at R50 or even R40 in the roof with half at 2x6 and the other side 9 1/2" I-Joists.
High density foam is R6.5/inch. So for a 2x6 you would have roughly R36. You might want to screw 2x3s to the bottom of them to get higher R value. Wherever you have doubled rafters be sure to caulk between them. Since there is no foam there, it is an air leak path.
building out to accommodate insulation for R value
Thanks, but I was searching for ways to avoid the horrific expense of many inches of closed cell foam. Nor, do I want to tackle the job myself and risk shrinkage away from the wood, outgassing or a failed inspection.
Do you have a picture....I have never seen a 4 story "attic"
Is it a mansard roof?
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