Bonus Room Roof Insulation & Code questions…
Hi folks.
I am having my contractor come out to closed cell spray foam my bonus room in an unvented fashion (per conversations with J. Lstiburek).
The rafters are 24″ o.c. & 8″ (7.25 actual). The contractor says he recommends 5.5″ of CC spray foam along w/ spraying the faces of the rafters to help cut down on thermal bridging. He said 5.5″ (R38.5) meets code for zone 5B in the NE. I asked why not spray the rafters at 6.5″ along w/ the faces of the rafters to bump it another R7? He said “It’s another $1,000.00 and is a waste of money, you’ll never feel the difference & you have to weigh the cost of the extra inch vs whether any money will actually be saved on the energy bill for the room. That room will be so tight that it’s not worth it & R39 is code.” He then stated the typical “I’ll take your money if you want me to, but I wouldn’t do it.”
They are also spray foaming the garage ceiling / floor of bonus room to R-14 (2″)
I was looking up codes and see conflicting information on sites varying between R39 & R45 to R60…
I was also thinking that IF R39 is code, I doubt it will be in 10 years… Everything is open now, once the room is finished, it’s finished.
A. Does anyone know the roof requirements for sure for 5B NH?
B. Opinions on another 1″ (7.25″ rafter filled w/ 6.5″ of foam vs. 5.5″of foam) for an additional 1K? On paper, it will be a move from R38.5 to R45.5.
C. Is there a specific code requirement for the garage ceiling / floor of bonus room when the roof is insulated as described above?
Thanks in advance.
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Replies
Do you know which foam he is proposing? An HFO foam would be better for the environment and Heatlok can be applied in 6.5 inch lifts for R-49 (according to the manufacturer). But some CC foams can only be applied in 3.5 inch lifts.
Lastly, did Dr. Joe actually say that R-30 was acceptable?
No idea on the foam, only that it is high density CC foam...
Lstiburek recommended putting as much foam in as possible. My impression is that this contractor is not impressed by the building science field.
I got lost on the "lifts" you spoke of, what does that mean?
A lift is the thickness of foam that can be safely sprayed. If the lift is too thick, the foam may not cure properly. For a contractor, this limitation may mean two visits (and setups and breakdowns) to a site if the project owner wants slightly more foam than the standard "lift."
If Lstiburek recommended installing as much foam as possible, I would follow his guidance. You might want to get a quote from someone who handles the more recent HFO products.
Thanks, I just looked it up & sent him a message asking what foam he uses.
Any opinion on the additional 1K for the jump to R45.5? I hear, Doc Joe, just wondering if it's worth it in the long run...
He can probably offer the HFO foam for a small upcharge. If not, between that an the anti-building-science attitude, you might want to find a new contractor.
Original post modified, I forgot question "C"
Any other input on this as far as my original question?
The reason you are finding conflicting information is that NH adopted a the 2015 code update recently, in 2019. It is now R49 for ceilings and R-30 for the floor.
https://insulationinstitute.org/wp-content/uploads/2020/08/NH_Code-FINAL.pdf
So even the $1k upgrade doesn't meet code.
The reason your lousy contractor doesn't want to meet code is that he's selling a very expensive type of insulation. There are other kinds of insulation that could meet code for less money.
As for whether it's worth it, I think the floor is most important. That's a comfort issue for standing on the floor. I'd pack the joist bays all the way full with dense pack cellulose.
Hi Charlie.
What type of insulation can I use to meet code in 7-1/4" of depth? (2x8)
And he is spraying the ceiling of the garage/floor of the bouns w/ 2" of foam to seal it & offer some insulation, I was then going to dense pack the rest as you brought up...
Do you know the R-value per inch of dense packed cellulose?
This is one of the few cases where the insulation contractor is giving good advice.
Because of the thermal bridging of the rafters, there is not much gained with the extra insulation. With 5.5" of ccSPF you are looking at an ~R30 roof assembly, bumping that up to 7" brings you up to R34. The energy savings between the the two will never pay for the extra SPF.
Usually the best assembly in these types of roofs is a flash and batt. Get your spray foam contractor to install only enough SPF for condensation control (40% of the overall R value) and have the rest as fluffy insulation. In your case this would be about 2.5" to 3" of cc SPF and some low density 2x6 batts squished into the remaining 4.75" space. This would get you an R29 assembly using much less foam and little extra work. This would be lower cost if you don't mind doing the batt install yourself, make sure to get faced batts or insulation support wires to keep the batts in place.
While the spray foam guy is there, have them flash the floor with an inch or so of SPF. Air sealing the floors in a bonus room goes a long way in making it a more comfortable place. The extra cost of this is well worth it.
P.S. If you can dense pack the floor as Charlie suggests, you can skip the SPF. Dense packing does a very good job of limiting airflow, not air tight but good enough.
Hi Akos,
He is spraying the ceiling of the garage/floor of the bouns w/ 2" of foam to seal it & offer some insulation, I was then going to dense pack the rest.
As for the CCSF... If he sprayed 6.5" into a 2x8 that is 7-1/8 to 7-.25 actual, & sprayed the faces as well, do you feel thermal bridging would still be that much? How about 5.5" or 6.5" and then do an inch or so of polyiso nailed or screwed to the rafters to address the bridging?
Also, I'm confused on the math. CCSF cures at R-7 per inch which is R-38.5 for 5.5" & R-45.5 for 6.5". Were your numbers factoring in the bridging?
Thanks for your input.