If you need to get it done right, you should handle air leaks, handle your recessed can issue, and add more than enough R-worth to at the very least fulfill minimum code needs. It is many get the job done, but it's not rocket science. Correcting these issues can be high priced, nevertheless.
Like Doug's design and style, the focus is on developing a significant perm layer for drying to the exterior, which will however make it possible for venting when blocking wind washing within the fluffy stuff.
Unbelievably useful (five*) thread. So, if you must use fiberglass insulation batts, and you dont have access to spray foam or shut mobile boards, what do you need to do? I guess the key is to really make it unvented and include in other air-impermeable levels. I'm going to insulate a new all-steel cathedral pitched gable roof while in the Caribean. The program would be to fill the cavity between the four" Z-purlins with R-11 batting (vapor side experiencing the dwelling Place). For added heat conduction resistance we plan to roll A further thinner (filleted?) layer of the batting over the top on the purlins (ie amongst the purlins plus the sheeting).
It appears if one were to employ dense pack cellulose inside a vented cathedral ceiling the vent channel product must be rigid adequate to withstand the force.
Nevertheless, two other areas of aspect-roof have now been dry walled about with fiberglass in addition to a plastic sheet -- the lavatory closet and the hallway. I am frightened to request but ought to I open People up once more?
It is surely not restricted to an R 80 Passive House roof. Just take out the parallel chord trusses and skinny it up.
1. You'll want to get an other engineer To judge the safety of your respective 2x4 rafters. "Furring down with 2x2s" does not improve the capacity within your 2x4s to bear the snow load. It really is attainable that an engineer will suggest you to sister 2x8s or 2x10s onto your present 2x4 rafters.
Thanks to your response Martin. Would you still be delighted to implement that unvented technique for just a renovation situation where There's non-breathable membrane (eg bitumous 'felt') over solid board sheathing?
I'm sorry being the bearer of negative information, although the sections of roof that happen to be insulated with 6 inches of fiberglass and inside polyethylene weren't insulated properly. In Individuals sections, the roof sheathing is at risk of moisture accumulation and decay.
When roof ventilation can reduce the potential risk of ice damming, it’s important for builders to Restrict the stream of heat into roof air flow channels by including one or more ceiling air barriers and by installing thick insulation, making sure that as minor warmth as you can escapes through the household.
The code limits on using air-permeable insulation amongst rafters were being developed to stop the roof sheathing from rotting. When fiberglass batts are installed in unvented rafter bays, the batts permit moist indoor air to reach the chilly roof sheathing.
Regarding dense pack cellulose: unsure why dense pack will be negated - I feel it perfectly suited.
This assembly was just lately constructed just south of Portland OR. I posted it two or three weeks back. Here it is yet again (Together with the builders remarks) I do think It is a fairly uncomplicated Make once you get previous the concept of adding assistance cavities to your Create.
As talked about previously mentioned, we hope to replace the roof this following calendar year. In that case, At the moment I'd like to up grade to both an unvented roof or if important a cold roof (a vented about-roof). (I don;t understand that it issues from the equations, but we are taking a look at buying and installing stamped steel shingles.