[Editor's Be aware: Bill Rose just sent me the following remarks in an e-mail; he integrated his authorization to article the feedback.]
I'm undecided how to proceed concerning the electrical for the existing lover, and for the not-nevertheless-set up but Significantly wished-for observe lights. From the aged roof, the fan's electrical offer ran along with the T&G ceiling, and was included by what looked like electrical tape, then by a 1/two" layer of seem insulation board, and then through the felt and shingles.
Our cooler mornings might make the interior of my metallic roof sheeting to sweat a bit because It'll be in contact with the warmer unvented fiberglass-insulated purlin "cavity" underneath. Once our hot Caribbean sunshine starts to kick in I need this humidity to dry and/or diffuse out of this cavity, in the gypsum sheeting, in the cathedral living Room under, to then be blown from my 4x3 gable window. A vapor barrier would totally retard this process.
November 18, 2011 Picture 1 of 3 A leaky ceiling doomed the roof sheathing. The ceiling of this 10-calendar year-aged dwelling was Slice for an electrical box, along with the oversized hole was under no circumstances caulked. Humidity-laden air entered the rafter bays through these cracks. Once the humidity encountered chilly roof sheathing, it condensed, bringing about moisture accumulation and decay. (The rubberized membrane inside the photo was used as A short lived patch for your hole inside the roof, and didn't contribute into the failure mechanism.) Picture Credit history: Peter Yost A leaky ceiling doomed the roof sheathing. The ceiling of the ten-year-aged residence was Slice for an electrical box, and also the outsized hole was never ever caulked. Humidity-laden air entered the rafter bays through these cracks.
As your home flexes with alterations of temperature it's achievable, even most likely that a few of the foamed-in air sealing will leak. It might be worth undertaking two" of open up cell foam on the interior aspect of which would be a more versatile and reputable long run air seal.
You happen to be proposing a vented roof assembly. To get a vented roof assembly, the code would not demand that any foam insulation be positioned in direct contact with your roof sheathing -- Quite the opposite.
The precise structure demonstrated my website was for the Passive Dwelling. The roof thickness & use of a service cavity may well seem like overkill for the majority of initiatives, but If you need an airtight lid, a service cavity can get you there - forever... And let you wire and light-weight the inside.
Many thanks once again for the solutions. Now I just want to find an installer During this spot who appreciates whatever they're carrying out (so far it's been iffy)!
Probably the approach to go is usually to settle for four" of froth around the cathedral ceiling, as opposed to 8" of foam, and never carry on the foam about the vented attic. There'll certainly be a Bizarre jog during the roof line wherever the foam starts off, but it will eventually largely only be visible in the back again of your home, not from the road.
Thanks for the reaction Martin. Would you continue to be joyful to utilize that unvented method for any renovation scenario the place There's non-breathable membrane (eg bitumous 'felt') earlier mentioned reliable board sheathing?
We actually Will not know if these roofs have correct vent channels, or which kind of vent baffles (if any) were being utilised to take care of the air flow gap involving the very best in the fiberglass insulation as well as the underside in the roof sheathing.
I am with Martin on this just one, your detail is labor intensive for minor if any attain for my part. The vent channels we explain can be carried out following the roof is on through the underside (dry facet). For all those of us building in a chilly local climate this can be a large benefit, we invest as very little time as is required within the roof.
I am sorry to become the bearer of negative information, nevertheless the sections of roof which can be insulated with six inches of fiberglass and interior polyethylene were not insulated accurately. In Those people sections, the roof sheathing is vulnerable to moisture accumulation and decay.
A. Both technique will work, provided that you get at the least the minimum amount code R-benefit for the roof, and provided that you use construction techniques that pay attention to airtightness.