If you'd like to put in a combination of rigid foam on top of your roof sheathing and air-permeable insulation concerning your rafters, you might want to be sure that your rigid foam is thick sufficient to keep your roof sheathing previously mentioned the dew position.
Ideally, you ought to have an airtight barrier over and underneath your fiberglass batts. If you can realize These two air limitations, then wind-washing is just not a difficulty inside of a roof like yours. (It can be inside of a vented unconditioned attic, not surprisingly, In particular close to the soffits.)
As The top of our neighborhood HBA, I've strenuously identified that foam in excess of a vented flat roof assembly won't supply the insulation values promised. Some builders have recommended they may simply just seal and stucco over the stucco vents and eliminate the ventilation.
The code constraints on the use of air-permeable insulation involving rafters were designed to prevent the roof sheathing from rotting. When fiberglass batts are put in in unvented rafter bays, the batts allow for moist indoor air to get to the cold roof sheathing.
A brand new standalone immediate vent fuel stove goes in within the much conclude of the area underneath the metallic box. I figure if we use XPS board, it must be pulled back many inches from all-around that space, but I failed to Assume it would avert me from working with XPS solely. Looks like Roxul is considerably less of a problem concerning warmth/fireplace.
It is just a code violation to put in an air-permeable insulation like fiberglass batts concerning unvented rafters. It's also a nasty notion, simply because dampness can accumulate on check this your own roof sheathing if you are attempting this method, and you may end up with sheathing rot.
Inside of a phrase, no — the code explicitly forbids this technique. Cellulose can only be Employed in an unvented roof assembly when there is an ample layer of rigid foam earlier mentioned the roof sheathing or an satisfactory layer of closed-cell spray foam beneath the roof sheathing. Cellulose by itself gained’t perform.
You describe your proposed air barrier as "taped felt." I don't Assume asphalt felt may be successfully taped, and I don't think that asphalt felt would make a very good air barrier.
I don't have knowledge developing from the Carribbean or creating metal buildings, so I am not the most beneficial human being to remark. But here are some reflections:
The Threat is inside moisture will migrate into the chilly sheathing, leading to condensation or dampness accumulation.
It is really Harmless to say that an current property doesn't have excellent roof air flow if there are not any soffit vents or ridge vents. It is also Safe and sound to say that, whether or not there are actually soffit vents and ridge vents, the roof isn't ventilated if it involves valleys, hips, dormers, or skylights.
If We will put some insulation previously mentioned the ceiling, then I would like to put Many of the insulation earlier mentioned the ceiling, and steer clear of the Charge and stress of a different lowered ceiling. Meaning a Make-up of 8", employing XPS. If we build up the roof line above the cathedral ceiling with click to find out more the household place by eight", we presumably need to build up the rest of the adjoining gable roof at the same time.
"The conventional roof air flow necessity Utilized in creating codes and asphalt roofing companies requires one sq. foot of "net free ventilation area" for every three hundred sq. feet of ceiling spot (attic flooring region) when vents are evenly divided — fifty percent of these substantial within the roof for the ridge, gable, or even a large roof, and fifty percent very low over the roof on the eaves.
This short article was EXTREMELY valuable, Thank you! I've just one problem about making a vented assembly by generating an airtght program with accuvents.