Your strategy to set up eight inches of rigid foam is a good one, but you could possibly set up thinner foam if there is a persuasive explanation to take action. Obviously, 8 inches of rigid foam has a greater R-value, and may conduct greater, than the usual thinner layer.
The primary flaw During this roof seems to be to be the ice and h2o membrane at the very best level inside the rafter bays. Would just typical felt paper have permitted adequate moisture to dissipate from the roof sheathing avoiding rot?, I sort of doubt it.
four. Once you have R-20 or R-25 of rigid foam on top of your sheathing, it is possible to safely and securely insulate down below your sheathing with Virtually almost any insulation you wish to use to carry your insulation approximately least code demands.
I have insulated the perimeters with R-19 fiberglass and now I'm asking yourself: was that a error? It's craft paper and I used to be preparing on the plastic sheet at the same time, need to I skip that?
If this were my dwelling, and Should the fiberglass batts are seen, I'd personally pull the entire insulation out of a few rafter bays to check out what's up there.
Within the absence of the airtight ceiling, roof ventilation can perform more damage than very good, due to the fact air motion in rafter bays can persuade indoor air to leak by ceiling cracks.
The previous Canadian rule of thumb -- not less than 2/3 of the overall R-price on the exterior facet of your vapor barrier -- is actually a tough-and-Prepared way to handle this query; It is also achievable to approach the question by undertaking a dew-position Investigation or simply a WUFI Assessment.
If you want to install a mix of closed-cell spray-foam about the underside in the roof sheathing and air-permeable insulation this contact form involving your rafters — an technique from time to time identified as “flash and batt†— the setting up code necessitates that spray foam (or, arguably, rigid foam insulation) be “used in immediate contact with the underside in the structural roof sheathing†and the foam insulation meet up with the requirements “laid out in Table R806.
I am guessing that neither of these details specifically matches your needs. But as I mentioned previously, If you'd like a custom element, you almost certainly need to have to hire an architect or an engineer. Great luck.
Thinking it as a result of on my Cape, I might choose to go back to the strategy you explain; make the air barrier jump back again within within the wall leading plate, vent the sloped ceilings that has a site-created vent channel between the rafters, and go back to a flat ceiling on the next flooring, using gable wall vents to vent an unconditioned attic.
Sure a cathedral ceiling depth would be really similar even so the obstacle of many cathedral ceilings may be the additional structural features, electrical packing containers, and the desire for wood board ceilings all which start off compromising the drywall layer which inside your detail is utilised at the air barrier.
I see the advice is that when beginning with board sheathing, a single need to place a watertight membrane over the sheathing right before installing the bottom layer of froth. Even so, in my case the roofer has presently accomplished placing new felt around the T&G board ceiling/roof deck. Can that felt substitute to the prescribed watertight membrane, right here in San Jose/Local weather Zone three?
Most setting up codes involve 1 square foot of Web cost-free air flow place For each and every three hundred square feet of go to these guys attic floor place, assuming that 50 percent of your air flow openings are located while in the soffit, and 50 % alongside the ridge.
Can we (does the code allow it)? Will it make realistic sense? Are there pitfalls on account of our local weather? How could possibly We have now to switch that to fit it to out problem?