In the absence of the airtight ceiling, roof ventilation can perform more harm than great, since air motion in rafter bays can persuade indoor air to leak as a result of ceiling cracks.
A lot of spray foam roofing contractors in our market are touting their capacity enhance effectiveness on previous warm tar and graveled flat roofs by incorporating three to four inches of shut cell spray foam. The majority of these old properties are flat roofs joisted with dimensional lumber, with parapets and also have stucco vents Reduce to the rim joists.
It is Risk-free to state that an present household doesn't have good roof air flow if there are no soffit vents or ridge vents. It is also Secure to mention that, regardless of whether you will find soffit vents and ridge vents, the roof isn't ventilated if it consists of valleys, hips, dormers, or skylights.
As an instance that a particular building apply ends in a 20% failure level. That follow would be thoroughly unacceptable to builders, who don't need callbacks or headaches. But that exercise would still cause eighty% of shoppers currently being contented.
Can I get some a lot more commentary over the "full roof" of Ice & Drinking water Defend? I feel this experienced very little to accomplish Together with the failure. The rationale why I talk to is I have an analogous "complete roof" design and style developing, Nonetheless, the rafter bays are all straight operates with soffit vents, constant vent baffles (one/2" plywood) and ongoing ridge vent. Dense pack cellulose, 2" XPS underneath 2x10's, air tight drywall (XPS may be sealed up way too).
I suspect that Monthly bill Rose is true: all of these failures involve dampness that is carried by shifting air. These are generally not diffusion failures. Should the rafter bays seriously are adequately dense-packed -- a big if -- the possibility of air movement is incredibly reduced.
Doug I agree, a news lot of wrongs "overthinking" and overdoing. I the moment needed to resupply a doctor building an plane with dozens of the aircraft bolts because they had been tightened to The purpose of breaking the bolts. A lot less useful source is a lot more occasionally... Along with the KISS rule.
Until finally recently, developing codes necessary that insulated sloped roofs include ventilation channels instantly under the roof sheathing. Many builders still follow this time-analyzed strategy.
You are proposing a vented roof assembly. To get a vented roof assembly, the code will not demand that any foam insulation be put in direct contact with your roof sheathing -- Quite the opposite.
My residence inbuilt sixty three here in Ohio features a cathedral ceiling without having air flow. The truth is there numerous cross-supports managing perpendicular to the leading joists as well as other framing things that will make this unfeasible. So I want to make it an efficient unvented roof. Half with the roof has 2x8 joists and the opposite 50 % has 2x12s. At the moment You will find a membrane masking (rubber) which is labored perfectly for over twenty years but is showing indications of deterioration and may want replacing before long. Possessing finished reworking on The within and going for walks about the roof I know that loads of the sheeting has to be replaced along with the minor insulation that may be there now. We've had condensation concerns previously so I now you will discover air infiltration and bridging challenges.
It really is wonderful so as to add foam board above the roof deck In spite of the closed cell foam-board (what sort?) on the interior. Roof decks are not able to dry to the exterior via 0.one for every shingles anyway, significantly since in zone five it will expend an important period of time lined in snow/dew/rain with the moisture drive heading inward, not outward.
Your plan will work high-quality, providing the layer of rigid foam in addition to your roof sheathing has an R-price of at the least R-twenty. When you are working with XPS, you will need not less than four inches of foam. For anyone who is employing polyisocyanurate, you will need at the least company website 3 inches of foam.
I don't believe the weight of plywood or OSB will probably be a difficulty, but If you're worried about the extra fat, you are able to usually check with an engineer.
Most rafters aren’t deep more than enough to support the insulation necessary to meet bare minimum R-values essential by code, particularly if the rafter bays consist of a air flow channel.