If you wish to install a combination of shut-cell spray-foam within the underside of your roof sheathing and air-permeable insulation among your rafters — an strategy from time to time referred to as “flash and batt†— the developing code involves that spray foam (or, arguably, rigid foam insulation) be “utilized in direct contact with the underside of the structural roof sheathing†and which the foam insulation meet up with the requirements “laid out in Desk R806.
I thanks for this impeccably timed blog, as I am at present framing my semi-fundamental cathedral ceiling hip roof (with shorter ridge). I want to explain my depth and check out to be aware of where I'm on the correct keep track of and much more importantly, exactly where I could have failures. Hope I am able to amuse many of you...I sense much like the a lot more I test to handle a priority, the greater of a priority it will become, And that i undoubtedly don't want to consider great time, care, and detail to aid the demise of my roof.
Although vented roof assemblies are meant to dry to the exterior, unvented roof assemblies are created to dry to the interior. That’s why an unvented roof assembly must never ever contain interior polyethylene.
My view would be that the steep aspect of the mansard roof is actually a roof. This is especially true if the exterior from the sloped assembly is completed with roofing.
Since I have spelled out the correct way to get it done, I can even Enable you to recognize that Lots of people have finished Everything you suggest.
I don’t Assume I am able to meet all the pointers which i’ve Keep reading this Site, supplied existing building constraints and reluctance of my contractor to put into official site practice insulation previously mentioned the sheathing and foam for the new cavity.
I have a 50 yr-old seasonal cottage inside a northern climate. The simple 6/twelve gable roof is made up of actual 2x6 rafters (24" oc), sheathed with one/2" plywood and protected with asphalt shingles. There is absolutely no insulation during the ceiling and I believe tiny to no productive insulation during the 2x4 walls. In the summer the heat acquire within can make dwelling almost unbearable. I think that the greatest bang for that buck would be to deal with the ceiling insulation challenge very first, but want to preserve the interior physical appearance.
sips are wonderful but during the coldest of climates they've got encountered complications. google problem programs in alaska - evidently a gaggle of homes there have been built but not adequate awareness to depth for that plumbing and roof vents were taken into account (Completely air restricted foamed in penetrations), mated panel seams and fastener punctures caused the very best degree osb to rot. Of course the whole roofs necessary replacement.
Your proposed assembly is a code violation. If you prefer an unvented roof assembly, you must keep the roof sheathing warm with spray foam or rigid foam. Cellulose insulation is classed as an air-permeable insulation and can't be Utilized in this type of roof assembly.
Another way so as to add R-worth for your roof assembly is to incorporate 1 or 2 layers of rigid foam from the roof assembly — possibly above the roof sheathing or down below the rafters.
If you would like a vapor-permeable substance that remains to be an air barrier, decide on fiberboard sheathing. But use caulk around the perimeter, and tape on the seams, to make certain that the fabric is mounted within an airtight method.
Martin, I feel your Observe re: 2009 IRC table R806.four, min impermeable insulation levels req'd for condensation control in unvented roof assemblies per local climate zone, requires clarification; you mentioned
Will you be wondering the 'flat' vented cavities would not provide the assembly by having an exhaust path for humidity?
Unless just one utilizes Severe care with the warm facet air barrier which consists of recognizing that every one fastener penetrations are sealed as well you should assume some air movement. The installation referred to listed here Using the ice and h2o defend under the shingles obviously made a far better air barrier than what ever was on The nice and cozy aspect.