If you want to build an unvented insulated roof assembly, you have got two decisions: (a) You could include rigid foam to the outside facet of your respective roof sheathing, followed by a second layer of roof sheathing and new roofing, or (b) You can insulate the underside within your roof sheathing with spray polyurethane foam.
I'd add to Martin's listing of products for rafter vent channnels, fiberboard sheathing. I exploit I joists for vented cathedral ceilings and staple one/2" fiberboard to the bottom of the top cord of the I joists. It could be ripped on a table observed and installs immediately, fiberboard does Possess a superior perm rating and should allow small quantities of humidity to pass through in the vent Place.
4. Once you've R-20 or R-25 of rigid foam on top of your sheathing, you may properly insulate down below your sheathing with Virtually almost any insulation you should use to bring your insulation as many as minimum code necessities.
Your want to use two-inch-thick EPS as your ventilation baffle will operate. The EPS is somewhat vapor-permeable, so it enables a small amount of outward drying. (In any case, for those who Construct a fairly airtight ceiling, there will not be any dampness During this assembly that needs to escape.)
A. The air barrier could be a vapor barrier, because the rigid foam is also more likely to become a vapor barrier (or near it) in almost any situation.
This is a code violation to put in an air-permeable insulation like fiberglass batts between unvented rafters. It is also a bad notion, because dampness can accumulate in your roof sheathing if you are trying this process, and discover this info here you will end up with sheathing rot.
Within a phrase, no — the code explicitly forbids this technique. Cellulose can only be Employed in an unvented roof assembly when there is an adequate layer of rigid foam over the roof sheathing or an sufficient layer of shut-mobile spray foam under the roof sheathing. Cellulose by itself gained’t perform.
Most business roof assemblies don't bother Together with the fluffy stuff. They simply meet a hundred% with the R-price prerequisites with the roof with rigid foam (both EPS or polyiso) and skip the batts solely. That is the way I counsel which you carry on.
That is a sophisticated subject matter, and For anyone who is concerned about code prerequisites in your city, then by all suggests you ought to talk to this problem at your neighborhood creating Office environment. Most often, renovation operate may be carried out with no bringing all facets of the house nearly latest code necessities.
Have space around garage center with closets on both sides amongst the closet kneewalls and the eaves. Insulation more than the room portion is six inches of froth slabs visit this web-site sealed by "Terrific Things" spray-in foam. Higher than this ceiling foam and underneath the roof plywood, there are 1 inch x 20. inch unobstructed foam encased ducts in between the rafters for venting for the roof peak vent. The side sections outside the knee partitions are insulated with rolled fiberglass fiber with durovent ducts amongst the insulation as well as the roof plywood. You'll find sizeable soffit vents at The bottom with the durovent ducts.
Many thanks once more. The roofer agrees that 2x4 framing to lift the height in excess of the vented attic will be a workable Resolution to match up the roof strains.
I see the advice is when setting up with board sheathing, 1 must area a watertight membrane around the sheathing before installing the lowest layer of foam. Nonetheless, in my scenario the roofer has now finished inserting new felt in excess of the T&G board ceiling/roof deck. Can that felt substitute for your prescribed watertight membrane, listed here in San Jose/Climate Zone 3?
I do not more believe that the burden of plywood or OSB will be a difficulty, but In case you are worried about the extra bodyweight, you can usually seek advice from an engineer.
Joe Lstiburek: "A vented attic, exactly where insulation is placed on an air-sealed attic ground, is Just about the most underappreciated constructing assemblies that Now we have during the heritage of building science."