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The stone work extends up between the rafters. If I use the ridged foam this should allow me to create a space for soffit venting. I will also be using ridge vents and probably adding a Cupola with a whole house fan built in. These old growth 2×4’s with about 30 growth rings would probably blow away a new 2×6 with 5 or 6 growth rings.
My plan was to cut and cobble 3″ polyiso in rafter bays. The build up would be tongue and groove, 2×2 nailers with 1.5″ polyiso in between nailers for thermal break of rafters, 6mil Vapor barrier, 2 3″ sheets of polyiso with very thick paper fiberglass faced, 3″ vented airspace, 2×4 purlins, foil faced bubble wrap directly under metal ...
2. Stack two layers of 2" Polyso foil-backed rigid sheets of foam, staggered and taped at the seams, secured to the rafters with 5 inch screws. 3. then a layer of Tyvek-roofing membrane or self adhering GRACE, or GAF against water penetration. 4. Then 2x2 or 2x4 straps screwed down, which will accommodate sheet-metal snaplock brackets, 5.
Expert Member. MALCOLM TAYLOR | Feb 21, 2013 11:26am | #7. Other advantages of sheathing are that it provides backing for fasteners at roof penetrations and flashing, makes for a walkable roof for maintenance purposes, allows a thinner gauge of metal to be used and is more resilient to damage from falling debris.
The orignal plan was to utilize shingles to limit costs, however after analizing the numbers a little further and accounting for the cost of removing the solar arrays to replace roofing 30-35 years from now it became apparent that if I could design the steel roof to limit the cost by eliminating the plywood deck it becomes a much better cost ...
Put down roof felt. Put full sheets of 2” foam on top of the sheathing and felt tacked in place. I know two layers of 1” foam would be ideal but that’s more expensive per R. Finally, lay down 1x4s parallel to the ridge at 24” spacing and screw those through the foam, felt and sheathing into the rafters.
Condensation in roof steel vs. wood vs. foam. In an unconditioned attic space above a residence, most of what I’ve read on GBA seems to agree that steel sheet roofing might develop some condensation on its underside, even if the ceiling below is properly sealed and insulated, just from the outdoor air warming faster than the surface of the ...
The roof assembly can be vented or unvented; insulation can be installed above the roof sheathing, between the rafters, under the rafters, or in a combination of these different locations. For a complete description of all the different ways to insulate a sloped roof, see “How to Build an Insulated Cathedral Ceiling.”.
Now Rafter Span is a little more complicated. Once again, thank you for the answer. pt. fitchplate |May 29, 2014 07:08pm| #3. Lets pretend the roof design details are conventional and so the roof deck sheathing will be 5/8" to 3/4". Many metal roofing dealers specify minimum of 7/16" sheathing.
Dana, You wrote, "Steel on its own isn't a recognized ignition barrier." I disagree. In sections R314.5.3 and R314.5.4, the IRC defines an ignition barrier as one of six permissible materials: 1 ½-inch-thick mineral fiber insulation; ¼-inch-thick wood structural panels (e.g., plywood); 3/8-inch particleboard; ¼-inch-thick hardboard; 3/8-inch-thick gypsum board; or corrosion-resistant steel ...