If you wish to put in a combination of shut-cell spray-foam within the underside in the roof sheathing and air-permeable insulation among your rafters — an strategy sometimes called “flash and batt†— the constructing code necessitates that spray foam (or, arguably, rigid foam insulation) be “used in direct connection with the underside from the structural roof sheathing†and the foam insulation meet the necessities “laid out in Desk R806.
It appears like you posted your thoughts on two distinct webpages. I have delivered an answer on one other webpage in which you posted. Here's the url to my response:
two. I do think your proposed element might be difficult to Create. How effortless is it to equilibrium over the rafters as you install the membrane, presumably with staples, and then install the 2x2 spacers, presumably with nails or screws, all without putting a foot among the rafters? I wouldn’t want to do it.
Inside the absence of an airtight ceiling, roof air flow can perform extra damage than good, given that air motion in rafter bays can stimulate indoor air to leak by ceiling cracks.
I believe that Invoice Rose is right: all these failures require dampness that is definitely carried by relocating air. These are definitely not diffusion failures. If your rafter bays truly are thoroughly dense-packed -- a giant if -- the possibility of air motion is incredibly low.
Martin, Thanks to your reply. Individuals articles are both extremely informative. I'm getting the perception that SIPs can be achieved perfectly, but can be beat in cost with exterior rigid foam devices while you've suggested, with equivalent or much better performance (with emphasis on air-tightness).
Most commercial roof assemblies Never trouble Using the fluffy things. They only why not try these out meet up with one hundred% in the R-benefit demands with the roof with rigid foam (both EPS or polyiso) and skip the batts entirely. That is the way I propose you continue.
Finally, I kow the recessed lighting is horrible, but what can I do if it is previously installed? With one of many lights I changed it in excess of into a pendant mild which minimized the warmth close to the roof but the air barrier remains to be a concern.
Simply because a roof assembly does not follow the principles set up with the making code or tips of developing scientists doesn't suggest the roof has
Do you know the original source for this photo and when it can be done to view other pictures of this intriguing failure.
I'm which include a photograph of the solution: spray foam held down from the best fringe of the rafters to ensure that air can be drawn up from soffit vents to gable vents while in the truncated attic cavity.
Am i able to get some look here additional commentary around the "entire roof" of Ice & Drinking water Protect? I believe this experienced little to carry out While using the failure. The key reason why why I inquire is I've the same "full roof" design coming up, Nonetheless, the rafter bays are all straight runs with soffit vents, steady vent baffles (one/two" plywood) and steady ridge vent. Dense pack cellulose, two" XPS under 2x10's, air restricted drywall (XPS can be sealed up as well).
Have room above garage center with closets on both sides concerning the closet kneewalls and also the eaves. Insulation about the area part is six inches of foam slabs sealed by "Terrific Things" spray-in foam. Higher than this ceiling foam and underneath the roof plywood, you'll find 1 inch x twenty. inch unobstructed foam encased ducts between the rafters for venting for the roof peak vent. The facet sections outside the knee walls are insulated with rolled fiberglass fiber with durovent ducts between the insulation as well as the roof plywood. You'll find considerable soffit vents at The bottom of your durovent he has a good point ducts.
Thanks on your response Martin. Would you still be joyful to implement that unvented method for the renovation scenario the place there is non-breathable membrane (eg bitumous 'felt') over good board sheathing?