Sorry, Martin, I now understand that "new development" doesn't necessarily suggest "new house for being created", and "an unvented attic, with R-fifty beneath the roof" should have been "an unvented attic, with the R-fifty roof'. Because It is really crystal clear to me does not imply It can be apparent to Absolutely everyone else.
Your assembly calls for about five inches of XPS, for a complete R-value of only R-twenty five. That's not A lot. In case you are going to all that trouble to construct an advanced roof assembly, you need to goal larger.
Positive It can be a lot of problems. It looks like less trouble that the depth posted as illustration within the blog earlier mentioned and makes use of no foam... Which can be a "biggie" for me.
A. As I wrote from the posting, "Most rafters aren’t deep more than enough to support the insulation needed to satisfy bare minimum R-values expected by code, particularly if the rafter bays include things like a ventilation channel. ...
Another way so as to add R-worth to your roof assembly is to incorporate one or two levels of rigid foam while in the roof assembly — either previously mentioned the roof sheathing or under the rafters.
I have insulated the edges with R-19 fiberglass and now I am wondering: was that a slip-up? It's craft paper and I used to be arranging on a plastic sheet in addition, need to I skip that?
1. Remove the can lights and throw them absent. Recessed can lights really should in no way be set up in an insulated cathedral ceiling.
Does it make sense to spray and Lower and cobble 4 inch shut mobile foam/board on underside of sheathing accompanied by fiberglass inside the bays and one inch of eps/iso beneath the rafter (to halt thermal bridging) right before finishing with drywall? Will I develop a vapor sandwich and superior leave the ultimate EPS and settle for the thermal bridging?
for an unvented design without any insulation previously mentioned the sheathing, what about employing wood fibreboard concerning the rafters straight under and in connection with the sheathing? All gaps concerning the boards and the rafters stuffed with growing foam / sealant. You might then cover the rafters with rigid foam to bring your insulation as much as necessary R amount and reduce the risk on the rafters and sheathing, and afterwards install your airtight drywall beneath this.
If you'd like to endeavor a midway Remedy that may or may not function, you could cut out a lot of the drywall close to the ridge, and set up spray foam read the article insulation over the underside in the roof sheathing, just in the area near the ridge beam.
Unless of course a single makes use of Intense treatment with the warm facet air barrier which consists of being aware of that all fastener penetrations are sealed in addition you ought to presume some air circulation. The set up referred to right here While using the ice and drinking water defend under the shingles of course manufactured a greater air barrier than whichever was on the warm facet.
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I'm like a photograph of the answer: spray foam held down with the prime fringe of the rafters so that air is often drawn up from soffit vents to gable vents inside the truncated attic cavity.
However, I believe you're Mistaken regarding your asphalt felt; I question Should the felt is impermeable to h2o vapor. Most sorts of asphalt felt are considerably permeable -- typically 5 perms when dry and up to sixty perms when wet.