The longer you wait to setup rigid foam higher than your roof sheathing just after your rafter bays are full of fluffy insulation, the increased the chance that the roof sheathing will accumulate moisture. 1 or 2 many years must be no challenge, but I would not stretch the work out much farther than that.
If you install 2x4s (or 2x3s on edge, put in with extended screws) perpendicular to your rafters, you'll address most of the thermal bridging concern without the ought to incorporate a layer of rigid foam.
Nicely the roof is going on with the 1st layer of insulation (on-top the purlins, underneath the roof sheeting). There seems to be adequate Area still left while in the four" purlin cavity for the next layer of R11 for being put in without any modification.
From the absence of an airtight ceiling, roof ventilation can do a lot more hurt than good, considering the fact that air motion in rafter bays can persuade indoor air to leak by ceiling cracks.
Thank you, Martin and Stephen. Fortunately we have been within a problem where by we can easily pause and reconsider, as The brand new felt has become placed, Nonetheless they have not commenced putting in shingles still. I'll go over the specific situation With all the contractor all over again. I could possibly get him to rethink.
I'm somewhat stumped on this a person - I would wish to vent this roof assembly, but I am unable to say no matter whether there'll be a natural convective circulation as there could well be with rafters sloping Together with the roof pitch. My rafters are running amount Nevertheless they sit on parallel curved leading plates. I can use 12" rafters and make ten" of batt work, leaving an abundance of ventilation Room. I am able to drill the tops from the engineered joist flanges to allow ventilation 'up-slope' (perpendicular for the rafters) as well as while in the rafter bays, and I can offer continuous perimeter ventilation (Cor-A-Vent strip) at my roof fascias (eave, ridge and gables).
If you are a GBA member, you by now are aware that GBA has many architectural aspects in its element library so that read what he said you can analyze and obtain.
Also, Why don't you zip panels taped after which roxul batts with drywall in excess of that. Roxul is wonderful stuff I are actually tests For some time in outrageous strategies endeavoring to see its capabilities. I are convinced zip panels, taped thoroughly, with roxul batts will last as long as the roof!
Though roof air flow may help dry out moist roof sheathing, it’s necessary to Restrict the movement of water vapor escaping within the household so the roof sheathing in no way receives moist in the first place.
one. You don't need an inside vapor barrier. Inside of a sizzling humid local climate, the vapor generate is usually from the exterior towards the inside (assuming your making is air conditioned). If the developing is just not ever destined to be air conditioned, the vapor drive will even now be from the outside to the inside, but there will not be Considerably vapor travel.
A. You will find a code need for a vapor retarder in certain types of assemblies, but there's no need for a vapor barrier. Your layer of rigid foam is already a vapor retarder. No additional vapor retarding layer needs to be set up.
You aren't the only person with this problem. For find more information those who (such as you) are worried about The problem, There's two selections:
As your home flexes with variations of temperature It truly is probable, even likely that many of the foamed-in air sealing will leak. It'd be well worth undertaking two" of open mobile foam on the interior side of which would be a far more adaptable and trustworthy long run air seal.
The old Canadian rule of thumb -- at the very least two/3 of the total R-worth on the exterior side of your vapor barrier -- is a rough-and-Completely ready way to deal with this query; it's also achievable to method the dilemma by carrying out a dew-stage Evaluation or even a WUFI Evaluation.