If you want to get it done correct, you must address air leaks, handle your recessed can dilemma, and insert adequate R-worth to at the least fulfill minimal code specifications. It truly is loads of operate, but it isn't really rocket science. Repairing these complications can be high priced, on the other hand.
The ideal tactic is to carry out each of the operate simultaneously: rigid foam higher than the roof sheathing (as recommended during the posting), and fluffy insulation beneath.
A. The air barrier generally is a vapor barrier, as the rigid foam can be more likely to be a vapor barrier (or near to it) in almost any scenario.
Should your local weather is not too severe It truly is probably alright to obtain just the R-10 foam in excess of the structural steel, Though there is certainly some possibility the metal could sweat in chilly weather. I'm assuming Additionally you meant to insulate the 2x12 joist bays to get your whole R-worth to an affordable amount.
Your approach to put in a stack of rigid foam rectangles in Every single rafter bay is known as the "Minimize-and-cobble" means of insulation. It is actually a technique generally preferred by homeowners, but under no circumstances chosen by insulation contractors.
Based on segment R806.five of the 2012 IRC, “Unvented attic assemblies (spaces between the highest-story ceiling joists and also the roof rafters) and unvented enclosed rafter assemblies (Areas among ceilings that happen to be utilized directly to the underside of roof framing associates/rafters as well as structural roof sheathing at the best of the roof framing users/rafters) shall be permitted†given that numerous circumstances are fulfilled.
. Unvented roof assemblies are Safe and sound. The main reason that many people install air flow channels higher than the rigid foam is simply because they live in locations with plenty of snowfall, and they prefer a "chilly roof" to attenuate ice damming issues. Thanks for the remark. I'll edit my posting to test to explain any ambiguity on this concern. .
Put in closed-cell spray foam versus the underside on the roof sheathing, and no other kind of insulation. Make sure that the thickness from the spray foam is ample to satisfy minimum amount code necessities. Bear in mind open up-mobile spray foam is risky in all local climate zones, and if open-cell spray foam is set up During this spot in a chilly local weather, the underside on the cured foam should be included with gypsum drywall that has been painted with vapor-retarder paint. Vapor-retarder paint is ineffective if it is sprayed straight over the cured foam.
Set up a layer of closed-mobile spray foam versus the underside of the roof sheathing, and fill the remainder of the rafter cavity by having an air-permeable insulation. Again, such a assembly is meant to dry to the inside, Therefore the assembly must in no way include an inside polyethylene vapor barrier.
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Thanks in your suggestions, Martin. Green Developing Advisor continues to be the most beneficial for answering particular issues I have experienced from like it your basement all of the technique to the roof. I wouldn't manage to Make my very own property solo like this with out you and various audience assisting me out with information.
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You describe your proposed air barrier as "taped felt." I do not Imagine asphalt felt might be correctly taped, and I don't believe asphalt felt makes an excellent air barrier.
If We'll put some insulation previously mentioned the ceiling, then I wish to put Each of the insulation above the ceiling, and stay away from the Price tag and inconvenience of a completely new decreased ceiling. Which means a Make-up of eight", using XPS. If we Create up the roof line above the cathedral ceiling in the family members home by 8", we presumably will need to develop up the remainder of the adjoining gable roof too.