Insulation in roof
I am looking to insulate the roof plane of a small library addition in Coastal Maine. This area is over the entry and librarian station in a section that connects our super-insulated addition (using dense pack cellulose in a double stud wall construction and dense pack cellulose in roof trusses) to the existing building. It has only 2×10 rafters. Can I specify dense pack cellulose between the rafters, Zip system sheathing on the roof, and then 1 or 2 layers of a new product: 1″ rigid VIP, Vacuum Insulated Panel by Kingspan, on the underside of the rafters and get the r-value needed? I need at least r-50+, preferably r-60. Then where does the vapor barrier occur? I understand that Zip panels have an integrated vapor barrier. Will I be introducing another vapor barrier on the under side with with the VIP panels?
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大多数屋顶材料已经是蒸汽屏障，这就是为什么屋顶甲板通常在屋顶甲板的下侧排出。在这方面，拉链并不是特别好或更糟。
Putting foil faced goods on the underside of dense packed cellulose tight to the roof deck would create a moisture trap between the roofing materials and the VIP (and a code violation.) If the underside of the roof deck has at least an inch of air space and is vented to the outdoors on both ends of each rafter bay it would have a code-approved drying path.
To go unvented in coastal Maine is all US climate zone 6, and at least half the total R has to be on the exterior of either the roof deck or the fiber insulation to have adequate dew point control. With closed cell polyurethane on the underside of the roof deck it's almost a moisture trap, but being well bonded it doesn't leak air, with no convective moisture transfer of moisture to the roof deck from the interior. With sufficient VIP or rigid foam or fiber insulation above the roof deck it's fine to use dense-packed cellulose on the interior side with only standard interior latex paint on gypsum board as the interior side vapor retarder.
用户-6825743，
First of all, can you tell us your name? (I'm Martin.)
Whether or not you can use a vented assembly approach depends on the slope of the roof. If this is a flat roof or a low-slope roof, you can't really make it vented. For more on low-slope roofs, see“绝缘低矮的住宅屋顶。”
If the roof has a slope of 3-in-12, or anything steeper, you can follow Dana's advice for a vented roof assembly -- assuming, of course, that there is an easy way to install soffit vents and a ridge vent.
For an unvented assembly, your choices are:
1. Install an adequately thick layer of continuous rigid foam on the exterior side of the roof sheathing, with or without some fluffy insulation between the rafters. For more information on this approach, see“如何在屋顶护套顶部安装刚性泡沫。”
2.在屋顶护套的下侧安装一层充足的闭孔喷雾泡沫，在固化喷雾泡沫的内侧有或没有一些额外的蓬松绝缘。有关此方法的更多信息，请参阅这两个文章：
"How to Build an Insulated Cathedral Ceiling"
"Flash-and-Batt Insulation"