Method to use permeable insulation at cathedral ceiling or sealed attic?
这里经常重复的规则是，在大教堂天花板和未通风阁楼的底面需要进行闭孔喷雾泡沫。推理是开放的细胞喷雾泡沫，纤维素或其他松散的绝缘材料是蒸气的，因此将使房屋的水分迁移到护套，并导致护套腐烂。但是，闭孔泡沫的最大缺点是环境问题和成本。
This article:
https://buildingscience.com/documents/insights/bsi-088-venting-vapor
seems to indicate that in climate zones 1-3, you can use vapor permeable insulation if you build a vapor vent. The article specifically references cellulose & fiberglass. Would this vapor vent revise the recommendations here for Climate zones 1-3? Would this vapor vent allow you to use open cell spray foam at a cathedral ceiling or underside of an unvented attic?
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C.L.,
Joe Lstiburek has been promoting his idea of "vapor vents" (more commonly called "diffusion vents") for the last few years. To the best of my knowledge, this method of venting is not yet recognized by any building code.
Lstiburek's initial excitement about diffusion vents had to be dialed back somewhat after a field test in Chicago yielded disappointing results. Data from warmer climates have been more encouraging, but this is still (in my view) an experimental approach. I wouldn't advise the use Lstiburek's approach until more field testing confirms initial findings.
As far as I know, Lstiburek has never advocated the diffusion vent approach for roof assemblies insulated with open-cell spray foam.
For more information on diffusion vents and the Chicago field study, seeA Researcher Looks at Insulated Roof Assemblies.
如果我们有大教堂的天花板，或者正在隔离开普敦风格的房屋，则在the子或桁架中安装通风口通道。我们空气密封通风口通道，通常使用致密的填充纤维素来填充海湾。我看不出为什么在那里使用开放式泡沫会是一个问题，但这不是必需的，而且花费超过花费的费用。
You can create a vented roof assembly with either open-cell foam or cellulose if you install site-built vent channels or AccuVent-style cathedral vents. Depending on truss design and target R value, open cell may actually be cheaper than cellulose.
When the labor and materials associated with venting are taken into account, a lot of the price differential compared to an unvented roof with closed-cell will disappear. If you go with closed-cell, be sure to find an installer who uses fourth-generation blowing agents, which have drastically reduced global warming impacts compared to earlier HFCs.
Some other options are a mix of closed cell spray foam and cellulose or a raised heel scissor truss (allowing a vaulted ceiling and a vented attic with cellulose).