无源房屋的低斜率无通向屋顶
我正处于纽约市被动房屋计划的早期阶段，所以还没有建筑师或建筑商。我正在尝试在雇用某人之前熨烫很多细节，以便我可以向他们展示我是否对我想要的东西感到满意。
Here are my design goals:
* Passive house compliant (~R-67)
* Flat roof
*顶部的太阳能电池板
* No spray foam (for maintenance, health, and environmental reasons)
* No cellulose (for fire safety reasons)
I’ve been reading everything I can find, but roof construction is very confusing for a novice! I just finished working through NYC 2022 building code (based on IBC 2015) and doing all of the load calculations. To get 25′ spans, I’ll need to use 2x12s. While this will probably be expensive, this gives nice deep rafter bays to fill with insulation. Given my constraints above, fiberglass and Rockwool seem to be my only options to fill the bays.
That leads me to a design something like:
胶合板/OSB甲板
5.5″ XPS (R-22)
11英寸摇滚乐（R-42）
Is this a reasonable design? I would really appreciate a sanity check or ideas for improvement! Also, where is the right place for an air barrier and WRB barrier in this?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
答复
QBRT,
您可能会发现这篇文章很有用：//m.etiketa4.com/article/insulating-low-slope-residential-roofs
Thanks, this seems to roughly validate my approach -- the articles and comments took me down a chain of articles that I think answered my questions :)
在我的CZ中，我需要31％的绝缘材料来自泡沫，而我占32％。这也许是为了舒适而过于近的距离，所以我可能会以R-4.4的R-4.4刚性泡沫的降低到9.5英寸的Rockwood，其余的泡沫为我44％。
//m.etiketa4.com/article/where-does-the-housewrap-gosays the WRB can either go underneath or on top of the foam. Since I'll probably go with an integrated air/water barrier (like zip system), I think that answers all of my questions. Thanks!
Qbrt,
Dense packed borate treated cellulose simply won't burn in any house fire. Similar to mass timber structures, there is too much mass, it might char but that is about it. By that time there is probably nothing left of the house.
如果您要购买实际的被动房屋证书，那么一定要建造R67屋顶。
如果您只是想要一个高效的结构，而不是用任何泡沫构建的R67，则具有零环境或财务意义。根据u因子（最有可能是R38）组件进行代码最小值。当涉及到热量损失时，屋顶几乎是另一个表面，除非您还有R67墙，否则拥有R67屋顶是没有意义的。您不需要接受我的诺言，我只是一个随机的人，有人在您的年度能源使用方面对不同选择进行计算。
在处理具有刚性绝缘材料的混合组件时，最有效的房屋具有大约相同的R值的屋顶和墙壁。您确实希望屋顶的R值稍高，因为您确实在夜间获得了更多的辐射损失，而不是2倍的墙壁。
As for your assembly, since it is a roof there is no WRB. Water barrier is the actual roofing. You do need a couple more control layers bellow the roof membrane.
From the inside out.
您需要一个温暖的III级蒸气阻滞剂和空气屏障。最简单的是涂有干墙。
Above that goes the batts or dense pack insulation between the rafters.
Your roof deck should be your main air barrier. Plywood or OSB with taped seams is the simplest. Make sure to figure out how to tie this to your wall to ensure air barrier continuity.
Rigid insulation above this and your membrane roof either directly onto the rigid or over a cover board.
您要在绿色版本中使用的最后一件事是常规XPS。它具有高GWP吹剂的爆炸，该剂的扩散很快，因此长期R值与EPS大致相同。您需要较新的低GWP XPS，EPS，GPS或Polyiso。
大多数膜屋顶都安装在Polyiso上，具体取决于厚度约为R5.9/英寸。即使对于R67屋顶，您也只需要3.75英寸左右的Polyiso。
Akos
谢谢，我非常感谢您的详细回复！如果应与墙壁类似地隔热良好的屋顶，为什么这么多的被动房屋程序建议这样的高价值？
借助纤维素，我的理解是火灾可以相对容易地开始，但是它们的传播非常缓慢。在实践中，这意味着纤维素绝缘材料会闷烧几个小时。
The high R value roofs are recommended when you are using cheap insulation like blown in fiberglass or cellulose. With these the incremental cost of more insulation is essentially noise compared to the house budget, even R100 is easy.
Once you add in rigid insulation or spray foam into the equation, the incremental R value costs goes through the roof. With high R value roofs, in terms of simple ROI on energy saved you are looking at centuries.
这不是最科学的测试，但我已经为标准的硼酸盐处理的纤维素放了火炬。它的魅力，但仅此而已。除了低成本和降低的碳足迹外，墙壁和天花板上几吨纤维素的良好侧面好处是，它使房屋变得异常安静。
XPS和EPS着火时，会产生燃烧着火的熔炉，从而散发出火。Polyiso Chars，所以更安全。玻璃纤维和矿物质羊毛本质上是不可燃烧的，因此在耐火性方面它们最安全，在这方面，矿物质羊毛优于玻璃纤维。
Aside from that though, I agree with Akos here -- cellulose has been used for many decades, and it's not known as a fire risk. If your main concern is fire risk, I would pay more attention to fire blocking and air sealing, which will help limit the spread of fire and smoke migration. I would also use 5/8" drywall throughout to slow the spread of fire. You could also put spring hinges on all the doors to keep them closed, which also helps to limit fire spread. Running all your electrical wiring in conduit will also help provide some additional protection.
我要说的是，纤维素并不是造成房屋火灾风险的重要贡献。还有其他事情更多的是一个问题。如果您真的想全力以赴，甚至可以放入洒水系统。使用5/8英寸的石膏板也是一种真正改善事物的廉价方式，具有更坚固的感觉墙壁和房间之间的声音变速箱的增加。
账单
Akos,
我以前看过此评论 - “当涉及到热量损失时，屋顶几乎是另一个表面，除非您也有R67墙，否则拥有R67屋顶是没有意义的。我非常了解什么可以使这一真实的物理学。
The exitance from the sun is mostly the irradiance on the roof, and not the walls. That's where the energy is coming from, trying to make its way into your house, through the roof. Perhaps its different in cooler climates, or more equal I should say, but in the south it's very apparent where they energy is coming from, and it only makes sense to slow its transfer down as much as possible, IE more insulation.
没有叫你出去，我只是想弄清楚为什么我一直看到这件事。
In colder climate, your heat loss is determined by the temperature delta between indoors and outdoor, area of the surface and R value of the assembly.
关于the only difference between a roof and a wall is that a roof will see a bit more loss during a clear night due to radiative loss and gain a bit during day as the sun will warm the roof surface. Overall these two effects seem to cancel out in most climates.
When it comes to cooling load, it is a different story. In that case most of your heat gain comes from glazing, air leaks and sun beating down on the roof. Even on a sweltering hot day, the temperature difference between indoors and outdoors is not that much this is why wall R value doesn't matter too much.
For example, around me my winter heating design delta T is 68F. The summer cooling delta T is only 9F.
Overall, in a heating dominated climate, a roof is just another surface no different from a wall. 1000 sqft of R30 roof will have about the same heat loss as 1000 sqft of R30 walls.