答复

1. 专家成员
   Kohta Ueno|Aug 13, 2021 06:17pm|＃1

   Can you clarify what the design intent in this roof/attic assembly is? I.e., are you thinking of it as an unvented attic, with a cavity completely filled with cellulose? That is definitely a risky assembly:

   BSI-043：不要致密 - 纤维素和密集包装绝缘
   https://www.buildingscience.com/documents/insights/bsi-043-dont-be-dense

   与墙壁的密集包方法一样出色，它是无通向大教堂天花板和扁平屋顶的非常愚蠢的方法。而且，无论我们中有些人努力阻止人们继续前进并做到这一点，他们都坚持不懈。首先，这是违反建筑法规的行为。其次，它违反了物理学。

   或者is the intent to create a vented assembly? That can be done with a combination of eave vents, cupolas/doghouses, etc.

   Insulating Low-Slope Residential Roofs
   Unless you’re careful, your low-slope roof can end up with damp sheathing
   //m.etiketa4.com/article/insulating-low-slope-residential-frofs

   这是建筑科学公司校长乔·劳斯布雷克（Joe Lstiburek）的一些建议：“If you have an airtight ceiling, and you have an air gap of at least 6 inches between the top of the insulation and the roof deck, and if you have perimeter air coming in at vents at the soffit or fascia above the insulation, and if you also have ventilation openings near the center of the roof through some kind of cupola or doghouse — not just a whirlybird turbine vent — there is nothing wrong with your roof assembly,” Lstiburek told me recently. “You can build a 2 foot by 2 foot doghouse that sticks up a few feet, and put in some rectangular vents. If the ceiling is airtight, then the makeup air comes from the outside. That’s the least expensive way to do things.”

   Lstiburek continued, “The problem with this type of roof is that it is rarely executed correctly. Usually, architects don’t want to provide any ventilation around the perimeter. Or the architect won’t provide a deep enough truss to get enough insulation. If you just have a few whirlybird vents and a leaky ceiling, the whirlybirds will suck moisture-laden air out of the building and the roof will rot.”

   另外，本专栏似乎很重要：

   如何隔离低斜坡屋顶
   The owner of a 1920s Baltimore row-house looks for the best insulation strategy
   //m.etiketa4.com/article/how-to-sunsulate-ansulate-a-low-slope-frad

1. 
   Erinbowman|2021年8月13日下午07:04|＃2

   非常感谢!我的屋顶是一个“橡胶火炬屋顶”。To my knowledge the roof is unvented... it is a townhome with other homes attached on the right and left. I've attached a few photos here of the attic.
1. 
   布莱斯·内斯比特（Bryce Nesbitt）|2021年8月15日下午10:12|＃3

   How old is the roof? Your other class of options is foam on top, a fire barrier, then a new TPO roof.

   看起来您有足够的深度。

   联排别墅的建设日期是什么？该行中的其他人隔热了吗？

1. 
   Erinbowman|2021年8月17日上午09:03|＃4

   Construction date is 1922, new roof was put on in 2017 so won't be doing that for a while. I think other folks have insulated, but not with a concern for green building techniques.

2. 专家成员
   达娜·多塞特（Dana Dorsett）|Aug 17, 2021 03:35pm|＃7

   是否可以爬到该阁楼空间？

   It can be moisture safe to do a hybrid approach with a few inches of closed cell foam directly applied to the underside of the roof deck, with the remainder being cellulose. In zone 4A as long as at least 30% or more of the total R is closed cell foam the cellulose stays pretty dry, and the roof deck is protected. If those rafters are full-dimension 2x10s (true 10" nominal cavity depth) installing 3" of HFO blown closed cell foam (R20-R21) with 7" of cellulose blown in netting (R26-ish) you'd have R46 total, with foam-R ratio of R20/R46= 43%, which is PLENTY of dew point margin. With only 2" of HFO blown foam (R13-R14) and 8" of cellulose (R30) you'd be at about R43, which would be at the bare-minimum ratio of only (R13/R43=) 30%.

   Loose blown foam on the attic floor would fit, but would all but guarantee high moisture content in the roof deck, along with a lot of moisture cycling in the cellulose which causes unusually high and rapid settling compared to how it behaves in a properly vented pitched-roof attic (the "humidity can wear away the cellulose within 7 years” issue the contractor was warning about.)

   Unlike open blown cellulose none of this is cheap. In my neighborhood the 3" of HFO blown foam would run north of $4 per square foot, and 7" dense-packed cellulose in netting is also >2x the cost of the 13-15" of open blown cellulose it would take to hit R49 in a better vented attic. Re-roofing and installing a continuous 6-7" of 2lbs density roofing polyiso (R34-R40) might not be a lot more expensive, and would meet code min on a U-factor basis by not having thermally conductive rafters passing through the insulation layer, and the roof deck would stay dry & rot free, since it would be fully inside the thermal envelope of the building.

2. 
   Jon R|Aug 17, 2021 09:31am|＃5

   Re #1:
   由于扁平屋顶的被动排气通常是不切实际的，因此探索主动通风会很有趣 - 阁楼/通风压力与内部匹配，因此建筑物没有温暖/潮湿的空气泄漏到阁楼中。也许只有在内部和外部露点点和阁楼％rh表明这将是有益的。

1. 
   布莱斯·内斯比特（Bryce Nesbitt）|2021年8月17日下午01:34|＃6

   您是否在考虑一些微型热恢复呼吸机系统，只是为了上述绝缘材料吗？

   这可能会起作用，特别是如果首先受到烟雾或鼓风机门测试的支持，可以找到天花板泄漏，因为永远不会有完美的压力匹配。

1. 
   Jon R|2021年8月17日下午4:04|＃8

   I suppose one could use heat recovery, but air above attic floor insulation is largely unconditioned - so little loss if it is replaced with outside air.

   同意，理论上不可能进行完美的压力匹配。但这可能是非常积极的（阁楼>内部），这意味着没有堆栈效应从内部到阁楼空间驱动空气运动。没有这种泄漏将水分带入阁楼空间，尚不清楚阁楼根本需要故意出口通风孔。

   虽然被动阁楼通风是常态，但在特殊情况下，动力阁楼通风可能是针对有效水分的屋顶的最具成本效益的解决方案。

   注意：这与经常受到批评的2000+ CFM驱动阁楼的不相似排气导致负阁楼压力的通风。