答复

1. Expert Member
   Michael Maines|Nov 20, 2020 09:56am|#1

   戴维（David），虽然本网站的某些成员不喜欢膜作为空气控制层，但根据我的经验，凭借正确的产品选择，它们的工作正常，并且比刚性材料更容易安装。特别是我喜欢Pro Clima Intello和Siga Majrex。

   Have you ever tried to install 1/4" drywall overhead? I have not, but 1/2" is floppy enough that I think you'll find 1/4" nearly impossible to install well, and it will sag between joists making it hard to tape properly, a requirement for it to be an air control layer.

1. 
   大卫·史密斯|2020年11月20日上午10:18|#2

   Michael, thank you for the reply. Exactly the kind of info I was searching for. I have not tried to install 1/4” drywall; only 1/2”, but I imagine you are correct about the installation difficulty.
   感谢您的重大建议。我会调查那些。

2. Expert Member
   阿科斯|2020年11月20日01:19 pm|#3

   No for the 1/4 drywall. Next to impossible to hang on a ceiling, way to soft.

   Definitely one of the fancier membranes will work but you can also use standard 6mil poly. Get the widest roll you can get so there are no or only a few seams. Make sure the seams are parallel to your rafters, this makes taping the seam much easier. Caulk around the perimeter and at all seams followed up with a quality tape.

   My cottage has this for ceiling, I'm not going to say that is is passive house air tight, but definitely not drafty.

   You can also go with 5/8 T&G and 1/2" drywall/osb/rigid insulation. Rigid insulation in this case would be much easier to deal with overhead than a membrane or drywall. It would only be slightly thicker than what you propose but definitely more robust.

1. 
   大卫·史密斯|Nov 20, 2020 02:48pm|#4

   Thanks, Akos. Two rooms in my house use the poly membrane with T&G and that was my first thought when I decided to do this, but I read it was a vapor barrier and that could cause condensation on the attic side. Maybe it works ok because I’m in a very dry climate, but because I have the time and will be exposing the rafters anyway, I wanted to avoid anything that might cause further issues later.

   I like the rigid insulation idea. I’m going to do some research on that as well.

1. Expert Member
   Zephyr7|Nov 21, 2020 08:23am|#5

   You shouldn’t have a condensation issue with poly on the ceiling if the ceiling is the floor of a vented attic. You can have issues with condensation if the poly is on the cold side of an assembly, but usually the issue with poly is that it prevents drying and can allow moisture issues within a wall. Ceilings are different, since the attic space is generally not sealed and always allows for drying as a result.

   Bill

1. 
   大卫·史密斯|2020年11月21日上午11:50|#6

   比尔，感谢您的澄清。阁楼绝缘层中是否有水分积聚的风险？在这种情况下，the子的底面会附着一聚，而after的海湾目前则用松散的矿物质羊毛填充，并用玻璃纤维棒覆盖，但我正在考虑将来用纤维素代替。

1. Expert Member
   Michael Maines|2020年11月21日上午11:59|#7

   David, you didn't mention your climate zone but a well-ventilated attic is the one location in temperate zones where polyethylene is reasonably safe from moisture accumulation. For a bit more cost, variable permeance membranes are still safer. Whether the cost savings is worth a bit of added risk is hard to say. For me it's not worth it, but it's your house.

3. 
   大卫·史密斯|Nov 21, 2020 12:46pm|#8

   迈克尔，我基本上是在科罗拉多州的7区（尽管该县在技术上是5区，但我在5和7之间的县线）。就像我之前说的那样，房子的一半有原始的T＆G带有多层衬里，尽管我没有彻底检查阁楼，但我没有注意到腐烂或在那里霉菌，我知道冬季有空气浸入阁楼，因为旧罐子漏水，需要更换。无论如何，在阅读了您的评论后，我对Poly感到更加满意，最终可能会走这条路。

   I bought the T&G yesterday and will be stacking it with stickers today to acclimate. Anyone have a recommendation for how many days, or should I just get a moisture meter?

   I appreciate all of your advice.

1. Expert Member
   Michael Maines|Nov 21, 2020 01:25pm|#10

   David, it sounds like you should be safe, then. There are various rules of thumb for acclimating but the only way to be precise is to use a moisture meter.

4. 
   大卫·史密斯|2020年11月21日下午12:59|#9

   Also, yes the attic is thoroughly ventilated: full length soffit vents on eave eave with baffles to keep the insulation off them and a full length ridge vent.