Exterior Insulation and Detailing a Rainscreen
I live in British Columbia where we make extensive use of rainscreens and are starting to use more external insulation and I’m flummoxed about how to handle the top and bottom details.
This is for a small insulated shed so I don’t have the luxury of working with an experienced local contractor or getting stuff custom made.
When I visit the big lumberyards (not Home Depot,) I see two things:
1) The furring strips are all PT plywood (2″*3/4)
2) I don’t see any Cor-A-Vent but I do see the Menzies perforated aluminum J-Channel. (https://www.menzies-metal.com/vent-flashings/perforated-j-channel-rain-screen-low-back/)
So I am left with two big questions:
1) What are people doing for keeping pests out of the Rockwool Comfortboard? I suppose I could block it with wood at the top and bottom.
2) If this is really what people are doing for rainscreens, isn’t it going to be a problem in 10 years to have all that unpainted aluminum in direct contact with the PT strips? I suppose I could wrap the end of each furring strip with TuckTape to avoid direct contact.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Malcolm Taylor may chime in.
In the meantime, you might want to read through Eric Whetzel's blog (https://kimchiandkraut.net/2019/07/11/passive-house-continous-insulation/). He offers some suggestions for keeping insects at bay.
On the furring, you can rip 3/8 (or larger) plywood into strips. That is often the most economical way to create an air gap.
谢谢。That is a great blog. The local stores have all the plywood pre-ripped for a reasonable price. However, local custom is to use PT for everything beyond the WRB. I'm fine with that as well but raises interesting questions about all the aluminum (flashing, bug screens, etc.)
https://hammerandhand.com/best-practices/manual/4-rain-screens/
谢谢！
Canada_Deck,
There is a distinction between vented and ventilated rain-screen cavities - ventilated being open at both the bottom and the top. Our code only requires a vented gap, because with that you get the great majority of the benefits of a rain-screen, without incurring the possibility of water intrusion that top-venting can bring.
您所需要的只是毛茸茸的条和穿孔闪光。使用2“外部绝缘材料，您可能需要使用1“ x4”作为毛圈。如果选择胶合板，请使用常规胶合板条。如果选择PT的胶合板，请获取不腐蚀铝的MPS，或将其固定为1/4”。在闪烁的后腿上方，因此没有接触。
Fasten a block of 1 1/2" x2" lumber to the base of the wall, and lap your WRB over it, then set your exterior insulation on top. Fasten the flashing to the block, and set your furring strips into it. You will need similar blocking at windows and doors.
Malcolm, always helpful, do you have a detail or image link for the flashing to block connection? I am having trouble picturing what you are describing. Thanks!
亚伦，
The J flashing just gets nailed to the outside of the block. Another option (which I prefer) if you are using exterior insulation, is to set the stud walls in several inches so the insulation is protected by the concrete foundation below, and then no block is necessary.
得到它，因此J闪烁是为了保护毛圈条和空间空间形式的错误等。不是毛茸茸和绝缘。非常感谢！
亚伦，
是的。您可以得到足够宽的自定义弯曲件，以保护绝缘的底部，但是我看不到固体块的缺点。根据那里的不同，WRB是您可能仍然担心水分撞到块的顶部。在这种情况下，您可以用一块果皮和棍子覆盖它，也可以简单地倾斜顶部。
A block at the top and bottom can also take some of the loading off the fasteners attaching the furring through the insulation.
谢谢。由于某种原因，我并没有想到将WRB放在绝缘底部的木头上，但这很有意义。