10 Comments

1. 
   hertzr | Dec 28, 2022 06:04am | #1

   I’ve become a big fan of using metal boxes recently. Any ideas on similarly designed air tight boxes made out of metal? I’ve done the liquid flashing method a couple times and you’re right - it works, but is messy and can use a lot of material.

1. 
   Northernbuilt | Dec 28, 2022 05:59pm | #4

   I haven't seen an airtight metal box, the only time we use metal is when they are inside both the air and thermal control layers. Lessco makes a box for a box, it's an oversized box that can be integrated into the interior air barrier. Once in place, the actual electrical box is installed inside. I've used them a few times many years ago. They weren't the easiest product to work with, so we switched back to the standard airtight box.

2. 
   user-723121 | Dec 28, 2022 08:46am | #2

   Thanks, Randy

   Your nod of approval really means something. I just sent 6 cases to a couple in NH building a Net Zero home. It is exciting to talk with people who have really done their homework as this couple had. They sought out Energy Vanguard for the HVAC design, ultra efficiency is a small but growing world.

   Doug

1. Expert Member
   MALCOLM TAYLOR | Dec 28, 2022 11:36am | #3

   Doug,

   Air-foil boxes are a great product!

   After all the re-registering at GBA I had no idea you were User ...121. Any chance of changing your name back?

2. 
   Northernbuilt | Dec 28, 2022 06:01pm | #5

   You make a great product that is an improvement over anything else on the market, I'm just glad my local electrical supply house stocks them.
1. Expert Member
   MALCOLM TAYLOR | Dec 28, 2022 11:43pm | #6

   I wish Doug would modify them for approval up here in Canada. I'd love to use and spec them.

3. 
   neilt | Dec 31, 2022 05:24pm | #7

   NuTek also makes an airtight electrical box in Canada. I've used them for over 20 years and they have performed very well. Unable to detect air movement through them during Blower door Tests. I use polyurethane calking at the entry point of the wire.

1. Expert Member
   MALCOLM TAYLOR | Dec 31, 2022 06:58pm | #8

   neilt,

   That what I've always used, and had good results too. The advantage of Doug's model is the ease of air-sealing at the wires.

4. 
   Patrick_OSullivan | Jan 01, 2023 12:17am | #9

   These are all wonderful details well executed, but this is a case where I'm glad I read the article carefully to focus on what (I think) is the lede: "My preference is to have the main air control layer on the house exterior. I think this location provides the best durability and it is easier to achieve good continuity for the control layer."

   Hear, hear!

   I am somewhat perplexed by the conscious choice to put the air barrier at the interior, whether via membrane or drywall, particularly in new stick framed builds. (I understand in retrofits your hand may be forced.)

   There tend to be more interior penetrations than exterior (and thus more points to detail), the interior is perhaps more prone to post-construction penetrations (fish a wire, etc.), and membranes floating over insulation are more delicate than sheet goods. (Credit to a friend who, when discussing this, pointed out how many times he's seen the corner of drywall during installation stabbed through a kraft faced batt incidentally (and likely an interior air control layer could receive the same stabbing).

1. Expert Member
   MALCOLM TAYLOR | Jan 01, 2023 12:19pm | #10

   Patrick,

   I generally agree, but let me play devil's advocate a bit.

   - Exterior air barriers still allow moist interior air to cycle through the wall to the vulnerable sheathing.
   - Unlike interior membranes, exterior sheathing doesn't look like an air-barrier, and as it is a fairly new practice means builders and homeowners are more likely to leave exterior penetrations unsealed after renovations or minor damage.
   - Interior air barriers are installed inside the envelope after lock-up in a more controlled environment, not dependant on weather, with easy access - meaning attention to detail is more likely.
   - Interior air-barriers are easier to inspect, especially for continuity.
   - Punctures in interior membranes don't always result in air-leaks, as they are covered by the interior finish, which usually acts as a secondary (if poorly detailed) air-barrier.
   - Interior membranes (up here in Canada anyway) are installed by a separate trade, who do the task everyday. Sealing exterior ones tends to fall to the framers whose interest and expertise is elsewhere.