Extreme Air Sealing - the Crawlspace Edition

Air sealing the duct work to the subfloor. The interior side of the duct work is taped as well. I like redundancy in air sealed layers.

As any regular readers of this blog will know (assuming there are regular readers of this blog outside of my friend, Lynn), I am crazy obsessed with air sealing. After studying how to build an energy efficient home over the past 4 years, this is clearly the most important first step in that direction. Also it happens to be something I can actually do. You don't have to measure or cut precisely, you just have to crawl or climb around to awkward places to squirt foam, goo or tape any and every potential opening in your thermal envelope - the separation between inside and outside. I am capable of doing that.

The last step in air sealing this house is sealing the duct work and connections in the crawlspace. I don't know if John's house technically has what you call a crawlspace because it is built on piers and the space is open to the outside, but it seems like a crawlspace when you have to crawl and duck floor joists for hours at a time.

As I noted in an April post, the HVAC ducts are sealed with some kind of DUCK tape which really doesn't hold well for any length of time - meaning for years of the usefulness of the duct work. I did not take off all the fiberglass insulation and re-tape the ducts with a more long-lasting tape. I just could not make myself do that, but I did reinforce EVERY SINGLE JOINT and EVERY SINGLE PIECE of DUCK TAPE with a very adherent and long-lasting tape, mostly Siga Wigluv. I am hoping that the ducts are so well encased that they won't move much and the tape underneath the fiberglass insulation sheets holding the ducts together will last better.

This tape has only been on for a couple of months and is already loosening. You can see here I have reinforced other areas with Siga Wigluv. I did that on every duct.

This is another example:

You can see all the little strips of paper from taping the pipes.

After the sealing is complete, then I will insulate the 9.25" joist bays with 2 layers of Roxul Mineral Wool insulation - 5.5" layer and a 3.5" layer. The ducts themselves will be encased in the leftover polyisocyanurate foam which you see on your left. I haven't figured all those details for insulating around the ducts yet. 

Rich finished the interior painting, John is building bathroom vanities and I am crawling around underneath the house, sneezing like crazy - air sealing which is what I do best. That's where we are today.