Using EPS and XPS in a conditioned crawl space
I live in Juneau Alaska, Climate Zone 7.
Living here, I often have to use whatever is available rather than the optimum. We just don’t have access and supply to everything. This being said, I am looking to insulate my crawlspace and convert it into a conditioned crawlspace by insulating the interior stem walls to the footings. In accordance with 2012 standards, I want to be sure that I have AT LEAST R-15 on the stem walls and joist bays.
Herein lies the problem.
The local hardware stores only have 43 units of EPS and 63 units of XPS in 2″x2’x8′ lengths. My access necessitates this size to maximize factory edge precision. The problem is that I need 90 sheets (including waste calculations). Therefore, I will need to utilize one layer of each material to achieve my desired results or wait until the next barge comes in (could be a year from now).
My quandary lies in the research. My understanding is that EPS increases in insulating performance in cold climates while XPS degrades in cold climates. On the flip side, XPS has better water resistance. So, what layer do I attach to the stem wall? It would seem that the XPS would perform better against water penetration against the stem wall, but would degrade in R-value against the cold wall. However, EPS against the wall would potentially perform better in our cold climate against the stem wall, but I sacrifice water penetration optimums.
Since my STEM wall does not show regular water penetrations, I am leaning towards installing the EPS against the cold surface and installing the XPS on the interior, warmer side. This would (apparently) maximize the insulating properties. ANd yes, I will stagger and tape/caulk/foam all seams as appropriate in each area.
Before I start, I would like some feedback regarding my quandary. What say you all? Pictures attached. And yes, my crawlspace will be emptied of all material and the bat insulation in the floor cavities will be removed prior to sealing and insulating the stem wall. 🙂
GBA Detail Library
A collection of one thousand construction details organized by climate and house part