I really enjoyed the great article by Josh Salinger, “Inside the Concrete-Free Slab.” 

https://www.finehomebuilding.com/project-guides/insulation/concrete-free-slab

We are building a cabin out in the Columbia Gorge (near Carson, WA), and we would like to do a similar floor in our crawlspace/basement.  Please see attached Section Drawings and Details.  The cabin is in climate zone 5B.

I talked to a Structural Engineer at work, and he suggested the retaining wall details shown on A2, A7, and A7.9, based on some earlier feedback from Malcolm Taylor.  This should make the North stem wall and footing more stable during any seismic activity.  I think the Engineer also suggested that lower drain shown on A7 and A7.9.  BTW, I added A2 to the end of the pdf set, since we’re mostly talking about the sections.

Last Fall, we finished getting the cabin dried in, so several of the details are existing. 

I’m not showing all of the same layers as are shown in the article, because we’d like to maintain the crawlspace headroom that’s shown.  The crawlspace is not a living space, but we’ll do our best to get the flooring level.  I’m hoping to get by with a 2″ layer of ¼” Minus gravel, as the bottom layer.

I plan to switch from a vented crawlspace to unvented, using one of the methods described on the last page of this great article, by Justin Fink: 

https://www.finehomebuilding.com/project-guides/insulation/crawlspaces-that-work

And to have the first floor and the crawlspace be part of the same conditioned space.  The amount of rigid foam that I’m showing might be overkill, but with the amount of insulation on the first floor, I’m assuming that I don’t want to skimp on the crawlspace insulation. Does that sound right?

Please disregard the 2” EPS Rigid Foam on the outside of the basement walls.  It’s there, but I know that it won’t contribute to the R-value, since it doesn’t go all the way up.

A Few Questions:

-Will the flooring work, with only the layers that I’m showing?  ¼” Minus Gravel, Rigid Foam, Vapor Barrier, Plywood.

-For the walls, I would like to use ½” OSB over the Rigid Foam.  With a Vapor Barrier in between, of course.  OSB anchored all the way through the foam, and into the concrete stem wall.  Do you see any issue with that?

-Am I showing my basement Air Barrier/Vapor Barrier in the correct place?  It’s shown in Red.

-Do you see any details that I need to revise?

 Thanks,
Miles