Wood pony walls for closed crawl space foundation stem walls
We are designing a home in Zone 2, about 60 miles south of Houston, 10 miles from the coast. 99.9+% of the homes around here built after 1960 (and not within a mile of the beach) are built on some type of slab on grade foundation, but we want a closed crawl space, with the floor of the crawl space about one foot above natural grade, and the first floor height four feet above the crawl space floor (about five feet above natural grade.
One big problem we are having is that the local foundation subcontractors don’t have any experience with crawl space foundations (closed or vented), so estimates are very expensive for a crawl space foundation with poured concrete stem wall (I assume to cover lack of experience). The foundation engineer we are working with suggested wood pony/stem walls on a concrete perimeter beam (top of beam about 12″ above natural grade) to reduce costs. He’s from Houston, where crawl space foundations are becoming very popular, so he’s knowledgeable about them, although most of his work has been vented crawl spaces.
The original plan was to go with poured concrete or CMU stem walls, and insulate the inside of the stem walls with two inches of closed cell foam. What is the best practice if PT lumber is used for the stem wall? If the stem wall is still insulated on the inside with spray foam, is it still 2″ of closed cell? Does all of the lumber, i.e., the “rest of the exposed 2×6” need to also be insulated?
Any opinions on wood vs. CMU vs. poured concrete with regards to strength, longevity, suitability, cost, etc.
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