Board-formed concrete wall
Finally began with the construction of our 6000 sq’ home in Central Texas. Still working on the pad for the monolithic slab foundation. The geotechnical engineer wants it to be overbuilt 10′ beyond foundation edges, which I have been told is way overkill by the local builders and the pad contractor who has been swearing at the geotechnical engineer everyday…Any thoughts on this. Our PIs were 30 on the soil test.
My main question has to do with the board formed concrete walls. 4 of the exterior walls are supposed to be done this way. I understand that we should put 2″ XPS foam (or equivalent) inside for insulation. My question has to do with the structure, the structural engineer designed it to be 8″ thick concrete outside, then a 2×4 stud framing in the middle and 6″ thick concrete inside. The builder and concrete contractors looked at this design and said “what the #$%#?” Why would the structural engineer design a studded wall inside the BFC wall, and then make it 18″ thick??? Its a single story house, when I saw builders put these walls up in my area, they have typically been 8-10″ thick with no wooden framing inside.
Any help would be greatly appreciated.
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Replies
Hi deerefan (be great to have a real name for the GBA Q&A community to use) -
Wish I could tell you ANYTHING about this wall configuration but I am completely stumped--have you asked the structural engineer about the wall he or she designed? Start with the horse's mouth...
Peter
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I wish working with engineers was easier. They don't want to answer any questions, when they do, they are very condescending and ask for thousands of dollars for a few hours of their time. Furthermore, there is so much CYA in everything they design that in the event of a problem it is usually someone else's fault and you have no recourse. No more engineers on this house, I am done!
The only time I've seen anything remotely similar was a modernist house where the concrete was exposed on both sides for aesthetic reasons. There was no framing, just foam.
https://www.theguardian.com/artanddesign/2018/oct/28/secular-retreat-devon-review-peter-zumthor-living-architecture-rowan-moore
Sounds like the engineer is trying to make an internally insulated mass wall, but I wouldn't do it that way. There are some recent threads here on using foam for internal insulation. There are even clips available to restrain the concrete through the foam. I would hate to see a wood framed wall sandwiched inside concrete. That's a perfect design for a mold farm. And you're in termite country, too. Sheesh.
Too many to list here. I mentioned Thermomass, HK Ties and CarbonCast in my thread about insulated concrete walls.
Mick
Mick,
Where can I find your thread about these walls? Thank you.
DeereFan,
Here is the link to Mick McBride's earlier Q&A thread: "Insulated concrete wall sandwich advice."
Is there some reason why you're building such a large house?
Yes, I am married to her:)