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Plumbing Penetrations through Post-Tensioned Foundation (Or: No Good Deed Goes Unpunished)[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>, <wood(--nospam--at)structuralist.net>
- Subject: Plumbing Penetrations through Post-Tensioned Foundation (Or: No Good Deed Goes Unpunished)
- From: "Bill Polhemus" <bill(--nospam--at)polhemus.cc>
- Date: Thu, 23 Oct 2003 10:07:20 -0500
[Prolog: I’m sending this to the WOOD list because I’ve been informed that the AEC-Residential list is “defunct” and I’m not sure where else to send it to get the attention of you residential guys]
This is mainly just to get something off my chest.
As I’ve mentioned before on these various forums, residential construction in Texas in unincorporated areas is not specifically governed by Building Code. In essence, the state legislature has prohibited counties from adopting and enforcing building codes, because of the strong lobbying of the contractors in this state.
So it’s “caveat emptor” if you build out in the county somewhere (which as you might expect covers the majority of new home construction going on).
As a result, many homeowners, if they’re smart, hire an engineer to do foundation design—foundations being the primary concern because of the aggressively expansive soils we have to deal with—and sometimes even (GASP!) design the remainder of the structure. And we are also often called upon to provide field inspection on behalf of the owner.
But many homeowners, even after going to that trouble, remain cowed by the builder because (1) they deal with him on a continuing basis, and (2) the builder holds the threat of escalated costs over his head (as in “oh, you want us to do it by the DRAWINGS! Wow, that’s gonna cost you…”) And believe it or not, many potential homeowners actually come to believe the builder is working in their best interests. Ludicrous at best, especially given that Texas does not (yet; see below) have a contractor licensing requirement and anyone with a hammer, a pickup truck and a Home Depot credit card can claim to be a homebuilder.
I have a current situation that I believe is an extreme example of this. The owners—a husband and wife in their late-50s or early 60s—hired me to design the foundation for a 6,000 s.f. home in a rural area that will cost about $500,000 at market prices (for you folks on the Left Coast, that would probably equate to about $2 or $2.5 million). They also wanted me to provide field inspection.
They had me design the foundation TWICE. The first time it was a pier-and-beam foundation. But they let the contractor cow them into thinking that would be too expensive (I’m not going into details; suffice it to say that this particular contractor knew he couldn’t build a pier-and-beam and make any money on it, so he pulled wool over their eyes).
So we then had to proceed to a post-tensioned slab on grade, which would be placed on fill. I won’t even get into the part where the contractor convinced them that compacting the fill using proper equipment would be “too costly,” and got them to allow him to just run over the top of it a few times with a dump truck.
Then, they commenced to install the foundation. First, they decided they’d go for a wood deck on the front porch and rear veranda, instead of the monolithic design that the drawings originally showed. Instead of having me modify the design, though, they just deleted the slab and went ahead and poured the beams out to the edge of the porches. So now, you’re going to have post-tensioned beams, WITHOUT an integral slab, sticking out beyond the edge of the slab itself. I have no idea what that’s going to do to (1) the anchorage forces, and (2) the increased stress in the beams which may cause displacement.
Then, they commenced to run plumbing stacks in two locations straight through the middle of beams. I have seen one instance, and had a couple more described to me, where this was done, and problems resulted including the post-tensioned tendon sawing through the plumbing stack and wreaking havoc with a sewer back-up. Not to mention the weakness in the beam that results.
When I pointed this out to the husband after my inspection visit, his response was “well, the builder said it’d be okay.” Engineers know nothing; the builder is the font of all wisdom. The wife was quite put out with her husband.
Anyway, just as I said, getting this off my chest.
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