BEFORE THE ARCHITECT – BUILDER DRAWINGS – DETAIL
Foundations For Residential Building Construction, Continuous Stem Wall . . . unusual
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As you may recall, the Spahaus is a residential spa enclosure of considerable size - nearly 600 square feet. Its design is highlighted in three other places on this website.
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Here come the details to the Spahaus foundation in some detail, complimenting the more overall work covered in Plans & Elevations, Foundation. Of themselves, these drawings exemplify the kinds of detailed treatments that need to be made, in order to communicate design interests and intentions to on-site contractors.
Each follows with brief comment, after we display an unannotated detail set of basic references.
This note of General Considerations has a second meaning; namely, the designer did not fall off the turnip truck on his way to drafting these plans. If the AG knew and respected the cement contractor's work, he probably would not write down these points - they'd be understood. But the AG does not know who'll do the site work. So, this is a sign that the old geezer arrived in a pickup truck, ready for a hard day's work doing it the right way.
Now, we'll get to more down-to-earth details.
First, the stem wall.
There's a lot of important detail on this one - width, height, substrates, etc. It's all standard stuff for a really good contractor. Still, it's better to be safe and boring and obvious, than wish you had. Foundations are a mother to modify much or move.
This next one's a different story.
In squared-off foundations, the point here isn't usually worth making; however, there's nothing squared-off about this foundation. The point worth making: rebar and concrete have different coefficients of expansion and contraction, and we want the footings to hold up over time. Running laps incorrectly to the inside and not the outside at corners and not pinning them with vertical bars right at each of their turns is asking for trouble. This is little-to-no extra effort in formwork and pouring, and there is a big difference in durability.
Now comes the AG obsessive streak. He's sure that unless he makes this design point a heap of times in the drawings, the formwork will pass it by and the job's screwed. What's the obsession? That the existing concrete pad under the tub is to end up about 3" below the top of the stem wall and the new concrete pad. That's all this is saying. (And will say over and over again.) And don't you forget it.
Drainage is key to the long-term success of this building project. The soil on the site is very expansive. Shedding excess moisture from the foundation helps to assure structural stability. Drainage overall must be carefully planned. There are three water sources to shed: runoff, sanitary, and in-ground. This detail drawing makes two major points:
Finally, back to the more or less obvious. The AG is not interested in miscommunicating intentions. What's on his mind here is to make sure that the foundation is big and strong and stable. This drawing puts dots on some i's and crosses some t's. If there was any temptation to set a little footing and stem wall a little ways down in the ground, this should rid that weak-mindedness. Farther north and we'd go deeper. This bad boy is going down in the southern U.S. and should go down to stay put.
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