Okay, so it really is a word, but one that none of us in the real world has ever used or heard before; or will ever actually have pass over our lips while talking to other real humans. “Honey, will you please knock down the spider web in the corner there, yes, the reentrant corner by the stairs.”
Before moving on to something actually useful, here is an interesting side note. The new International Residential Code (IRC) doesn’t call them “reentrant”, but rather, interior, and for that matter, exterior; and actually has a diagram of same, Figure R602.10.5. This is such a critical piece of information, and I assume most readers of this column don’t walk around with a copy of the IRC strapped to their belt, that I have reproduced that sketch here (courtesy of the International Code Council, 2003 International Residential Code).
You will note the striking similarity between these two sketches. Detail (b) is the “reentrant” corner because gypsum wall board should always be on the “inside” of the building.
Now, lets say you’re pouring a slab with a “reentrant” corner. Here is a sketch showing where my previously mentioned two sticks of rebar should go to minimize the crack. (To avoid confusion, the grass and shrubs go on the “outside” of the building.)
Another thing you should know about “reentrant” corners: if you have one and it is a “bad” one (i.e. pokes more than 15% of the building’s overall dimension inward), and you are in seismic zone D, E or F (the “bad” seismic zones), you will have to overdesign certain earthquake resisting elements by 25% (IBC1620.4.1).
To answer the question about in-floor heating (a.k.a. “hydronic”) and slab thickness, I offer my own experience. The main floor of my house is wood-framed with a 1-1/2-inch thick stained concrete cap with hydronic heating tubes throughout. There are 3/8-inch deep sawcuts at 3-feet, each way. Other than some aesthetic stain/sealer problems that had nothing to do with thickness, my floor has performed beautifully. I know others insist on using thicker slabs with hydronic, but my experience doesn’t support that notion. My greatest concern was grazing a heating tube while saw cutting, but I had a real pro on the saw, and it didn’t happen.
Postscript. All this business about “reentrant” brings to mind a couple other important terms you can impress your friends with: minutiae – trifles, details; and esoteric – used and understood by a select few.
Tim Garrison of ConstructionCalc.com, is a professional engineer, author and software producer for the building industry. Send e-mail to buildersengineer@constructioncalc.com. Tim reads every one.
This column cannot be reprinted without permission from the author.
The views expressed in this article represent the personal views, statements and opinions of the author and do not necessarily represent the views, statements, opinions or policies of the National Association of Home Builders. NAHB does not necessarily endorse any of the views expressed by the author and NAHB is not responsible for any direct or indirect consequences arising out of the views expressed in this article.
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