Jon,
You have received a lot of good advice from the list regarding your garage
project. A couple of points I can think of ....
Local conditions play a big role; meaning climate, code issues, and your
particular site.
People here in Maine are quite skeptical of slabs, and tend to overbuild
them as a result. 4 inches of thickness is plenty, even with 3,000 PSI
concrete, in terms of wheel loading from normal passenger vehicles. But,
properly detailed and installed reinforcement, careful placement, minimal
slump ( not letting the driver add too much water to the mix at delivery ),
and thickening under load bearing walls and columns ( and lift footings )
is desirable. Doing a good floor is a very particular skill largely
unrelated to other masonry and concrete work. Find a good contractor and
check out some examples of his installations.
Your original question concerned vapor barriers. I have no experience in
places like New Mexico, but in a temperate climate, they are essential if
you want to heat the space during the cold months. For ground contact uses
I like ultra heavy ( 20 mil+ ) poly...one brand name is tu-tuff, with an
integral fiber scrim like rip-stop nylon. If you are in a really cold
climate and particularly if you are considering the in-floor heating, an
investment in properly installed rigid insulation made for ground contact
under the slab would be highly recommended.
Another type of radiant heat uses ceiling-mounted gas fired steel tube
burners that are essentially horizontal chimneys. They heat the objects in
a space rather than the air...( tools, vehicles, floor ). Very nice, and
cost effective compared to the in-slab, but not as toasty.
Regarding compressed air, I've seen shops pre-plumbed with both PVC plastic
and copper water pipe used as air lines to selected locations, where flex
hoses could then be plugged in closer to the work. Allow for drainage of
condensate at low points, especially with metal pipe.
If you are limited to length of the building, a door in both ends can be
handy. This is a very site-specific consideration, however.
If you can't buy all the size you'd like to have right away, design the
location and structure to be easily modified for expansion.
Happy building,
Richard McSherry
Norway, Maine
...too many cars, not enough garage
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