Slab on grade house and garage : can I pour the floors once the shell is up?
I currently have the footings frost walls (4′), and the sandy base filled in and tamped for the slab. The house is roughly 50’X30′, 2 storey, and the floor joists can technically span 30′ (24″ deep trusses), but the plan has a “supporting” wall roughly in the middle of the width to keep the floor span at 15-17′.
The garage is 30’X40′, with no supporting walls (wide open).
My question is, I know I can raise the shell of the garage before pouring the slab (with 12′ ceilings access will be fine through the 16′ garage doors), but what about the house? Can I frame up the outside walls, get the floor trusses and floor installed, and then pour the slab? Will the floor trusses sag at their max 30′ span? Will if be hard to “jack them up” once the slab is poured and the supporting mid span wall can be installed? Is it wotth while to install a temporary mid span wall on the sand base, and just remove it when the floors are glued and screwed, just before the slab pour?
Ideally i would pour both slabs before the framing, but concrete contractor does not recommend open pour because he fears the slab may dry to quickly. Also having the shell and floor up would probably make the poly/foam/in floor radiant tubing install easier as I would be protected from the weather.
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I wouldnt even think about not pouring the crawl slab before building, for all sorts of reasons.
And I hope you're thickening the slab under your midspan wall. Crawl slab doesnt need to be pretty so if that slab gets away from him, so what? Not to mention he can have a retarder put in the mix.
T. Carlson,
The way I read the question, Mai Tai is talking about a slab on grade, not a crawl space slab.
Mai Tai,
In light of the need for a bearing wall in the middle of the house, I agree with T. Carlson. Pour the slab before installing the floor joists, and make sure that an engineer has looked at the slab thickness to ensure that the center of the slab can bear the expected weight.
There is a supporting frost wall in the middle of the span to take the loads. Thanks for the confirmation, looks like I will be looking for a 4 day no rain window to install poly/foam/tubing and pour (ideally followed by a few days of light rain after the first "set" day).
Mai Tai,
There are lots of ways to delay curing of a slab (thereby improving the concrete strength), ranging from polyethylene to damp burlap to hay to using a sprinkler to applying a liquid-applied evaporation reducer.
More information here: How to Manage Moisture Loss and Temperature of Freshly Placed Concrete.
Ha, thats makes a little more sense than crawling around in a crawlspace but in light of my stupidity, and the fact their is bearing midspan, you could frame the midspan wall on layers of treated 2x and frame the whole thing and pour.
I wouldnt want to build on sand and wouldnt personally do it that way, but its not out of the question.
I framed my passive solar house and shingled the roof before pouring the slab on grade inside the frost walls. Mostly because of lack of money. So the framing wouldn't be as exposed to the weather if I couldn't secure more funding quickly. Used a wheelbarrow to move concrete around the interior, more work.
Reading your question, it seems you are asking structural questions that an engineer or truss supplier should answer before your finalize your design.
Mai Tai, there is a good chance your 24" floor trusses can span 30' without failing; they will just be bouncy until you install the center support. But it depends entirely on the truss design, so it's a good question for your engineer or truss manufacturer.
Having always worked where the weather is unpredictable, if the slab is intended to remain exposed, I prefer to pour after the roof is on; it's sometimes necessary for scheduling reasons anyway. The only issues are access and moisture load, which are serious concerns, so if you choose that route, make sure you have considered both.
If you choose an open pour, you should be able to install everything except the concrete without worrying about the weather. If rain turns your vapor retarder into a pool liner, use a sump pump and/or shop-vac to get most of the water out. A little extra water at the bottom won't matter once the concrete is placed.
A few more tidbits:
I have already planned on using liquid applied evaporation reducer on all surfaces (front porch, garage and house slabs). Apparently they use Diamond Clear 350, which looks fine.
Mike,
Thanks for confirming water will not be a huge issue. I was actually thinking of embedding some small pieces of vinyl tubing to reach below the foam, so I can suction any water up and over the frost walls if need be.
Martin,
It's a tough call, as most slab covers (tarps paper etc.) tend to impart a mottled finish to the slab. Since I would like to run the slab bare for the foreseeable, I'd like to to avoid that if possible.