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customer wants a new front porch across the front of her house, 24’x 10′
there is a poured concrete slab at least 6″ thick there now and a small stoop I would like to use enginered floor joist to span the 24′ so i wouldn’t have to remove the whole slab, can these be used on the exterior??? there will be a roof., and i will be using syp porch flooring
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Does the slab extend beyond 10' from the house?
My problem would be that in order to get any type of decent performance from that span, you'd be looking at a 14" or 16" deep joist with maybe a 2 1/4" flange, 12", maybe 16" apart. I don't have my span tables handy. Still, you'll be looking at long-term deflection and the "drum syndrome" when you walk on it...you'd probably need to add sheet material on the bottom of the joists as well to reduce reverberation.
I'd consider a ledger attached to the house, then use a concrete blade to pop a few holes through the slab 10' away from the house. Spacing your posts 6' apart would only require 5 posts, 8' would require 4. Pour a footing, set your posts, run a built-up 24' beam across the posts, set 10' away from the house. Then set your 10' long joists from the header, out across the top of the beam.
You could use engineered, 24' long joists. While the floor may be strong enough to carry the load, and it may be stiff enough, it may just not feel right underfoot. Engineered joists can be peculiar that way.
If you're set on the 24' joists, at least consider popping one hole through the slab and running a 10' beam, perpendicular to the house, to support the engineered joists at mid-span. It would drastically reduce your required joist size and greatly improve the performance of the porch floor.
All that just concerns a 10' by 24' platform.
How about...the roof? If there is to be a roof overhead, how is it going to be supported? By posts attached to the 24' long front rim joist? (rut row...) Or will they run to the ground to simply sit on top of the slab, unattached? (rut row...) Or will you need to pop holes through the slab to construct a proper fotting and attachment points for the posts that will support the roof? If you're going to pop holes through the slab...go back up a couple of paragraphs.
I'd seriously consider cutting the slab back to within 9' of the house, then properly placing posts that would run up to support the roof. Hang your front beam off the posts, hang a ledger off the house, and run your 10' PT joists perpendicular to the house. By getting rid of the slab that goes beyond the front of the porch you'll be able to add more attractive lansdscaping/plantings instead of looking at the dreaded slab.
More work up front, but easier in the long haul. My opinion anyway. Good luck!
*Stan - Mongo has a point about the depth of a floor system possibly being a problem. I wouldn't suggest spanning that far with anything less than 18" deep. You can get either I-joists or floor trusses in those depths. Don't let anyone talk you into a shallower floor system by reducing the on-center spacing - That will result in the "drum effect" that Mongo mentioned.Keep in mind that if you use I-joists or floor trusses, they will have to be protected from the weather somehow.
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customer wants a new front porch across the front of her house, 24'x 10'
there is a poured concrete slab at least 6" thick there now and a small stoop I would like to use enginered floor joist to span the 24' so i wouldn't have to remove the whole slab, can these be used on the exterior??? there will be a roof., and i will be using syp porch flooring