Grump, I think Subfixer there got it about right, depending on size, the ONE thing you need make damn good and sure of down here in Florida is the SITE PREP, this sandbar has a nasty habit of not supporting concrete slabs very well, witness the slab breakups in most modern developments, there are homes with slab breaks and those that WILL HAVE slab breaks....trust me on this, I seen lots of it, LOTS....I"m in the home remodeling business, get tons of calls over this and other problems associated with lousey land and site prep.....
what you need do is put in the foundation about 2' wide and 2' deep, solid contrete with reedbar, and forget the fiberglass---A Florida highway /bridge engineer customer of mine said he has no faith in the added fiberglass--it don't hurt anything, he just sees no help....frankly I have the fiberglass in a 6" thick slab I poured...only 14x16 but it's got a hairline in it, with only less than a year old,.....and it was well prepped so I thought.....but then again, I"m pickey....
so you let that settle under plenty of rainfall over a month or more, use a lawn sprinkler if you have to.....grade out the land nice and smooth....
now you want to put about 1-3 layers of block around the edged, onto which you will put your 2x4 sills and studs, or 2x6 if you want strength....hurry-cains do arrive....
of course the blocks are all filled with concrete and the tie down studs are every 2' into the pressure treated sill, and then the tie down straps on every stud.....I recommend 2x6 and 16" centers, overkill and expensive, but worth it in the long run....
on the outside I would use the 4x8 Hardiboard, and NOT ANY WOOD PRODUCT.....that Hardiboard is a masonry product and so is totally waterproof, with a coat of primer and 2 coats of paint, you good for decades, not just years....
now depending on your roof/trusses/strength needs, you may want just 2x4 trusses, or maybe 2x6 with a beam and deck up there for storage... up to you....I favor the open attic so I can store crap....but it's expensive....no lie....
IF you got the bux, you may want to use 3/4 ply for underlayment and SCREW it down with galvanized sheetrock screws into the rafters...every 12 inches in middle and every 6" along the edges.....this way it's NOT blowing off with anything less than a tornado...period, end of conversation...
course if you in a flood plain....well good freaking luck, you need it....;-(((
I heartily recommend at least ONE layer of block around edges, for the extra height, and weatherproofing, all backfill for slab need wetted down, of course....and let sit untill settled in, no sinking feeling/cracks that way...
GENE
