Topic Title

I don't deal with the bidding side of things too much and I can't get ahold of my normal go-to's for cost estimating so thought I'd see if I could pick your brains. What would be a rough number for the cost increase for construction of going from a 4" standard concrete slab to a 18" raised wood floor system (11-7/8" joists) on a simple 2 story residence? (see attached sketch) Wouldn't include front porch. Obviously I know there are tons of variables but I am just looking for a big ballpark idea. I have one number but it seems too high. Thanks!

Josh,

Clarifying question: what is the 18" floor referring to? 2x12's plus 3/4" subfloor on a double 2x sill on ... ?

I would think the 18" reference is between wood and ground so not to be required to use Pressure Treated Lumber per code.

So, a frost wall and the floor framing over a gravel crawl space (greater than 18" high)?

We don't have to deal with a great frost depth out here (minimum footing depth is usually 12" below grade) and I think Josh's 18" reference is from grade to top of finished plywood/OSB.

I've never looked at a cost difference because most clients out here would do a slab only, unless the grade differential was so great that you'd spend WAY more on trying to form the footings/grade beams/stem walls and backfill just to get a slab. My gut guess is that it's going to be slightly more expensive to go to the raised wood floor than a slab **IF** it's a flat site; if it's a sloping site it will be less expensive to go with the raised wood floor.

I don't have an actual cost to offer up but I would guess that the wood floor system over a crawlspace with a perimeter foundation wall and footing would be about double the cost of a slag-on-ground system. I think that the cost of the foundation wall and associated footings and piers would about equal the cost of what an overall slab-on-ground might cost. So, the cost of the wood floor system would then be a complete additional cost over the slab option.

There might be associated advantages to a wood floor system over a crawlspace, such as accessibility to put piping in the crawlspace (and always be able to get to it) and having a "softer" and warmer floor to walk on in the house, but they are intangibles and not cost considerations.