Slab vs Crawl Space Cost

Quick Summary:

• Compare slab to crawl space wood floor cost
• Pros and Cons of slab
• Pros and Cons of crawl space wood floor

Karen lives in Saint Cloud, Florida. She emailed me the following:

"I would like to build a home that is about 600 sq ft with 1000 sq ft roof to cover the front patio and side carport. Would it be less expensive to pour a concrete slab or a crawl space foundation?"

She's like many consumers and wants to know what different things cost for any number of reasons. In this case she wants to know the difference between a slab foundation and a home that has a crawl space with a wood subfloor.

Without definitive specifications, it's almost impossible to quote a price. For example, will the slab have reinforcing steel in it or not? It should so all shrinkage cracks stay hairline and don't spread.

What type of wood joists would be used? Regular dimensional lumber, engineered floor joists? Would the lumber be treated to be less appetizing for termites that congregate in the moist sub-tropical Florida environment? 

Does the lot slope and would a slab require lots of fill that costs money?

But before you get frustrated and stop reading, you can do some quick calculations to see how the chips may fall.

Here's the quick list of the major material items you need to calculate for a slab:

• site preparation and fill
• termite pretreatment
• vapor barrier
• type and amount of steel reinforcing
• cubic yards of concrete - don't forget to check with local code officials to see if the edges of the slab need to be thickened for frost protection and bearing wall requirements

Here's the quick material list for a crawl space wood floor system:

• site preparation for footer trenches
• concrete for footer
• reinforcing steel for footer
• concrete block or poured concrete for crawl space walls
• steel i-beam for floor joist support
• wood joists and sill plates
• wood subfloor
• termite pretreatment
• high-performance vapor barrier

You'll probably discover the crawl space wood floor system materials cost more than the slab foundation. The amount of concrete or masonry involved in the crawl space starts to approach the total cubic yards of concrete required for a slab foundation, especially if you do the right thing and fill the voids in the block walls with pea gravel concrete.

But wait, there's more - as is often said in an infomercial on late-night TV!

What are the benefits of a slab versus a crawl space wood floor system?

Slab Pros and Cons:

• Cooler floor surface on hot days
• Great solid surface for tile installation
• Plumbing drain pipes inaccessible in future
• Slab failure / settlement expensive to fix

Crawl Space Wood Floor Pros and Cons:

• Termites will eventually eat the wood
• Ceramic Tile requires special underlayments and FLAT floors
• Cool floor if covered with tile
• Complete access to all plumbing and any other mechanical systems in crawl space

You can see it's not an easy decision and there's a reason why many many floor systems in Florida and the South are concrete slabs.