2ft of fill for garage slab?

Me and my girlfriend are in the process of designing a house with an integral garage. The area is very flat and has a fairly high clay content. We want the house to be on an unvented crawlspace foundation approximately 2ft 6in above grade, due to the areas history of heavy rainfall and water levels reaching about 1ft above grade for a few days. We want the garage to also be 2ft 6in above grade, level with the house floor, and with a sloping driveway down to grade.

Given that the garage space will be enclosed by perimeter foundation, is it possible/sensible to fill the space with 2ft of compacted soil, gravel, moisture break and sand, and then place a 6 inch floating slab on top, to bring it level with the house floor?

We wish to avoid the high cost of having a solid elevated slab.

 

You can certainly do that.

When you refer to filling the area inside the perimeter foundation, you should use good, clean compactable soil (not clay). A mixture of sand and gravel would be good. Make the top 6" crusher run or some sort of base material and compact that. A vibrating plate compactor works best and compact in 6" layers. Damp (not wet) soil compacts best.

I would suggest having 4 to 8" of block projecting above your highest floor elevation to make cleaning easier. Slope the floor for drainage.

You code will probably require the garage floor to be 8" inches or so below the home's floor elevation. Check with you local code office for guidance.

A floating slab inside a perimeter is very common and is the standard method of construction in many areas. Unfortunately, builders usually do compact the soil and just cover up everything with a slab.

Good luck with your new home!!

Dick