How do I design and build an addition using a concrete slab-on-grade foundation?
Typically, you will need a foundation applicable to your climate zone. You need four inches of gravel base, six-mil plastic sheeting on top of the gravel, and then four inches of 2,500 to 3,000 psi concrete. Some jurisdictions require perimeter insulation and reinforcement in the slab. Check with your local building department before starting work to learn of their requirements and if there are any required permits and inspections.
