The Slab Decision
We are excited about Helical Pier Foundations. However, for the purpose of Seed Home 2 - the slab has a distinct labor advantage in rollout - Phase 1. Here's why:
- Overall house cost is comparable. A slab appears to be more expensive by itelf(estimated $10/sf based on $8k avarege + $1k gravel + $1k excavation) see Concrete Slab.
- Owner-builder labor is reduced significantly. In our model, a foundation is outsourced (beyond the scope of a novice owner-builder) - whether helical pier or concrete slab. In the slab case - the labor savings is the floor. In the helical pier case - a framed floor module with 3/4" plywood is no longer needed! That is 1-2 days of work saved.
- Our Seed Home 2 budget has $1611 for floor, and $1500 for foundation (per 256 sf). This is a total budget of $12444 for 1000 sf for the floor + foundation. We are likely to get a concrete slab foundation for $10k, and the other $2k can go for floor finish (polished concrete, vinyl, carpet).
- Unknown - for expandability upwards, we require 8000 lb per pier. This indicates higher pier foundation costs, as a 3-helix 10' P2 Pier cannot hold 8000 lb - it needs an extension with additional 2-3 helices - in 1500 psi clay soil. This would be fine in stronger soils, but we're trying for a more robust solution.
