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Most residential basements are 8 to 10 feet deep. You can dig deeper depending on building codes, but it does become more difficult. You’ll likely need to install stronger foundation walls and additional supports to handle the increased load. Depending on the water table, you may also need a water management system. Clay soil can support a deeper foundation than sandy soil. A structural engineer will be able to tell you the maximum, feasible depth.

Slab foundations are more affordable than crawl spaces because they require minimal excavation, as the slab sits directly on the ground or on footers that only sink a few feet into the ground. Crawl spaces require excavation of the entire footprint of the home to several feet below the surface. Not only does that mean higher labor costs, but more materials are necessary for the concrete foundation walls.

The best type of soil to build on is a mixture of sand and clay, known as loam soil. Loam soil has the best combination of these soil types to build a foundation on. The clay particles help with water retention, so it won’t erode like sandy soil might, and the sandy particles help with drainage, so you won’t see unsafe soil expansion or have an increased risk of leaks from water sitting against your foundation.

A perc test takes an average of around two hours, but it can range from one hour up to around six hours. Perc tests that require wider or deeper holes and those that require multiple holes dug throughout your property will take longer because there’s more excavation involved. The actual filling of the hole and monitoring to gauge the rate of percolation should take under an hour per hole.