Ask the Architect

The foundation: How deep?

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Q. We have a high water table and are being told our new foundation can only go down 2 feet before we hit water. The architect’s plans say we need to be below 3 feet, but the contractor says it’s either impossible or expensive. New York Rising won’t pay us for pumping water out (we checked), so we want to know how serious it would be to have a foundation that’s just 2 feet in the ground instead of 3.

A. It’s very serious. It’s a real concern that oceans and groundwater levels are rising. Boats are taken out of the water in the winter because the slow, constant pressure will crack a hull. You can demonstrate the potential damage a shallow foundation will create by taking a glass bottle — like an empty peanut butter jar — filling it with water and placing it in the freezer overnight. In the morning it will be cracked or broken apart. The same will happen with your foundation, and since concrete foundations are supposed to support heavy buildings, and since you won’t want to replace the foundation each year, a foundation depth below the natural 3-foot-deep frost line is critical.

Aside from building codes, the observation that frost, and freezing, occurs down to 3 feet below the surface has been a natural occurrence for hundreds of years (or more). Further north and at higher elevations, the frost depth is greater, and as weather changes become more extreme, frost will develop deeper each winter. In Alaska, the frost depth goes to 8 feet, and doesn’t defrost any deeper than 3 feet in most areas. That’s why trees in Alaska aren’t very tall and have shallow root systems.

You don’t want your foundation to heave or crack, so you must address the depth issue head on, and boldly decide that each section of concrete pile cap or foundation wall will need to have a water pump working and be poured in low-tide conditions with a formulation of concrete meant for wet areas. The other choice is one I haven’t seen anyone doing, but was common practice where I first designed pile foundations, above flood plains along the marshland edges of Lake Erie. We installed deep-bedded wood piles that extended out of the ground and acted as the structural support for building floors and walls. Today you can use fiberglass piles that do the same thing and won’t decay.

The real problem is that you’ve been teased by a very passive-aggressive NY Rising program that promised it would pay for everything, as I heard stated several times by construction managers, only to learn that once you committed, they started adding limits and qualifications that have little to do with the reality of building a home well that will last. Good luck!

© 2016 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.