Know Your Building Lot

In your mind you’ve got a dream house, but in reality you have a building lot. Before you get locked into a building plan, research your site, because site conditions affect your design and the cost to build it. No designer should draw house plans for you without a detailed site plan, and no builder should estimate the construction costs without knowing what’s under foot.

Gathering Information

It’s best to have complete site information before you build, but you can gather a lot of good data on your own before you hire a civil or geotechnical engineer. Ask neighbors; they’ll probably know if there’s a ledge, a high water table, or problem soils. Get a local soils map from the building department or local library. Take a good look at the site, noticing exposed rock, water plants, or new plant growth that may indicate fill.

Start with Soil

Since you may have layers of different soil types on site, your builder and designer need to know what’s there. The critical layers go from the surface down to about eight feet below the depth of your planned foundation.

Foundation codes are written for sand or gravel soils, which are the best natural soils for construction. Heavier silts and softer clays are not ideal and may require more than the minimum code requirements. Most building departments will want information on soils before they sign off on a permit; they may even require an engineer’s site report or stamp on your foundation design.

An engineering report is based on a site survey and test pit samples. If real problem soils are suspected, the engineer may do “soil borings,” but they are usually reserved for commercial projects.