Expert: Richard Taylor, AIA - 7/1/2009

Question
Hi Richard

We are going to buy a brand new house. Actually it is still under contruction. According to the owner, when they build the basement, they dig out a lot of sand. I heard that building a house on sandy land is no good, as it may have settlement for the first 5 years and the brick may crack. This is my first question, so generally it is no good to build a house on sand land?

Secondly, I found the basement has some wet area(for 2 weeks and no windows around that areas), these few days we have showers (not rains) from time to time, I doubt the basement water proofing is no good.

pls advise whether it is wise to buy the house or not? or an further investigation for example is needed? should we find an inspector / engineer or architect to inspect it first? should an inspector ok?

Thanks

Answer
Jennifer - thanks for your question!

You're right to be concerned about the soil your foundation sits on.  While there's no "rule of thumb" regarding settling, soils differ greatly in their ability to support construction loads.

Sand doesn't compact like some other soil types do, which is good, but sand also doesn't support vertical loads well.  In coastal locations where sand is prevalant, foundations are made with pilings to increase the load-carrying capacity of the soil...very different than the typical "spread" concrete footing.

The presence of sand almost always indicates the presense of water, and that's bad for foundations since sand is easily eroded by moving water.  I assume that's why they've dug it all out.

Whenever suspicious soil types are found, the footings and foundation wall should be engineered to address them.  Ask the builder or architect if this was done...just removing the bad soil may not be enough.

Regarding the wet areas, it's going to remain wet inside the basement until the house is closed in and the foundation drainage system is completely installed - the water you're seeing now probably isn't anything to worry about.

But for your own sense of comfort, you might consider hiring an architect or other construction professional (not a home inspector) to review the house.

Assurances from the builder that the foundation won't be a problem aren't good enough; once the problems start, you'll be fighting with him endlessly.  Better to be absolutely sure right now that it's been done right, or walk away.

Hope this helps,

Richard Taylor, AIA
www.rtastudio.blogspot.com
www.rtastudio.com
www.rtaplans.com