Expert: Roger Zona - 3/22/2010

Question
We are currently making an offer on a new construction house to be built on a lot just 3 doors down from where we live. The lot lies on a grade down from our current house, and the grade continues for another block before leveling out. In talking to the contractor, he told us that he was planning a house without a basement, but just a 4 foot crawl space. This was basically to keep the cost of the house down. However, when we looked at the plans and the builders agreement sent to our Realtor, both stated that it was to be a slab house (4 inch slab over rock and visqueen.) We had been told that a slab house where water could be a problem was a bad idea. Would one be better than the other, or are they just different. And how much do I have to worry about the grade in either case?  Thank You

Answer
Hello Michael,

Your question is well timed.  Never enter into a contract without knowing all the specifications that should be either on the Architect's plans or completely outlined in the contract.

You didn't say where you are located so I can't address the grade issue completely. What must be considered is the depth of the water table, the type of soil, the absorption rate and the underground infrastructure for storm water.  Also, do you have a freezing winter and how deep is the normal frost line?  Is a basement a poor structure because of the drainage and water table?  These considerations are important in making a decision.  I highly recommend you meet with your Building Department (in your city or county) and ask them about the various types of foundations and structures.  

I'm in Florida and we build "slab on grade" nearly everywhere.  Our soil is sandy and drains rapidly.  However, the water table is not very deep.  

Lets assume your house will be built on soil other than sand.  Water absorption is slow in clay and other soils. I personally like a crawl space - as long as it is deep enough to move around easily.  If the frost line is 2', then the bottom of the footings should be at about 3'.  Then with a block wall five courses high, you will have ample space.  Next I recommend that the entire crawl space be excavated to the depth of the top of the footing, then poison the ground, install a layer of visqueen folded at the laps and a 2" slurry coat of concrete be poured over the visqueen.  Also don't forget to provide an access to the crawl space and ventilation with screening that can be repaired or replaced.

The house will then have a wood structure floor and you can use many types of floor coverings including hardwood or laminate or tile or carpet. Plus a wood deck is much more comfortable to walk or stand on.  You can have the heating and A/C duct system in the crawl space with a down draft air handler or even install the air handler in the crawl space.  

Slab on grade is obviously less costly.  If the frost line is deep, it would be wise to have a basement.  You should provide extra drainage around any type of foundation since your lot is not at the crest.  Here in Florida we cannot allow rainwater to drain onto a neighbors property.  We must provide swales and storm drainage.

How are the other homes in your area built? With basements, crawl space or slab?  If you have options, then your budget may dictate the method.  

I hope this has been helpful.

Roger
Ask The Contractor

You may contact me directly at askthecontractor@live.com