Expert: Ted Barnhill (Principal, Design45 LLC) - 4/26/2008

Question
QUESTION: Hi Ted,   I am interested in converting a cottage built in 1940 to a year round residence.  The cottage is currently on concrete and stone piers and I would like to replace them with a real foundation or crawl space.  In the west side the piers are about 36" above the ground and about 12" on the east side.  The cottage has dimension of 32 X 26 with a center fireplace. What is the best way to winterize the home?   Should I find someone to raise the home and add a poured concrete foundation or will it be as effective to create a crawl space with a dirt/gravel floor?

ANSWER: Johan,

The answer would depend on your needs and goals.  Would you like a basement for storage, mechanicals, tornado-shelter...?  How concerned are you with the exterior look of the foundation?  Are the piers and beams structurally adequate, or is there a structural reason for the new foundation?

If your piers are structurally adequate, to create a crawlspace that will keep frost and critters out from under your home you need only build insulated walls between your piers down to the frost line.  These can be permanent treated wood walls resting on well-drained gravel, or more commonly, masonry.  Although it will require a lot of hand-digging, these could be built without disturbing the existing home.

On the other hand, if you want a basement, or have other structural needs, it is possible to raise the cottage and build a full poured or block foundation under it.  If you have enough space, you could also relocate the cottage onto a new foundation that you build elsewhere on your lot.

Incidentally, I have heard the opinion among building scientists that a properly-done pier foundation is the best from a durability and health point of view, as you remove any contact with ground moisture.  Of course, you have to provide a winterized plumbing chase and solve the problem of cold floors.  If you chose this route, you might look at using hydronic floor heating depending on your climate and budget.

Good luck, and feel free to post follow up-questions.  -Ted



---------- FOLLOW-UP ----------

QUESTION: Hi Ted,   I like the alternative of hand digging a basement but I worry that I would have to go deeper than the piers to reach the frostline.  The only thing that the crawlspace would need to be used for is a heating unit. The floors are oak hardwood and I would like to keep them.  How do I learn where the frost line is.   The home is in New Hampshire at 1100 ft elevation and even though it is nearly May there is a small patch of snow in the shade.  Thanks.
Johan

Answer
Johan,

Obviously it is crucial to know the local frost depth as well as the depth of your existing piers.  The frost depth locally will be common knowledge to local experienced contractors, though in some areas the frost depth varies significantly within a county due to elevation changes.  The definitive source for your frost depth is your municipal building department.  This might be in your city, township, or county - whoever issues building permits for your area.

Good luck, and feel free to follow-up with more questions.  -Ted