Fig. 4
WOODEN FORM FOR PIERS
The number of foundation supports or piers will be determined by the size of the house. “Not less than seven feet on centers” is a good rule of thumb.
Concrete piers are not hard to make. Their size will depend on how deep you must dig to reach solid earth or rock. First, build several tapered box forms of rough lumber. ([Fig. 4].) These should be about 24 inches square at the bottom and taper to about 12 inches at the top. The taper makes it easier to get the forms off the finished concrete. Pour a footing of concrete at least 10 inches thick and six inches larger than the bottom of the pier on all sides. Then set the form for the pier on top of this footing.
A satisfactory mixture for foundation piers is one part Portland cement, two parts clean sand, and three parts gravel—two-inch aggregate is about right. It is a good idea to add to the mixture hydrated lime—about 10 per cent of the bulk of the cement—to prevent the mass from setting too rapidly and to make it work more smoothly.
This type of foundation allows perfect ventilation under the cabin, but it will not keep out wandering rabbits and other night prowlers.
A boulder foundation is quite enough for the average semi-permanent summer cabin unless you plan to spend time there during the winter, in which case an all-around foundation is advisable to keep out the cold.
Full concrete or rock foundations are more expensive and more work to build but hard to beat for permanence. To construct them, dig a trench to the dimensions of your cabin but at least twice as wide as your finished foundation wall is to be and to solid ground below the frost line. Pour in a “footing” of concrete to a depth of 10 inches. This base will distribute the weight of the cabin. ([Fig. 5].) On this footing build wooden form walls to the proper height—about one foot above ground level at the highest point of your grade is usual—and fill them up with the proper mixture of concrete. To prevent dry rot of the wood construction, air vents should be constructed at intervals in the concrete wall above grade. These should be covered with screening to keep small animals out. Thickness of foundation walls varies according to the weight of the building. A good rule is to make the top of the foundation two inches wider than the logs or timbers it is to support.
