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.
[Illustration: Fig. 5]
BOLT FOR SILL LOG
METAL TERMITE GUARD
CROSS SECTION OF FOUNDATION WALL
The sill logs or timbers are laid on top of the foundation. If your
cabin is to be of logs, select a number of the strongest and straightest
and lay them so as to form the outside “frame” of the cabin. They should
be bolted tightly to the concrete by means of long iron bolts previously
buried in the foundation walls. If the sills are to rest on piers or
boulders, spike them together. The weight of the cabin will hold the
sills in place. The 2×6 floor joists are cut in or notched over the
sills. They should be set with the 2-inch side uppermost and securely
spiked.
The footing for the fireplace is made just like the concrete
foundations—6 or 8 inches beyond the dimensions of the fireplace plus
the hearth. Pour a slab of concrete about 10 inches deep, in which are
buried ½ inch steel rods laid in both directions—checkerboard
fashion—and wired at the intersections. This may seem like a lot of
extra work but the steel rods prevent settling and cracking. On this
slab build a wooden form to the height of the bottom of the floor joists
and fill with a mixture of concrete, sand and plenty of small boulders.
At this point block off the section to be used for the hearth and fill
in the fireplace proper up to the floor level. This will leave a space
to be filled in later with hearthstones, brick or whatever you decide to
use for the hearth.
[Illustration: Reinforcing rods in fireplace base.]