Next dig a hole at one corner, about 18" in diameter and about 2½' or 3' in depth. In this hole set a post about 6" in diameter, sawed off squarely at the upper end, and of such a length that when pounded down to a firm and upright bearing the top of it will reach the string stretched between the levelling stakes. When you fill up the hole put in only a little earth at a time, "tamping" each layer compactly around the post with an iron bar or stick before adding more earth. Contrary to what one might naturally think, the earth can be tamped more compactly with a bar or stick than with a heavy joist.
Set another post in the same way at the next corner, fixing it accurately in position by means of the strings, as in the case of the first post, and seeing that the distance from the outside of this post to the outside of the first one is that required by the plan.
Set the other corner-posts in the same way, testing all the distances (including the diagonals) as before. You can try the height of each post now and then as you dig, and thus avoid making too deep a hole.
If you prefer, you can set all the posts in the right positions at first, but without trying to level the tops, merely seeing that the tops all stick up above the line. You can then strike a horizontal line all around with a cord, and saw all the posts off by this line—a process which you very likely have seen when watching the work on a pile-bridge or wharf. Sawing off the posts squarely will be much easier, however, before they are set in the ground.
The posts may be of locust, cedar, cypress, or chestnut. Locust is considered very durable, but is the most expensive. Cedar is excellent, and will be perfectly satisfactory. Chestnut will do very well for a house of this sort, and is comparatively cheap. If you do not mind the slight increase in cost, cedar is better. If you wish to be as economical as possible, chestnut will answer.[34]
The reason for selecting wood of greater natural durability for the posts than for the rest of the house is to withstand the greater exposure of the posts to alternate moisture and dryness. Timber will last for centuries if placed in a sheltered position and exposed to a free circulation of air. It will also last for a long period when immersed in fresh water or sunk underground, so as to be beyond the influence of atmospheric changes. But the alternate exposure to dryness and moisture, as in the case of posts partly above and partly below ground, or piles for a wharf or bridge, causes decay in a comparatively short time (see [Appendix]).
If your site is too rocky for posts, you will be saved some digging, but must provide a level and stable foundation in some other way. It rarely happens that the surface will be quite level, and you must use stone or timbers for underpinning. If there are one or two corners that must be raised, owing to inequality of the surface, and you cannot find large stones that will be sure to stay in place, you can rest the raised parts of the house upon posts securely braced. Rock is not the most desirable foundation for a building with a regular underpinning and cellar—the biblical parable to the contrary notwithstanding—and there is no foundation superior to sand or gravel (only the sand or gravel must be confined and not free to slide or move). But as your house merely rests on the surface, and has no cellar to be dug or drained, there is no disadvantage in putting it on a rock, provided you support it properly. Do not rest one end of it on a pile of loose cobble-stones, five feet high, only to have the stones slip some wet, stormy night and let the building down.
Having the foundation set, the next thing is the frame, which for a small building of this kind can be made of almost any kind of wood which you can readily obtain, provided, of course, that it is dry enough and not weakened by large knots or other defects.