216. Girders should never be laid over openings, such as doors or windows, if it can be avoided; but when it is absolutely necessary so to lay them, the wall-plates, or templets, must be made strong, and long enough to throw the weight well upon the piers. It is, however, a bad practice to lay girders very obliquely across the rooms; it is sometimes better to use a strong piece as a wall-plate.

In the bearings of floors the caution of Vitruvius must be attended to; that is, when the ends of the joists are supported by external walls of considerable height, the middle part of the joists should never rest upon a partition wall that does not go higher than the floor; * otherwise the unequal settlement of the walls will cause the floor to be out of level, and most likely fracture the cornices.

217. Wall-plates and templets should be made stronger as the span of the girder is increased; the following proportions may serve for general purposes:

in.

in.

For a 20-feet bearing, wall-platea ......................

4 1/2

by

3

30

"

" .....................

6

"

4

40

"

" ..................... ..

7 1/2

"

5

218. Floors when first framed should always be kept about three-fourths of an inch higher in the middle than at the sides of a room; also the ceiling joists should be fixed about three-fourths of an inch in 20 feet higher in the middle than at the sides of the room; as all floors, however well constructed, will settle in some degree.

In laying the flooring, the boards should be made to rise a little under the doorways, in order that the doors may shut close without dragging; and to assist in making them clear the carpet.

* ' Vitruvius,' lib. vii., cap. 1.

The following observations, from Evelyn's ' Silva,' are worthy of notice: "To prevent all possible accidents, when you lay floors, let the joints be shot, fitted, and tacked down only the first year, nailing them for good and all the next; and by this means they will lie stanch, close, and without shrinking in the least, as if they were all of one piece: and upon this occasion I am to add an observation that may prove of no small use to builders, that if one take up deal boards that may have laid in the floor an hundred years, and shoot them again, they will certainly shrink (toties quoties) without the former method." *