This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The sill is the first part of the frame to be set in place. It rests directly on the underpinning and extends all around the building, being jointed at the corners and spliced where necessary; and since it is subject to much cutting and may be called upon to span quite considerable openings (for cellar windows, etc.) in the underpinning, it must be of a good size. Usually it is made of 6 X 6-inch square timber, but in good work it should be 6 X 8 inches and nothing lighter than 6X6 inches should be used except for piazza sills. For piazza sills a 4 X 6-inch timber may be used. The material is generally spruce, although sometimes it is Norway pine or native pine (depending upon the locality).
The sill should be placed on the wall far enough back from the outside face to allow for the water table, which is a part of the outside finish, which will be described later; and 1 inch should be regarded as the minimum distance between the outside face of the sill and the outside face of the underpinning, Fig. 92. A bed of mortar A, preferably of cement mortar, should be prepared on the top of the underpinning, in which the sill C should rest; and the under side of the sill should be painted with one or two coats of linseed oil to prevent it from absorbing moisture from the masonry. In many cases, at intervals of from 8 to 10 feet, long bolts B are set into the masonry. These bolts extend up through holes bored in the sill to receive them and are fastened at the top of the sill by a washer and a nut screwed down tight. They fasten the sill, and consequently the whole frame securely to the underpinning, and should always be provided in the case of light frames in exposed positions.
Fig. 91. Example of Balloon Framing.
The beams or "joists" D, which form the framework of the first floor, are supported at one or both ends by the sill and may be fastened to it in any one of several different ways. The ideal method is to nang the joist in a patent iron hanger fastened to the sill, as shown in Fig. 93, where A is the sill, B the joist, and C the hanger. In this case neither the sill nor the joist need be weakened by cutting, but it is too expensive a method for ordinary work, although the saving in labor largely offsets the cost of the hanger. The usual method is to cut a mortise in the sill to receive a tenon cut in the end of the joist, as shown at A in Fig. 94. The mortises are cut in the inside upper corner of the sill. They are about 4 inches deep and cut 2 inches into the width of the sill and are fixed in position by the spacing of the joists.
Fig. 92. Method of Setting Underpinning, Sill, and Joists.
Fig. 93. Joist Hung in Patent Hanger.
Fig. 94. Example of Sill Mortised to Receive Joist.
HARPER MEMORIAL LIBRARY BUILDING AT THE UNIVERSITY OF CHICAGO.
LIVING ROOM IN SUMMER COTTAGE FOR THE MISSES DUMMER, AT HARBOR POINT, MICH.
Pond & Pond, Architects.
Mortises are also cut in the sill to receive tenons cut in the lower ends of the studs, as shown at B in Fig. 95. They are cut the full thickness of the studding, about 1 1/2 inches in the width of the sill and about 2 inches deep. The position of these mortises is fixed by the spacing of the studding, and by the condition that the outer face of the studding must be flush with the outer face of the sill in order to leave a plain surface for the boarding.
The sills are usually halved and pinned together at the corners, as shown in Fig. 96; but sometimes they are fastened together by means of a tenon A cut in one sill, which fits into a mortise cut in the other, as shown in Fig. 97. This method may be stronger than the other, but the advantage gained is not sufficient to compensate for the extra labor involved. Sills under 20 feet in length should be made in one piece, but in some cases splicing may be necessary. In such cases a scarf joint should always be used, the splice should be made strong, and the pieces should be well fitted together.
Fig. 95. Sills Mortised to Receive Studs.
Fig. 96. Sills Halved and Pinned at Corners.
Fig. 97. Sills Sometimes Joined by Tenon Joint.
In some parts of the country it is customary to "build up" the sill from a number of planks 2 or 3 inches thick, which are spiked securely together. A 6 X 6-inch sill can be made in this way from three planks 2 inches thick and 6 inches wide, as shown in Fig. 98. Planks of any length may be used, and may be so arranged as to break joints with each other in order that the sill may be continuous without splicing. It is often easier and cheaper to build up a sill in this way than it is to use a large, solid timber, and if the parts are well spiked together, such a sill is fully as good as the other. When a sill of this kind is used, however, it should always be placed on the wall in such a way that the planks of which it is composed will rest on their edges, and not lie flat.