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 exterior wood framing of city buildings will in most cases be confined to roofs, since no exterior walls within the building limits of modern cities are allowed to be constructed of wood. Wooden roofs covered with slates or other fire-resisting materials are allowed, however, in many cities, up to a certain height above the sidewalk. The only difference which we shall find in this wooden construction, from the suburban house considered in Part I. will be, that usually the spaces to be covered are larger and the roofs must be consequently of heavier timber.
The same thing will be true of floors, and, from the variety of uses to which the buildings will be put, from comparatively light buildings to heavy stores or warehouses, a great range of floor construction will be required. For brick dwellings, the floor construction will differ little from the wooden house already described, the principal difference being the greater spans, and consequently heavier timbers, and also the fact that the outside bearings are taken by the brick walls instead of wooden girts. The joists in this case should run onto the wall at least four inches and should be bevelled, at the end, so that, in case of fire, the floors may fall without destroying the wall. (Fig. 168.) The joists must be anchored to the walls about every five feet with iron anchors secured to the joist at the side, and low down, to allow the joist to fall out if burned. These ties should be continued across the building by tying the inner ends of the joists together and putting an anchor in the opposite wall, in as nearly a direct line across the house as possible. All large timbers, such as girders, should have anchors and should rest on cast-iron wall plates. Partitions should have a stud set close against the brick wall and bolted to it, and all large openings, such as stair wells or skylights, should have headers hung to the trimmers by stirrup-irons or patent hangers, shown in Fig. 169.
SHOOTING LODGE FOR MR. ALBERT G. MEIER, HIGHGATE, MO.
Dean & Dean, Architects, Chicago, Ill.
Walls of Logs, and Roof of Split Shingles. Built in 1907.
PLAN OF SHOOTING LODGE FOR MR. ALBERT G. MEIER, HIGHGATE, MO, Dean & Dean, Architects, Chicago, Ill.
If there are openings in the brick walls which come so near to the bottom of the joists that an arch cannot be turned, a header should be cut in or a steel beam inserted in the wall. Joists are sometimes hung to the walls by hangers, and do not run into the wall at all; but while this preserves the full strength of the wall, it does not make so good a tie and is not generally done. The wall plate of a brick dwelling will usually be made of a plank the thickness of the wall, and secured by 3/4-inch bolts which are built into the wall, as in Fig. 170. These bolts should run at least twenty inches down into the wall, and have a large washer plate at their lower end. When the wall has been brought to the required height, the plate is bored with holes to fit the bolts, and a nut and washer screwed on. Over the plate the rafters are notched, and the roof constructed as for a wooden house. Store and Office Floors. In the construction of stores, warehouses, or office buildings, with wooden floors, the use of partitions for carrying the floor should be avoided, and columns and girders substituted. The reason for this is that, under heavy loads, the studding will often spring enough to crack the plastering, and besides, the occupancy of this class of buildings by different tenants will require numerous changes in the partitions from time to time. The large girders and posts also offer greater resistance to the action of fire, and permit of fewer concealed spaces. Many city laws require the use of brick walls, trusses, or columns and girders for support, if floor spans exceed thirty feet, and this is a good rule to observe.
Fig. 168. Bevelling of Joists.
Fig. 169. Joist Hangers.
In establishing a line of columns and girders, the columns should be spaced about twelve or fourteen feet apart for wooden girders, but can be brought up to twenty-five feet for the span of steel girders. If solid wooden posts are used, they will last better if bored from end to end through the center with a hole about an inch and a half, with a half-inch hole bored into the center at the top and bottom. This allows a circulation of air through the center of the post, and guards against dry rot, especially if the post is not thoroughly dry when set. This central boring should be done from one end, and, if it comes more than an inch out of center at either end, it will weaken the post and should be cause for rejection.
All wooden posts carrying girders and posts above, should have an iron cap with side plates to receive the girders, Fig. 171, allowing the post above to be supported directly by the post below, and not to stand on the girder. This must be done for two reasons. One reason is, if the girder ran over the top of the post and the post above were set upon it, the natural shrinkage of the girders would be multiplied by each succeeding floor, and in a building of four or five stories.
Fig. 170. Plate Bolt.
Fig. 171. Steel Post Cap.
this might amount to two or three inches, so that the upper floor beams at their inner end would be that much lower than the outer ends which are supported by the rigid masonry. Another reason is, that the crushing strength of the girder in its longitudinal position is not so great as the post standing on end, and it might be unable to support the accumulated weight of several stories. This support was formerly obtained entirely by the use of cast-iron pintles, Fig. 172, which are cast with top and bottom plates to fit the posts, the weight being transmitted by the cross-shaped metal. This is an effective method, but has been superseded by the more modern steel caps. The bearing of the girders should be at least five inches on either end, and a box hanger of some kind should be used to support the wall end of the girder, as shown in Fig. 173.