The four most widely used methods of wood-frame
construction over the past two hundred years are braced-frame, balloon
frame, and platform frame, and lightweight wood truss construction.
Braced-Frame Construction In the eighteenth and nineteenth centuries, the first large wood-frame buildings constructed along the East Coast, which still stand today, were of braced-frame construction, sometimes called "post-and-girt" construction. This type of wood-frame structure has a braced framework of vertical timbers called "posts," which are positioned at each of the four corners of the building, and horizontal timbers called "girts," which are found at each floor level. These large timbers reinforce the entire two-by-four-inch wood-frame structure and are connected together by mortise-and-tenon joints. (The large timbers and the mortise-and-tenon joints are indicators of braced-frame construction.) The ends of the horizontal timbers are cut down to fit mortise openings which are cut through the vertical timbers.
As the population moved westward in the nineteenth century, the need for housing increased, and cut and finished large timbers and skilled craftsmen became scarce. A lightweight, quickly assembled wood structure, which needed no large timbers, called "balloon frame construction" replaced the older Eastern braced-frame method of constructing wood structures. To erect a balloon frame structure, four wood exterior walls are constructed flat on the ground. Two-by-four-inch wood studs, extending in one piece for the full height of the wall, form the enclosing walls; the four walls are then lifted upright from the ground and connected like a box at the corners. The advantage of this type of wood construction is speed and the absence of large timbers. The drawback is a vertical void between the wall studs, which extends from the foundation sill to the attic cap and allows hidden fire and smoke that penetrate the wall space to spread vertically for two or three floors. This unobstructed opening between each stud in the exterior wall, extending from the foundation sill to the attic cap, is an indicator of balloon construction.
The platform construction method builds a structure one level at a time. One complete level of two-by-four-inch wood enclosing walls are raised and nailed together; the floor beams and deck for the next level are placed on top of these walls. The next level of two-by-four-inch wood enclosing walls are constructed on top of the first, and the floor beams and deck for the next level are placed on top of these exterior walls.
Lightweight wood truss construction is the most common type of wood construction built today. Sheet metal surface fasteners are used to connect the truss members. The photo to the right shows a burn truss with remaining sheet metal fasteners. The burning truss floors and roof can collapse within 10 minutes of the arrival of the firefighters. It is not possible to extinguish a fire in the concealed spaces of lightweight wood construction. Easy and inexpensive construction results in more dangerous buildings for fire fighters than platform construction, which in turn are more dangerous than solid stone and brick houses which are no longer built in the U.S.A. | |||
 Insulation (yellow) where the roof and the wall join; white is base for stucco; and lower down, bricks. |
 Brick veneer over a wooden frame as shown in the overhand with lighting
fixtures. |
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