Timber frame construction is an economic alternative to steel and concrete that possesses an aesthetic quality not found in light-frame construction. Timber-framed houses are preferred by many homeowners for a number of reasons, not the least of which is the fire resistance of heavy timbers. Heavy timbers are much slower to burn than light framing members and will retain their structural integrity long after other materials have been destroyed by fire.
Heavy timber construction is a building technique that has been practiced worldwide for centuries and has been enhanced by modern methods and materials. This article will give a brief overview of heavy timber construction and will discuss some of the elements and accessories that are unique to timber frame structures.
Working with Heavy Timbers
Heavy timbers are often used in combination with concrete or brick masonry. Connections between the 2 elemental materials must be secure but with a degree of flexibility. Timber in contact with masonry must be treated to prevent decay caused by moisture. Wood in particular is susceptible to thermal expansion and contraction especially in the direction perpendicular to its grain.
The structural connections described below are designed to accommodate minor shifts and settlements brought on by seasonal changes and moisture content. The problem can be eliminated completely by substituting laminated beams for heavy timbers.
A heavy timber beam can terminate at a load-bearing masonry wall in several ways. A typical connection consists of a beam anchored with bolts to a steel plate bearing on a recession in the masonry wall. The beam end is chamfered so that if it fails or rotates out of the pocket, it will not bring down the entire wall.
One method for interior girder/column connections makes use of a cast-iron pintle that joins the column base to the supporting girder, and a steel column cap that joins the column to the girder above with lag screws. An alternate method has the upper column bearing directly on the column below separated by a steel bearing plate.
Instead of bearing on the columns themselves, the intersecting beams are supported by bearing blocks secured to the columns with split ring connectors. Tongue and groove decking is installed directly onto the beams, covered by a layer of the finished flooring.
Both sawn and laminated timbers can be used to erect the structural framework of a timber frame house. Long curved timbers reminiscent of the early cruck frames can be fabricated from laminated wood to form the massive arches seen in many churches or auditoriums.
Timber roof frames for residential structures generally make use of some type of truss. The timbers used to construct the top chords, bottom chords, and diagonal bracing are bolted together with steel plate connectors and reinforced with steel tension rods.
Lateral bracing is provided by purlin equally spaced along each top chord and spanning the length of the roof. Roof decking is installed at right angles onto the purlin.