Timber Frame Houses
As shelters grew in size, so did the posts and beams needed to support them, and a system for assembling ever-more-complex structures developed. In the process, the various components acquired names according to their place in this system — king post, hammer beam, purlin, sill, and so forth — names that are still used today.
Without the benefit of industrial hardware, early framers also created and refined the elegant wood-to-wood joinery techniques that remain the hallmark of timber post-and-beam construction.
The Timber-Frame Difference
The woodwork that makes up a timber-frame house is designed as much for its handsome, graceful symmetry as for its strength and longevity. Its rugged posts and beams are invariably left fully exposed, giving interiors an architectural grandeur that surprises and delights, while providing the structure upon which the rest of the house is built.
By contrast, conventional "stick-built" houses — made with studs, joists, and rafters fashioned from dressed, or dimensional, lumber — have a wood framework that is meant to be hidden beneath drywall, paneling, and other finished materials.
According to standard lumber classifications, a timber is a length of wood with a dimensional cross section greater than five inches (13 centimeters) on each side. Of course, the posts and beams that make up a timber frame can be, and usually are, considerably larger.
Mill construction, a specific fire-code designation, calls for even larger structural wood-frame members starting at a minimum of eight inches (20 centimeters) on a side. (Because heavy, solid-wood beams char slowly rather than burn up, they are fire resistant to some extent and provide a dependable means of fire rating for insurance purposes.)
However, post-and-beam is often used as a general descriptive term without specific size or strength limits. A post is simply a vertical wood member, and beams are horizontal components.
When it comes to actual construction, the terms timber framing and post-and-beam framing are virtually synonymous, but there is a subtle difference between the two.
Post-and-beam structures are more expedient in their design and assembly. Commonly available materials such as laminated, or "engineered," lumber may be used, and the components are typically fastened with stainless-steel carriage bolts, brackets, and other modem fasteners.
Timber framing, on the other hand, evokes a centuries-old building craft and refers as much to its art as its construction. The timbers are often cut and dressed by hand, jointed and interlocked in the traditional way, and fastened throughout with wood pegs called trunnels, or "tree nails."
On occasion, special hardware may be required by local building codes or to ensure strength in a particular joint, but the framers work hard to de-emphasize its presence. "We use mostly mortise-and-tenon joints in our frames," explains Richard Neroni of Timberpeg Homes.
"When we have to use metal hardware, it's usually for some complex reason, and then we use things like hidden bolt-connectors that are buried deep in the wood so they're never seen."
Perhaps the real marvel is that time has shown these methods to be every bit as good as, if not far superior to, most modern-construction fastening systems. A proper timber joint not only ties the wood together, it also transfers the load carried by one post or beam along to the next, creating frames that amount to incredibly strong and durable unified assemblies.
Carrying Loads over Long Spans
Timber frames use less wood than comparably sized, conventional stick-frame houses, but they are elegant in their simplicity and immensely strong for their fewer parts. Depending on the frame's complexity, the size of its timbers, and the owner's wishes, a timber structure can include anywhere from several dozen to several hundred individual pieces.
The framework is designed like a web to transfer the load, or weight, of the entire structure and everything within it — the timbers, other building materials, snow and rain, interior furnishings, and the occupants — to the ground via the most efficient route.
This weight is ultimately carried by the main posts, so most timber frames are "point-loaded" structures. Conventional houses, with their network of thousands of interconnected lumber pieces, are referred to as "distributed-load" structures.
Because timbers can carry enormous loads and can span greater distances than conventional building lumber, they allow for much larger unsupported interior spaces. It's not unusual to see timber-frame houses with vast open areas stretching from one exterior wall to another and reaching upward two or three stories to a vaulted roof.
In fact, cathedral ceilings are a hallmark of timber-frame houses simply because they are so easy to create. And with the framework carrying virtually the entire building load, interior load-bearing walls are often not required. Only non-load-bearing partition walls are needed to enclose private spaces like bedrooms and baths, or for plumbing, electrical wiring, heating, and air-conditioning-duct access.
Although some form of timber framing was probably employed at the dawn of civilization, it's hard to know just when this construction method really began. But we do have well preserved examples of timber-frame structures, in places as distant as Europe and Japan, dating as far back as the ninth century.
Michael Morris is a homebuilder and author who writes frequently about timber-frame houses. Dick Pirozzolo is a travel photographer who has written numerous articles on timber-frame design and construction.
This article is excerpted from Timberframe Plan Book copyright © 2000, available from Gibbs Smith, Publisher and Amazon.com.
In the Marling House, stone and wood elements are balanced because the large stones are in scale with the heft of the beams.
Photo: Don Kerkhof
Ground floor plan of the Marling House.
Image: Richard Merlie
Upper floor plan of the Marling House.
Image: Richard Merlie
In this timber-frame house, the catwalk and staircase define the intimate dining area on the ground floor.
Photo: Brad Simmons
On the Curry Home, in the Great Smoky Mountains of North Carolina, by architect Chris Wood, an extended prow roof provides shade in the summer and rain protection in the winter.
Photo: Harley Ferguson
All the wood in the Curry Home was cut from eastern white pine that was hand-hewn and weather aged to give the structure a 200-year-old appearance.
Photo: Harley Ferguson
Curry Home, ground floor plan.
Image: Chris Wood
The Timberframe Plan Book from Gibbs Smith, Publisher.
Photo: Esther and Franklin Schmidt
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