Learn to Timber Frame: Craftsmanship, Simplicity, Timeless Beauty
160
Learn to Timber Frame: Craftsmanship, Simplicity, Timeless Beauty
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Overview
Product Details
| ISBN-13: | 9781612126692 |
|---|---|
| Publisher: | Storey Publishing, LLC |
| Publication date: | 05/03/2016 |
| Sold by: | Hachette Digital, Inc. |
| Format: | eBook |
| Pages: | 160 |
| File size: | 41 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Jack A. Sobon is an architect and builder specializing in timber-framed buildings. A founding director of the Timber Framer’s Guild of North America and founder of the Traditional Timber Frame Research and Advisory Group, Sobon has devoted his 38-year career to understanding the craft of timber framing. Using only traditional hand tools, he has framed and erected over 50 structures. He is the author of Build a Classic Timber-Framed House and coauthor of Timber Frame Construction. A graduate of the Rhode Island School of Design, Sobon teaches and consults nationally on traditional building structures and timber-framing techniques.
Read an Excerpt
CHAPTER 1
What Is Timber Framing?
Timber framing in much of the world can refer to any framing system using wood components, but in North America we use it to mean solid timber (greater than 5 × 5 inches in section) joined together with traditional wooden joinery. It's a type of post-and-beam construction — picture the barn raising in the movie Witness.
A Historic Art
Rather than using small framing members (2×4s, 2×8s, etc.) that are closely spaced and simply butt-joined and nailed together, timber framing uses larger pieces spaced farther apart and mortise-and-tenon joinery held together with wooden pins, or pegs. It is the traditional method of framing brought over by the colonists to the New World and can be found worldwide in areas that had abundant timber before the age of sawmills, drying kilns, and mass-produced nails. The same techniques were used to build Asian temples and great wooden ships. The homebuilders in the colonies were often shipwrights, using basic hand tools and minimal material processing (but great skill) to provide shelter. In much of Europe, where centuries-old wooden buildings are still lovingly preserved and valued, carpenters are trained as timber framers and are highly skilled in the techniques shown in this book.
Timber Framing vs. Stick Framing
In North America in the 1830s, settlers migrating west needed a way to build quickly with unskilled labor. The newly built railroad made it possible to ship smaller-dimensioned lumber to the treeless prairie, and the new technologies of sawmills, drying kilns, and mass-produced nails helped promote a new construction system called stick framing. This system relied on the repetitive use of many small pieces of lumber (2×4s, for example) to overcome the scarcity of skilled labor. Now anyone could build a house — and faster, with a smaller crew. Since the framing was nailed together, one didn't need the skills of a joiner. Stick framing became firmly established as the predominant method of light construction after the Great Chicago Fire in 1871, when a large part of the city needed to be rebuilt quickly.
Timber framing, however, remains a viable option, even though it requires more skill. The structures, with their large, open floor plans (no load-bearing interior walls) and exposed timber and joinery, are a joy to make and to live in. If you have a woodlot or access to local sawmills, the materials can be cheaper than buying kiln-dried "sticks" from a lumberyard.
The following chart outlines some of the principal differences between stick framing and timber framing.
Let's look at each of these differences more closely:
SIZE OF PIECES
Timbers are defined as members that are 5 inches by 5 inches or greater; lumber is 2 to 4 inches in its smallest cross-sectional dimension, and boards are 1 inch or less in thickness. This is standard lingo; most of us have a fear of looking dumb at the lumberyard or sawmill, so it's important to have our terminology straight.
Softwood and Hardwood
Softwoods generally shrink and move less than hardwoods. Eastern white pine has one of the lowest shrinkage rates and thus ranks at the top of the list of ideal woods for timber framing. If you choose to use mixed species, then usually it's best to frame the larger timbers from softwood and smaller ones (braces, joists, wall girts) from hardwoods.
SPACING
Over the last century or so, stick framing developed into a highly modular building system based on the standardization of 4 × 8-foot sheet materials — plywood sheathing on the exterior and drywall panels on the interior. Spacing the wall studs and other framing members at 16 or 24 inches on center (measured from the center of one member to the center of the next), ensures equal support for the edges of the panels.
By contrast, traditional timber-frame structures used long, solid-wood planks for flooring and sheathing, and the spacing of the framing was not dictated by the size of the planks, allowing for broad spans between supporting members.
While our timber frame design could be built with lumber, we choose timber mainly because of the aesthetic qualities of the exposed framing and joinery. The insulation and sheathing will wrap outside of the frame rather than bury the frame within the walls and roof.
SPECIES (and sourcing materials)
Most framing material at the lumberyard is softwood — typically spruce, pine, or fir — that has been distributed through a worldwide commodities network and may come from trees halfway around the world. It has been graded, dried, and planed to produce a consistent product that can be used in mass-produced buildings. Due to the drying, shipping, and storing required, the energy footprint of store-bought lumber is much greater than that of locally milled materials.
Timbers can be of any species and come from your own property, provided they are structurally sound. They can come from a nearby sawmill (of which we have plenty in New England) and thus support the local economy. You can also buy a chainsaw mill or portable bandsaw mill and cut the timber (and lumber and boards) yourself. Hardwoods and softwoods have different characteristics and advantages that will be discussed in the next section. Our timber frame is designed to use eastern white pine (Pinus strobus), though other species can be substituted (see Species of Wood).
MOISTURE CONTENT
Freshly cut trees contain a lot of water, and as the wood dries it changes shape, as evidenced by shrinkage, cracking, and perhaps warping. Since store-bought lumber used for stick framing is kiln-dried and then planed, most of these changes have been shaved away. In the rush to get product to market, however, rapidly grown plantation trees are dried minimally and may still move a bit after construction. Softwood lumber is easy to nail into after drying, which is one reason it's used for framing; hardwoods, although perhaps stronger, are generally much harder and heavier.
Timbers milled locally and recently will be green, so for timber framing it's best to cut the joinery and get the frame erected, then let all the movement take place once the frame is locked together. It's easier to cut joinery in green wood, especially if it is hardwood and you are using hand tools. For wood to air-dry, it takes about a year per inch of thickness, and kiln-drying large pieces is impractical. (There are a couple of radio-frequency, or microwave, kilns in North America that can do the job, but this technique is expensive and works only with certain species.) Using reclaimed timber from old buildings is another strategy for getting "preshrunk" stable timber, but it may need to be re-milled, with a careful eye for hidden embedded metal.
CONNECTIONS
Stick framing evolved in part thanks to the mass production of wire nails. With the multiple redundant pieces used in stick framing, nails were more than sufficient to hold the building together.
Timbers, on the other hand, are too large to nail together, and there are fewer of them, so the joinery connecting them is much more critical. This joinery is usually designed to connect the end of one timber into the side or end of another and often consists of variations of the basic mortise-and-tenon joint.
BRACING FOR LATERAL LOADS
Stick framing usually relies on structural sheathing — plywood or oriented strandboard (OSB) sheets — nailed to the framing every 6 inches or so to provide stiffness and resistance to racking forces from wind and perhaps earthquakes. These sideways forces are known as lateral loads.
Timber framing does not have a stud or rafter every 16 or 24 inches to carry these sheet materials. Instead, diagonal braces provide rigidity, usually running at 45 degrees between a post and a beam, forming the hypotenuse of a right triangle. Shear walls (explained later) may also be required by some building codes in areas with high lateral load potential from seismic or hurricane events.
ENCLOSURE
With stick framing, the regular spacing of framing members provides bays of equal width to accept standardized batts of insulation, as well as support for exterior sheathing that in turn carries siding and roofing. These same framing members are then covered up on the inside with gypsum drywall or other materials (after wiring and plumbing runs are installed), so the frame is completely concealed.
For timber frames to be enclosed in the same manner, a redundant stick-framed system would need to be built outside of the timber frame (if you want to see the timbers exposed on the interior). Because the timber frame is carrying the loads, however, this light frame, or curtain wall, would not need all the components (such as headers) that a structural stick-framed system would have. This external light frame is common, but the popularity of timber framing really exploded with the advent of the structural insulated panel, or SIP. These panels are made of rigid foam insulation sandwiched between layers of plywood or OSB and can be built to span areas as great as 8 × 24 feet. They are attached to the outside of timbers with long screws. SIPs have made it unnecessary to build another light frame outside of the timber frame.
SKILLS REQUIRED
Both stick framing and timber framing require carpentry skills such as reading plans and a tape measure and being able to cut a straight line with a saw. A stick framer, though, is usually working with standardized materials of uniform dimensions and following established patterns and methods for assembly. This is why there are rarely stick framing plans included with a set of construction drawings; once the carpenter knows the dimensions of the building and locations of doors, windows, and interior walls, he or she can frame the building using the chosen on-center spacing.
Timber framing, however, requires more of the skills of a woodworker. Wood as it comes out of the sawmill is green and somewhat irregular. Designing, locating, cutting, and assembling joinery in such material must still result in a structure that stands plumb, level, and square. This requires patience, attention, understanding, and specialized skills, including the ability to visualize the finished structure while the raw timber is sitting on the sawhorses. Since the timbers and joinery will usually remain exposed, greater care must be taken since errors won't be covered up. A job well done, however, results in that much greater satisfaction.
TOOLS REQUIRED
Stick building may only require a saw, square, hammer, tape measure, chalk line, level, and pencil. Power tools and pneumatic nailers make the job go faster, but not necessarily better.
Timber framing requires additional tools, mainly to execute the joinery. Timbers are large and heavy and may require a cart or many hands to be moved. Because of irregularities, framing squares and combination squares are useful for keeping joinery true to reference planes in the building. Tenons can be cut with saws or even with an axe, but mortises are generally harder to cut. They require a boring tool, such as a drill with large bit, an antique boring machine (beam drill), or modern electric chain mortiser. Mallets and timber framing chisels are the primary hand tools for cutting, and even finishing, joints that have been roughly cut with power tools. Mallets may be used for driving pins as well, with heavier versions called commanders (also beetles or persuaders) used to drive timber assemblies together.
CONSTRUCTION PROCESS
Most stick-built houses (excepting manufactured kits) are still cut and assembled on-site, with floors built on foundations that will serve as the platforms for ever-higher walls and, finally, the roof. Weather, access, and distance from the builder's home can affect the speed at which the project is completed.
Timber framing is, in a sense, a kit or "pre-manufactured" structure. You can cut the frame in a barn, shop, or garage away from the site, protected from the weather, and close to home. Then you take the pieces of the frame to the site and erect it in a matter of hours. You need an area to store the timbers (covered, ideally) and to work them, and then a truck or trailer to transport them to the site. Of course, if the woodlot sourcing the timber is the same as your building site, it would make sense to work them there.
Both stick-framed walls and timber-framed bents are typically assembled flat on the deck and then are tilted up into place. Since timbers are heavier, you usually need more people to raise a timber assembly, or even to install individual rafters. Cranes, forklifts, or other mechanized equipment are used on big jobs.
COST
In terms of the amount of framing material used, similar-sized structures usually use the same volume of wood whether they are stick-built or timber-framed. Wood volume is measured in board feet; one board foot (bf) is the volume of a board 12 inches by 12 inches by 1 inch thick. If you are comparing lumberyard framing materials at $1/bf to local sawmill timbers at $0.75/bf, it's cheaper to do timber framing. Buying timbers from across the country, however, would end up being more expensive. If you're paying for labor, timber framing is usually more expensive because of the skill involved. But if you're doing the work yourself, labor cost is not a factor. However, it will usually take longer to build a timber frame (though you'll have that pride of accomplishment).
Other factors affecting cost are the enclosure and insulation system and the level of finish. Often people who have a nice timber frame upgrade the rest of the systems to match. Using local sawmill lumber and boards for sheathing, siding, paneling, cabinets, and flooring can produce significant savings. Finally, timber frames have a lower life-cycle cost: the frame lasts longer (sometimes hundreds of years), since it is protected inside an insulated envelope and is often well-maintained.
All in all, if you're providing your own labor and buying local materials, a timber frame can cost less than a stick-built structure you build yourself with lumberyard materials. The timber frame built with local materials is also environmentally friendly and has a strength and beauty valued by its owner. Of course, if all you want is an uninsulated storage hut in the garden and plan to pay for labor, it's pretty hard to beat the cost of a stick-built prefab shed from a big-box store. But that's not why you picked up this book.
CHAPTER 2
Getting Started
For millennia, people have timber framed without the benefit of building codes or standardized materials. It's only in the last century or so that the building "industry" has become so prescriptive that a narrow set of guidelines — recipes, if you will — usually dictates how to build a house. For those who wish to build with traditional methods, such as timber framing with local materials, a more thorough understanding of the materials and techniques of the craft is necessary. The species, sizes, and shapes of the building materials are guided by the builder's vision and often go beyond what is specified by the building code.
(Continues…)
Excerpted from "Learn to Timber Frame"
by .
Copyright © 2016 Will Beemer.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
Foreword by Jack A. SobonPreface
Chapter 1: What Is Timber Framing?
Chapter 2: Getting Started
Using Ungraded Native Lumber - Timber Frame Engineering 101 - Ordering and Storing Timbers
Chapter 3: Layout Systems
Mill Rule
Mapping
Scribe Rule
Square Rule
Chapter 4: Tools
Tools for Layout
Cutting Tools
Boring Tools
Chapter 5: Procedures for Layout & Cutting
First Steps in Layout
Laying Out the Mortise and Tenon
Cutting Procedures
Rules of Thumb for Joinery Design in Square Rule
Chapter 6: The Tiny Timber Frame
Plan Drawings
Timber List
Sills
Joists
Posts
Girts
Braces
Collars
Door Posts
Tie Beams
Plates
Rafters
Chapter 7: Variations on the Frame
Moving Doors and Windows
Adding a Loft
Changing the Roof Pitch
Overhangs
Making the Frame Smaller
Making the Frame Bigger
Chapter 8: Raising the Frame
Equipment for Raising Day
The Raising Script
Chapter 9: Foundations & Enclosure Systems
Foundations
Insulation and Enclosure
Epilogue
Glossary
Resources
Bibliography
Index