046 Douglas-Fir - The Fir That Is not Really a Fir

Know Your Woods Series

Douglas-fir is one of the most important softwoods in North America, valued for its strength, straight grain, workability, and usefulness in everything from framing lumber to beams, flooring, siding, and fine woodworking. Yet despite the name, Douglas-fir is not actually a true fir.

That little surprise makes Douglas-fir an especially interesting addition to the Know Your Woods series.

Not Really a Fir

True fir trees belong to the genus Abies. Douglas-fir belongs to the genus Pseudotsuga, which places it in a different botanical group altogether.

The scientific name of the most common Douglas-fir is Pseudotsuga menziesii. The hyphen in the common name, Douglas-fir, is intentional and helps remind us that it is not one of the true firs.

Other woods commonly called fir, such as balsam fir, white fir, grand fir, and noble fir, are members of the true fir genus Abies.

Where Douglas-Fir Grows

Douglas-fir is native to western North America. Its natural range stretches through large portions of the Pacific Northwest, western Canada, the Rocky Mountains, and into parts of the western United States.

It is not a native tree of the northeastern United States, which makes old Douglas-fir lumber found in eastern buildings especially interesting. If Douglas-fir appears in an older eastern structure, the wood may have been transported a considerable distance.

What Douglas-Fir Looks Like

Douglas-fir generally has a straight and fairly pronounced grain. One of its most noticeable features is the contrast between the lighter earlywood and the darker latewood formed during each annual growth ring.

The heartwood often ranges from yellowish brown to orange-brown or reddish brown, while the sapwood is usually considerably lighter.

Depending on how a board is sawn, the grain may appear as straight parallel lines or as wider sweeping patterns.

Old Douglas-fir can darken considerably with age, which sometimes makes historic boards look much richer and darker than freshly milled lumber.

A Strong Softwood

Douglas-fir is classified as a softwood because it comes from a conifer, but the term softwood does not necessarily mean the wood is soft.

Douglas-fir is relatively strong and stiff for its weight. That strength is one reason it became such an important structural lumber.

It has been widely used for:

• House framing
• Heavy timber construction
• Beams and posts
• Floor joists and rafters
• Bridges and industrial structures
• Doors and windows
• Flooring
• Siding
• Millwork
• Furniture and woodworking projects

Working With Douglas-Fir

Douglas-fir generally machines well, but the strong difference between its softer earlywood and harder latewood can sometimes make it challenging to work.

The softer portion of the growth ring may compress or tear more easily while the harder latewood remains firm. Sharp tools help considerably.

The wood can also develop long splinters or stringy fibers, especially when a board is weathered, damaged, or worked against the grain.

Anyone handling old Douglas-fir quickly learns that those splinters can be surprisingly long and sharp.

Douglas-Fir and Siding

Douglas-fir has been used extensively for exterior building materials, including clapboard and bevel siding.

Traditional bevel siding is thicker along the lower edge and gradually becomes thinner toward the upper edge. The boards overlap one another as they move up the wall, allowing rainwater to shed away from the structure.

Douglas-fir's strength and ability to hold fasteners made it a useful siding material, particularly in regions where the tree was readily available.

When Douglas-fir siding appears on an older building far from its natural range, however, another question becomes important: When did the lumber arrive?

Could Douglas-Fir Have Been Used on an Eastern House in the 1800s?

By the nineteenth century, large lumber industries were developing in the western United States, and lumber could travel considerable distances by ship and later by rail.

Transporting western lumber to eastern markets was possible, but local woods were usually much less expensive. Builders in Pennsylvania and New York had enormous supplies of white pine, hemlock, spruce, cedar, and other regional woods available to them.

For that reason, finding Douglas-fir on an eastern building dating from the middle of the nineteenth century would be interesting and worth investigating carefully.

The later the construction or remodeling date, the more plausible long-distance transportation becomes as rail networks and national lumber markets expanded.

A Zehr Estate Wood Mystery

Zehr Estate provides an interesting example.

The original house dates to 1854, with major work occurring again around 1874. Portions of the exterior are covered with approximately six-inch-wide beveled clapboard siding. The boards are thicker along the lower edge and taper toward the top.

The siding wood is relatively lightweight, darker in color, and noticeably stringy when worked.

Those characteristics raise an interesting possibility: could some of the siding be Douglas-fir?

It is much too early to make that identification with certainty. Color alone is rarely enough to identify an old piece of wood, and more than one softwood can become dark, dry, splintery, and stringy after more than a century of service.

Fortunately, original pieces of the siding have been saved.

A freshly cut end grain, freshly planed surface, growth-ring pattern, resin characteristics, and microscopic wood structure can all provide much better clues. Comparing those features with known samples may eventually solve the mystery.

Why Old Wood Can Be Difficult to Identify

Historic lumber rarely looks exactly like a freshly cut board.

Sunlight, moisture, oxidation, dirt, paint, heat, insects, finishing materials, and more than a century of seasonal movement can dramatically change a piece of wood.

A freshly cut or freshly planed area often reveals characteristics that have been hidden for generations.

End grain can be especially useful because many important identification features are found in the structure and arrangement of the growth rings.

Douglas-Fir Versus True Fir

Although Douglas-fir and true firs may look somewhat similar as standing trees or pieces of lumber, their wood properties can be quite different.

Many true firs are relatively lightweight and soft. Douglas-fir is generally stronger, harder, and more structurally capable.

This difference helps explain why Douglas-fir became such an important construction lumber.

The Beauty of Understanding the Wood

Learning wood species is about much more than memorizing names.

Every species tells part of a larger story involving forests, geography, transportation, architecture, woodworking, and the people who chose the material.

A board of Douglas-fir in Oregon may simply represent a locally available building material.

The same board discovered in an eastern house built more than 150 years ago could tell a much larger story.

That is one of the reasons old buildings are so interesting. Sometimes a simple piece of siding can leave us asking questions about forests thousands of miles away, nineteenth-century railroads, lumber markets, builders, and decisions made by craftspeople whose names may have been forgotten.

Know Your Woods

Douglas-fir deserves its place among North America's great woodworking and construction woods.

It is strong, attractive, useful, historically important, and botanically a little misleading.

And perhaps the easiest fact to remember is also the most surprising:

Douglas-fir is one of America's most famous firs — and it isn't actually a fir.