The Deck Handbook: Part 2
Domestic Wood for Decks

Wood is by far the most popular material for decks. Wood decks can be created in an endless variety of tones and patterns, and modern sealing products ensure they will last for many years with regular, routine maintenance.

Homeowners face a wide range of choices when planning a wooden deck. Some wood products are extremely costly – particularly tropical hardwoods. Others, while inexpensive, may require more maintenance than most homeowners prefer.

When planning a deck, it makes sense to use more expensive wood where it will show, and less expensive materials for concealed structural members. For example, it is typical to use relatively inexpensive pressure-treated pine for structural members and more expensive, exotic woods for the decking and railings. Some designs go one step farther and use a less costly wood for the decking, and highlight the railings and fascia with more attractive materials.

Domestic Wood for Decks

Wood used in decks must be rot-resistant. If it is not naturally resistant to decay, it must be treated to make it so. Southern yellow pine is the most common treated wood used in the U.S. The treatment varies (and some treatments work better than others), but generally, a chemical that bugs cannot eat is pressure infused for a few millimeters into the wood to make them resistant to rot and decay. Since the chemical does not go all the way through the board, if it is cut or ripped, the newly exposed untreated surface must be treated on site before the board is used.

Janka Hardness

Janka hardness is a good indication of how well a wood species will resist denting and wear over time. For flooring and decking, dent resistance is particularly important.

The Janka scale ranks the dent resistance of wood as determined by measuring the force required to push a 0.444 inch diameter steel ball into a block of clear wood to a depth of 1/2 the ball's diameter.

In the U.S., the result is stated as pounds/force (lbf) needed, usually in the form "xxxx Janka". For example, the hardness of southern yellow longleaf pine is 870 Janka, meaning it takes 870 pounds of force to sink the steel ball half way into the wood. The higher the number, the harder the wood.

The test was adopted by the American Society for Testing and Measurement in 1927 as ASTM D143.

Hardness usually varies with the direction of the grain. If testing is done on the surface of a plank, with the force exerted perpendicular to the grain, the test is said to be of “side hardness.” This is the standard.

End grain tests are unusual, but if done, the fact that it is an end hardness test must be stated in the results. End grain is usually more dent-resistant than side grain.

Moisture content also affects wood hardness. Wet wood is softer than dry wood. Tests are usually conducted with a moisture content of 12%, typical of air-dried wood.

Janka Hardness of Selected Wood Species
Species Hardness
Balsa 100
Western Red Cedar 350
Douglas Fir 660
So. Yellow Pine (loblolly & short leaf) 690
So. Yellow Pine (longleaf) 870
Tamarack 886
Eastern Red Cedar 900
Paper Birch 910
True Teak (Tectona grandis) 1000
Black Walnut 1010
Red Oak (Northern) 1290
Ash 1320
White (Burr) Oak 1360
Cypress 1375
Hard (Rock) Maple 1450
Hickory/Pecan (All Varieties) 1820
Jarrah (Australian) 1910
Mesquite 2345
Bamboo (Woven Strand) 2850
Jarrah (Atlantic) 3190
Cumaru 3540
Ipe 3680
Lignumvitae (Ironwood) 4500

The untreated Native American woods most commonly used in decks are Western Red Cedar, Redwood, and Cypress. Redwood is expensive, increasingly scarce and a very, very un-"Green" material. More common in California, it is rapidly being supplanted by imported tropical woods such as Ipe.

Cypress is in the same category. The large Cypress swamps native to Florida and Georgia have been largely harvested. Much of the cypress now on the market comes from salvaging and cutting logs buried in swamps where they have been immersed in water for many years — difficult and expensive work which is reflected in the price of quality Cypress wood.

This leaves Western Red Cedar (WRC) which is still relatively abundant and available from just about any lumber store. Its heartwood is naturally decay resistant and with proper maintenance will last as long as 25 years.

Treated Pine

By far, the most wood most commonly used for decks is pressure-treated pine. Industry analysts report that more than 70% of all decks in the U.S. are treated pine. So, if you are planning a pine deck, you are in good company. Even if another wood is used for the visible portions of a deck, you can bet the house that the structure underlying all of that pretty wood is plain old pine.

Pine is not naturally a decay-resistant wood. Exposed to the elements, pine will decay to uselessness in about two years. To make is more resistant, the surface of a pine board is infused with a chemical solution containing copper. The former standard treatment that included arsenic (Chromium Copper Arsenate or CCA) is no longer used. The trade-off, however, is that pine boards treated with the new technology — Alkaline Copper Quaternary or (ACQ), Copper Boron Azole Type A (CBA-A) or Copper Azole Type B (CA-B) — contain so much more copper that they corrode steel nails and screws very quickly. Special coated fasteners must be used these days to build treated pine decks. But, one nice feature of the new treated "greenboard" is that it is no longer green. The new boards are usually a more attractive "brownish" color.

The reasonable life expectancy of the exposed boards in a treated pine deck is between 25 and 50 years with constant and regular maintenance. This is quite a step up from the 10-15 years that used to be the case — an indication of how far we have come with wood treatment and preservative stains. Structural boards (more sheltered from the elements) will last quite a bit longer. This all depends, of course, on proper sealing and maintenance. New sealants can last 5 years or more before re-coating is required. But once the wood has started to deteriorate, no amount of re-sealing will help. Which is shy the sealant barrier needs to be carefully maintained.

Joists, beams, posts and stair stringers, which are important for structural integrity, require pressure treated pine in most localities. Deck flooring boards, railings and other non-structural parts of a deck may be made of other woods or synthetic materials such as composites or plastics. These elements do not have to be as strong. Most composite and vinyl manufacturers stress that their materials are non-structural. This means that the newel post, deck post or beam that you see that looks like composite or vinyl is probably pressure treated pine wrapped in composite or vinyl for appearance. Railing balusters or spindles can be made of manufactured materials because they are considered non-structural although they do have to be strong enough to prevent people from crashing through them.

The Cedars

Of the native woods, the cedars are arguably the most beautiful wood for decks. The rich grain and color of the natural wood make the material a prime choice where appearance is important.

Dimensionally stable, the wood lays flat and is less prone to warp and twist than treated pine. It stains evenly and holds stain well. The natural oils in the heartwood of cedar are non-toxic to humans and pets but discourage insect attack and slow decay due to exposure. This accounts for the wood's reputation as slow to deteriorate. However, much of the cedar harvested today comes from smaller, younger trees that are mostly sapwood. Sapwood has no such protection, and in fact, decays about as quickly as pine unless sealed and maintained. So, don't look on today's cedar deck as a low maintenance investment. It requires about the same attention as treated pine.

The cedar most commonly used in decks is Western Red Cedar ("WRC") (Thuja Plicata), also known as Giant Arborvitae, Western Arborvitae, Giant Red Cedar, Pacific Red Cedar, Shinglewood, and Canoe Cedar. Not a true cedar, but a member of the Cypress family, Western Red Cedar is a commercial wood, harvested on the slopes of the Continental Divide in huge quantities and available at almost any home center or lumberyard. In most of the country, this is the only cedar readily available.

Cedar comes in a variety of grades from very knotty to very free from knots (clear). The Western Red Cedar Lumber Association recommends four grades of cedar for use as decking: Architect Clear, Custom Clear, Architect Knotty, and Custom Knotty. Architect Clear, the clearest, is also the most expensive.

The grade you will typically find in your local big box lumber store is Custom Knotty, the least expensive of the group. Prices vary widely in different parts of the country. Cedar is typically less expensive in the West, closer to where it is harvested, than it is in the East, where shipping costs can dramatically raise the price.

In Nebraska, however, we have more choices because of our locally harvested rot-resistant deck woods. The most common is Eastern Red Cedar ("ERC") (Juniperus virginiana), which is, interestingly enough, a juniper, and a member of the Cypress family. (Obviously, the Cypress has a large family). It has all of the same insect and decay-resistant properties of WRC and looks and even smells like WRC. Eastern Red Cedar grows throughout the Eastern United States and most of the Midwest. In fact, it enjoys the widest geographic distribution of any American conifer. As a consequence, it has so many known common names that we will not even bother to list them here. Nearly every region of the country has its own pet name for the Eastern Red Cedar.

You are probably most familiar with this Nebraska native as Aromatic Cedar used in closet linings — its primary commercial use. A lot of Nebraska's cedar is shipped back East to be turned into closet panels and aromatic chipboard, then shipped back to Nebraska to be sold in Home Depot, Lowes and Menards as closet lining. With grain that is a little more striking than that of WRC, the Eastern variety is also more aromatic — giving off that characteristic cedar smell that repels insect pests of all kinds. A deck made of any Red Cedar is a natural bug repellent, but Eastern Red Cedar smells better longer than Western Red Cedar.

Eastern Red Cedar is also a harder, tougher wood. Western Cedar is a very soft wood (350 Janka) that is easy to work with, but also dents and mars easily. Eastern Red Cedar is much harder (900 Janka) and denser, and consequently much more resistant to the accidents of normal use.

Purple-red when first harvested, the Cedars after a very short exposure (one day or less in Summer) to sunlight fade to a pale brown. Over time, the wood becomes an attractive silver gray. Fading may be halted at any time by merely sealing the deck with a UV-protecting sealer. This allows you to pick your deck color and preserve it when that color is reached in the natural fading process.

Cypress

The North American Cypress (Taxodium distichum), can be found in wet, swampy areas along the East Coast from Delaware south to Florida and west along the Gulf Coast and up the Mississippi River Valley. It grows best in the swampy areas of Florida and the lower Mississippi River where it can reach heights of up to 145 feet. Common names for cypress include Bald Cypress, Swamp Cypress, Southern Cypress, Red Cypress, Yellow Cypress, White Cypress, Tidewater Cypress, Gulf Cypress, Black Cypress, and Cow Cypress.

Cypress trees are one of only two American deciduous conifers, meaning conifers (softwoods) that shed foliage in the fall, a characteristic normally found only in hardwoods. The other is Tamarack (see below). Although a softwood, it has traditionally been grouped with hardwoods and is graded as a hardwood by the National Hardwood Lumber Association.

Cypress is naturally rot- and insect-resistant - very rot resistant. Logs submerged for decades in swamp water are routinely raised and harvested for sound wood. The wood needs no chemical treatment or sealing to survive up to 100 years in a deck — far longer than the typical treated pine supporting structure will last. It is also very dent and wear resistant at 1375 Janka — harder than oak, and nearly as hard as rock maple. Much of its rot resistance can be attributed to the fact that Cypresswood is especially watertight. It takes a long time to remove moisture from Cypress, but once dry it resists reabsorption with the same tenacity. The wood also contains cypressene, a natural resin that repels insects and prevents fungus and mildew but is harmless to humans and pets.

Stable and not very prone to twisting or warping, cypress will weather to a nice splinter-less gray appearance, holding its nails, screws and shape very nicely for dozens of years.

We discourage the use of Cypress, however, because it is not by any conceivable measure a "green" material. We are quickly running out of it. The large, old trees that contain abundant cypressine are especially rare — and the massive destruction caused by Hurricane Katrina did not help the situation at all. Nor does the fact that young trees are routinely cut down and ground up for mulch. Fortunately, even fallen cypress trees submerged for many years can be raised and harvested for sound wood, a process that has extended the supply. However, the current rate of harvest is absolutely not sustainable, and native Cypress is fast disappearing. Australian Cypress (Callitris glauca) is being imported to supplement the native supply.

Tamarak

Known by various names including American Larch, Eastern Larch, Takmahak, and Hackamatack; Tamarack (Larix laricina) is a hard (886 Janka), extremely durable North American softwood native to Northern marshland forests, primarily along the Northeast coast and north to the Hudson Bay.

There is also a disjunct Alaskan population. Its cousin, the Western Larch (Larix occidentalis), found only in the Northwest U.S. and Southwest Canada is also sometimes called Tamarack, causing a nice bit of confusion once in a while. To add to the fun, one subspecies (Murrayana) of Lodgepole Pine (Pinus contorta) is also commonly called the Tamarack Pine.

The Tamaracks are coniferous, but also deciduous — losing their needle-like leaves every fall and growing them back in the spring. The only other conifer that does this is the Cypress (see above). Eastern Tamarack thrives in wetlands where it helps drain and dry out the soil so that trees like oak and pine that prefer firmer, drier habitats can get a foothold. Eventually, these more aggressive newcomers drive out the Tamarack.

The name "tamarack" supposedly comes from an Algonquin word, "akemantak", meaning "wood used for snowshoes." More commonly, its historical use has been in water-edge structures such as wharves and docks, and as ships' timbers.

Eastern Tamarack is very much the Cypress of the north. Its natural resistance to decay, rot, insect damage and salt makes it an excellent wood for long-life exterior decking. Similar in appearance to Western Red Cedar, it does not age quite as well, tending to look a little shaggy after a few years.

In the Midwest, it is virtually unknown. But on the East Coast, it is becoming a significant player as a replacement for Western Red Cedar. Expect its role to grow in the next few years as Cedar becomes more scarce and more expensive.

Exotic and Imported Deck Woods

In the ever-widening quest for wood that looks good, is structurally adaptable and resists rot and decay, imported hardwoods have become significant niche players. The most common are Ipe (pronounced "ee-PAY") and the old standby mahogany. Others include Teak....(Continues)

Rev. 05/20/18