Trex Outdoor Living

MORE INFO THAN YOU PROBABLY CARE TO KNOW ABOUT LUMBER AND YOUR DECK

While the type of materials used to build decks continues to expand, pressure-treated lumber is still the most popular choice. The material is relatively inexpensive; it resists insects and rot; and it’s readily available. However, many homeowners in Northwest Arkansas are turning to other materials, such as redwood, exotic hardwoods and synthetic materials for the decking and railing systems (the areas that are in full view). These products offer a variety of looks that cannot be matched by pressure-treated lumber. In most cases, pressure-treated lumber is still used for the structural portions of the deck, including posts, beams and joists.

LUMBER

Because your deck is out in the weather all the time, you want to use wood that will resist decay and insects. There are several choices, but the most popular are treated lumber, redwood and cedar. Other options include cypress, recycled plastic decking, untreated lumber and tropical ironwood.

To get the wood that’s right for your project, it’s not enough to choose a certain species. Other factors that influence a wood’s performance include moisture content, method of drying the wood, what part of the tree the lumber comes from and the quality or grade of each piece.

You also want to choose wood that won’t warp or check after it’s installed. All wood swells when it gets wet and shrinks while drying, so you should expect a certain amount of twisting, cupping and splitting. But choosing the right type of lumber for the different locations on your deck should keep this problem under control.

LUMBER BASICS

Most lumber is surfaced – smoothed with rounded edges on all four side. This is called S4S, meaning surfaced on all four sides. If you want a rough-sawn look (for the fascia or posts perhaps), we can use cedar or redwood that is either rough all over or is smooth only on one side. This lumber may be a bit thicker and wider that S4S.

LUMBER SIZES

The nominal size of a piece of lumber, for example, 2×4 refers to its size prior to drying and surfacing. So the 2×4 will actually be 1.5 inches by 3.5 inches. A 2×6 is actually 1.5×5.5 inches. A 1×8 is .75×7.25 inches and so on. In most cases, lumber yards carry pieces in 24-inch increments beginning at 8 feet.

Many people use either cedar or pressure-treated boards for the decking and sometimes for the top cap on the railing. This material is actually 1 inch thick and 5.5 inches wide. Rounded edges minimize splintering. Often only one face will be usable. To satisfy most codes and to build a strong deck, you will have to space joists no more than 16 inches on center to use this material. 

Most people choose deck boards that are 5.5 inches wide, such as 2×6, either because they like the wider appearance or because they are less work to install. But the price for wider boards is rising fast because more lumber now comes from smaller trees, so 2×4 decking is becoming a more economical choice. However, lumber prices tend to fluctuate, so it makes sense to price out both types.

LUMBER DENSITY

As a general rule, lumber of greater density will be stronger but also more prone to splitting and warping. Likewise, lower-density wood is weaker and may splinter and twist less. This is because lower-density wood can act like a sponge, absorbing moisture when the weather is wet and drying when the sun comes out. Dense wood does not have the ability to transfer moisture quickly, and the internal stresses cause warping and splinters. Treating lumber does not affect density but only adds temporary weight in the form of moisture. So higher density wood, Douglas Fir or Southern Yellow Pine, for instance, works well for the substructure, where strength is important and splinters and warping do not matter as much. And because you want to avoid splinters on the decking and rails, lower-density wood, such as redwood or cedar, may be a better choice.

LUMBER GRAINS

All trees have two types of wood inside: sapwood and heartwood. Sapwood is located toward the perimeter of the tree and carries sap to the branches. Heartwood comes from the center of the tree and is denser than sapwood because it is older. it is also more stable than sapwood. All parts of the tree can be used, and lumber taken from either the sapwood or heartwood region is graded accordingly. Because a lot of lumber today is cut from younger, faster growing trees, you may find fewer distinctions between the heartwood and sapwood areas.

HEARTWOOD AND SAPWOOD

The wood near the center of the tree, which is inactive because it has not been growing for some time, is called heartwood. Lumber milled from this portion of the tree is more resistant to rot and insects and less porous than sapwood, which is taken from the area of the tree near the bark. This is a significant difference: decking made of redwood or cedar heartwood will last far longer than will sapwood decking from the same species.

VERTICAL AND FLAT GRAIN

Different sawing techniques at the mill will yield different grain patterns on the boards. Lumber generally either has vertical grain, with narrow grain lines running along the face of the board, or flat grain (also called plainsawn), with wider lines that often form rippling V-shapes. Most boards are a combination of the two, and in any given load of lumber, you will find boards that are both primarily flat grained and primarily vertically grained. Vertical grain is less likely to shrink and warp, and most people think it looks better.

LUMBER GRADES

Lumber is sorted and graded on the basis of number, spacing, size of knots, milling defects and drying technique. The highest quality, and most expensive, lumber is called select structural. This lumber has the fewest knots and other imperfections.

Most often, you will be dealing with common lumber, which is graded No.1, No.2 or No.3. No.1 is the strongest and usually the best looking wood as well. No.2 is the grade most commonly used in deck framing. No.3 lumber is less structurally sound.

Another grading system uses the words Const (for construction), Stand (for standard or Util (for utility). These three classifications are generally used to grade  2×4 and 4×4 lumber and No.1, 2 and 3 grade 2×6 and wider stock.

No.2 is the most common grade and will be fine for most applications. Most building codes require No.2 or better. For railings and other areas that are highly visible, you may want to spend the extra money to get No.1 or even select structural lumber. Lots of lumber is now cut from corporate forests, where fast-growing trees mature quickly but have widely spaced growth rings and yield less lumber.

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