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How to Choose Lumber for your Shed

Here we have an introductory lesson on how to choose lumber for your shed.  Our free article center was formed to help you build, plan, and execute your wood working project as smoothly as possible.


How to Choose Lumber for your Shed
Lumber is the heart of your shed.  Even the best shed plan can go to waste if you don't use the right lumber.  This article is intended to give you a brief overview of how to choose the right lumber for your shed, so that you can build a shed that will last a lifetime.  Before you leave, be sure to check out our Complete Shed Plans or Gazebo Plans Package and you will hopefully see how we have the best shed plans on the market.

Choosing the Right Lumber for your Shed

The illustration below will give you an idea of some of the defects found in dimensional lumber.  Typical defects are checks that result from the separation of wood across annual rings, knots that result from a portion of a tree branch incorporated in cut lumber, and splits which are a separation of the wood due to tearing apart of the wood cells.  A shake is a lengthwise separation of the wood which usually occurs between the rings of annual growth.  None of these defects should cause you to reject lumber outright.  However, wood with a bow, cup, crook, wane, split, or twist should be avoided in building construction.

lumber defects shed plans

Dimensional lumber is typically sold in incremental lengths of 2 feet.  For example, 2x6 lumber comes in 8, 10, 12, 14, 16, and 20 feet.  When you plan your shed, you should try to consider standard board lengths in the overall dimensions of your shed.  A 12' x 16' shed will be far more economical to build than a shed measuring 11' x 19' due to waste.

Standard Dimensions of Surfaced Lumber
Nominal Size Surfaced (actual) size
1 x 2 3/4" x 1-1/2"
1 x 3 3/4" x 2-1/2"
1 x 4 3/4" x 3-1/2"
1 x 6 3/4" x 5-1/2"
1 x 8 3/4" x 7-1/4"
1 x 10 3/4" x 9-1/4"
1 x 12 3/4" x 11-1/4"
2 x 3 1-1/2" x 2-1/2"
2 x 4 1-1/2" x 3-1/2"
 2 x 6 1-1/2" x 5-1/2"
2 x 8 1-1/2" x 7-1/4"
2 x 10 1-1/2" x 9-1/4"
2 x 12 1-1/2" x 11-1/4"
4 x 4 3-1/2" x 3-1/2"
4 x 10 3-1/2" x 9-1/4"
6 x 8 5-1/2" x 7-1/2"

For example, a 2x6 board measures approximately 1-1/2" x 5-1/2" depending upon moisture content and surface.  Lumber that has a rough surface will measure close to the nominal size in comparison to lumber that is surfaced on four sides (known as S4S).

The most critical factor in determining the actual sizes of dimensional lumber is the moisture content of the wood.  Look for the grade stamp imprinted on the lumber to determine the moisture content.  Typical moisture content ratings are:

MC 15 (less than 15% moisture content)
S-DRY (less than 19% moisture content)
S-GRN (greater than 19% moisture content)

A 2x6 surface unseasoned board (S-GRN) will actually measure 1-9/16" x 5-5/8" compared to 1-1/2" x 5-1/2" for a 2x6 rated surfaced dry (S-DRY).  The chart above shows actual versus nominal sizes of dimensioned lumber which is S4S and S-DRY or better.  Avoid unseasoned lumber especially in framing your shed.  Lumber which is unseasoned can shrink considerably as it dries naturally and is certain to cause structural problems as your shed ages.

Choosing the correct lumber for your shed can be as consequential as determining the correct design.  For use in a shed, the lumber you select must perform well in an exposed outdoor environment.  Performance is measured according to the following criteria:

Freedom from Shrinkage and Warping.  Lumber which has dimensional stability will not cause problems in your shed later.
Decay Resistance.  Generally lumber cut from heartwood (center of the log) is more resistant to decay than lumber cut from sapwood (outside of the log).  However, chemical pressure treatment can provide decay resistance to species which lack this property.
Workability.  Refers to the ease with which you can saw, nail, or shape lumber.
Nail Holding.  Determines whether or not a given species possesses good nail holding power.
Paint Holding.  The ability to hold a finish.  Some species which contain high levels of natural extractives (such as pitch or resins) do not hold a finish well.
Fire Resistance.  All woods are combustible, but some do resist fires better than others.  Woods which do not contain large amounts of resin are relatively slow to ignite.
Strength and Weight.  Wood which is relatively light in weight but possesses great strength is ideal.

While no single species performs ideally according to all of the criteria above, your local lumber dealer will be able to advise you regarding the lumber species most suited to your area.  Often you must balance consideration of economy with performance.  For example, redwood is considered a premium construction material, but high transportation costs outside the area of manufacture make pressure treated pine woods a more economical alternative.

Here is a concise guide to some common softwood species used in shed construction:

Cedar, Western Red.  Popular for the durability and decay resistance of its heartwood.
Cypress.  Cypress resists decay, has an attractive reddish coloration, and holds paint well.
Douglas Fir, Larch.  Douglas fir has great strength and is used best in the framing of your shed, especially in the floor joist members.
Pines.  Numerous pine species have excellent workability but are often pressure treated for use in exterior construction.
Southern Pine.  Unlike the soft pines described above, southern pines possess strength but are only moderately decay and warp resistant.
Poplar.  Has moderate strength, rests decay and warping.
Redwood.   A premium construction material because of its durability, resistance to decay, and beautiful natural brownish-red coloration.

Remember that in certain circumstances you can use two different species of lumber to construct your shed.  For example, redwood can be used for exterior trim while douglas fir is used for strength ins the shed wall and roof framing.

Whatever lumber species you select, it is important to learn the difference between the grain patterns in dimensional lumber.  Flat grain lumber is cut with the grain parallel to the face of the board.  Typically used for decking, flat grain boards should be used with the bark side up in order to minimize cupping and grain separation.  Vertical grain lumber, a more expensive grade used for finish work, is cut with the grain perpendicular to the face of the board.

Using Engineered Lumber

Due to recent developments in timber cutting practices and the reduced availability of certain sizes of framing lumber, engineering lumber manufactured from plywood, wood chips, and special glue resins offers and attractive alternative to dimensional lumber used for joists, beams, headers, and rafters, for your shed.  Unlike sawn dimensional lumber, engineered lumber is a manufactured product that will not warp and shrink over time.

Engineered lumber is manufactured to meet stringent criteria for strength, uniformity, and reliability.  Glu-lam beams offer great strength over spans.  Wood I-beams provide a lightweight alternatives to conventional rafters.
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