Preparation: Inspect Your Deck Building Lumber and Materials


Deck building requires a lot of varied materials. This can be a lot for a DIY deck builder to figure out. Here are a few things you should know when shopping for, or accepting a delivery of building materials.

How to Visually Inspect Materials

There are four essential qualities that need to be inspected before accepting a delivery, or purchasing deck materials.

  • Dimensions of the material must be correct
  • Materials should conform to certain standards in shape, especially lumber
  • The appearance of trim and deck top materials is essential to the deck’s appearance
  • Structural integrity should be consistent

How to Check Dimensions

There are three dimensions that matter when inspecting lumber. Hardware and other materials often have important dimensions as well but are fairly standard and can be returned if they are wrong. Lumber is often not returnable, or carries a hefty restocking fee. Getting it right saves time and money.

  • The thickness of the board should be consistent from one to the next in lumber that is the same size
  • The width of the board should also be consistent within the same size
  • The length of the board should be at least the length advertised, sometimes a quarter to half inch longer

Understanding Nominal Dimensions

Lumber is named for its “nominal” dimensions, which are typically larger than the actual dimensions of the board. This is because the piece is rough cut to the dimension it is named for, (for example a two by four)then smoothed on a planer to get the actual dimensions.

  • As a standard rule, the finished dimension of lumber under one inch thick is named for its actual dimension and should be very close to that thickness
  • The finished dimension of lumber one inch thick is approximately ¾ inch thick, having ¼ inch shaved off of the top and bottom faces in the milling  process
  • The finished dimension of lumber more than one inch thick is approximately ½ inch thinner than its named or “nominal” dimension. So a four by four is approximately 3 ½ inches thick.
  • Dimensional lumber is ½ inch narrower than its nominal width. So a two by four, or one by four is 3 ½ inches wide.
  • Sheet goods, such as plywood, are named for their actual dimensions
  • Lumber comes in lengths with two foot intervals starting with six or eight feet, running up to 16 or 20 with longer pieces available by special order

Inspecting Your Lumber

All lumber should be the same thickness and width within a single board size. If, for example, your two by fours (typed as 2x4 from here on) are 1 5/8 inch thick, and all boards are the same, this could cause issues with hardware, but would not weaken it. If the boards were 1 3/8, they would fit the brackets, but would be considerably weaker.  

Check enough boards to get a representative sample. It is not necessary to check each board. Dimensions are typically very consistent. Identify the size of each group of boards to ensure you have the right materials.

Use your materials list as a check list. Mark off each item as it is verified and counted. You will also want to check for the following factors.

  • Twisted, curved, or “cupped” boards. Slight curvature can be straightened in construction. Anything that will not stack properly should be rejected.
  • Checks, splits, or cracks more than an inch or two long and visible on both faces indicate structural weakness, reject this lumber
  • Framing lumber with some bark, or roughness at edges is fine. If it is extensive, or makes the board hard to use, reject it.
  • Decking material and trim should be as close to ideal as possible. Reject material that you find unacceptable visually. You may have to accept the best available material in some cases.

Other Materials

Check dimensions and quantity of fasteners, bolts, brackets, and other hardware. Labeled sealed boxes can be checked by their label. Open bin hardware should be checked for correct dimensions.

Reject rusted, corroded or visibly damaged hardware. The strength of your deck will rely on the fasteners and hardware. As with lumber, use your materials list and check each item for quantity and mark it off your list. It is always best to buy a few extra of everything. One extra bolt could save a half day of going after more hardware.

If you are receiving a delivery, check carefully, since your signature may indicate you are waiving your right to return material or agreeing to pay the restocking fee on returned material.