Lumber – Nominal vs. Actual Dimensions

[DavesHammer]

While building a deck I noticed that two 2x10x8 AC2 boards had different measurements. One was 9 2/8″ (standard actual size) and the second was 9 4/8″. Is one board larger due to moisture in the wood and if so, will it shrink to 9 2/8″? I don’t want to lay out my joists and have a wavy deck due to inconsistent dimensions for 2×10 joists. If the joists will shrink to 9 2/8″, do I need to wait for them to shrink before adding the decking?

Thanks, DavesHammer

[carl21l]

the differences in the width is more due to the tolerances allowed on pressure treated lumber than to the moisture content. it is best to allow the material to air dry prior to installation, especially if there is a great difference in the amount of moisture in the material. most of the home boxes get the material in banded pallets and let is set banded so that the material on the inside of the pallet dries slower than the material on the exterior of the pallet. to air dry, you will need to stack in an orderly stack with cross sticks (1/4 inch thick strips if 1x material) placed at the ends and every 18-20 inches along the length. material to be stacked flat. if you have various lengths, start with the longest, then stack shorter lengths on the pile. when ready to use the material, use joist hangers to attach, and set the hangers for each joist as you install them so that you can keep the tops all on the same plane. this will give an even deck surface.

Carl

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