Quick Reference: Weight of Pressure-Treated Lumber
Roof Online Staff, July 2019
The following table provides the heaviest approximate weight per linear foot of pressure-treated lumber that you are likely to find. Around 85% of the pressure-treated wood in the US is made from southern yellow pine. There are a few different sub-species of southern yellow pine, with different wood densities. We used the longleaf variety to calculate the values shown below.
See Weight of Dimensional Lumber for the weights of other wood species commonly used for lumber.
Pressure-treated lumber is produced by using high pressure to force a solution of water and chemical preservatives deep into the wood. Stacks of lumber are placed in a large steel cylinder in a bath of water and preservative. This tank is pressurized until the wood becomes saturated. After the wood dries out, the preservative remains throughout the wood, protecting it from decay for years.
The noticeable extra weight of pressure-treated lumber is due to the water added during the treatment process. As the wood returns to its normal air dried weight over the following weeks or months, it also returns (almost) to its pre-treated weight.
Once it dries, the weight difference between pressure-treated lumber and untreated lumber is entirely due to the weight of the preservative retained in the wood. This weight is minimal. The maximum additional weight due to preservative is around 1.5% for “ground contact” designated lumber using CCA (chromated copper arsenate) or ACQ (alkaline copper quaternary) as a preservative. For much of the pressure-treated lumber available today for residential use, the additional weight will be less. “Ground contact” lumber treated with the widely-used CA-C (copper azole, type C), for instance, will only weigh about 0.37% more than untreated wood.
This table is intended to give you an idea as to what pressure-treated wood might weigh at its heaviest, so the values given use the heaviest wood species (southern yellow pine, longleaf) commonly used to produce pressure-treated lumber, with the highest amount of water commonly added to the wood during treatment (close to four gallons, or about 32 lbs., per cubic foot), immediately after being treated, before the wood has had a chance to dry at all.
The values given in the table are meant to provide a general idea of typical pressure-treated lumber weights, and should not be used if precise values are needed for critical engineering calculations. When precision is necessary, always refer to the specification sheet for the actual, specific product you intend to use, or contact the technical department of the producer.