Prime Lumber is a grade description for a special product variation of two inch dimensional lumber intended for use where appearance is a consideration.
For No. 2 PRIME, the grade is based upon #2 dimensional lumber characteristics except the holes, skip and wane are closely limited to provide a high-quality product. While PRIME lumber may “look” better, it has the same design strength values as lumber which does not classify as PRIME. (Readers – “skip” is a place on a piece of lumber that failed to surface clean when run through a sawmill planer.)
PRIME lumber is especially prized for use on outdoor members where it will be seen on a frequent basis – decks, patio covers and picnic tables would be some of these cases. Much PRIME SYP (Southern Yellow Pine) is pressure preservative treated and used for decks.
Most frequently PRIME lumber can be often found at “big box” lumberyards such as The Home Depot® where building owner/consumers are more discerning as to appearance and less concerned with price – as PRIME lumber is going to be more expensive.
Contractors are often more skilled at “making things work” as long as the materials meet the minimum structural requirements. Low price seems to become more of a driving factor than how a board looks.
In pole building construction, the use of PRIME lumber for wall girts and roof purlins, with limits on wane, makes it increasingly probable for all screws to be installed through the steel siding into the framing, without having to push or pull purlins or girts back and forth.
As mentioned in my last article, for a #2 grade (which is what is most commonly found at lumber dealers), wane is allowed to be up to 2/3 thickness and ½ width for ¼ length. On a 12 foot long 2×6, the wane could be 2-3/4” on the wide face, 1” in depth across the 1-1/2” face and three feet in length.
The very same 2×6, under PRIME requirements can only have ¼” deep or wide of wane, except an occasional piece may have wane on one edge up to 3/8” deep by 3/8” wide for a foot!
When deciding which lumber to purchase, keep in mind all of my discussions recently on wane, EE (eased edge), heat treated lumber, grade stamps – are designed to help you justify your purchase according to what you are using the lumber for. Lumber is not just lumber. It has many variations with cost considerations. Pick the right product for the right use.