what is SYP you folks talk about---thanks

[barbender]

Red Pine is pressure treated too, but only for above ground use that I have seen.  My treated wood basement is SYP.

[GeneWengert-WoodDoc]

Almost any species can be and has been pressure treated.  On the low density end, I have seen pressure treated aspen.

Those species that are not porous enough (correct term is permeable), then a small knife is used to make slits in the outside of the piece being treated so that the preservative can get into the outer sections of the wood.  This is called incising and is common with Douglas-fir, especially inland.  This extra step of incising costs more.  Also, as most treated wood is used in a structural application, as SYP treats easily and thoroughly, and as SYP is so much stronger than other pines and softwoods, SYP is the dominant species that is treated.

Hardwoods can also be treated.  In fact, almost all RR ties are hardwoods and they are pressure treated with creosote rather than the water soluble salts used for SYP.

OK?

[Dave Shepard]

What is the correlation between strength and ring count in SYP? I know that SYP is strong, great stuff generally, but the junk I see at the box stores with no more than 3 rings to the inch seems to be garbage. I see 4x4 and 6x6 posts snap across the piece quite often. In fact a 6" stub is all that my neighbor has for a mailbox post right now, for the second time this winter. :D

[GeneWengert-WoodDoc]

What is SPF?  Well, it depends where you are.  Much of the SPF in the U.S. marketplace comes from Canada; the term is actually a marketing term (There is no SPF tree.) used by the grading associations to group several similar species together--it is easier on the mills not to have to sort species.  The species included are lightweight.  For someone building a "stick-built" house, the weight is a big plus.  Also, the species in this grouping are not prone to warp and are easy to nail into.

In fact, a few years ago, well over 2/3 of the framing lumber sold in GA (the #1 forested state in the 13 southern states) was SPF from Canada.  In eastern Canada, SPF includes red spruce, black spruce, jack pine, and balsam fir species.  In western Canada, it includes white spruce, Engelmann spruce, lodgepole pine, and alpine fir.

SPF is not widely used for roof structures due to its low strength and therefore short spans.  Likewise, for patio decking.  However, it is widely used for framing 2x4s and 2x6s.  Most of the SPF species do not treat as easily as SYP.

[GeneWengert-WoodDoc]

Some wood species, such as the ring porous hardwoods like oak and ash, and probably all of the species that have a big difference between the wood grown in the early part of the year versus the late part of the year (i.e., a big color difference within a single growth ring, as well as a density difference), will have a big difference in strength due to growth rate.

The ring porous hardwoods that grow slowly will have a higher percentage of the large open pores, reducing strength.  So, from a practical point, southern oaks are stronger than northern.

Softwoods like southern pine, when slow grown, will have more dense wood (dark, redder colored within the ring) and this is stronger.  So, slower grown is stronger (the opposite of hardwoods).  With SYP the difference when grading is 6 rings per inch...more rings is called dense and has higher design values.  Also, 4 rings per inch can be dense if the ring has over 50% of the dark, dense latewood.  (Example:  A No2. 2x6 SYP 16" o.c. floor joist can span 10'8" if dense and 10'0" if not.)

OK?

[Ga Mtn Man]

OK!

[WDH]

Much of the SYP lumber is graded using a machine that determines board strength, maybe board density, I am not sure.  This lumber is called MEL or machine-evaluated-lumber if it makes the threhsold strength grade.  Much of this MEL lumber is used by the wood truss manufacturers.  Boards with few rings per inch will not make the MEL grade.  The boards that meet the #2 or better appearance grade, but do not make the strength grade, are sorted out and this is some of what you see for sale at the Box Stores.