PWF - what type of wood is used?

Can PWFs use the same wood as the kind used in decks, or do they us a wood that is specially treated just for PWFs?

Pressure treated plywood

Southern Pine is the preferred species for PWF’s.

Ok already.
What is a PWF?

Preserved Wood Foundation ?

Plywood made from Southern Pine? It is the plywood that forms the main barrier against decay, right?

Stands for “Powdered Wood Foundation” Bob.

OK, sorry, I’m not an admirer of them.

The industry term invented by the people who manufacture them is “Permanent Wood Foundations”.

They might be OK if the contractor adheres strictly to the manufacturer’s recommendations, but many don’t. When contractors don’t, foundations fail. They fail by buckling and decaying.


I am just surprised they still use them.

Are we talking about the same acronym Ken…Permanent Wood Foundations?..where SP is the main species used and pretreated?


Jeff, yep… same thing. CA and AO Hem fir is used for treated lumber.

They are not uncommon in this neck of the woods, I put one in 20 years ago, and the house is still standing (I guess) My 10:00 inspection today is a PWF, I’ll take good pictures.

Typically, the pressure treatment saturation point is increased for ground contact, etc.


Pressure Treatments

We specialize in treated wood products. We sell wood and pressure treated lumber products to your specifications and in accordance with national and local regulations.

Most dimensional pressure treated lumber is treated to .25 or .40 pcf in ACQ. Larger dimensional lumber (2x8 and above) can be treated to .60 pcf with CCA but only for use in certain commercial construction applications. We usually recommend .60 pcf (CCA or ACQ) for freshwater use, ground contact, or extreme weather conditions, .80 CCA for government specifications or brackish (salty fresh) water, and 2.5 pcf CCA for projects in saltwater.

The term used in lumber yards is G.C. or Ground contact. Most posts are GC rated, but not all. “treated” is now a more generic term in my opinion, at least not specific enough. The term doesnt tell you if it it GC or not.

Larry, We still need to meet for coffee sometime. Summer busy?

I’m due to inspect a wooden home foundation this week. Any tips on what to look for beside detailed moisture testing and bowing.

I read some more and found what I was looking for. Should have read more first

As a point of possible interest, in very old structures in the northeast, maybe elsewhere too, you may find ground contact post and timbers hewn out of black locust. It is the densest, strongest wood in northern New England and has a natural resistance to WDO. It was used as sills and very often as fence posts. I know of one particular fence post that still is functioning which was old 50 years ago so probably 100 or so now. 50 years is what was considered working span for black locust posts of 6-8". Here the decay range for posts is ground surface down to around 16" generally so posts could be reused. Being very precious and hard to cut and work for the old timers, it was used for long term applications. It also has vicious thorns. It makes very good firewood although tricky to get burning for the novice. Black locust was taken out west and raised for timbers in mine shafts due to the properties of the species. It was sometimes used for tool handles but hornbeam was more popular due to much smaller tree diameter and similar strength.

Disclaim! Disclaim! Disclaim!
How’re you going to know if it’s rotted 6 feet down?

What did you find when you found what you were looking for?

Hi Kenton, just a note to mention that there is no such tree as hem-fir. The actual tree is Western Hemlock that supposedly has the same structural characteristics as Douglas Fir. Hemlock is the structural pressure treated lumber of choice because the treatment goes deep into the wood. Douglas Fir pretty much rejects the treatment. In PT plywood made on the west coast it is all hemlock.

You’re right David, it is Western Hemlock, but Hem-Fir was what the stamp on the pressure treated lumber said when I was in the trades in CA and CO.

Yeah Kenton, the stamp does say hem-fir. That signifies that the hemlock has the same strength characteristics as fir. Once was at the lumber yard buying some studs. The lady at the contractor counter was talking about hem-fir trees. I didn’t have the heart to tell her the real story.