PWF construction uses PT wood. Doesn't the engineering specify what grade of PT wood is to be used? Hopefully you bought a structural grade ground contact product.

Agree with the above, you have to use Ground Contact/Structural Use Lumber rated UC4B

Intended for critical structural, ground contact, and freshwater use.

i bought regular pressure treated brown wood. The outside of the house is watertight and the wall he wants to build is on the inside of the block wall( in my basement). All the wood will be wrapped in poly.

Make up your mind about what you have there... You have a block foundation or you have a wood foundation? In any case, you should have an approved drawing with a cross-section, detailing the materials to be used.

That said, If you have a block foundation and you finishing your basement, the only PT lumber you need is the bottom plate, the rest can be regular 2x.

If you have a wood foundation you already got the answer.

Good luck.

thanks for the advise it is a block foundation. But the engineer wanted me to build a pwf wall inside the block wall to brace it since it was bowing.

I never saw the wood foundation being used for this type of repair (did you get a 2nd opinion before you went with this fix?) There are much better and more effective ways of stabilizing bowed foundation walls nowadays to prevent further movements.

To address the original question there is a difference in retention and chemicals used between the two products.

Retention level is basically how deep the preservative penetrates the wood and the amount which is indicated by pounds per cubic foot. (Pcf). UC4B, as GN builder mentioned has a retention level of 0.60 Pcf and used for ground contact. UC4B pressure treated lumber and PWF are both treated to 0.60 PCF but there is a difference in chemicals used.

PWF still uses CCA, (chromatin, copper and arsenate). CCA was removed from retail consumer products in 2003 but still used for commercial products like PWF. The stuff you buy at lowes, menards, home depot all use one of several preservatives which are all arsenic free for health concerns, because they don't want you to build decks, sandboxes and swing sets with CCA. You must look for CCA treated wood with a .60Pcf retention, and chances are unless you go to a REAL lumber supply the big box stores won't have it in stock and must be ordered, (if they can).

So what did you order and where was it from? If it's standard retail treated lumber with the exception of 6 x6's the retention will be 0.4 treated or less, with one of 4 different preservatives. If the retention level is 0.01 to 0.2 it's one of nine different preservatives, and none will hold a candle to CCA which will last 100 years with ease. Now you know. I don't think they use CAC anymore.

*Chromated Copper Arsenate (to be nitpicky about it).

thanks kevin i bought regular pressure treated 2x6 for the wall. I bought pwf exterior grade plywood from star lumber But my 4x8 sheets of plywood have the .6 pwf stamp on them i got those from windsor plywood. I managed to get a hold of my engineer and he told me as long as my plywood is pwf that’s the biggest thing since eveything else will be wrapped in vapour barrier

GN Builders No in hindsight i maybe should have. I had done research into the steel beams and carbon fibre straps. I was expecting him to suggest the beam method however he said was only effective for concrete walls. And that frost heave and hydrostatic pressure would exert force on every block. He explained that we could do that but it would be 10x more money than the pwf wall.