Pressure Treated Lumber 1

[Woody1515]

Hi everyone,

I have a few general question regarding pressure treated lumber, specifically pressure treated deck joists.

Before the joists are treated, are they graded in the same way a non-pressure treated joist would be? For example, in Canada most lumber joists would be SPF No. 2 Grade or better. Almost all lumber in my area is SPF, but I’m not sure about a structural grade for treated lumber. Would a treated joist still have the same lumber stamp that a normal joist would that states all of this info, along with a treated stamp? Contractors often seem to not know what species or grade of wood the treated joists they use are, but I would think the supplier would have the species and grade of the wood specified?

Thanks for your input in advance!

 

[Harbringer]

Graded the same as non-treated lumber.

 

[Woody1515]

Thanks for the fast response! Is there the same grading stamp on the teated lumber as a non-treated joist? And calling out a “PT SPF No. 2 Grade or better joist” is the correct way of doing it?

 

[mmarlow]

Woody,

In the Northeast, SPF is the most common lumber for wood framing. However, PT lumber is typically Southern Pine. I have typically seen PT framing called out as "P.T. 2X10" on the plans and in the general notes or specifications the requirements for PT lumber is defined

Hope that helps

-MMARLOW EIT

 

[phamENG]

As a followup to MMarlow's post, the reason for the difference is the ability of the species to take the preservative treatment. SPF is a 'refractory' species and doesn't absorb the treatment effectively, so it has to be incised. This damages the grain and reduces the capacity of the member. Southern Pine doesn't have to be incised and is stronger anyway, so it's a common choice for PT lumber. Whether or not it's available in your area is another question. I live in the south, so it's everywhere. About the only thing that typically comes as SPF around here is 2x4s, though in the lumber shortages of last year we started seeing a lot of 2x6's.

 

[dik]

From my wood expert...

All softwood species are treatable with ACQ, however you would need to check
local sources to see what is in stock. For design, I use SPF 1/2 grade.



Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I should have noted that ACQ is corrosive and you should be using HDG or SS fittings and attachments.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ChorasDen]

dik, you're technically correct that all softwood species can be treated, but it's a matter of effectiveness.

On the west coast, SP lumber doesn't exist, so we have to use cedar or incised, treated Hem-Fir. The strength/stiffness of the member has to be adjusted per NDS for both wet service factors, reductions for treatment factors, and reductions for incision factors.

The problem with this? Hem Fir doesn't treat worth crap. Penetration is abysmal, and retention is even worse. There is a legitimate reason why there is not a treater on the market who will provide a warranty for their treatment. It's all provided 'as is' and up to the project owner to observe and maintain. I've seen more decayed treated hem-fir than I care to count. Doug Fir treats even worse than Hem-Fir, so that isn't even an option. Not certain how SPF behaves, but I wouldn't expect much better. It also has low design properties to start with, so taking the hits to stiffness/strength for the above factors are really going to limit the application.

To answer the original question, the lumber is graded prior to treating, not after treating. Much easier to visually grade lumber prior to discoloration and checking effects due to pressure treatment than it is after.

Edit: sorry, just noticed OP is in Canada, so they would be following CSA 086, not NDS. But I would expect similar adjustments required for design of treated members.

Disclaimer: I work for a multinational wood products company.

 

[dik]

Thanks, for the added info... It may be difficult, or maybe a different process; I understand that they can still get the retention, but don't know for certain. I've used PWF treated Doug Fir and Doug Fir plywood in past.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ChorasDen]

To add to my previous post, lumber is graded prior to treating, because generally speaking, the lumber manufacturer is not aware of who the customer is, and what lumber will be treated, if any. Out west, treatment is performed by a third party, and is not facilitated by the lumber manufacturer.

Dik, you make a fair point, there are (2) general subspecies for Douglas Fir, dependent on where it was grown. Coastal DF tends to treat better than inland DF, however, it may be hard to get exclusively DF sapwood for treatment by a treater. They would have to have an agreement with the lumber supplier for chain of custody and sourcing to confirm product as Coastal DF, while not impossible, this may be hard to achieve.

 

[dik]

Thanks... First PWF was done about 50 years back... used a process called the Boliden process... Architect was from Iceland, and I had never heard of it... still standing, so I'm OK. Wood is not my area... I guess Vic's comment to check with local sources is, kinda, the correct thing to do.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik