Some TREATED LUMBER Rots Faster Than Others! WHAT'S THE DIFFERENCE?! (Ground Contact Vs. Non-GC!)

Check Out Our FREE GUIDE: *25 Must-Have Carpentry Tools...Under $25 Each!*

Did you know that there are multiple varieties of TREATED LUMBER? And that some treated lumber will rot much faster in certain conditions? This short video from The Honest Carpenter explains the various treated lumber USE CATEGORIES!

Check Out Our Other Lumber Videos:
Is Treated Lumber Toxic?:

Is Particle Board The Worst?:

Treated lumber and wood doesn't last nearly as long as it used to. This is because we shifted our pressure treatment process in 2009.

For years, Chromated Copper Arsenate was used to treat the vast majority of lumber in USA. But CCA contains a trace amount of arsenic, which caused concern. So, the EPA encouraged companies to switch it out for two other treatment fluids:

Alkaline Copper Quaternary (ACQ)
Micronized Copper Azole (MCA)

These fluids don't protect lumber quite as well, and they also contain a higher concentration of COPPER, which makes them expensive to use.

In order to avoid very high lumber prices, lumber companies began grading treated lumber and treated wood based on how much treatment chemical was present in various grades of lumber after drying out. This quantity is known as TREATMENT RETENTION.

These retention quantities fall into USE CATEGORIES, since different retentions are suitable for various ideal uses.

Use Categories fall on a scale of 1A to 5C.

Lumbers up to the UC3C range are considered ABOVE GROUND USE, or NON-GROUND CONTACT lumbers, because they can't stand up to the high moisture saturation levels in various soil substrates.

However, lumbers graded UC 4A or higher are GROUND CONTACT lumbers, since their retention levels can handle contact with or immersion in the ground...or even directly in water!

These lumbers are used for deck posts, fence posts, structural exterior members, foundation piers, and more...

To find out more about the various Use Categories, check out some of these websites, which have great, detailed information!:

Thanks for watching!
The Honest Carpenter

[consumeand]

Had no idea! Just assumed if it was Pressure Treated, It was good to go for all outdoor use! Thanks for this great content.

[Firedog-nycq]

I have had far too many PT 6x6 posts rot at ground level in less than 10 years. My son built a house with wrap-around decks and he used milled 8x8 locust posts with T&G locust flooring. It was code approved and should outlast the both of us.

[arajalali]

Great info. In some countries they actually dye the lumber with a certain color so that it would be easy to recognize. that's why for instance in New Zealand all new houses' skeletal structure look as if the builder had been Elle Woods from the movie Legally Blond. It's all pink :)

[heidbumbee]

Locally, here in Scotland, every cut in pressure treated wood is regarded as an exposure to untreated wood. Pressure treatment only penetrates so far, so any cut exposes untreated wood. Local mills recommend that treated wood when cut is re-treated to heal the "wound" and offer full protection. We don't use arsenic based treatments. Almost all of the treatments cannot be used in water / ponds or it will affect pondlife. They work on the assumption that pressure treated wood is safe to use for stables etc, on the principle that a large animal horse / cow cannot graze/chew/gnaw on enough wood to cause harm, but at a microbiological level it's a no no, so no using scraps for bird boxes etc

[mrgee]

Great info! The details that you covered are so important for a successful project (and for saving $$ over the medium and long term) Nice job

[urchant]

Great information. I did know anything about the grading but I've always stuck to GC lumber when outside. Probably wasted some money, but rather go better than have to replace boards after a few years.

[Slaphappy-_-]

This is so true! I didn’t know and no one will tell you at Lowes!!!!

[Robin]

Thank you for this video HC. I had no idea there were so many treatment grades for lumber.

[eyewest]

Do you have any experience with charring wood for ground contact? I believe it's a Japanese method for preservation. I'm building some raises garden beds that will be growing vegetables and I'm charring all the wood being used. Trying to keep them chemical free and long lasting.

[PM]

Ethan, I've been using wood for the home projects for many years and amazed at my ignorance about the grades, so thanks for sharing. Also want to thank you for the other video about the circular saw, it was very useful too!!

[davidhunden]

Back about 10 or so years, we built a deck on very sandy soil that drained very well. We didn't know about all the differences between PT lumber (above, on, and below ground), so we bought what was available, which included above and below ground, but we used them indiscriminately for the project. At some point, we had to rearrange some of the partially buried lumber and we were astounded that some of the pieces were substantially decayed just shy of a year in the sand. We were much more particular after that when buying PT lumber.

[ontheroadwithralph]

I really appreciate that you keep your videos short and to-the-point. Thanks for the concise information.

[fluffymustdienow]

I am a structural engineer, licensed PE, and I had no clue. Just got a call from a contractor who erected a deck I designed 14 years ago. I specified "preservative treated" but did not specify the "grade" of preservative treatment. A few of the deck joists (joists, not floor boards, not posts, but joists) have melted from the middle out. Literally big gaping holes between the top and bottom edges. My google searches led me here. Thank you HC. This is very eye-opening information.

[thebobloblawshow]

Because they DON’T treat it properly anymore. On a 4x4 post it was green all the way through, almost. Now it penetrates 1/4 inch at best. PT doesn’t stand for Pressure Treated anymore. It stands for Pre Treated. Another scam.

[billm.]

Always appreciate your insight & expertise. Had no idea there were that many various ratings for treated lumber. Great job as always Ethan. Keep ‘em coming.

[markarita]

There's DEFINITELY been a very noticeable change. Thanks for all the info.

[j.hueston]

How about a video about what you can do to enhance the rot resistance. I coat any part of a post that touches the ground with black roof patch. Let it dry out and then use it. Don't know if it helps too much but my thought process was anything to keep moisture from contacting the wood would help.

[DavidL-iiyn]

Great information. I've never seen a rating shown in any of the major lumber stores for treated lumber so I'll look for this. In contrast, I have a century home, and untreated 120 year old lumber with some weather contact seems to be in amazing shape... but I know they don't make trees like they used to.

[jacquelineparham]

Hey Honest Carpenter. Thanks for giving the info I requested. Can you, please tell me how long I can expect for the fencing I had installed in 2022 should last? Treated wood. Over $3000 dollars.

[kencoleman]

Thanks for another useful video. There are so very many grades of lumber, PT and other, that's it's difficult to know exactly what I should be purchasing or sometimes what I bought from a limited selection.