This post is not meant to be a complete tutorial on Pressure Treated Lumber.
A complete presentation of all of the information is left better to manufacturer’s websites or like this one from the Southern Pine Council. I just want to introduce you to the fact that not all pressure treated lumber is the same. It seems most people think that “pressure-treated” is “pressure-treated.” The reality is that not only are there several different “grades,” of pressure treated materials, there are different types of chemicals that can be used to treat the wood as well.
One thing that will be true of them all is that each piece of lumber will have a tag stapled to it that explains what it is.
The tag will tell you how much preservative is in the material, what type of preservative was used—-along with a bunch of other information—-including the year it was treated and where.
It is important for the installer/builder to be familiar with what all this labeling means so that the correct materials get used for the right job.
The Grade of pressure treatment refers to the “amount” of preservative that is required to be forced (under pressure) into the piece of wood—-per board foot. These percentages run from 2.5 ounces per board foot for pilings used in salt-water (marine) applications, to .25 ounces per board foot for some deck railing and surface installations. When you get up into the higher number of ounces per board foot there are only certain species of wood that will actually accept that much preservative—-Southern Yellow Pine for example. (Don’t tell that to the NW timber industry however.) For all its other great characteristics, Douglas Fir is lousy at being pressure treated and Hemlock is likely not much better. For most purposes, wood that is going to be in contact with the ground will have a saturation level above .40 ounces. This is very typical of most deck structural posts, beams and joists. For wood meant to be buried—-as in Permanent Wood Foundation Systems (PWF’s)—-we want to see .60 ounces per board ft.
The problem is that because most people—especially “Weekend Warriors”—-don’t know the differences between all these grades of treated wood, we end up with the wrong grades being used in the wrong places. Another factor is that materials designed to be buried are only available at real lumber yards. You are probably not going to find them at Weekend Warrior hunting grounds like Home Depot, Lowes, or OSH.
Here is a picture of your garden variety .40 Hemlock pressure treated 6×6. Because the treatment of this wood “species” (at this grade) can’t penetrate all the way to the center of the wood—-the center just rots away.
So when you are using pressure treated lumber—make sure you have the correct grade and that the weekend warrior has good information.
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Charles Buell, Seattle Home Inspector
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Great article. A subject that needs clarification. Most of the weekend warrior deck jobs I see use the pressure treated lumber from the big box stores and it’s almost always rotted where they bury the post in the ground.
Dan, thanks. There are so many instances where “Foundation Grade” should be what is used and not what is commonly referred to as “Ground Contact.” Most people assume that this means it can be buried. Everyone knows the difference in durability between “appearance grade” (sunwood) and “ground contact.” Well there is even more difference in terms of durability between “ground contact” and “foundation grade.” Of course the biggest difference being that it won’t rot 🙂
Interesting point. I spent most of my career in the fence industry and here in the northeast we use native white cedar for fence without treatment. Many do it yourself installations purchase booklets of instructions that are generic. Some tell you to put concrete around the post. I have never seen an instalation guide that fit all situations. Here in the northeast, for a cedar post to last 25-30 years, you excavate the hole to the required depth, set the post with the soil that came out of the hole and compact it well every 4-6″ . Then crown the soil around the post at ground level to shed water from the rain. Frequently when I was asked by my customers why their fence posts were rotted at ground level I would find indentations around the post that allowed water to accumulate and bring on early decay. This should never occur. I advised my customers to inspect their fence yearly and correct any of these situations to ensure the life of the fence. The only time concrete should be placed in or around a wood post is if the ground is not stable and then it should be used as a collar well below the surface so that any moisture can escape. If concrete is placed under the base of the post, you may as well set it in a bucket of water and kiss it good by. Backfilling the hole with any materials other than the natural soil removed such as sand, gravel or crushed stone will draw more moisture the area around the post, especially in heavier soils. Paper tubes will rot in 7 years and leave a void that will collect water and exacerbate decay and movement. It also helps to keep the pickets of the fence a minimum of 2″ above grade. When the picket comes in contact with the ground, the sun will draw any groundwater up through the picket and shorten the life of the fence. If you are trying to keep small animals in or out, place some hex mesh wire on the bottom and bury a few inches of it in the ground. Weed whacking with a string trimmer is life shortening to a fence. Each tiny nick is like a wound on your body except this one doesn’t heal and attracts moisture. The post will eventually rot at the ground
My daughter and her husband put on a new deck with this wood. She shoved a splinter into her foot. She has been suffering with this wound ever since. About 2 months now. What in the world is in this wood?? Any thoughts on treatment? She’s been to podiatrist and bone Dr. Shouldn’t people be warned about this???Thanks for any help you can give!!
I am no doctor and it sounds like they should see one even though they already have. There are many different kinds of treatment chemicals, species of wood etc. There may also still be a piece of wood still in the wound and there may have been something on the wood unrelated to the treatment process. Then there are allergic reactions that might be individual. Find the right doctor is all I can say.
Thank you for this article. As a Weekend Warrior, I built my deck, sinking my 4×6 pilings into concrete. Now, about 30 years later, I found them badly rotted inside the footers. I also used 2×10 “pressure treated” boards to act as a retaining wall to level out a patio area I constructed about 10 years ago. These completely desintegrated! A screen enclosure built before I bought the house (35 yrs?) on a wood foundation is still fine. A graphic lesson to what you’ve said. Going to replace the deck risers and use the surface mount on a metal fastener (will be easy to simply pour concrete into the old 4×6 post holes after I extract the rotting residue in them) and will look for “foundation grade” 2×10 to redo the patio borders.
Thanks again.
Gordon
I recognize the tag. It’s in my modern carpentry text book from when I attended a vocational school a decade ago. They changed the “year of treatment” by 10 years and the ‘preservation.”
Charlie,
I just found your blog. Maybe you can direct me to some information regarding the use of pressure treated lumber used for framing. Is this use of PT lumber advisable or not?
Thanks,
Wayne
It most likely can be but there are issues with its being structurally weaker so you can’t use normal span/sizing charts.
My husband is a weekend warrior right now and is currently looking for the right wood to use for a pergola he is going to build. It will be free standing and the posts will be sitting on cement. What wood do you suggest? I am not opposed to painting pressure treated wood or staining cedar or leaving redwood bare. But the difference in price is ALOT. Is the cedar or redwood that much better visually and structurally then pressure treated?
This is such a complicated topic as esthetics are involved. Redwood in my opinion is too precious to use. Modern cedar will not last very long and most PT is not going to “look as nice”—unless you can find PT Yellow Pine. I personally would look at cedar with sufficient roof overhangs to keep the wood from ever getting wet.
Mr. Buell,
You have save me from myself. I am about to do a huge project and was going to use whatever was at Lowes and or Home Depot. Being a woman and very skeptical of anything a contractor or most others “home service professionals” tell me; I have been taken advantage of way to may times to not be skeptical.
I can not tell you how appreciative I am to your valuable information. Now I know that the contractor I am going with wasn’t just saying something to make an extra dollar. If you have any suggestions as to what grade and type of wood i would appreciate it. I am putting up an 8 ft wide by 24 ft long covered porch that is not connected to the house and an 12 ft wide by 12 ft long deck in the back yard again not connected to the house. I live in the Northeast. Thank you again.
Bridget B. H.
In the East you have access to yellow pine PT wood and it generally performs quite well. Best practice is to use Foundation grade if it is going to be near the ground.
Great article that probably saved me some heartache. I need to install about four 12ft pieces of lumber (preferably 2×6 ripped down to 2×3) vertically into the ground. Thinking of dropping about 2 feet in the ground so 10 feet will be above ground. The purpose is to support outdoor led string patio lights that I am hanging around my deck. 2 questions: 1) Does ripping a 2×6 board to 2×3 impact its rot resistance by exposing the inside of the wood to ground contact? 2) What grade/type of wood would you recommend as it will not be bearing much weight, but will be installed in ground? Can your recommendation be purchased at Lowes or HD (most convenient) or am I headed to a lumbar yard? I am in VA. Thanks!!
Any cut ends or sides of pressure treated lumber should be treated with appropriate wood preservative, but not cutting is certainly best practice. As a side note, I would anticipate treated wood of that length and small size to warp and twist badly. You might want to consider round steep posts instead. Anything to be buried in the ground should be foundation grade 6oz material if you are going to stick with pressure treated. You will not likely find this a big box stores but you might be able to order it.
Thanks for your reply. When you refer to “round steep posts”, do you mean something like landscape timbers that are often used as flower bed borders? What are the dimensions of the lumber to which you are referring, and are they typically available in 12ft lengths? Is there an alternative to pressure treated wood that might work better? (I googled “round steep posts” and got nothing useful).
Ideally, there is something out there that will not be gaudy…would like something that will do the job while also being relatively “low profile”. I’m trying to do this once and not have to worry about decay and replacement in the near term while also being mindful of cost. Thanks again!
Hi, thanks for taking the time to help us WW’s! Couple of questions:
1st – I am replacing the boards on a 16′ (2x12x16) trailer any special considerations for that use?
2nd – I’ve already placed several posts for a fence from HD. How can I make them last? The previous ones rotted in the center. I was thinking of cutting off the top at an angle to allow water to roll off better. Any suggestions?
Thanks!
Larry from Knoxville, TN
I cannot speak to its use on a trailer. Sounds like the posts are not .6oz materials? At any rate, cutting the ends off at an angle will only increase the exposure of the less treated center. Of course the end in the ground is the bigger problem. All cut ends need to be field treated. A cap on the top would be a better option. There are metal caps made for this purpose.
Good article. I notice that none of the standards appear to specify the amount of penetration in inches. We custom ordered some large rough (full dimension) pressure treated douglas fir beams to build a trellis. 8×12’s on top and 8×8 posts. The lumber has a tag that says ground contact, .40, CCA, and a lot of other stuff. When we cut it to length, the penetration was about ⅛” all around the periphery. If I had known, I would have asked for a higher rating than .40. Can you offer any suggestion as to what rating would provide at least an inch of penetration?
Different species treat differently. Doug Fir is one of the most difficult to treat all the way through and I doubt one could on even a 6×6 never mind an 8×8. Anything marked .60 with cut ends treated is about as good as you are going to get. Structures like this perform better when build of assembled components that have no dimension greater than nominal 2″xX.” These will typically treat all the way through at .60.
Tell that to the architect! The design of the trellis specifically uses large dimension lumber as a design element.
I wanted to add some photos that show the depth of penetration and the actual grade tag. I noticed that the grade tag says .40 PCF, which may mean pounds per cubic foot, not per board foot, but I would still expect the depth of penetration to be deeper for large dimensioned lumber than smaller dimensioned lumber.
I was waiting to see if someone else would catch pressure treating being pounds of chemical per cubic foot of wood 🙂
I would question the treating on the piece shown. Contact your lumber supplier and be persistent, eventually you should be able to get a field test done where samples are taken of your treated timbers and the chemicals assayed to determine if adequate chemicals are present.
David, the post says “board foot” not cubic foot. This is what happens to all larger than 2x pressure treated lumber in the PNW. The types of wood used for treating simply cannot take the treatment to full depth.
Hi Charles/readers
Great article! Question –
any recommendations on good PT wood types for ground contact, i.e those with greater than 0.6 ounces / ft as recommended in the article….aside from Southern Pine? Southern Pine PT wood does not seem to be available in the CA Bay Area 🙁
Thanks
Mathew
Mathew, just talk to your local lumber yard (a real one—not a big box store) and ask them about 6 oz treated wood—they will surely https://www.buellinspections.com/wp-admin/edit-comments.php#comments-formhave a source.
Hey Matthew, I’m running into the same issue: not in CA! Have you ever found a source in the Bay Area?
I am a DIY kind of guy and when my wife and I had our house built in 1984, in which we still live, I had all kinds of projects to do after the builders left. Because we had babies; hence diapers, a clothes line was one of the first things to established, (back in 84 cloth diapers were still used). It was extra work, but at least none of those diapers are in some land fill. Anyway, my building material was 4×4 treated lumber. It was a quick project, with a post hole digger I dug a hole as deep as I could and before putting the post in the hole I brushed on roofing tar, then I placed the pole and back filled with the soil excavated. Thirty-four years later those poles are still there and if you push and pull on them there is no sign that they are going to break, I know, I’ve tried to do it now that I don’t want them there. I think what allowed them to last this long in the ground, empirically speaking of course, was me coating the subsurface wood with tar prior to placement.
Yes, that can work, but it can also make it worse. If there is a path created through the tar, water might not have a path to dry. You don’t say where you are located but perhaps the 4×4’s were treated all the way through—instead of just part way.
I am from Havre de Grace, Maryland and the 4x4s would have been purchased at one of three lumber yards; 1 Moores Lumber Yard, which is no longer there; 2 The Lumber Yard, also no longer there and ; 3 84 Lumber, which I am not sure was there in 1984. I did not know about different grades of treated lumber, and the Internet was not around then to learn about the subject matter, I only knew I needed treated lumber.
Charles, this is a great forum and source of important information. I am currently looking at building a pergola in Southern Florida at our Condo. It will be a stand alone with 6×6″ posts, double 2×8″ headers and 2×8″ rafters. I would like to make it out of PT Southern Pine. But others are concerned about it lasting very long ( 15-20 yrs or longer). Do you think the PT Southern Pine is suitable for this application ? The posts will be anchored to an existing concrete slab.
Thanks
Yellow pine is awesome and just find some with the FDN stamp on it—should last forever.
I took down a 32 yr. old pressure treated 8 ft. fence 2 yrs. ago. The fence was 275 feet long and made of 1″x6″x8′ planks, 2″x6″x8′ and 16′ stringers, and 10’x4″x4″ set in concrete. I can’t say who the wood was treated by but here’s what I came up with. I built a 14’x20′ two story building, building the bottom using all the above said lumber as follows. 4″X4″, I cut to 9 foot for wall studs, 2″x6″ stringers cut for floor joists and blocking in between joists, covered the bottom floor and the second story floor with the 1″x6″ planks. Used the rest of the 1″x6″ planks for siding. Turned them sideways and made clapboards out of em. Covered the front from ground to ridge and the other 3 sides from ground to second story floor. All built from 32 year old pressure treated lumber. As for condition of lumber, The planks have some splits but are still very solid, solid enough for 2 foot on center spacing. Just trimmed each end for a nice edge. Same goes for the 2″x6″ pieces. I think 2 pieces I had to toss due to excessive splitting. The 4″x4″ in concrete, they didn’t rot, just after busting off the concrete it removed a little of the outer layer of wood. Only 1 post had any signs of rot and that was where it entered the concrete and about 3″ above that point. Don’t tell me the old P/T isn’t the best. Who cares if it’s got arsenic in it, you’re not suppose to eat it.
I want to make a pergola with 6×6’s. I’m planning on burying the posts in concrete 2′ deep and attaching a fence to them as well. I found this link at Lowe’s. Do these look suitable? They are yellow pine..https://www.lowes.com/pd/Severe-Weather-Common-6-in-x-6-in-x-16-ft-Actual-5-5-in-x-5-5-in-x-16-ft-2-Treated-Lumber/4745855
Those look good for that purpose to me.
Hi Charles,
I have an above ground pool and the uprights and top rails are rusted beyond repair. SO, I fabricated the pieces using “Weathershied” (Big Box) 2 x 4’s for upright (sit in plastic base) and top rails out of 1 X 8’s. Secured with stainless steel screws. The wood is inconsistent where one 2 X 4 will be dry and lightweight and another wet and heavy. The first question is how long does it take before the 1 X 8’s dry and can be painted (Can you recommend a paint?).
Read where treated lumber should not come in to contact with steel because of corrosive additives. Uh oh. True?
I am dissatisfied with the quality of this wood (junk) and will go searching for an 8″ wide plank of higher quality wood. I am in Chicago, do you think I should do the top pool rails in an alternative to pressure treated? Bamboo?
Do you have a lumber yard of choice that you can recommend up here in the Seattle area? Looking to build a low retaining wall!
We are building a new screen enclosed deck and requested Premimum decking boards with stainless steel screws. What we just saw was “standard” tag on decking boards they are using which has many many knot holes in them. We have contacted contractor about this decking not being premium quality boards. Can you tell me what I need to know to be sure we are getting what type decking boards we are paying for. Many thanks, simple homeowner
Since a certain amount of knots is allowed for each grade, I am not sure I can give you additional information without knowing more about what the contractor provided.
Thanks for the article. This article got me to realize there are actually different grades of pressure treated wood.
One thing I don’t think this article mentions is that the retention level also depends on the preservative used. For example, ACQ is 0.6 for PWF, but CA-B and CA-C (which seems to be what Home Depot and Lowes sell) are .31 for PWF, at least according to:
http://www.finehomebuilding.com/2015/01/07/whats-the-difference-pressure-treated-lumber
I would like to put up a pole barn and I have ground water at 2 to 3 ft. Will this situation decrease the life of the post (foundation grade)? Will post protectors (plastic sleeves) help? Should I use concrete columns below grade?
Sorry, I have no idea. I recommend consulting a qualified pole barn builder.
Great article and it was the info I needed.
I used 4 * 4 southern yellow pine for a chicken house fence here in NE Florida and in a few years they were rotten at ground level and below. I’m getting in the lumber selling business for a local company and wasn’t wanting the same thing to happen to my customers.