Lifespan of Pressure-Treated Wood
How long do you expect pressure treated wood to last ?
I have a deck in new england (not costal) that has what I believe are ACQ deck boards. Full southern exposure. Stained every year. Southern yellow pine (I assume).
A handfull of deck boards started showing signs of rot about 8 years after being installed. I am now about 12 years in and I replace one or two boards every year.
Replacing one or two boards a year is hardly a disaster but it strikes me that a product with as much potnetial for environmental damage as pressure treated wood with only a 10-20 year life cycle before it starts to disintegrate is kind of problematic. The newer copper based formulations are obviously much better than CCA in terms of toxicity but copper in large quantities is not totally benign. The volume of this stuff that goes into residential construction is crazy.
Is my experience typical ? Are folks seeing better results with different pressure treating formulations ? Has anyone every tried to makle a claim on a manufactuers warantee for presure treated wood ?
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I've seen similar disappointing results. Perhaps one should use ground contact treatment even above ground? Or naturally rot resistant woods (eg, black locust).
Pierre, I'm also in New England and have similar experiences. Repeated wetting/drying seems to be the biggest factor in early failure. Also when larger-dimension material is used, the ends rarely get sealed and the members rot from the inside. I still use PT for deck framing and mud sills, but don't see the advantage of using it over naturally rot-resistant materials like cedar. As Jon says, you can use ground-contact material instead, but there are health, cost and aesthetic downsides that approach as well.
Where are you seeing the rot, specifically? Top and center of decking (are they cupped?), sides, underneath, nail penetrations?
Does full southern exposure imply full sun? How close to ground? Roof draining onto deck?
I have no knowledge about how well modern day PT is holding up, but I think in any case, good design (drying potential) is key. It seems odd that one would see rot in the time frame you state with staining every year, even if the wood was not PT.
I am working with a homeowner in NJ who has a pretty serious rot problem in his 8 year old PT Deck. About 1/3 of the structural lumber has relatively advanced rot and another 1/3 is showing beginning signs of rot. Some of the rot is bad enough that the lumber had to be replaced. The last 1/3 is completely clean. This deck is up off the ground with good ventilation and drainage. He's going to be making a claim with the PT manufacturer, and we'll see how he does.
Same experience here in the PNW. None of the newer formulations, ACQ or MPS last anywhere near as long as CCA did. New-growth cedar is much worse though.
Extending the lifespan of decks relies on detailing them as though they weren't rot-resistant. Strips of membrane over beams and joists, nowhere for debris to accumulate, good air-movement.
If at all possible though I build patios instead. One less weekend a year spent on maintenance, less safety hazards, and a better, more seamless, relationship to the surrounding yard.
"New-growth cedar is much worse though."
Interesting. Do you think there is more sapwood present with the seconds growth, or do you think even the heartwood is less resistant?
Old Growth cedar grew extremely slow and is almost an entirely different product than the faster-growing stuff you get now. I would not consider it much more rot resistant than doug fir, maybe slightly. I'd say the whole tree, sap and heart is this way comparatively.
Tyler,
The decks I used to do repairs on here on Vancouver Island a couple of decades ago were almost exclusively built from cedar, and usually needed some remediation after twenty years or so. Now it's common to see cedar dimensional lumber used as railings or decking fail after seven or eight years. I ascribe that to it being new growth, but have no idea what the mechanisms in play are. Less tannins? Wider growth rings? Increased prices mean better boards get exported for premium? I'm just guessing.
Malcolm, I’ve been told there is a big difference in rot resistance between the heartwood and the rest of the tree for cedar. What I can’t remember is which part of the tree was better and which was worse.
Bill
Generally the heartwood is considered more rot-resistant in any species because only the heartwood contains 'extractives' — chemicals which presents toxicity to fungi.
I'm not sure if 'oils' are distinct from extractives or if they offer a separate mechanism for decay resistance.
Extractives do accumulate in the heartwood over time, so the heartwood of second growth timber may have less of it than the old growth (speculation).
I attached an in-depth analysis of extractives in Western Red Cedar.
The sapwood/heartwood resistance gets flipped a bit with PT, however. Sapwood is more easily impregnated with the treatment, and so it is oftentimes the sapwood that has more decay resistance.
It's possible that the treatment is not impregnating the wood well enough and is being washed out. Even if the newer ACQ (and other) chemicals are sufficiently toxic to fungi, perhaps there are issues with its ability to penetrate and stick around in the wood?
You can buy products with different treating pressures and different amounts of treatment added. This is the case with at least some of the ground rated PT. i.e. the chemicals may not differ from 'above ground' rated but they have higher preservative 'retention' values.
+1 for proper detailing. In my experience, anywhere water can pool and debris can accumulate will start rotting out. Oak debris seems to be especially bad about that. Detail everything properly, and keep it clean to help things last. I’ve been told using ground contact rated PT lumber everywhere does help too.
The utility guys have been using creosote treated poles for probably a century or more. That stuff lasts. They still use CCA too, which is still permitted for a few limited applications. They had poles treated with a silver/blue material for a while too but I don’t know what that was. I’m not sure if regular dimensional lumber can be ordered with anything but the newer treatments though.
Bill
OTOH, I have a large deck on our house in Martha's Vineyard that's now 37 years old....Structure is PT and has no rot issues at all, perhaps because I have the earlier "bad" PT lumber. Decking is all 1x4 vertical grain fir space about 1/8" apart. We apply a coat of Thompson Clear Water Seal every other year. Starting about 10 years ago, a few boards have shown some decay, and I'd say we replace a few percent of the boards each year....I'd say at least 65% of the deck still has original boards.
Sounds like I am not the only one seeing failures after ~10 years.
-Where are you seeing the rot, specifically? Top and center of decking (are they cupped?),
-sides, underneath, nail penetrations?
The rot occurs in sections of individial boards and progresses from there. Generaly somewhere along the length of the board (not the ends). Hard to say if the locus is top or bottom. Looks to me like the rot is confined to areas where the pressure treatment concentration was either insufficient originally or leached out. Could also be sections of the tree with less rot resistant/less dense wood.
-Does full southern exposure imply full sun? How close to ground? Roof draining onto deck?
Defintely full sun. Well off the ground (>6 feet). Roof does drain onto deck. Others have mentioned that wet dry cycling is a particular problem and that is for sure an issue here.
-Perhaps one should use ground contact treatment even above ground? Or naturally rot
-resistant woods (eg, black locust).
Seems to me that there is an underserved market for rot resistant native hardwoods. I ocasionally see small mills offering black locust for outdoor applications (mainly fenceposts) but is is still a niche product. Anyone with experience doing a deck in black locust or other native hardwood ? If so, where did you get the wood and what was the price premium vs presure treated ?
Interesting datapoint... The railings on my deck are red oak. Unlike the presure treated deck boards, the railings have not been stained yearly. Red oak is really not a rot resistant species. Despite this, it looks like I am going to get at least 10 years service from the red oak before it needs to be replaced. I bought the red oak lumber green/rough sawn from a local mill. It was not much more expensive than softwood dimensional lumber. I am sure that if I could have gotten somehting like white oak (which is rot resistant) instead of red oak, the service life would be significantly longer than what I am seeing with pressure treated southern yellow pine.
I didn't do the purchasing so can't comment on pricing, but I have built boardwalk with white oak and some cohorts often build with Black Locust (based in Vermont). It's mostly small local mills, like you say.
You have to be thoughtful with the process as White Oak shrinks more than most softwoods and if laid green in full sun can develop stress cracks. Quarter sawing will help (and kiln drying).
Locust being smaller trees, decking will likely be narrower (might be a good idea for White-Oak too). I'd suggest trying out random width decking, looks nice (my opinion) and uses material better in the case of small mills.
Treated wood can last for many years with proper care and maintenance. However, the specific lifespan of treated wood depends on the type of treatment used. For example, pressure-treated wood that has been treated with chromated copper arsenate (CCA) can last up to 40 years without rotting or decaying. Similarly, acetic acid-treated wood can also last for several decades. In general, however, you can expect treated wood to last much longer than untreated wood.
I think this might help - https://woodworkingclarity.com/how-long-does-pressure-treated-wood-last/