building a deck that will last...responsibly

Hi All,

After an historic winter in New Brunswick in terms of snowfall that left 10 ish feet in some spots the large (approx 1500 square feet) deck that attaches to my parents house is finally in need of replacement. The current deck, built around an in ground pool was completed in 2000 and constructed completely of locally harvested and milled Eastern White Cedar decking on full dimension 4x6 framing on concrete posts. It was treated annually with a coat of water seal. Although the deck did not collapse under the insane amount of snow this winter, it will likely not survive another. Both the decking and framing are suffering from rot in places and some of the beams from stress due to the snow load.

One possibly fatal design flaw of the current/old deck was that the decking itself was laid without significant gaps between the boards. During construction the boards pressed tight against one another and though water did not appear to pool during the seasons when the deck is not covered in snow I can't help but think this shortened the lifespan.

My dad started ripping it out this week in hopes of replacing it by mid summer. The new version will be smaller at about 1200 square feet. I just spoke with him about it and he mentioned he was considering using pressure treated this time around.... I'm trying to convince him otherwise. I understand that the new style of pressure treated lumber is less nasty and doesn't contain arsenic but I still have a hard time trusting it. Although he is reluctant to do so, he isn't happy with the lifespan of the outgoing deck and has been looking to engineered products such as pressure treated and laminated products (trex, hardi board/deck). We both agreed that the laminated/composite products don't last in the climate as we've seen some examples of them being destroyed by freeze thaw cycles within a few years. Things are very wet here, a maritime climate that sees freezing temps through most of the winter often with multiple freeze/thaws toward the beginning and end of the cold season...not a rainforest but stuff rots quickly compared to drier places with similar temps/winters. He is considering going with some kind of alternate (possibly steel or aluminum) beam as well if it could be more resilient.

I know that there must be an example of a design that could last longer in our climate, but all examples in the area are pressure treated, mostly painted and have been built at longest 25-30 years ago.

What is the longest that an exposed (no cover, ideally a natural finish) deck of untreated materials last in this climate?

Are there design practices which could help mitigate the issues and extend the life?

Are there any safe, proven engineered materials to use that are worth it or could significantly extend the life of the structure?

Any thoughts or suggestions would be greatly appreciated!

I'm hoping that even if the lifespan of a 'natural' built deck can't compare to one built of engineered products I can convince him based on safety and cost savings of using locally available non manufactured materials. I'm really hoping however that a 'natural' built deck CAN compare to those other products...

Edited to Add: The new porcelain finish product SigmaDek has come up in conversation. Its basically brand new as far as I can tell and more or less unproven but any opinions on it would be great. HOWEVER, locally sourced straight up lumber is the solution I'm pushing for as it is known as a material, non toxic, and has low embodied energy not to mention low cost by comparison. The trick is to get it to last!!!

THANKS!
j

Maybe have some one source/mill some naturally rot resistant wood.

Exceptionally resistant: black locust, red mulberry, osage orange, and Pacific yew.

Resistant or very resistant: old-growth bald cypress, catalpa, cedar (either eastern or western red cedar), black cherry, chestnut, junipers, honey locust, white oak, old-growth redwood, sassafras, and black walnut.

Moderately Resistant: second-growth bald cypress, Douglas fir, eastern larch, western larch, old-growth eastern white pine, old-growth longleaf pine, old-growth slash pine, and second-growth redwood.

I am not sure what your building codes are, but some inspectors want at least graded wood here in usa. Some are impossible and want treated lumber only.

Thanks for your input Chad..

Unfortunately most of those suggestions are fairly unavailable locally. New Brunswick has a long history of poor forestry practices and there is no old growth anything available anywhere I'd wager. Even second growth would be quite rare. Eastern White cedar however is quite plentiful, I believe that is what makes up the majority of what is sold in NB as cedar. Could be that there's some red cedar in there too, but according to my sources its not native, or prolific in the area. I've even read in a couple places that Eastern White is superior to Western Red in terms of rot resistance.

Personally, I think Black locust decking could be brilliant but the tree is almost unheard of in NB even though it should be native to the area. I can't find any mills locally that sell it...its all in the US it seems

I imagine Black Locust on White Oak frame would be awesome and would be exceptionally strong. I also imagine it wouldn't cost more than the engineered products under consideration with the exception of pressure treated.

As for the inspectors I doubt that they will ever know the project is under way. Though the folks are situated in town, the property is 9 acres of forest and field surrounded by more forest..also he used to be the inspector, a volunteer firefighter for 20+ years, and generally involved with the town so he can more or less do what he wants.

I'm also thinking that some of the problem with the previous deck, particularly the rot problem should be able to be helped with some intelligent design around where the beams meet the concrete posts. I'm thinking a lot of the rot occurred due to moisture sticking around where decking met beam and beam met post. Maybe some kind of mechanical fastener or interstitial something or other would be appropriate?

If anyone has any info on suppliers of Black Locust Decking anywhere East of Manitoba, or has been able to get some from the US into Canada I'd love to hear about it. I'm not sure the policies and politics on getting lumber across the border but I know its supposed to be tightly controlled.

THANKS!
j

Natural non lumber specific trees last much longer than hybridized lumber forests. I am not sure if it applies to wet rot, but a common source of borax can be to treat atleast against spores and fungi. Wood shouldnt be touching concrete. If piers are a must, use some sort of method to keep at least 1/2 inch space from each other. There are people better than me in this subject. I prefer full blown natural building, but i understand not everyone enjoys the aesthetics. Is the rot crumbley, or does it fall apart under pressure? I am going to assume crumbley. Wood doesn't necessarily mind being wet, but it does mind when fungi moves into those wet spots. So a mild fungicide, naturally resistant woods, and well though design are my only ideas. Maybe some beeswax covering the tops of jointed wood? Idk, maybe these people could point you in the right direction.


Peter de Graaf; Berwick N.B. E5P 3A1 (sawmill)
506-433-1381

London lumber
1979 Melanson Rd, Greater Lakeburn, NB E1H 2C6
506-859-2440 

https://forum.canadianwoodworking.com/showthread.php?41786-Hardwood-Lumber-suppliers-by-province

Thanks again Chad,

Unfortunately I'm unable to say the exact nature of the rot since I'm not there and the folks are now away for a bit. I wish I could get a look at it to see where exactly the rot took place but won't know that for a couple weeks when they get back. In terms of the concrete posts they were poured 15 years ago and are standing strong so I don't see much use in not using them this time around, even if they aren't what you or I would choose if this were a project starting from scratch. I honestly am not sure if he laid the beams directly on the post or not, but I seem to remember him using large shims (chunks of framing) attached to the beams between them and the concrete piers/posts. I think the intention would have been that as they rot, they would be able to be replaced. I definitely like the idea of using a bit of borax to help slow the fungal invasion and rot. Maybe the rot began where the concrete met the shim meet and migrated? Is that a thing?

To be clear this is not about natural building vs. conventional building, or aesthetics, its about trying to learn about the best natural local materials and practices for creating a lasting structure in the climate and trying to understand what the realistic longevity of such a structure should be. Honestly the previous structure was pretty 'natural' in that it was locally sourced untreated material...even if it was surrounding a pool. I'm trying to convince someone to go the more natural route, but I need to understand how the available materials and designs compare t one another and what I can expect from them in terms of longevity.

Still no luck after following through with some of the links finding anyone who sells black locust in the area, again I have my doubts seeing as no one seems to even know about it, and I've literally never seen it growing in the province. There is a nursery that sells a curly black locust as an ornamental, but that's all I've found. Oak is a possible option but seems a bit excessive price and strength wise for something that is only supposedly as rot resistant as the eastern (aka northern) white cedar that was initially used. Non of the other options noted of exceptional or even moderate rot resistance are very available here. I've also found no references to there being a lumber hybrid of eastern white cedar after doing a quick search. It grows all over the place in NB (my land has a good lot of it) and the only hybrids I've been able to learn about are a small but fast growing variety used in landscaping. I highly doubt the decking used previously was cut from a hybrid.

So - maybe I should shift my questions a bit and get a bit more specific....Let's assume that I have only something such as Eastern (northern) White Cedar, which is widely understood as being the most rot and pest resistant lumber available locally. If your not using pressure treated, your using cedar. SO in that case...


What are best design practices for building a deck with longevity in mind using eastern white cedar?

we've covered making sure there is some kind of stand-off between the concrete post and the beams.

possibly leaving a gap between the decking of at least 1/8" to make sure it drains properly.

what about a borax treatment 10 years in?

is there some kind of non-toxic oil, stain, or seal that could help the situation?


What could one honestly expect to get out of a deck constructed using these practices and materials?

For all I know 15 years is a reasonable lifespan for a deck of this kind in this climate..anybody have experience in this space?

THANKS!
j

Hello Jay,

First let me apologize if I repeat anything that Chad has already suggested...

I will go through and try to add only new infor or make suggestions where applicable. This entire subject of "decks" has been coming up a lot in the past few years as folks try to build them more "naturally." Good news is...it can be done, and they can last, often longer than the "modern methods." I do let folks know that any wood likes to be under a cover (i.e. porch style) but wood exposed can work for a long time (most well built old ships could last 75 to 150 years with only good maintenance before major overhauls are required...)

The other subject that has come up as of late is "safe wood treatments"....Of the commercial variety, I suggest reading about: Acetylated wood

For additional reading (so I don't have to rewrite stuff...) these Permies.com post and web sites are very infomative...

recipes for treating wood

Wood Preservatives

Mineral based "pest control" with Borates

Timbor is a natural insecticide/fungicide...

As I read (scaned) through your posts here are some things that jumped out at first...

"Water seal" like Thompson's is probably one of the worst things to ever put on wood...It is one more "modern product" that doesn't do as advertised, or at least not as well as the chemical companies would lead us to believe...I find it cause way more issues than helps...

"On concrete posts," Bad and very bad...not a thing to do even with pressure treated wood, yet it happens all the time...Wood...does not!....like OPC and wood should be off of grade at least 300mm...

Yes!!....lack of gaps between boards for exposed wood is a recipe of disaster!

My dad started ripping it out this week in hopes of replacing it by mid summer. The new version will be smaller at about 1200 square feet. I just spoke with him about it and he mentioned he was considering using pressure treated this time around.... I'm trying to convince him otherwise.

PLEASE DO!!

As this will last only half as long in most cases unless he goes with something like the Acetylated wood, yet the "jury is still out on this too..."

Go with a species like cedar or related rot resistant one like locust which is found up there. It is a matter of "design" and proper "means, methods, and materials," more than anything else...

...he isn't happy with the lifespan of the outgoing deck and has been looking to engineered products such as pressure treated and laminated products (trex, hardi board/deck). We both agreed that the laminated/composite products don't last in the climate as we've seen some examples of them being destroyed by freeze thaw cycles within a few years. Things are very wet here, a maritime climate that sees freezing temps through most of the winter often with multiple freeze/thaws toward the beginning and end of the cold season...not a rainforest but stuff rots quickly compared to drier places with similar temps/winters. He is considering going with some kind of alternate (possibly steel or aluminum) beam as well if it could be more resilient.

He shouldn't be happy with that level of durability, yet I believe it is more "method" than material...that is at issue. Photos would be great.

How high off grade is this deck??

...I know that there must be an example of a design that could last longer in our climate...

Well...I haven't published mine as of yet, and I am getting pressure from "those business types" in my life to stop "given' stuff away," but I am tempted to make my timber frame deck plans available. At minimum I go through key elements here...

What is the longest that an exposed (no cover, ideally a natural finish) deck of untreated materials last in this climate? What could one honestly expect to get out of a deck constructed using these practices and materials? ]For all I know 15 years is a reasonable lifespan for a deck of this kind in this climate..anybody have experience in this space?

I suspect...if designed well and maintained, I don't think 30 years is unreasonable and maybe as long as 100...It depends on the quality of the wood also as well as variables in seasonal changes in weather...

In some areas, with certain species, and method of build...15 is a reasonable time to last...Then its off to the "hugelkultur pit,"

Are there design practices which could help mitigate the issues and extend the life?

ABSOLUTELY...!!

Are there any safe, proven engineered materials to use that are worth it or could significantly extend the life of the structure?

If modern material...all stainless steel...If natural (my pick) all stone...or stone and wood...

Here is a motivational photo for you...

I'm hoping that even if the lifespan of a 'natural' built deck can't compare to one built of engineered products I can convince him based on safety and cost savings of using locally available non manufactured materials. I'm really hoping however that a 'natural' built deck CAN compare to those other products...

If your Father needs to talk with someone with "gray hairs" on this subject, I am always glad to chat...

... SigmaDek has come up in conversation. Its basically brand new as far as I can tell and more or less unproven but any opinions on it would be great...

Well...Sigmadek is an aluminum version of the what I referenced above. It is new...it is unproven, but I will admit that the company is working hard at sustainability, and a employing a system that is recyclable...Will it be recycled?? Can it be?? Will it not also corrode over time and how long...What will it be the ?? "the devil we know" or the "devil we don't yet understand..." I don't have a square meter cost for this yet confirmed but what I was "told" is...very expensive!!

What are best design practices for building a deck with longevity in mind using eastern white cedar?

Well I am working on a post for that...until then see if these give you some ideas and/or more questions...

scribing posts to stone

Attaching roundwood posts to poured foundation piers

"Line Rule" methods of layout for Timber and Log

Korean Hanok

possibly leaving a gap between the decking of at least 1/8" to make sure it drains properly.

If you are in a moist biome, and/or too close to the ground, I suggest more like 20 mm

what about a borax treatment 10 years in?

See referenced posts...

is there some kind of non-toxic oil, stain, or seal that could help the situation?

See referenced posts...

Hope this all helps...When you get through reading this, let me know if I can answer more questions...

Regards,

j

Jay,

As usual thanks for the epic post! I'm familiar with a lot of those threads already and once my dad is back on the continent we'll have a chat and maybe get some pictures of the situation to see if we can diagnose where the breakdown of the old deck began and move forward from there.

Thanks, and more soonish I hope!
j