Definition of 'wet service conditions' 1

[atrizzy]

I'm designing an outdoor deck that the contractor wants to sheathe with plywood and waterproof with a weather membrane on the top and sides. The contractor's proposing to use pressure treated posts, but for the joists and beams he's asking if non treated lumber will do. From a strength perspective, I'd love to avoid the strength reductions associated with wet service and treatment.

I'm personally not sure. The framing will be exposed to moisture but likely only minimally to actual water.
So... who's got an opinion about this? Or better yet, a reference?

I'm working in Canada, if it helps.

Thanks ahead of time!

 

[r13]

Ambient air contains moisture, will, or wont it causing some problem for wood in outdoor environment? Link

 

[atrizzy]

Good question, retired! Almost like I asked it myself. I don't believe the link addresses it specifically.

 

[jayrod12]

In the Canadian wood design manual there is a paragraph describing what would be considered wet service conditions. I'm not going to type the entire thing out but in my 2015 WDM it's on page 672 in the reference information chapter.

There's also a brief definition under service condition in CSA O86. It essentially says the average moisture content of teh solid wood over a year is 15% or less, and no greater than 19%. to get the wood to 19% it almost needs to be submerged if I remember correctly.

 

[atrizzy]

Found it! Thank you jayrod! I believe this clarifies it for me.

 

[r13]

As suggested in the linked paper above, submerged wood is rather durable, the detrimental effect is due to cyclic wetting-drying. However, the effect is less important in the North America than the south. Just something to keep in mind.

 

[atrizzy]

Yeah, my issue won't have any submerging whatsoever. Rather the occasional splash and frequent exposure to moist air (not water).
I'm leaning heavily towards dry service due to the presence of waterproofing.

 

[dik]

If exposed outside, the issue may be that moisture can be trapped in the joint between the deck and joist... or whatever... this can lead to brown rot conditions (aka 'dryrot').

Dik