roof sheathing: anyone ever use pressure-treated plywood?

[jaotguy]

use the cheaper OSB or plywood ... coat with shellac or marine varnish on the underside ( exposed surface to your moisture ) ... install on trusses ... tar paper the first 4-8 feet from lower edges ( or whole roof surface if you're $$$$ enough ) ... install regular shingles ...

the shellac will soak in and seal the wood ... marine varnish will last a long time ... the tar paper protects the leading edges and stops the tar from the shingles bleeding out and into the wood surface ( if you don't, the shingles lose 5-8 years of life ) ... and any "warranty" you see on shingles is pro-rated on the shingles only ... not worth the powered to blow your nose ...

just some other options to look at ....

 

[Tollster]

My father lived in Arkansas on a large lake that was subject to high winds, and humidity never seen before by a yankee, he used corrugated metal roofing on his boat dock and boat hoist building with no ill effects. I believe it was installed in 1996 and is still in place..

I know it may not offer the more refined look, but it served very well and continue to do so.. His dock was custom fabbed, 4 or 6" pipe serve as the piers, and the rafters where welded up on sight, yes, they are metal, and I wanna say they came from a metal chicken barn.. The only wood is the planking. The roof is screwed into the metal rafters, and I believe he used some sort of washer system.

 

[roadhunter]

I've build many boat docks in Oklahoma and we would never use wood for anything. Galvanized metal is the best material for structures around water IMO. On the roof I we used 7.2 panel in 24 gauge primarily. Much stronger than the cheap 26 and 29 gauge r panel on most pole barns. If I was you I would not use sheathing as I believe it will hold moisture/condensation between it and the sheet metal. Every boat dock I have been on that had sheathing or insulation had moisture issues from condensation.

Pics of this type of construction
KitDock

 

[PILOON]

If I can add my 2 cents, I'd also urge the metal roofing. You can get it in galvanized as well as in different gauges.
Rather than using the usual screw patterns you could do every purlin and every ridge if you are concerned with winds.
Galvanized roofing screws are also available.
Rafters at 24" with purlins at 16" will carry a he** of a load.
Metal roofing wants to breathe and your project will satisfy that requirement.

 

[Pete Judd]

How old are you, and are you and are you thinking of leaving it to the kids, or selling in the near future? Makes a dif in materials used.

 

[s219]

I am looking into metal options for the roof -- I can get 29 ga, but 26 would be harder to track down. Any thoughts as to whether 29 will be strong enough? I'd prefer as few screws as possible, which makes me think 26 would be more desirable, if I can get it.

 

[radioman]

I really dont think weight will be an issue AFTER its been installed and aired out. Almost all pt wood here becomes much lighter when it dries out and I never had twisting if it tied into other parts of structure within the same week, like nailed in, screwed, etc. You can always add blocks in between the rafters to give it more structure support and reduce twisting. It helps with snow loads and winds too.
As for carrying the wood - I wouldnt try to carry all that stuff that far plus walking down the stairs with plywood -- its an accident waiting to happen. I would drive to the closest dock and load up majority of wood on a boat or barge and take it to the site. This way there is less chance of getting hurt on the stairs. I dont know if you have a boat or barge or pontoon big enough for this though. I seen both asphalt and metal roofing as well in the bay I worked on. The ones with asphalt looks more homely, but the metal ones you can tell if it cheap or luxury type of install.

 

[s219]

The hardest part with plywood would be carrying it through the woods. Once at my stairs, it can slide on the railings while I walk down.

I do think I have found a good metal roof solution that will only cost a couple hundred more than asphalt, including freight. So I am going in that direction now. It would be 26 ga PBR panels 3' wide, which will weigh about 21 lbs in the length I need (they can custom cut to exactly what is needed, so I will order them to get a 2" overhang past rafter tails).

I am seeing mixed information about metal roofing on treated wood purloins, so I left a voicemail with the metal supplier to get their take. I am thinking I could put a strip of roofing felt down between the panels and each purloin and then use galvanized screws. But if that is still not recommended, I can probably go with regular wood on the purloins and not have issues (rafters and all else would still be treated).

 

[roadhunter]

I am looking into metal options for the roof -- I can get 29 ga, but 26 would be harder to track down. Any thoughts as to whether 29 will be strong enough? I'd prefer as few screws as possible, which makes me think 26 would be more desirable, if I can get it.

Stay away from the 29 gauge IMO. Its' thin and flimsy compared to the 26 gauge. 26 gauge would be minimum thickness for this project IMO.

 

[s219]

OK, so I put in an order for 26 ga PBR panels with charcoal paint finish, 16 of them, along with ridge cap, gable trim, and foam gasket for ridge. Should be here in about 10 days. Will order galvanized screws separately.

The good thing about the 26 ga PBR is that it will support my weight, which is a big deal in this case due to limited access around the roof. Here's a shot looking down the ladder this evening as I finished up the header framing:



The panels are 21 lbs each, which will be easy to transport and get up onto the roof.

I need to run through some wind load calculations to see what spacing I need for rafters and purloins now that I am going with metal. My default would be 24" spacing for both, but wind loads may push one or both to 16" spacing.

Thanks for all the inputs, I appreciate the advice/feedback.