Aloha! I live on the Big Island of Hawaii on the Hilo side, where I get on average over 100 inches of rain a year.
I have several deck I want to build/rebuild in the new year and one problem I am trying to tackle is the existing short life of uncovered of uncovered wood decks I already have (e.g. exposed deck stair built 6 years ago are now rotted away).
The existing decks, built prior to be buying the place in 2019, definitely could gave been built better for rain exposure (no SS fasteners, no joist tape, poor paint/sealant).
Im wondering though if its worth the cost to build all of the decks (deck boards, posts, joists, etc) out of structural grade plastic lumber. Not the home depot stuff, but the big guns from someone like American Plastic Lumber (APL).
I have not received a quote yet from APL to do a material price list comparison, but am guessing it will be at least $10-20k over normal wood, once you figure in shipping. Its probably about 1500 sqft of deck space.
Anyone here have any experience building with structural plastic lumber? Or have good resource on how to rain-proof traditional wood deck builds from the crazy rain we get. Limitation is that only a portion of these decks can be covered, some by nature will be exposed.
Merry Christmas and Mahalo!
Here in Australia exposed wooden decks are common and last a lot longer than that. We do get rain as well as sun. It seems like in the USA treated wood has gotten a lot less durable but here we often use hardwood or naturally durable wood like cypress for decking and structural members.
You do see some composite but you also see it go interesting shapes sometimes in the heat. Can be too wide spacing or bad install but I don't know how posts etc would behave. And the cost would be ridiculous. And the end of life implications of tonnes of plastic give me some serious yuck haha.
If you're looking to spend more look into what a tropical hardwood deck would set you back. Merbau is common here and lasts ages.
What you need to change to make a wooden deck work will depend on what you're seeing rot on, but basically the fix is to let it dry cause it will get wet.
Deck boards need spacing, for exposed decks narrower boards are good to have more drainage per area, joists and stair stringers sometimes rot out from water held in tension so needs to be designed to avoid that, underneath needs to breathe (cross ventilation), grade below should take water away, posts will last longer with a raised footing (we still often put posts in the ground though. USA redditors seem to hate that)
Oil finish will let the structure last longer as it can be renewed easily (so you're more likely to actually do it) and won't hold moisture under paint flakes or hide rot behind a layer of paint. If you see an area staying wet you know there'll be a problem there.
You should get a lot longer than 6 years, though you'd likely want to add more oil at that point haha.
We have the Owens Corning Compisite lumber available from a local deck supplier. I have not built with it yet, but a 12' 2x6 costs about $110. A PT 2x6 runs me about $12. Your framing is going to cost about 10x what it would cost with a standard pressure treated frame.
You may want to look into aluminum or steel framing as well in your search.
I think your estimate of 10-20 over normal lumber might be low. I know the structural members where i am are insanely expensive compared to pt, at the minimum triple.
Look into the aluminum channel, replaces all wood. It's pretty impressive, but no idea of cost
Galvanized steel framing with composite decking/ aluminum railings probably 100per square foot
Personally I don't think composite is ever the right choice. Paying a premium for plastic just feels bad, better to pay for a rot resistant hardwood or maybe try one of the newer modified woods like Accoya (put their warranty to the test).