Decks, Patios, Porches and Docks - Lake Dock Refurbush

I have a dock on a large lake in Florida. The top planks
are 2x6 treated lumber and were last replaced in 1985.
Now some are a little saggy, and all have cracks and splitting
from weathering. I can't complain about a 20 year life span.

However I am thinking of replacing the planks with a composite
planking. The pilings and joists between them are in great
shape so they will stay as is. The joists are spaced about 3
feet apart and are notched into the pilings. (Yhe only other
structural members are 2x8 tieing each piling to the one
parallel to it.) The deck planks are a total of 4 feet wide ( one eight foot 2x6 cut in half). The dock extends 200 feet from the shore.

I know compsite decking needs a lot of support. Do the planks
come in various dimensions? If I use a composite plank, what
structural support changes should I make?

Thanks,
Jim

Jim: you won't be able to span 3 feet with the composite decking. We normally only span 16 inches with 5/4 composite, although you may be able to push it a little. If all you have is a 4' span with 2x lumber with no mid support, you are probably the luckiest dock owner in Florida considering the age of the wood. I would split the difference between the joisting and add more to support the composite. Using the composite screws (a little more expensive), and not deckmate or nails, you will have a neater job and little feet won't get boo boo's from nail pops. Lefty is our composite guru from California, and when he wakes up he will chime in on this, I'm sure.

Thanks Chandler.

Though the deck width is four feet, the
actual span is probably closer to three feet, with a six inch
overhang on each side. So if I add a middle 2x6 the center
to center span for the decking would be 18 inches. Adding
2 joists would make it 12 inch spans but probably would
verge on being too expensive given the already high initial
cost of the composite decking. The dimensions are pretty
common around this lake and in our case were establised in
1945 when the first structure was put up (before I was born).

I think a 12 inch span with composite decking would produce
a high quality, sturdy dock, but perhaps not one I would recoup
the costs of if I ever sold the property. To stay closer to the
consturction in this area maybe I should use 2x6 treated boards
for the decking but use something like Thompson's water seal
to retain a better surface conditions over the years? Given this
dock is 200 feet long its not a small job.

I am editing this post to add an idea that I had while sufing the web.
ThruFlow of Canada has an interesting product and is referenced
by the Army Corps of Engineers in Florida for use in docks that are
in areas of seagrass (not my situation). But looking at their installation
guide it made me think of a running the deck material in the long direction
of the dock, rather than 4 foot planks across the stringers. This would
require 2x6 cross pieces between the stringers which could then be
placed at any span required. Decking would not have the be cut, and
fewer cut ends might lead to a longer lasting deck. I've not seen a single
dock on my lake decked this way, but except for ladies' high heels I
doubt it would effect walking. Of course no, or very little overhang would
be on each side (so the edge planks might need ripping if the dimensions
weren't just right, and when does any rough contructions have just right
dimensions?).

Any comments? I haven't ruled out the ThruFlow product but need to check
prices for composite deck material as well as the ThruFlow HTPE components.

Jim

Jim