Just moved into a 5 y/o house with a "maintainence free" Trex deck. Underneath, it's supported by lumber as shown below

enter image description here

When it rains the water drips through the deck slats and leaves this green moss on the lumber. I'm wondering a few things:

  • Does this lumber require any maintence? Ie do I have to weather seal this every so often?
  • Does the green moss cause the wood to deteriorate faster?
  • Can this type of wood be pressure washed? If so, does it need treatment after?


  • Not clear from the picture if you have "moss" or just copper oxides from the pressure treated lumber. Both are green, one is highly unlikely, one is very likely and not a concern.
    – Ecnerwal
    Commented Oct 4, 2020 at 17:03
  • I'm quite positive it's moss or something because it gets worse after rain and during spring/summer. Is the moss the ok one of those two ? Commented Oct 4, 2020 at 17:49

1 Answer 1


That framing will last decades with no maintenance. I just replaced the decking on my mother's 20-year-old pool deck which had not been well-maintained through the years. The framing was all in good shape though the decking was rotted and warped.

With that said, if you want to wash it for cosmetic reasons, it won't hurt to do that.

  • That's great new sthanks. Commented Oct 4, 2020 at 17:49

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