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Wood Rotting on Tree House

456 Views 6 Replies 4 Participants Last post by  HotRodx10
I purchased a home two years ago and about a hundred yards off the house there was a tree house my daughters love. I've built a new roof, walls and ladder. During COVID, my daughters and I took up all of the rotting exposed deck boards and put down some new ones. Unfortunately, a few weeks later, I can tell that several of the boards seems to be loose and it looks like I drilled them into a rotting board.

Unfortunately, the board in question is the main board holding up the tree house on that side as well as how the ladder attaches to the tree house. My idea is to get another board, pressure treated wood and cut it to length, maneuver it into place under the deck and then drill and carriage bolt it to the rotting board. Then drill the deck boards into the new board.

However, I think it'll be really, really hard to fit the board, there are braces holding the original board to various other pieces that the new board wouldn't be and I can't think of how to replace the actual board with a new one given that it's holding up that side of the house.

Hoping that I'm overthinking this and someone has an easier solution :)


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So I'm reading about using something to drill out the dead rotting wood and then filling in with an epoxy wood filler. Does anyone know if I can drill a hole into a wood filler and expect it to hold?
Could you fit in three or more shorter joists running a few inches away from and sistered to each other after placement and parallel to the rotted board (rim joist?)? Enough to hold the other pieces together in proper positions and also support the rest of the structure without people in it?

From the vantage point of the lower picture the new pieced together joist would run from a little above lower left to top right of center.

Temporarily add some extra boards ont top of and parallel to the deck boards to hold the ladder a little ways away from the rotted board while you work.

Then cut away the rotted board completely little by little and insert a full size full length replacement?
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Inspection of what you had should have been job one.

Cut way the rot, paint everything with a copper treatment and sister on new beside them.
Is the entire joist (board) rotted, or just the top inch or 2? It's common for joist like that to deteriorate at the top edge, but be solid the rest of the way down. If that's the case, you should be able to sister a 2x4 or 2x6 (depending on the depth of rot) on to one side or the other. If there's too many obstacles to put it behind, you can put it on the outside and just use longer screws to attach the new deck boards (unless you're willing to replace the deck boards with longer ones).
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Thanks for all of the suggestions! I think from these suggestions, I'll put in a sister board right next to it and drill the floor boards into that one. For the one that's there, is it better to cut away the rot or leave it? It does look like it's only the top inch or so at the worst. But is it better to cut it away or leave it alone?

Thanks again for all of your suggestions!
It's probably better to cut off the rotten part and then put a sealer on it (deck stain, spar urethane, penetrating sealer, etc.)
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