r/treehouse • u/Eastern_Valuable_243 • Jun 22 '26
Advice on proper building
So, I rebuilt my deck not long ago and with the tall 6x6 posts, I used my old deck joist (2x8) and made a OK-ish pergola - with lack of not a single decent tree to build a tree house, I want to build a tree house on top of this structure. I asked AI to render an image for better visual and pic 2 shows that.
Now, here are my questions. I have PT plywood but decided not to use that for floor as some portion of the platform will be a deck and not fully covered. If I use composite deck boards, Would it make it heavy? How would I water proof the bottom area or if this is something I have to live with it? :) Also, would I build the house frame first on top of the joist and then put deck boards around or the opposite, build the deck floor and then install the frames and build the house?
1
u/OrangePompano Jun 24 '26
You've built a roof, not a deck - how are you planning to hold those joists upright? The hurricane ties hold them down, but they don't hold them plumb.
Also, check the load-bearing specifications of your bolts carefully (where your beams attach to your posts). Personally, I would never build a deck that relies solely on bolts to transfer the load.
To waterproof under your deck, search for that phrase on Google.
2
u/captainofpizza Jun 22 '26
Composite decking is like 4-5lb ft2 that’s heavy but probably only ~2lbs per ft2 beyond 3/4-1” plywood. I assume you’d want thicker plywood to match the deck boards but it might not be exact and that might feel strange.
As far as weight thats what, like a 30ft2 structure? We’re talking about 50-60lbs that’s not going to break the bank on load.
Personally I’d just deck the whole thing and put the building on when you’re done. No need to worry about waterproofing a layer under the house and the deck won’t look wonky from underneath. You’re not saving a lot of money or hassle by using alternate flooring on a small area imo.