Mounting plywood directly onto deck joists -- bad idea?

Due to space issues, I'm trying to plan out a woody that would mount directly onto my deck joists. There's about 4-5 feet of clearance, so idea is to mount a couple lengths of plywood along 3-4 joists and do some roof climbing. The rub is that it would mean screwing the plywood directly onto the joists. No easy access to fix T-nuts or any extra clearance if bolts are longer than 3/4". Would this be a total game breaker? I can live with a few T nuts going bad, or needing to glue/screw them into place before I put it up. But what about the bolts?

Unless it's a poorly/strangely built deck, it should pose no issues. Use lag bolts or structural screws to attach the plywood to the joists and it will be crazy strong.

Depending how this is positioned, the only thing I can think of that might be a problem is if water drains from above and is allowed to pool on the thing. Is it exposed to the elements?

Thanks. It'll be covered by the decking above, which is not water proof but will offer some protection from the elements. Also planning on painting the ply before it goes up.

What about having no clearance behind the plywood for bolts? Is that an issue? Not sure, given this is my first home woody. I suppose I could drill a little into the joist behind to create space for trouble makers, but that seems not ideal.

Get screw-in T-nuts as opposed to the pound-ins, and a thread tap & dye. Pending any weather-related damage, I'd say at a minimum you can make it last 5+ years without needing to pull the panels off for maintenance.  There's no greater frustration in route setting than when you are putting on a hold that is resisting because of manked threads, and the pound-in T-nut pops out on the back side.

Edit to add: 3/4" clearance on the back-side is fine. Just make sure to have a good variety of bolt lengths to ensure proper thread engagement without bottoming out.

i am having a hard time visualizing why there would only be 3/4" clearance for the bolts(?).  I am picturing deck planks on top of joists. Assuming the joists are 2x6 (guessing/example), and you are screwing plywood onto the bottom of the joists you would have 5-1/2" clearance for the bolts(?).

The plywood panels would be going onto either side of the joists, in parallel with them. The holds would hang on either side. That means no clearance behind them because the joists would be there. So just the 3/4" of the plywood itself and then solid joist. 

If that's the method you're set on then just screw 2x4 spacers between the joist and plywood.  Or just screw the plywood to the bottom of the joists for a true roof experience.

Worried about water pooling on top of the plywood if mounted underneath the joists as just a straight flat roof. Maybe I'll see about using a few strips of doubled up plywood every 12 inches or so to create some spacing for bolts on the backside. Thanks. 

I would definitely NOT mount plywood straight onto the underside of a raised deck joists. That will rot in no time and be a big, expensive mess. If you just trying to make a training rig, I screwed on some various pieces of outdoor trim straight to the 2x12s and have a solid 30 move power endurance rig.

I've thought about putting in a more formal wall and if I did that I would install a drainage system, they make a ton of different options. Just look up dry storage raised deck and you will find them. 

This just sounds like a bad idea. If your deck joists are only 2x6 that starts with a bad idea.

Tank Evans wrote: I would definitely NOT mount plywood straight onto the underside of a raised deck joists. That will rot in no time and be a big, expensive mess. If you just trying to make a training rig, I screwed on some various pieces of outdoor trim straight to the 2x12s and have a solid 30 move power endurance rig.

I've thought about putting in a more formal wall and if I did that I would install a drainage system, they make a ton of different options. Just look up dry storage raised deck and you will find them. 

Yes and/or just attach the holds onto the deck joists with lag bolts. You're not going to be setting problems so no real need to change the holds. I'd start with holds, then large campus board style rungs, then progressively smaller campus board rungs, until they are so small you fall off. Then you could work on getting farther and farther to smaller rungs as you got stronger. It would be fun to try to progress past your personal best. Maybe interspace some smaller and smaller holds between the campus board rungs. So big holds > big campus board rungs > medium holds > medium campus board rungs > small holds > small campus board rungs.

Edit: just reread the OP and saw you don't have a lot of clearance. So maybe my idea wouldn't work because you'd want to be dropping onto your feet.

Not sure I totally understand your dimensions, but I built this under-the-deck scenario last month, if it's at all helpful as a reference for discussion/visualization...

Attaching some pictures to make clearer -- sorry, it's a bit of a weird setup which is why I'm asking for advice. I have about 8' long x 5.5' wide by 4.5' tall to work with. Joists run long ways and there are concrete stairs on one side, so don't want to go over those. I suppose I could just mount screw-ons right to the joists, like Eric did. I was just hoping to create some modularity and ability to move stuff around (I doubt my abilities to nail route setting the first time!).

Thinking at this point, to give clearance for bolts, I can use an extra layer of ply every 12 inches or so, as spacers, and put T nuts in between. There's 16" between joists. So to have space to mount everything and move around, I could alternate panels back and forth. Like so:
Idea is with these panels running on each side of 3 joists or so, plus some strategic screw-ons on the posts or outside edge of deck, I can create a pretty flexible little cave setup.

so all of the holds would be mounted to vertical surfaces, like eric metzgar's photo?   seems like it would make the climbing awkward (always reaching around/over joists), and not really realistic - it is a lot easier to grab holds at that angle.  if you are doing it this way, it seems like just using screw on holds and going directly to the joist would be better.

You know it actually does not feel unnatural, surprisingly. My little training route climbs really well, but gets a bit old running laps un a horizontal roof. It definitely does not work the spectrum of climbing muscles but does get a raging forearm pump. I would highly suggest it to anyone with a raised deck, cost me about $30 and is a great workout given the circumstances.

Eric Metzgar wrote: Not sure I totally understand your dimensions, but I built this under-the-deck scenario last month, if it's at all helpful as a reference for discussion/visualization...

Overall, something like this is a much better option as it will net you a longer lasting, better looking cheaper, and simpler setup.

Tank Evans wrote: You know it actually does not feel unnatural, surprisingly. My little training route climbs really well, but gets a bit old running laps un a horizontal roof. It definitely does not work the spectrum of climbing muscles but does get a raging forearm pump. I would highly suggest it to anyone with a raised deck, cost me about $30 and is a great workout given the circumstances.

that's interesting to know.  i figured it would be kind of similar to when you are climbing an arete, and you reach around the side - the tiniest crimp feels like a huge jug.

Just use 5/4 decking boards instead of plywood with big gaps for air and drainage

For those keeping score at home and just to wrap this up, I eventually just built a steep wall under the deck that tops out on the outside edge instead of mounting holds underneath.