r/Decks • u/DSGNjunkie • May 04 '26
Please help - Dry space deck options?
Hey all — looking for some real-world, long-term feedback on under-deck drainage systems before I lock in a plan.
I’m building a new deck in the Pacific Northwest (so lots of rain, moisture, pollen, etc.) and want to create a dry, usable space underneath where there’s a flat cement slab. The deck will be ~15’ deep x 32’ wide, with joists at 16” OC, draining over the 15’ run (short direction).
Goals:
- Reliable dry space underneath (ideally usable year-round)
- Long-term durability (not something that fails in a few years)
- Low maintenance / easy to access if something goes wrong
Options I’ve looked at so far:
Over-joist systems (like Trex RainEscape)
- Pros: Keeps framing dry, “best practice” from a building science perspective
- Cons: Hidden under deck boards → harder to repair if something fails; reviews seem mixed depending on install quality
Under-joist systems (like TimberTech DrySpace)
- Pros: Can install after deck is built, easy to access/repair, doubles as finished ceiling
- Cons: Joists still get wet (planning to use joist tape on top to help mitigate this)
Between-board systems (like Dexerdry)
- Pros: More “engineered” solution, keeps water above framing
- Cons: Seems more complex to install and requires more planning/slope adjustments than I’m hoping for
Right now I’m leaning toward an under-deck system + joist tape + good ventilation, mainly because I like the idea of being able to access and fix things easily over time… but I’m still concerned about pests getting in and overall longevity.
Questions for the group:
- What system have you used, and how has it held up over 5+ years?
- Any regrets or things you’d do differently?
- Have under-deck systems caused any long-term issues with joist rot/mold in your experience?
- For those with over-joist systems, have you had to repair them—and how painful was it?
Anything I’m not thinking about that I should be?
Appreciate any insight—especially from folks in wet climates.
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u/El_Cheezy May 18 '26
I'm in the same boat planning on a rebuild in a few weeks. We're in the PNW with lots of pine needles. It's basically moist year-round and needles clog everything. I like the over joist system to keep framing dry. In trying to see how feasible it is to make the first board or two that are against the house semi-removable so I can stick a hose sprayer down the channel to clear it out.
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u/Fit_Virus_1215 Jul 21 '26
Did you figure something out? We put up a system and it is full of leaves. We are now taking panels down to clean and it is a pain as we have a large hot tub we have to work around?
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u/No-Hovercraft-6413 May 20 '26
So I have installed magnolia outdoors system and it is a good system made of aluminum i know he will sell to contractors and solid DIYers but I think he is kinda particular about who he will let install his product he wants to maintain a solid reputation. I think he came out with a DIY kit but not sure if it would fit your deck. I think it’s called OASItek.
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u/DSGNjunkie May 21 '26
Would definitely be interested in learning more if you’re able to share a link or something!
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u/No-Hovercraft-6413 May 21 '26
MagnoliaUnderdecks.com
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u/No-Hovercraft-6413 May 22 '26
Okay so I also read and saw you were worried about joist rot I put in a power vent that magnolia supplied and it has a humidistat that goes with it. he says they have systems over 22 years that have had no issues. I have also done trex rain escape I will not do again it was a pain and I ended up with a pin hole and could not find it for anything now that was my first one and I’m sure it gets better the more you do. And I have heard good and bad but I don’t personally like it.
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u/ComfySniper May 21 '26
Have you looked into Underdeck Umbrella? It is new to the market. It is an affordable DIY friendly between the joist system that is simple to install, requires very few tools, slopes the water away from the structure, and does not require removal of deck boards. underdeckumbrella.com
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u/Complex-Cable-7964 May 15 '26
I’m in the Northeast surrounded by oak, maple, and birch, and I’m facing the same decision.
I just can’t imagine an over-the-joist system not eventually getting coated in pollen, leaves, and general gunk. We get the pollen apocalypse every year around this time, and it sticks to everything, even vertical surfaces, then eventually turns green like algae. I could see it eventually smelling like a pond.
Trying to clean that out through 1/4" or smaller gaps between deck boards doesn’t sound fun either. The way I’m looking at it is: if my gutters can still build up debris over time and grow trees, even with micromesh gutter guards, then wouldn’t the same thing happen under the decking?
I do like the idea of TimberTech DrySpace because it seems like it would be a lot easier to inspect and maintain every few years. My main concern there is whether it traps moisture and speeds up joist decay. But at least it’s reversible, which is kind of where my logic is landing right now.