Under-joist vs between-joist deck drainage
Some systems hang a ceiling under your joists. Others go between or over the joists, under the deck boards. The big difference is whether your boards come off.
Side by side
| Feature | Under the joists (ours) | Between or over the joists |
|---|---|---|
| Where it goes | Below the joists, with the deck boards in place | Between or over the joists, under the deck boards |
| Material | Aluminum with a baked-on finish | Varies. Aluminum channels or a membrane, depending on the system. |
| Rust and corrosion | Aluminum doesn't rust | Depends on the material |
| Install on an existing deck | Yes, from below. Most decks take 1–3 days. | Yes, with the deck boards lifted |
| Deck boards removed? | No | Yes, then put back |
| Best time to install | Existing decks, or new ones once the framing and decking are done | During a new build, before the boards go down |
| Headroom used | Typically 3–5 in. below the joists | The drainage sits between the joists, not below them |
| Cleaning and access | Hose rinse; panels unclip for a deeper clean | Gutters and downspouts still need cleaning |
| Lighting options | Flush star lights, plus mounts for fans, surface lights and heaters | A finished ceiling below can take recessed lights, fans and speakers |
| Typical installed cost | About $33–$52 per sq ft, $6,500 minimum. A 16 × 25 ft deck: $14,800 – $18,400. | Varies. On an existing deck, the job includes lifting and relaying the boards. |
Our price comes from the same calculator as the estimator, with standard colors and no add-ons. Other systems differ by maker and installer, so where we say “varies”, ask for the specifics. Price your exact deck
When a between-joist system is the better choice
You're building a new deck
The joists are open before the boards go down, which is when these systems are meant to go in. On a new build, downspouts can be hidden inside columns.
Your deck boards are coming off anyway
If you're replacing the decking, the joists will be open regardless. Some systems also cover the tops of the joists with an ice-and-water shield while they're exposed.
You want the drainage hidden and recessed lights
The drainage sits up between the joists, hidden by a finished ceiling below. That ceiling can take recessed lights, fans and speakers.
How to choose
- 1
Ask whether the boards are coming off anyway. If you're building or re-decking, look at a between-joist system. If not, an under-joist ceiling leaves them alone.
- 2
Measure from the patio to the bottom of the joists, then ask each installer how much of that their system takes.
- 3
On a new build, decide before the decking goes down, and talk to your builder early.
- 4
Ask how you would reach the gutter, downspout and drainage later.
Questions about under-joist and between-joist systems
Do you have to remove my deck boards?
No. On an existing deck everything installs from below, under your joists. Your deck surface isn't touched. Systems that go between or over the joists sit under the boards, so on an existing deck the boards come off and go back on.
Which is better for a new deck?
Either can work. A between-joist system goes in while the joists are open, before the decking. Ours goes in after: we coordinate with your builder and install once the framing and decking are done.
Which uses less headroom?
A between-joist system puts the drainage up between the joists rather than below them. Ours sits below them, typically 3–5 in. below the joists.
Can I get recessed lights?
A between-joist system with a finished ceiling below can take recessed lights, fans and speakers. Ours takes flush star lights set into the panels, plus mounts for fans, surface lights and heaters.
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