Under Decking Systems
Turn the wet, wasted space under your raised deck into a dry room you can actually use. Installed by a Riverside contractor with 35 years on the job.
Dry Space Under Your Raised Deck
If you have a raised wood deck, you already know the problem. The boards have gaps between them, which is exactly how a deck is supposed to drain. Every rainstorm, every time someone hoses off the deck, water runs straight through those gaps and dumps onto whatever is underneath. The patio set rusts. The storage gets soaked. The whole area sits there as dead, muddy ground when it could be a dry, covered room you actually use.
Under decking fixes that. We install a drainage system in the joist bays beneath your deck boards. It catches the water that falls through and channels it to a gutter and downspout, the same way a roof does. Once it is in, the ground below stays dry. You can put a patio down there, run an outdoor TV, store a mower and tools, or just have a shaded spot to sit out of the rain. The deck on top works exactly as before. The space below finally earns its keep.
Ben owns BPP Construction and has been building and finishing decks in Riverside for 35 years. He runs every under-deck job himself. That matters here because an under-deck system lives or dies on the slope and the flashing. Get the pitch wrong and water pools in the trays. Skip the flashing detail at the ledger and water finds its way into the framing. We have seen plenty of botched systems over the years, and we install ours so the water goes where it is supposed to go and the wood overhead stays protected.
Four Ways We Drain the Space Below
There is no single right system for every deck. The framing, the deck height, the look you want, and your budget all steer the choice. Here are the four approaches we use most, and Ben will tell you straight which one fits your deck during the walkthrough.
Aluminum Channel Trays
Sloped aluminum trays drop into each joist bay below the deck boards. They are tough, they do not rot or sag, and they carry a lot of water fast. This is the system we reach for on most jobs because it holds up to Inland Empire sun and lasts as long as the deck does.
Vinyl Membrane Panels
A continuous vinyl panel system installed under the joists. It gives you a clean, sealed ceiling below the deck and a smooth surface that hides the framing. Good choice when you want the under-deck room to feel finished rather than industrial.
Sloped Ceiling Systems
A pitched panel ceiling mounted below the deck that doubles as a finished ceiling for the space. It drains to a perimeter gutter and lets you add recessed lights, a fan, or speakers underneath for a true outdoor room.
Gutter & Downspout Tie-In
Whichever tray or panel system goes in, it all has to drain somewhere. We run a gutter along the low edge and a downspout that carries the water away from the foundation. This is the part most DIY jobs get wrong, and it is the part that keeps the area dry.
Where the Water Goes
The principle is simple, but the execution is where experience pays off. Water falls through the deck board gaps and lands in the trays or on the membrane below. Every tray and panel is set on a slope, usually a quarter inch of fall per foot, so the water runs toward the low side of the deck instead of sitting still. Standing water is the enemy here. It breeds mosquitoes, it stains, and over time it works its way into the framing.
At the low edge of the deck, the trays empty into a gutter. The gutter ties into a downspout, and the downspout carries everything well away from the house. We pay close attention to the foundation here, because the whole point of moving water off the deck is wasted if it pools next to the slab or the footings. On expansive Inland Empire soils, you do not want roof or deck water saturating the ground next to the house.
The other detail that makes or breaks the job is the flashing where the deck meets the house. The under-deck system has to integrate with the ledger flashing so water cannot sneak in behind it. This is the same connection we treat carefully on every deck we build, and it is the first place a poorly installed under-deck system fails. We get the flashing right so the system protects the framing instead of trapping moisture against it.
From Walkthrough to Dry Room
Every under-deck project runs the same disciplined way, refined over 35 years of deck work in Riverside. The process keeps the slope correct, the flashing tight, and the finished space dry from the first rain.
On-Site Walkthrough
Ben comes out, gets under the deck, and checks the joist spacing, the deck height, the slope you have to work with, and where a downspout can run. He tells you which system fits and gives you an honest, written quote before any work starts.
Install the Drainage
We set the trays or panels on the right pitch in every joist bay, integrate the flashing at the ledger, and tighten down every connection. The deck boards overhead are never disturbed. You keep using the deck while the room below takes shape.
Gutter, Downspout & Finish
We hang the gutter along the low edge, run the downspout away from the foundation, and finish any ceiling or trim. We test it with water, walk it with you, and confirm the space below stays dry.
Why Under Decking Makes Sense in the Inland Empire
Out here, an under-deck room is a real upgrade. Most of the year the weather is good, so a shaded, dry spot under the deck stays usable spring through fall. You get real use out of it, not a handful of weekends. The covered area stays out of the direct sun, so it runs cooler than the open yard on a hot Riverside afternoon. Homeowners turn it into a second patio, an outdoor kitchen nook, a kids’ play area, or covered storage for the mower, bikes, and the patio furniture that would otherwise bake in the sun.
It also protects your investment. When water and direct sun keep hitting the underside of a deck and the ground beneath it, the framing degrades faster and the area stays unusable. A properly drained under-deck system keeps moisture off the structure and routes deck and roof water away from the foundation, which matters on the expansive clay soils common across the Inland Empire.
BPP Construction is locally owned and has worked in Riverside and San Bernardino counties for 35 years. We know the soils, the sun, and how local decks are built, because we build a lot of them. Reach out and we will tell you honestly whether under decking is the right move for your deck.
More of Our Outdoor Work
Under decking is one piece of what we do with outdoor wood structures. Many homeowners pair it with a new deck or a balcony rebuild. Whatever the project, the same crew handles it with the same attention to slope, flashing, and code.
Decks
Custom raised and platform wood decks built to California structural code, with proper ledger flashing, engineered footings, railings, and stairs. The perfect deck to pair with an under-deck drainage system.
See Deck Work →Wood Patio Covers
Solid and lattice wood patio covers engineered for the Riverside climate. Permitted, inspected, and built to shade your outdoor living space through decades of sun.
See Patio Covers →Wood Balconies
New balcony construction and structural balcony rebuilds done to current California code, including the waterproofing and inspection requirements for elevated exterior structures.
See Balcony Work →Under Decking FAQs
What materials do you use for under decking?
It depends on the deck and the look you want. We install sloped aluminum channel trays, continuous vinyl membrane panels, and full sloped ceiling systems, and we tie all of them into a real gutter and downspout. Aluminum trays are our most common pick because they are tough, they do not rot or sag, and they stand up to Inland Empire sun and heat for the life of the deck. Vinyl and sloped ceiling systems give you a more finished, room-like look below the deck. During the walkthrough, Ben will look at your joist spacing, deck height, and the slope you have to work with, then tell you which system fits and why. We do not push the priciest option. We install what holds up.
Do I need a permit for an under-deck drainage system?
An under-deck drainage system on its own usually does not require a structural permit the way building the deck does, since it does not change the load-bearing structure. That said, requirements vary by jurisdiction across Riverside and San Bernardino counties, and if the work involves any structural changes, electrical for lighting, or a substantial addition, a permit may apply. BPP Construction has worked with the local building departments for 35 years, so we know which jobs need a permit and which do not. We handle whatever permitting your specific project requires and never cut corners to skip a needed inspection. If you are unsure, call (909) 227-4193 and we will give you a straight answer for your situation.
How does the drainage actually keep the space dry?
Water falls through the gaps between your deck boards and lands in the trays or on the membrane we install in the joist bays below. Everything is set on a slope, usually about a quarter inch of fall per foot, so the water runs toward the low edge of the deck instead of pooling. At that low edge, the trays empty into a gutter, and the gutter feeds a downspout that carries the water well away from the house and foundation. Done right, the ground and the room below stay dry even in a hard rain. The two details that make it work are the slope and the flashing at the ledger, and both are exactly where a DIY or inexperienced install tends to fail.
How much does under decking cost?
It varies with the size of your deck, the system you choose, the deck height, and how the gutter and downspout have to run to clear the foundation. A small deck with an aluminum tray system costs a lot less than a large deck with a finished sloped ceiling, lighting, and a long downspout run. Rather than quote a guess, Ben comes out, gets under the deck, takes real measurements, and gives you an honest written quote with no obligation. Call (909) 227-4193 or request a walkthrough and you will get a clear number for your actual deck, not a ballpark off the internet.
Does under decking work on every type of deck?
It works on most raised wood decks, which is exactly where it makes sense, since you need usable height below the deck to gain a room. The deck has to be high enough off the ground to walk under and to give the drainage system its slope. The framing and joist spacing matter too, because the trays or panels mount within the joist bays. Very low decks, ground-level platforms, and some unusual framing layouts are not good candidates. The only way to know for sure is to look at your deck, which is why Ben does an on-site walkthrough before quoting anything. If your deck is not a fit, he will tell you straight rather than sell you a system that will not perform.
Does an under-deck system need maintenance?
Very little, but it is not zero. The main thing is keeping the gutter and downspout clear, the same as you would for the gutters on your house. Leaves, debris, and dirt that wash through the deck boards can collect at the low edge over time, and a clogged gutter will back water up into the trays. A quick clear-out once or twice a year, especially after the fall, keeps everything draining the way it should. The aluminum and vinyl components themselves are built to last and do not need sealing or coating. If you ever see water making it through, it is almost always a clog or a settled connection, and we are happy to come back out and sort it.
Make the Space Under Your Deck Usable
35 years of deck and outdoor construction in Riverside and San Bernardino counties. Honest quotes, clean installs, and a dry room when we are done.
(909) 227-4193 ben.bpp@gmail.com Request My QuoteWhere We Work
Based in Riverside, CA, serving homeowners across Riverside and San Bernardino counties.