What is Underdecking?

We have built so many 2nd story decks over the past 15 years and so many of them create a space underneath them that is dark and uninviting. To keep that patio space under your deck dry and give it a finished feel then you need underdecking.

Underdecking is a system of panels, channels, or chutes that are designed to catch the water that leaks between the decking and joists of a deck. The water is directed to gutters and downspouts. Underdecking creates a finished look and feel, effectively creating more livable space under a deck.

If this sounds like the solution your deck needs to make that patio area a usable one, then let’s dive into what makes up an underdecking system and what this project will cost.

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What do you put under a second-story deck to keep it from dripping onto a patio below?

Well, underdecking of course! So the underdecking systems that we install are made up of a few main parts:

  • The Track 
  • The Outer Frame Pieces (g and j channel)
  • The Gutter (and downspouts)
  • The Panels

How do you install Underdecking?

To start the underdecking project, we will first assess all of the different variables surrounding your deck. We will of course already have the materials in hand so we are not trying to assess what we need, but rather exactly how to install in with your current deck setup.

The first thing that needs to be figured out is fall; as in, water-fall. We need to decide which direction we want the water to flow, towards the house or away from the house. Now some of you might be thinking, why on earth would you want to direct water back towards the house? 

A scenario where you would potentially want something like this is when the house has gutters leading down the house into underground PVC. This ‘system’ for directing the water underground and away from the house would be a great place to tie into so in this instance, we would recommend channeling the water toward the house and into the underground system.

After the gutter location is decided, measurements have to be taken to make sure that the whole system will have enough fall to direct water into that gutter. Some things to note at this stage are things like deck framing lumber. Meaning, what framing material did they use to build the deck? If the frame is smaller material like 2×6 for instance, you will have less material under the deck to attach the outer frame to. In fact, some material may need to be added like framing material or even fascia material to hide the sides of the system if it hangs too low.

Putting up the tracks

After the plan is finalized the tracks can start to go up. The tracks are these really long (12ish feet) black metal pieces that have small teeth built into them that hang down from the ceiling ready to grab the panels. These teeth are designed for the finished panels to snap into.

The number of tracks that you put up will depend on your project but you will essentially be putting up supports to hold the panels and should they start to get weight in them, ie water, it will get heavy out there in the middle of the deck. For a smaller deck, you may only need 1 or 2 rows of tracks where a larger deck may need 2 or 3 rows.

Each row of tracks will have to start at the same place so that they are all lined up perfectly. The rows will also have to be at different heights from the ceiling depending on the fall needed for your specific project. These are generally held up with a 3 to 4-inch screw that’s hanging down a bit so that you can adjust the whole track up and down.

Creating the frame

Now the frame pieces are coming out of the boxes and onto the job site horses. These pieces are aluminum that feature a faux wood finish of your color choice. They are also very long pieces, somewhere in the 12-16-foot range, and have a couple of different shape profiles.

The two different shapes can be seen looking down the ends of the frame channels. One looks like a G and one looks a J. These different shapes make up the side panels and back panels of the frame and the fourth piece of the rectangle would be the gutter.

Every deck can be so different so this process really is a custom one. Ideally, you want the gutter to be one seamless piece covering the outside edge of the deck. Then two side panels what are cut down in just right into the gutter back to the house with the last part of the frame across the siding. What can get tricky is if you have large columns and/or if you have stone! Now you are freestyling with your frame creation skills.

The gutter needs fall from the middle of the deck towards the outsides in most cases. Make sure you have a 4-foot level handy and can make sure that water will actually leave this system. Near both ends of the gutter, you will want to drill/ cut out for your downspout inserts. These plastic inserts and the end caps will need to be installed with the help of some gutter sealant.

Getting the tracks and the frame installed are the most time-consuming parts of the entire project. There is so much calculating and the material that does go up doesn’t really cover anything, it’s just the skeleton so far. But after you get to this point, this is where the project really starts to fly.

Putting up the panels

Now all that’s left is to put up the aluminum panels that make up the finished ceiling. These panels are also an area of color choice with the faux wood or plain white. We will use special saw blades to cut them to just the right length and account for any custom shapes.

The panel goes in up and over the gutter, and then are pulled into place inside the outer perimeter’s ‘C’ channel. Once that first panel is installed into place, the rest go up with amazing speed. The panels have a lip that goes into the black metal track we installed earlier and then we just snap the other side closed into the teeth.

The metal teeth snap-in system makes for a no-fastener, very beautiful finish that can also be taken back apart if necessary.

Now it time to just let everything seal and set and then test it out. After the gutter sealant has complete cured you can grab the hose and start spraying down the deck with water while someone is watching underneath the deck to see if there are any trouble spots. If so, reassess with caulk and if not, enjoy your new space.

If you would like to talk to someone right now about a quote for your specific project goals, then give us a call at 970-663-2868.

At TNT Home Improvements we’ve been building decks, patio covers, pergolas, and installing new windows and siding since 2005. Please give us a call or visit the contact us page to learn more about getting underdecking installed under your deck.