Installing the Otterteck® Ottertite Underdecking System


Illustration of Otterteck® Underdecking parts
Boundary gutter component illustration.
Fasteners needed for the Otterteck® underdecking system.
  1. 1. Poly Pitching Rails
    1. 1a. 1/2" x 2 3/4" x 8'
    2. 1b. 3/4" x 2 3/4" x 8'
    3. 1c. 1" x 3 1/2" x 8'
  2. 2a. J-Channel
  3. 2b. End Strip
  4. 3. 12" Underdeck Panel
  1. 4. Boundary Gutter
    1. 4b. Downspout
    2. 4c. Gutter and downspout accessories:
      • • Gutter endcaps
      • • Downspout elbows
      • • Downspout clips
      • • Gutter screws

5. 10' Vent Strip

6. 3" Circular Vent


  • 4s. Gutter screws
  • 3s. Stainless steel screws
  • 3w. Washers
  • 1s. Pitching rail screws

Installation Steps


Ensure that your existing deck-to-house connection is properly flashed so any water that runs between deck and house will drain out onto underdecking panels.

Install the poly pitching rails.

Install Poly Pitching Rails (1a., 1b., 1c.) as needed based on slope requirements. 1 1/4" of slope in 12' is recommended. See illustration below this list of steps. If your deck itself is already sloped at least 1 1/4" in 12', you only need to use 3/4" x 2 3/4" (1b.) pitching rails. Poly Pitching Rails should be installed perpendicular to deck floor joists every 28 1/2" starting from the house and moving toward the gutter placement end of deck. Use pitching rail screws (1s.) to fasten to deck joists.

Install the J-channel.

Install J-channel (2.) around perimeter except for where gutter will be mounted. Ensure proper amount and direction of overlap when a splice in the J-channel is required. It is recommended to use a bead of silicone on J-channel splices to prevent any leaking. Use stainless steel screws and washers (3s. and 3w.) to install J-channel and do not mount directly against pressure-treated wood.

Install the 12" Otterteck® underdecking panels.

Install 12" Otterteck® Ottertite underdecking panels (3.) starting at one side with short flange side of panel in J-channel. Use stainless steel screws and washers (3s. and 3w.) to fasten wide flange edge of panels to pitching rails and continue by interlocking next panel into first and proceeding in such manner to other side of deck. Panel length should be 1 1/2" shorter than it measures from house to beam where gutter will be mounted. Never install panels in direct contact with pressure-treated wood.

End strip should be snapped onto the cut edge of the last panel.

If necessary to customize the width of the last panel (3.), measure to the inside of the J-channel and subtract 3/16". Score the panel with a utility knife and bend to break off the excess. Snap the end strip (2b.) onto the cut edge and seal with a bead of caulk. Push the assembly into the J-channel, starting at one end and working your way to the other.

Install the gutter at the bottom of the slope.

Install gutter (4.) with 7" gutter screws with ferrules (4s.) Keep gutter 3/4" below underdecking panel and slope slightly toward the end on which you wish to install downspout. Gutter should not be installed in direct contact with pressure-treated wood.

Install the downspout to carry the water away.

Install downspout (4b.) into desired position in gutter and use mounting clips to fasten to porch post or other surface. Use end caps and elbows (4c.) as required to finish downspout appropriately. Make sure to drain toward outside of patio and consider installing PVC pipe to carry drain water away from foundations to prevent erosion.

Vent the sides of your deck.

Vent the sides of the deck by attaching 3/4" x 23/4" (1b.) poly pitching rails flush with the bottom of the deck skirt board using pitching rail screws (1s.). Fasten vent strips (5.) onto pitching rails, using stainless steel screws (3s.). Insert screws vertically on underside of overhanging lip. If the sides of your deck are enclosed, vent by drilling 3" holes every 32" in the deck skirting on the gutter end of the deck. Insert the circular vents (6.).

If your deck does not slope, combine various thicknesses of pitching rails to slope the underdecking.

Scenario 1

If your existing deck is level, use a combination of the 3 pitching rail thicknesses to create slope from the house side of deck toward the gutter side. Use the illustration above as a guide.

If your deck has sufficient slope, simply use the .75" pitching rails.

Scenario 2

If your existing deck is already sloped, you do not need to add slope with the pitching rails. In this case simply use the 3/4" pitching rails (1b).Use the illustration above as a guide.