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Install Your Basic Magnolia Underdeck Ceiling in Nine Steps

1.  Establish the height and slope of the ceiling.

  • Using a laser lever (or other reliable method) establish a true level. Mark each corner of the perimeter. Based on the true level, determine and place a mark for the height and slope of the ceiling on each corner of the perimeter using the following guidelines.
  • Drop a minimum of 3 inches below the lowest point (usually the bottom of the joists) on the high side (The side opposite the gutter). Mark a line at this level
  • Allow a minimum of 1/8" per foot drop from the high side to the high end of the gutter. Mark this spot.
  • Allow an additional minimum of 1/16" per foot drop from the high end of the gutter to the downspout. Mark this spot.

Snap a chalk line around the perimeter to outline the height and slope you just measured. This line marks the ceiling height. It defines the bottom of the wall channels and ceiling panels and the top of the gutter



2. Install support boards for gutter and wall channels, if needed.

Install 2" x 4" treated lumber between posts, or between posts and wall. Attach with deck screws


3. Install cosmetic trim and flashing components between posts, if needed.

This is ordinarily all the flashing that is needed for a  rectangular underdeck


4. Install the gutter.

If using gutter hanger brackets provided by Magnolia, attach them every 24 inches. We recommend the use of stainless steel screws. Apply sealant



5.  Install skirt boards, if needed.

Skirt boards cover the  outer edges of the underdeck, making an attractive appearance from the exterior. Also, wall channels may be attached to the skirt boards. Use 2" treated lumber and attach with exterior grade deck screws. Often installers opt to rip the skirt board on a slant so that the bottom will be even with the bottom of the gutter or wall channel.


6. Install corner boxes and wall channels.

Attach with exterior grade screws. Apply sealant.(We recommend and offer both stainless steel screws and sealant.) Make sure the wall channels do not overlap one another within the corner boxes. Also ensure that the wall channels do not extend beyond the inside lip of the gutter.

Corner Box Being Installed

7. Water test.

If a leak occurs, it will happen around the perimeter (not on the panels). After applying the sealer, and before installing the panels, apply a stream of water on the walls above the wall channels and gutter. Re apply sealant as needed. There is no need to wait for the sealer to dry.


8. Install the ceiling panels.


9. Enjoy your Magnolia waterproof ceiling





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