Covered patio or second floor deck leaking?  Here are 23 simple moisture-proofing strategies to help prevent damaging water intrusion into your deck system.

Cantilevered structural deck systems safely separate exterior habitable areas from the surrounding ground surface environment. When covered, these deck (a. k. a. terraces, patios, etc.) structures shelter occupants from the undesirable effects of direct exposure to the outside environment. When elevated and structurally connected to building walls, these deck systems allow unobstructed panoramic views while safely supporting their occupant loads.

Building material products sensitive to adverse weather such as hardwood floors, unprotected structural wood members, and sheetrock must be adequately protected to prevent their damage and decay. Dry wood structural members can expand, twist, distort, and deflect unpredictably when exposed to ongoing excessive moisture. If rainwater infiltrates into the deck and wall structural cavities, it provides a continuous moisture source to the dry wood structural components supporting each deck (North and southeast decks). The result:    structural component deflection which transfers excessive tension stress to its connected brittle material coverings causing  visible stucco and tile separations.  Here are twenty three tips to help waterproof your cantilevered patio deck:

  1. Stucco penetrations such as metal deck railing should be properly flashed or integrated into the water-resistive barrier before lath and stucco installation.
  2. Water-resistive barriers degraded by moisture exposure or damaged by tearing should be replaced before applying the stucco.
  3. Place water resistive barriers to assure all exterior moisture sensitive material surfaces are completely covered.
  4. Install wood based deck sheathing panels in accordance with APA requirements with 1/8 inch spaces between all meeting panel edges.
  5. Water-resistive barriers that have been degraded by moisture exposure or damaged by tearing should be replaced prior to the application of stucco.
  6. Place water resistive barriers to assure covering the entire exposed surface of the floor support beams and girders where possible without having to remove undamaged materials or demolishing functional structural connections.
  7. Paper backed stucco lath shall have at least one barrier layer of an approved water resistant paper backing.
  8. An approved water resistive barrier is one layer of No. 15 asphalt felt, free from holes and breaks, complying with ASTM D 226 for type I felt, or an equal alternative or better. Equal alternatives are DuPont Tyvek (Home wrap, Commercial wrap, and Stucco wrap) or equal.
  9. Placement of at least two water resistant barrier layers is recommended (not required) between stucco metal lath and any untreated natural wood surface to enhance long term prevention of moisture infiltration into the stucco system.
  10. Assure OSB sheathing substrates are classified as Exposure 1 or Exterior Grade.
  11. Assure wood framing and wood based sheathing is reasonably dry with a moisture content of 19% or less when the water-resistant barrier and lath are installed.
  12. A framing inspection should take place before a lath inspection. Appropriateness of flashings, treatments of penetrations and rough openings should be evaluated at that time.
  13. Water-resistive barriers should be installed with staples that do not protrude through the back side of the sheathing.
  14. Water-resistive barrier should be installed flat and taut to the substrate surface.
  15. All flashings and water-resistive barriers should be installed for positive drainage.
  16. Metal flashing materials should be a minimum 26 gauge galvanized sheet metal or anodized, coil coated or painted aluminum.
  17. All trim accessories should be galvanized steel, zinc alloy or anodized aluminum.
  18. Joinery of abutting ends of trim accessories should be spliced or lapped and sealed with appropriate sealant.
  19. Joinery of flashing sections should be appropriately lapped, sealed and mended together by application of sealants, adhesive backed membrane or other appropriate means of continuity.
  20. Any water-resistive barrier or membranes covering OSB joints should be lapped across said joints where appropriate and should remain unbroken where possible.
  21. Expansion joints should be located at points where significant building movement is anticipated: Wall penetrations, structural plate lines, junctures of dissimilar substrates, existing construction joints (stone), columns and cantilevers.
  22. Pullout resistance of drill and drive fasteners, power or powder actuated fasteners should meet the requirements of the fastener manufacturer.
  23. If there is any question about the effectiveness of the pullout strength of drill and drive fasteners, power or powder actuated fasteners into concrete or concrete masonry block, sample testing is recommended.