The Best Moisture Barrier Options for Decks

Elevated decks, framed with wood, require deck moisture barrier protection to ensure the deck’s durability and long service life. Shielding your deck from moisture infiltration and accumulation will limit or stop the growth of structural damaging mold and corrosion and lessen maintenance and repair costs. Ultimately a moisture barrier for your deck will help protect the value of your home or building. The best moisture barrier options for decks must include over-the-deck and under-the-deck moisture barriers.

The Best Moisture Barrier Options for Decks

Moisture Barrier Over-the-Deck Floor

Typically manufacturers offer two moisture barrier over-the-deck floor options: wet/liquid and rolled/sheet membranes. With their less complicated application process, many builders find rolled waterproofing membranes more effective at creating an even moisture barrier surface than less expensive wet membranes. However, the success of the moisture barrier significantly depends on following manufacturers’ instructions.

Before deciding on an over-the-deck floor moisture barrier, check the flooring for cracks or holes. If present, remove the finished floor layer (usually plastic, wood, stone, or composite tiles) to expose and check the substrate (typically concrete or wood) — the last line of defense between the vital structural parts of the deck floor and moisture.

In addition to a quality moisture barrier, like Polyguard’s Balconyguard™ Membrane, ensure the deck has a slope of at least 2 percent (1/4 inch per foot) for positive drainage.

Why Rolled Waterproofing Membranes Are the Best Moisture Barrier Option for Decks

Rolled or sheet membranes come in long, adhesive sheets that lay across the substrate or subfloor, producing an even surface and acting as a reinforcement layer for the subfloor. In addition, rolled or sheet membranes install easier and quicker than liquid membranes. Polyguard’s Balconyguard™ Membrane, along with our high-performing companion products, offers decks the best rolled moisture barrier option.

At Polyguard, we designed self-adhesive, 60-mil Balconyguard™ Waterproofing Membrane explicitly for wood decks, terraces, and balconies, covered with lightweight concrete – ideal for projects with many decks, balconies, or patios, like multi-family or hotel construction.

The Best Moisture Barrier Options for Decks 2

Simple to install, Balconyguard™ Membranes offer several significant benefits for waterproofing decks and exposed multi-story walkways covered with lightweight concrete:

  • Tensile strength meets ASTM D412
  • High-strength PET film
  • Treated removable release film
  • Elongation meets ASTM D412
  • 48-inch wide by 50-feet rolls (200 ft2 rolls), minimizing seam occurrence by up to 25 percent, compared to 36-inch wide products — a time-saving feature that reduces the number of required seams
  • For simple installation and detailing, our Balconyguard™ System includes custom corner boots to save contractors money and time.

Before installing Balconyguard™ Membrane, we recommend contacting Polyguard Technical Services or an authorized company representative for assistance with job-specific details or shop drawings.

Guaranteeing a Waterproof Deck with Polyguard Companion Products

In addition, Polyguard offers several products to help ensure a water-tight deck.

Polyguard 105 Flashing Membrane

Polyguard 105 Flashing Membranes divert water along with the exterior flashing application, including the spandrel beams sills, copings door and window,r headers, and flange flashings.

Polyguard 650 LT Liquid Adhesive

Rubber-based, Polyguard’s 650 LT Liquid Adhesive, in a solvent solution, primes structural masonry, concrete, or wood surfaces before applying waterproofing membranes, creating superb adhesion for the Polyguard® waterproofing membranes.

Polyguard Balconyguard™ Outside Corner Boot

60-mil Balconyguard™ Outside Corner Boot (a combination of polyethylene and asphalt) easily applies to the outside face of the deck at the wall-deck interface. The 6-inch x 6-inch x 6-inch simple-to-install boots come 25 to a carton, saving labor and time on the job site.

Polyguard 650 WB Liquid Adhesive

Water- and rubber-based 650 WB Liquid Low-Tack Adhesive provides superior adhesion. The VOC content of 5 g/L. 650 WB Liquid Adhesive looks pink. Priming dry surfaces with 650 WB Liquid Adhesive ensures the dust-free substrate required for applying Polyguard Waterproofing Membranes.

Polyguard Detail Sealant PW™

High-performing, non-corrosive, flexible, and non-staining Polyguard Detail Sealant PW™ fills small, concrete masonry cracks, cast concrete cracks, gypsum sheathing joints, penetrations, and gaps at head joints, producing a continuous smooth surface. Polyguard Detail Sealant PW™ applies to most below-grade waterproofing applications at terminations and penetration, along with trowel-on rough opening of flashing/waterproofing above-grade applications.

Polyguard Detail Tape

Flexible, robust, and self-adhesive sheet Polyguard Detail Tape consists of high-density polyethylene, cross-laminated film bonded to a rubberized asphalt waterproofing compound layer.

Polyguard Detail Tape applies as detail strips on the inside and outside corners, penetration control joints, expansion joints, and cold joints to patch damaged spots of the membrane.

Polyguard LM-85 SSL

Polyguard LM-85 SSL is a two-component, asphalt modified, semi-self leveling, urethane liquid membrane that comes in a pourable sealer. We designed the Polyguard LM-85 SSL specifically for use in conjunction with the Polyguard waterproofing membrane in Dual Core and pitched pan applications.

Moisture Barrier Under the Deck Floor

Maintaining the integrity of a new deck and extending the deck’s lifespan requires under the deck floor waterproofing techniques, like deck joist tape and deck drainage panels.

Deck Joist Tape

Contractors cold-apply self-adhering deck joist tape as a flashing on ledger boards and deck joists to create a water barrier between the treated lumber and non-corrosive galvanized metal hangers to prevent vulnerable joists from water damage.

Without the moisture barrier created by deck joist tape, debris and water will accumulate in the spaces between the joists and deck boards, which can break down the wood joists (untreated or treated)—leading to damaging rot. Additionally, deck joist tape between treated wood and metal hangers prevents leaching copper (used as a preservative in treated wood) from corroding the joist hinges that hold together the deck.

A high-quality deck joist tape, like PolyWall’s Rot Shield Joist Tape, will protect the top of the deck joist, rim joint, and ledger board against wood decay and rot. In addition, the flashing tape stops water infiltration and helps seal around metal fasteners, screw holes, and hidden deck fasteners to prevent cracks and corrosion of the metal surface.

PolyWall Rot Shield Joist Tape

Easy to apply, PolyWall’s (a division of Polyguard Products Inc.) Rot Shield Joist Tape protects the value and integrity of your new deck by providing a durable barrier between the ledger board, joists, and deck boards, which stops water damage and rot, fungus, and mold growth. Furthermore, Rot Shield Joist Tape prevents contact between galvanized metal fasteners and treated wood to prevent corrosion.

PolyWall’s Rot Shield Joist Tape includes a rubberized-asphalt ‘sticky’ compound with a high-density polyethylene (HDPE) plastic film face that protects the deck’s integrity, by preventing water damage and stopping corrosion. Additionally, the brown-colored Rot Shield Joist Tape camouflages below deck boards. Furthermore, contractors can apply the tape in cold weather and without priming.

Deck Drainage Panels

Under deck drainage panels installed below or above the joists will catch and funnel water to one of three areas of the deck – between the joists and decking, the deck’s surface, or below the joists.

A high-quality under-deck drainage panel, like Polyflow® BD Sheet Molded Drainage Mat, will protect your deck’s substructures from moisture and help maintain the deck’s long-term integrity and attractiveness. In addition, the deck drainage system will create and protect the usable living and storage space below, even in severe weather.

Selecting an easy-to-install deck drainage panel will help ensure a properly placed and functioning deck drainage system. Additionally, a straightforward method to install drainage panels will lessen the need for skilled workers and specialized, expensive tools – saving DIYers and contractors money and time.

You may also want to select a deck drainage system that permits gas and electrical installation that will also allow you to add features like ceiling fans, lights, entertainment components, etc., to the below-deck space.

Polyflow® BD Sheet Molded Drainage Mat

Polyguard designed our high-capacity, lightweight Polyflow® BD Sheet Molded Drainage Mat, compatible with Polyguard’s Balconyguard™ Membrane, to provide a solution to lightweight under-deck drainage. It comes as a sheet-molded drain that produces pathways for deck water management. The fabric permits water flow to drainage exits. Additionally, the punched core enhances the water release rate from within the system.

Polyflow® BD Sheet Molded Drainage Mat contains a geocomposite of a fabricated pre-punched impermeable polymeric core, with both sides covered with a non-woven filter fabric. Polyflow® BD’s compressive strength of 5,200 lb/ft2 and flow rate of 12.5 g/min/ft allow for use in foot-traffic only decks with less than 3-inch concrete.

Simple-to-install Polyflow® BD guarantees successful installation to ensure the efficient removal of water from the deck, increase its lifespan, and save both time and money during and after installation.

Deck, Balcony, and Elevated Building Codes

The 2021 International Building Code (IBC) contains several codes that focus on the protection and design of the structural framing for decks, balconies, and elevated walkways:

  • Section 107.2.5 (exterior balconies and elevated walking surfaces) requires that the construction documents detail elements of the impervious moisture barrier system and barrier manufacturer’s installation instructions when used to protect the structural framing.
  • Section 110.3.6 (weather-exposed balcony and walking surface waterproofing) requires inspection of the impervious moisture barrier system protecting the structural framing before concealing.
  • Table 1607.1 requires a minimum uniformly distributed live load for balconies and decks 1.5 times the occupancy served. Balconies extending from a residential area required a minimum live load of 60 psf (40 psf x 1.5). These codes align with the ASCE 7-10 Minimum Design Loads for Buildings and Other Structures.
  • Section 2304.12.2.4 requires the impervious moisture barrier system protecting the structural wood framing to provide positive drainage. The drainage will remove moisture penetrating the moisture-permeable floor topping, like concrete.

Section 2304.12.2.5 requires cross-ventilation for enclosed spaces of exterior balconies and elevated walkways if exposed to moisture. Openings shall provide a net-free cross-ventilation area of at least 1/150 of the area of each separate space.

In addition, you must consider local building requirements. A qualified project design professional should understand the codes applicable to your project, and provide sufficient instructions and details to ensure a safe and durable structure.

Polyguard Offers the Best Moisture Barrier Options for Decks

Sufficient over and under-the-deck waterproofing with Polyguard’s moisture barrier options will help preserve the deck’s aesthetics and durability, and significantly reduce maintenance and repair bills. Conversely, a leaky deck can lead to costly structural damage and unhealthy living conditions.

The Best Moisture Barrier Options for Decks

Fortunately, Polygaurd’s Balconyguard™ Membrane and companion products and PolyWall’s Rot Shield Joist Tape and Polyflow® BD Sheet Molded Drainage Mat can provide the best moisture barrier options for your deck, securing its value and integrity for years to come.

For more questions on the best options for moisture barrier options for your deck or decks, don’t hesitate to contact the Polyguard professionals today.