Matching Composite Decking to Deck Stairs

Understanding Composite Decking Profiles for Stairs

Composite decking is available in various profiles, each designed for specific applications. For deck stairs, it's crucial to select profiles that are approved for structural use as treads or that can be adequately supported. Standard deck boards are typically not designed to span unsupported as stair treads due to their inherent flexibility and the concentrated loads they experience.

Many manufacturers offer specific stair tread boards, often thicker or reinforced, or recommend using standard boards in conjunction with additional structural support underneath. It's essential to consult the manufacturer's documentation for the specific composite decking line you choose to confirm its suitability for stair treads and any required substructure.

Structural Support for Composite Deck Stair Treads

The substructure beneath composite deck stair treads is critical for safety and longevity. Traditional wood stringers form the backbone of most deck stairs, providing the necessary support for the treads. When using composite decking, ensure that the stringer spacing meets or exceeds the manufacturer's recommendations for tread support.

Some composite decking products may require even tighter spacing or additional blocking between stringers, especially for wider treads or heavier expected loads. Always verify these specifications with the product's installation guide.

Fastening Composite Decking to Stair Stringers

Proper fastening is vital for securing composite deck boards to stair stringers. Face fastening is commonly used for stair treads, involving screws driven directly through the top surface of the board into the stringer below. Use screws specifically designed for composite decking to prevent mushrooming or splitting, and ensure they are long enough to provide adequate penetration into the stringer.

While hidden fasteners are popular for deck surfaces, their suitability for stair treads varies by product. Some systems may offer specialized hidden fasteners for stair applications, but often the enhanced security of face fastening is preferred for the high-traffic nature of stairs. If using hidden fasteners, confirm they are approved for stair treads by the manufacturer and installed precisely according to their instructions.

Riser Boards and Fascia for a Finished Look

Riser boards, installed vertically between treads, contribute to the finished appearance and can help enclose the stair structure. Composite fascia boards, often thinner and designed for vertical applications, are an excellent choice for risers. They offer a clean, consistent look that matches or complements your composite decking.

When installing riser boards, ensure they are securely fastened to the stringers. Consider the color and texture match with your chosen decking. Lumber Plus offers a range of composite decking options from Trex, TimberTech, and Fiberon, which typically include coordinating fascia and riser profiles to create a cohesive design. These products are known for their consistent color and grain, board after board, ensuring a uniform finish. (S1)

For a complete look, consider using a picture-frame border around your stair treads, similar to how you might border the main deck. This can add a refined edge and further integrate the stairs into the overall deck design.

Navigating Local Building Codes for Deck Stairs

Deck stairs are subject to specific local building codes that dictate dimensions such as tread depth, riser height, and handrail requirements. These codes are in place to ensure safety and must be strictly followed. Before beginning construction, review your local building department's requirements or consult with a qualified contractor.

Common code requirements include uniform riser heights and tread depths, minimum tread depth, maximum riser height, and specific handrail heights and graspability. Your project plans should clearly detail how the composite decking will be incorporated into a code-compliant stair structure. This planning is crucial, especially when considering the material's dimensions and how they contribute to the overall stair geometry.

Worked Example: Planning Composite Stair Treads

Let's consider a hypothetical deck stair project: a 4-foot wide stair with 5 risers. The local code requires a maximum riser height of 7.75 inches and a minimum tread depth of 10 inches.

For a 4-foot (48-inch) wide stair, we would need 5 stringers placed at 12-inch intervals (0, 12, 24, 36, 48 inches). Each stringer provides critical support. To achieve a 10-inch tread depth, we will use two 5.5-inch wide composite boards per tread, creating an 11-inch depth (allowing for a small overhang).

With 5 risers, there will be 5 treads. Each tread will require two 4-foot long composite boards, totaling 10 boards for the treads. If we also plan to use composite fascia for the risers, and assuming a 7.5-inch riser height, we would need five 4-foot long fascia boards. This example highlights the need to account for both tread and riser material, as well as the underlying structural support.

Before you order

• Verify composite decking product is approved for stair treads by the manufacturer.
• Choose appropriate fasteners (face screws, specialized hidden fasteners) for stair treads.
• Select matching or complementary composite fascia for risers.
• Review local building codes for stair dimensions (riser height, tread depth) and handrail requirements.
• Calculate the number of composite boards needed for treads and risers, accounting for cuts and waste.
• Plan for proper ventilation around and under the stairs, similar to the main deck.

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

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