How To Build Deck Stairs

While it may seem daunting, with the right tools, materials, and guidance, you can create sturdy and attractive stairs that complement your deck. In this article, we’ll walk you through the process of building deck stairs, from calculating measurements to installing treads and risers. In the video above, This Old House general contractor Tom Silva demonstrates the key steps and techniques for constructing reliable deck stairs.

Building Deck Stairs: Planning and Preparation

Before you begin building your deck stairs, gather the necessary tools and materials and make calculations to ensure your stairs are safe and compliant with local building codes.

Tools and Materials

To build deck stairs, you’ll need the following tools and materials:

• Circular saw
• Clamps
• Composite decking material (if desired)
• Decking screws (3-inch)
• Drill/driver
• Framing square
• Handsaw
• Jigsaw
• L-brackets
• Pressure-treated lumber (2×12 for stringers, 2×6 for treads, 1×8 for risers)
• Straight edge
• Tape measure
• 4-foot level

Calculating Stair Dimensions

Accurate measurements are essential for building safe and comfortable deck stairs. Here’s how to calculate the key dimensions:

1. Determine the total rise: Measure from the deck surface to the ground where the stairs will land.
2. Choose the number of steps: Divide the total rise by seven inches (a common riser height) to determine the number of steps needed.
3. Calculate riser height: Divide the total rise by the number of steps for the exact riser height.
4. Determine tread depth: Typically, tread depth is between 10 and 11 inches. In the video, Tom Silva uses two pieces of composite decking material for each tread, resulting in a 10 1/2-inch depth.

Remember, building codes often require that the difference between the largest and smallest riser height should not exceed 3/8 inch. 

Accounting for Materials and Costs

To budget properly for your deck stairs, consider the following categories:

• Lumber: Pressure-treated lumber is standard for outdoor stairs due to its durability and resistance to moisture and pests. Purchase 2x12s for stringers, 2x6s for treads, and 1x8s for risers.
• Decking Material: If you opt for composite decking, it is generally more expensive but requires less maintenance over time. 
• Fasteners and Hardware: High-quality decking screws, L-brackets, and other hardware will ensure durability. Using stainless steel is advisable as it is resistant to rust and corrosion.
• Tools: While you may already own essential tools, additional purchases or rentals could include a circular saw or a specialized framing square.

Creating the Stringers

Stringers are the diagonal supports that form the backbone of your stairs. They need to be cut accurately to ensure level treads and consistent riser heights.

Marking the Stringers

1. Set your framing square to the calculated riser height and tread depth.
2. Use the framing square to mark a saw-tooth pattern on a pressure-treated 2×12 board.
3. Make sure to mark enough steps to cover the total rise of your stairs.
4. Notch the stringer with a circular saw, being careful not to saw beyond the cut lines.

Cutting the Stringers

1. Use a circular saw to make the majority of the cuts, being careful not to overcut at the corners where the tread meets the riser.
2. Finish the cuts with a handsaw to avoid weakening the stringer.
3. Use the first stringer as a template to mark and cut the remaining stringers.

Adjusting the Stringers

After cutting, you’ll need to make two important adjustments to your stringers:

1. At the top of the stringer, cut off a portion equal to the thickness of your riser material. This ensures the first step is the same height as the others when the riser is installed.
2. At the bottom of the stringer, cut off a portion equal to the thickness of your tread material. This adjustment accounts for the bottom tread that will be installed.

Installing the Stringers

With your stringers cut and adjusted, it’s time to install them on your deck.

Attaching Stringers to the Deck

First, position the first and last stringers at the edges of your stair opening, securing these outer stringers to the deck frame using L-brackets. Next, space any intermediate stringers evenly between the outer ones, Silva advises that there should be no more than 16 inches of space between stringers for better stability. Finally, attach intermediate stringers by driving three-inch decking screws through the deck frame and into the back of the stringers.

Ensuring Structural Stability

Proper attachment schemes and materials ensure that your stringers provide a safe, stable base for your stairs. Be sure to use the correct number of stringers for your stair width. Wider stairs may require additional stringers for support. Additionally, secure connections to both the deck and the ground contribute to long-term stability.

Adding Risers and Treads

With the stringers in place, you can now install the risers and treads to complete your stairs.

Installing Risers

First, cut your riser boards to fit between the stringers. Attach the risers to the front of each step using three-inch decking screws, ensuring each riser is plumb (vertically straight) before securing it in place.

Attaching Treads

Next, cut your tread material to length, allowing for any desired overhang (typically 1/2 to 1 inch). If using composite decking, you may need to use two boards per tread, as Silva demonstrates in the video. Secure the treads to the stringers using decking screws. If installing railing posts, use a jigsaw to notch the treads around the posts for a clean fit.

Adding Railings

For safety and building code compliance, most deck stairs require railings.

Installing Railing Posts

1. Cut 4×4 posts to the appropriate length for your stair railing.
2. Attach the posts securely to the stringers and deck frame using bolts or lag screws.
3. Ensure the posts are plumb before fully tightening the fasteners.

Completing the Railing

1. Install a top rail and bottom rail between the posts.
2. Add balusters between the top and bottom rails, spacing them according to local building codes (typically no more than four inches apart).
3. Finish with a handrail that’s easy to grip and complies with building codes for height and graspability.

Choosing the Right Railing Materials

Common railing materials include:

• Wood: Wood provides a classic look but requires regular maintenance to prevent rot and weathering.
• Metal: Metal offers a modern look and is extremely durable, though it may require treatments to prevent rust.
• Composite: Composite often matches composite decking materials and requires minimal maintenance, providing a cohesive look with longer-lasting performance.

Tools