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How to Build a Deck: Composite Stairs and Stair Railings

With the composite decking and the deck railings installed, complete the look with composite stairs. Building deck stairs for composite decks is similar to building wood stairs, with a just few slight differences. Here's how to build a set of composite steps.

See the complete deck project from design to finishing touches at Lowes.com/BuildaDeck.

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Deck Stair Basics

Illustration of Composite Deck Stairs.

This deck already has composite decking and deck railings installed. See the steps in How to Build a Deck: Composite Decking and Railings. It's common to build the framing with treated lumber and use composite surface material, as with the decking and stairs on this deck.

Composite deck stairs are typically made from 2 x 12 pressure-treated stringers spaced about 8 to 16 inches apart. They rest on a solid foundation and are attached to the deck with hangers. They have risers (also called toe kicks), treads and railings. Stairs should be at least 36 inches wide.

You can build your own custom stringers or get pre-cut ones at Lowe's. Custom-built stringers allow you to match the dimensions of a set of stairs in your home, which will feel most comfortable. Whichever you choose, always make sure you follow building codes.

Stair Measurements

Illustration of Determining the Location of the Stairs.

Determine the location of your bottom step. Set a long level or straight 2 x 4 on top of the decking, and measure the height at the point where you want your steps to end. Use this measurement to determine the number and height of the risers.

For example if the height is 55 inches, divide this measurement by 7, the ideal height in inches for each step. Round to the nearest whole number to get the number of risers — in this case 8. Now divide 55 by 8 to get the actual height of the risers — in this case it's 6-7/8 inches.

55 ÷ 7 = 7.86 rounded up to 8 risers

55 ÷ 8 = 6.875 or 6-7/8 inches

If you use the deck itself as the top riser as with this deck, subtract one step.

The stair treads will be made of composite decking planks — two for each step — making the run for each step (the distance front-to-back) about 11 inches. There are risers or toe kicks on the back, made of pressure-treated wood and composite boards without grooves.

Good to Know

Some codes require toe kicks.

You may want to check the height of steps or stairs that are already familiar to you — such as interior stairs of porch steps — to get a sense for a comfortable height. If the initial planned height of your steps is too short for comfort, reduce the number of risers by 1 and calculate again.

Creating a Stair Landing

A concrete pad is one common type of landing. It has a 4-inch layer of gravel underneath and extends beyond the steps about 36 inches. You can find step-by-step instructions for pouring a concrete pad landing in How to Build a Deck: Wood Stairs and Stair Railings.

This deck uses another option — concrete footers like those that support the deck frame. You'll need to determine the correct location for the footers.

Good to Know

Our Concrete Holes and Pillars Calculator helps you estimate how many bags of concrete mix you need to set your posts.

Step 1

Illustraion of the Total Run of a Set of Stairs.

Calculate the total length of the run by adding together the runs for each individual step.

Step 2

Mark the deck where the steps will attach.

Step 3

Install Footers for the Stair Posts.

Install the footers and posts in line with the two outer marks, at the total distance of the run. You can make the footers even with the ground. Look at Build a Deck: Post Holes and Framing to get step-by-step instructions for creating footers and setting posts.

Cutting the Stringers

When you have the rise and run determined and the footers installed, mark the stairs on 2 x 12s to create stringers.

Step 1

Stair Gauges on a Framing Square.

Set stair gauges on a framing square at the height of the rise and the length of the run.

Step 2

Mark the Run for the Top Step.

Hold the square at the corner of the 2 x 12 plank and mark the top run.

Step 3

Mark the Rise and Run for All Steps.

Slide the square along the plank and mark both rise and run for the next step. Continue marking until you have the correct number of steps laid out.

Step 4

Illustration of the Top of the Stringer.

At the run mark you made for the top step, subtract the thickness of the toe kick — treated board and composite board — and strike a perpendicular cut line. This line indicates where the stairs attach to the deck. There won't be a toe kick at this point of the stairs.

Step 5

Illustration of the Bottom of the Stairs.

At the bottom step, subtract the thickness of a tread from the rise and mark a line perpendicular to the rise. This is a cut line to allow you to shift the entire set of stairs down. When the treads are installed, this cut will make the bottom step the same height as the others.

Step 6

Cut the Stringer.

Cut the stringer with a circular saw and finish the cuts with a handsaw.

Step 7

Use the Cut Stringer to Mark the Other Stringers.

Use this stringer as a template to mark and cut the others.

Good to Know

You may also want to trace the stringer onto composite material to cut two fascia boards that will cover the outside stringers. Use composite boards without grooves.

Attaching the Stringers, Toe Kicks and Treads

Step 1

Install a Support Board for the Stairs.

Cut a board (for this deck a 2 x 8) the width of the steps to support the stringers below the rim or end joist. Use pieces of the same 2 x lumber to attach the board against the bottom edge of the joist.

Step 2

Install a Brace for the Support Board.

Use an additional piece of 2 x material to brace the back of the support board against a joist or beam. Attach the braces with joist hangers or decking screws.

Step 3

Attach the Stair Posts to the Footers.

Attach the posts to the footers just as you did for the deck frame in How to Build a Deck: Post Holes and Framing.

Step 4

Trace the Hanger on the Support Board.

Hold the stringers and hangers flush with the top of the 2 x 8 support and mark the each hanger location.

Step 5

Attach the Stringer Hanger.

Remove the stringers and secure the hangers to the support board with 10d nails and screws.

Step 6

Attach a Stringer to the Hanger.

Drill pilot holes and attach the outer stringers to hangers with nails and screws. Secure the bottom of the stringers to the bottom posts with screws.

Step 7

Attach the Stringer and Bottom Toe Kick to a Post.

Cut a pressure-treated wood toe kick for the bottom of the stairs. Drill pilot holes and attach it with screws.

Step 8

Brace the Post.

Attach the remaining stringers and secure the posts to the bottom of the stringers with bracing, anchors and carriage bolts. Look at How to Build a Deck: Composite Decking and Railings for step-by-step instructions on bracing posts.

Step 9

Cut the remaining toe kick pieces from pressure-treated wood and composite material without grooves. Remember to cut a composite piece for the bottom of the steps. Cut stair treads from composite decking to overhang the toe kicks by about an inch.

Step 10

Attach the Remaining Toe Kicks.

Drill pilot holes and attach the toe kicks, securing treated boards first and covering them with composite boards.

Good to Know

When attaching the composite toe kick elements and the treads, use matching-color composite screws.

Step 11

Use a Screw to Set a Gap Between Tread Boards.

Drill pilot holes and secure the treads, using a screw to set a drainage gap between the boards on each step.

Step 12

Composite Board Covering Stringer.

For a cleaner look, install composite stringers to cover the outer wood stringers.

Installing the Stair Railings

The stair railings include vinyl top and bottom rails, as well as balusters.

Step 1

Post Cover and Collar.

Slide post sleeves over the posts. Cut the sleeves to length as needed. Glue the collars in place with PVC cement. Follow the package instructions.

Step 2

Mark an Angle on the Bottom Rail.

Hold a bottom rail against the posts with the baluster holes centered. Mark the angle at each end. You'll need to subtract enough from your measurements to allow space for the two mounting brackets. Cut the rail.  Repeat the process with the other bottom rail.

Step 3

Mark the Bottom Rail Angles on the Top Rails.

Align the holes on each bottom rail with a corresponding top rail. Transfer the angles to the top rails and cut them accordingly.

Step 4

Mark the Locations of the Bottom Rail Brackets.

Slide the brackets on a bottom rail and mark the bracket locations on the top and bottom posts. Drill pilot holes and secure the rail with screws. Repeat the process with the other bottom rail.

Step 5

Use a T-Bevel to Determine the Baluster Angle.

The balusters need be cut to match the angle of the rails. Hold a T-bevel against a post and bottom rail to get the correct angle.

Step 6

Mark the Baluster Angle on the Balusters.

Mark and cut the balusters accordingly.

Step 7

Add Baluster Inserts to the Bottom Rail.

Place stair baluster inserts in the holes on the top and bottom rails. Attach the balusters to the bottom rail.

Step 8

Secure the Top Rail.

Position the top rail and secure it in place with screws.

Step 9

Completed Composite Deck Stairs.

Finish the railings with post caps and fill in around the footers with gravel or soil.

Step 10

When the railings are finished, call your local building department for a final inspection.

Caution

Always follow the manufacturer's recommendations for fasteners and structural hardware.

Working with Pressure-Treated Lumber

Guidelines

  • Use fasteners and hardware labeled for treated lumber — stainless-steel or hot-dipped, galvanized screws.
  • If the lumber is wet — it typically is when delivered from the store — butt it together tightly when building. Pressure-treated wood shrinks as it dries.
  • Drill pilot holes in the ends of boards to prevent splitting when you nail or screw them together.
  • Use wood rated for ground contact when necessary for the project.

 

Safety

  • Wear a dust mask and eye protection when handling or cutting wood.
  • Wash your hands after working with treated wood.
  • Dispose of sawdust and waste according to local regulations.
  • Don't burn pressure-treated wood.
  • Don't use pressure-treated wood as mulch.

Read more about pressure-treated lumber and wood preservatives on the EPA website:

Overview of Wood Preservative Chemicals.

Finishing Touches

With the deck complete, make it stand out with the right furnishings and accessories. See how in How to Build a Deck: Finishing Touches.

Watch the complete deck series at Lowes.com/BuildaDeck.