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How to Build Deck Stairs

Pro Referral > Home Guides > Deck & Porch > How to Build Deck Stairs
How to Build Deck Stairs

Table of Contents

  1. Important Terms
  2. Tools and Materials
  3. Questions and Considerations
  4. Stair Locations
  5. Planning Installation
  6. Calculations
  7. Locating Posts for Rails
  8. Setting up the Stringers
  9. Cutting Notched Stair Stringers
  10. Tying into the Deck Structure
  11. Installing Risers and Treads
  12. Adding Rails

The goal of any set of stairs is to allow for the easy and safe movement of people up and down. This is generally achieved by providing a consistent height for each step. To a lesser extent, the associated depth of each will also dictate ease of use.

In general, building a deck requires some basic math skill. With deck stairs, you’ll in fact need to know four key bits of information. You’ll start by calculating first, how many steps are needed. You’ll also calculate the stairs’ “span”–the overall distance from the deck to its farthest point, the point at which it is to contact the ground.

    1. Important Terms

    There are some specific terms used when discussing the anatomy of a stair build. Some of the important terms you’ll need to know:

    • Stringer: The structural supports in a stair system. Framing members that either support or hold a set of stairs together.
    • Tread: The stair step(s). The flat board(s) making up a step.
    • Riser: The vertical space or trim, the kick board, found between each step.
    • Bearing Block: Short framing members extending from footer to grade and providing additional support to stringers.
    • Gusset: Short blocking members that tie stringers together and to posts.
    • Post: The vertical structural supports in a rail system.
    • Rail: The upper and lower framing members in a rail system, the rail.
    • Cap: The top most portion of the upper rail; what is grasped.
    • Baluster: The individual pickets in a rail or guard system.
    • Rise: The height of each individual step.
    • Run: The depth of each individual step.
    • Rim Joist: The outside joist in a structure like a deck. The point at which deck stairs are attached.

    Familiarizing yourself earlier with these various components can help smooth the process of building your stairs.

    2. Tools and Materials

    The tools and materials listed below are what you need to get started with your deck building project.

    Tools Materials Skill Level Estimated Time
    • Calculator • 2x12 pressure treated Advanced 6 hours to 2 days
    • Framing square • (2) 4x4 pressure treated (ground contact)
    • Pencil • (2-3) 2x4x8 pressure treated (1 ground contact)
    • Circular saw, Chop saw, Jigsaw Hand saw • Tread material (2x or 5/4x weather resistant)
    • Drill driver • Riser material (1x weather resistant)
    • 3/16” twist bit 1/2” boring bit 1” spade bit (optional) • Rail material (milled or 2x for balusters - weather resistant)
    • 3/16” twist bit 1/2” boring bit 1” spade bit (optional) • Copper-based wood preservative
    • Hammer (or pneumatic nailer) • Galvanized sloped hanger brackets (or equivalent)
    • Impact driver and ratcheting wrench • Galvanized connector nails (aka Tiko - 8d and 10d)
    • Levels (various two-, four-foot, line or laser • (4) 3/8” by 6” galvanized carriage bolts with nuts and washers (minimum)
    • Bar or pipe clamps • Ceramic-coated deck screws (2 ½”, 3” and 3 1/2”) 8d Galvanized finished nails (alternatively – stainless trim screws)
    • Plumb bob and masonry string • (2-4) Landscaping stakes
    • Rubber mallet • Gravel (sand and landscape fabric - dependent on installation)
    • Hand tamper (and other miscellaneous landscaping tools) • High-strength and fast-setting concrete (depending on post installation)
    • Post hole digger (optional for burying posts or digging footings) • Tubular concrete forms (optional)
    • Wheelbarrow (and other concrete mixing tools) • Galvanized post bases – 4x4 (if mounting rail posts in concrete + anchor bolts) (optional)
    • Structural fasteners, landspace spikes, or masonry screws–4", 6”, or 8” (optional)

    3. Questions, Considerations and Options in Materials and Techniques

    Will a formal landing be incorporated within the stairway? Taller decks (requiring 12 or more steps) must incorporate a landing, basically a larger step, installed at a midpoint in a set of stairs. For our discussion, we'll assume our deck is only three or so feet off the ground, and will not require an integral stair landing. (It will require a stair guard or rail.)

    On a shorter length of stairs, landings still appears both at the head of and also at the base of stairs. This landing at grade can be "formalized." For formalized landings, you'll most commonly find them in poured concrete, but you may also see them built out of pavers, flagstone, or gravel. Will your project incorporate a formal landing at grade?

    Materials introduced in recent decades--composites and vinyl/PVC specifically, have changed our approach to deck, and hence, deck stair building. The most traditional solution is wood, with cedar and redwood both being very widely used. Exotic species like ipe or teak for decks have also grown in popularity in recent years.

    While these materials may replace certain elements in a set of stairs, structural elements remain pretty consistent regardless of how we choose to "skin" our deck. While some pros may opt for steel in building the structural elements of decks, pressure treated pine or fir remains the go-to for exterior framing. Decks and deck stairs, here, are no exception.

    4. Locating the Stairs

    While our stairs may exit the deck almost anywhere, it is not uncommon that they would appear in one of two places: 1) Mounted directly against the house, that is--“closed” within the deck’s footprint or extending from it; or  2) Located at a far point from the connected house. In our tutorial, for example, we will focus on a “freestanding” or “open” set of stairs that step out and away from the deck.

    Be mindful of pitches, level, and variation of grade at the proposed landing location. These factors, too, may have impact on where you ultimately decide to locate stairs.

    It often makes sense to locate steps at the end of a natural walkway. Imagine a deck fully loaded with deck or patio furniture, a grill, potted plants, and whatever your decorating heart fancies. Your natural walkways will likely occur at the perimeter of the deck. Beyond opting to provide a built-out landing, always afford yourself 36” x 36" of unobstructed deck space for entry to and exit from the deck.

    5. Planning the Installation

    Typically stairs are designed in lock step with the deck design, as the steps themselves may impact how your deck build might precede. Decisions on design and layout are often made long before deck (and stair) construction is to begin.

    By code, stairs are no less than 36" wide, and require at minimum two stringers (three, for notched stringers as described herein). Additional stringers should be added based on either the thread material used or on the overall width of the stairs.

    Important! Two decisions you’ll have to make earlier on:

    1. 1. Whether you will install riser material. Optionally, you can choose to leave riser heights “open” and not install riser boards.
    2. 2. How exactly will you place the step nearest to the deck? Will you “hold down” the stringers such that an additional step out from the deck, acting like a sort of mini-landing, is added? Or will your stringers be held tight to the finished decking, such that the last and first riser distance is made up by the deck’s rim board.

    In our installation, we'll use three stringers (notched), 1x pine for risers and we'll finish the top of the stringers flush with our decking material. This information is required for laying out the stringers below.

    6. Now for the Math

    Here are the four basic calculations you'll need to perform:

    • • Find the Number of Stairs (Treads): Measure the vertical drop from the deck to grade in the location where the stairs will exit the deck structure. Alternatively, obtain these measurements from drawings. Divide by seven and round off to the nearest whole number (up or down).
    • • Find the Rise: Take the vertical drop and divide by the number of stairs (figured above). By code the maximum rise is 7 3/4". Remember you need to factor the step to grade or to the deck in your design. Variation in step height by code cannot be greater than 3/8”.
    • • Find the Run: Paired 5/4x6s or 2x6s will finish at a depth around 11 1/4"; a single 5/4x12 or 2x12 around 11 1/8". Determine where you'd like your stairs to land and adjust accordingly. The minimum run on stair treads is 10" by code.
    • • Find the Span: Multiply the number of treads by the run. (Number of treads in our installation is one less than the number of steps).

    7. Locating Posts for Rails

    Any stair set with two or more steps will require a rail.

    Having thought ahead and provided a stair opening in your deck's rail, transfer marks to the deck's rim at each outside edge. This opening is likely already “framed” with a set of posts, which themselves will also accept the rail we are providing with our deck stairs.

    Lay your longest and straightest 2x4 on the deck, immediately above and inside the marking(s) made above. (Remember, again, we are flushing our stringers with the top of our finished decking, which may or may not be installed at this point.) Assuming you were diligent during your deck installation, square this 2x4 to your deck and the posts. Using your framing square as a reference, clamp this 2x4 firmly in place with one or more 12” or 16” triggering bar clamps.

    Measure out along its length and mark off the stair's span (identified in the planning phase above). Drop a plumb bob from the outside edge of this board and use a mallet to tap in a landscaping stake just at the point where the bob touches the ground. Repeat this for the other side of your stairs. Measuring back half the depth of a single tread (roughly 4"), mark for the front inside edge of your post (optionally installing another landscape stake at this location).

    Assuming you have not installed a concrete pad or other formal landing (an installation itself that bears its own set of requirements), use a post hole digger to trench for footers. Dig 18” deep or to the frost line (whichever is deeper), plus six inches. Pour high strength concrete to a height of six inches, following manufacturer recommendations for creating footings. These footings provide a solid base for our 4x4 posts. Posts are installed immediately adjacent to our stair opening and can actually be used later to help us align our stair stringers.

    In this installation, posts are inserted and our post holes receive a backfill, which at minimum includes gravel. Ground contact-rated bearing blocks are attached to posts (prior to insertion) using 3 ½” decking screws and run (below grade) from the footer to the point where stringers ultimately meet grade.

    At minimum provide a gravel bed at the location where the underside of stringers will meet the ground. Between both newly installed posts, cut out an area of turf to a depth of three to six inches. This excavation should be as wide as the stair set, extend back below the stringer location, and be 36" out from the stair's span point. Tamp. Fill with builders sand and level. Install landscaping fabric and pour at least two inches of gravel into the cavity in two separate pours. Use your hand tamper again to compact your gravel between each of these two layers.

    Important! If you have not done so already, check the level of your proposed landing location side to side and front to back. Plan to make amendments as needed.

    Alternative: You may choose a method that more closely resembles a common deck post installation. Again, assuming you have not poured a concrete slab (with integrated footings), dig to frost depth (plus six inches) and insert a tubular concrete form. Pour high-strength concrete per manufacturer recommendations. This time incorporate an appropriate galvanized post base bracket. By doing this, you are effectively creating a space or “standoff” between your post and the ground. Following the requirements provided by the hardware manufacturer, attach one each of a 4x4 cut in half after concrete has sufficiently cured.

    When setting posts, use a four-foot level to check and maintain plumbness throughout the stair install.

    8. Setting up the Stringers

    While treads could be placed between “closed” stringers and held in place using galvanized brackets (with optional cross fastening), we’ll opt instead to install our stairs using notched stringers.

    Notched stringers can be found precut at building centers, but be careful here. The rise and run of these units may or may not be exactly what you are looking for. (Remember you must always consider the first and final step.) Only select this option if you are confident you can effectively make adjustments both at the point of connection and at grade or the landing.

    A better option is to have that same building center custom cut your stringers based on the dimensions you have calculated. Otherwise, we will lay them out and cut them on site using a circular saw.

    Important! Any cuts made in pressure treated lumber should be re-treated using wood preservative.

    Your stringers top end, the one that meets the deck's rim, will be cut consistent and parallel with the final riser. The bottom end of your stringers will receive two cuts--one equidistant and parallel to the treads; the other consistent with the riser. This second cut will effectively square off the stringer and is made as such to finish the front edge of the stringer perpendicular to the ground.

    9. Laying Out and Cutting Notched Stair Stringers

    This is likely the most important step in the entire install, so take care.

    • • Having determined the rise and run of your steps above, work on a stable flat surface carefully laying out your stringer cuts.
    • • If motivated, create a drawing on graph paper. This is an additional opportunity to finalize your calculations, adjusting the rise (between six and eight inches) and the run (between ten and twelve inches) to create a uniform set of stairs. Remember to account for the actual thickness of materials you are using when laying out.
    • • With your 2x12 cut to rough length, layout on the stringer using your framing square. Starting at the bottom end, hold the square in an inverted V against the outside edge of your stock. Use the square's markings to match your required dimensions. Twist the square back and forth into place until you have found the needed pairing of measurements. Use a pencil to draw two (complete) lines for each element of the individual stair--tread and riser. These two lines will form a 90 degree angle.
    • • Mark additionally for the required setback created by your material. This second set of lines represents the element's thickness. Mark with a pencil or otherwise place a piece of tape on your square at both measured points (rise and run). This creates a template allowing for quick repeatable marking. Slide your square down the outside edge of your 2x12 until all steps and cuts are laid out.
    • • Notch cut at markings with a circular saw, making certain that any “overcut” appears on what will be the inside of the stringer. Set the circular saw at a depth a 1/4" deeper than your material, and plan to pull up short at insertions. You will complete all cuts at inside corners using a hand saw.
    • • Repeat until all stringers you will need for your install are laid out and cut. Note: All should match perfectly as adjustments to grade are much easier.

    10. Tying into the Deck Structure

    We are using three stringers in our installation. If you are using a material other than wood for treads, follow manufacturer recommendations or otherwise plan to install a fourth across a three-foot spread. Manufactured material will simply flex more, requiring additional support. Note: More stringers will be required the wider your stairs spread. Plan to support treads, in this case, at an interval between 12" and 18".

    Depending on your design and layout, your stringer’s top end can lay in varying ways. In our installation, we will install our stringers flush with the finished decking surface. With assistance from a helper, dry fit your outside stringer(s) using the marks we made while locating posts above. At this point, mark the rim both with the inside and the bottom edges of the stringer. (If required, otherwise transfer the bottom edge of the rim to the stringer.) We will attach stringers to the rim using sloped galvanized brackets (or equivalent).

    In some cases, it is more convenient to attach your selected galvanized brackets or sloped hangers to your stringers prior to setting them. Nail off according to the hardware maker’s requirements, typically filling every hole within a given bracket. Attach both outside stringers. If not called out by the manufacturer, use 10d joist hanger nails, again nailing off each hole found in the bracket.

    Clamp the front edge of your outside stringers to your previously installed posts. Locate your third stringer at the exact midpoint between the two outside stringers. Mark this location on the rim joist and install appropriate hardware as you did above. Install your center stringer.

    Measure the tread closest to the deck for the inside distance between each of your now set stringers. Using these measurements, cut matching lengths (6 total) from a pressure treated 2x4 or from an equivalent piece of scrap. (Ideally, this material’s width and height should match that “first” rise in your stringer. Execute a rip cut to achieve this, if needed.)

    These members are known as gussets and will serve two purposes once installed. Paired gussets, turned upright, provide lateral support to your stringers. They also provide the opportunity to tie (again using galvanized brackets) to the post structure. Additionally, a third gusset laid flat can allow for attachment downward to the ground.

    Attach gussets to stringers (or vice versa) using fasteners appropriate for selected hardware. Otherwise, attach posts to gussets using 3 ½” decking screws. Install a bottom set of gussets laid flat. Then install a back row in such a way that the gussets standing upright will ultimately help create a channel. Optional: Of these two members, one or the other could be wider, e.g. a 2x6. Fasten the flat member to the "ground" using landscape spikes or other appropriate structurally-rated fastener.

    Addressing each post, drill 1/2” holes through both the post and the stringer, being conscious to align with the channel created by the gussets. Install two stacked 1/2” galvanized carriages through bolts, adding a washer and nut at the inside of the stringer. Tighten down using a ratcheting wrench. Finish by installing the front row of gussets to complete your channel assembly.

    Check throughout and make adjustments to level at the bottom spread of stringers as needed.

    11. Installing Risers and Treads

    Likely the easiest portion of this job, use your tape measure to measure from outside edge to outside edge of your outside stringers. Measure at the first step, the center step, and the last step to ensure that your installation is still true. If you are on point, you could pre-cut your riser and thread material using a circular saw or a 12" chop saw.

    Install your risers first, cutting their length 1/8” long of your measurement. Risers are installed such that they run top to bottom from the inside corner of the next tread to the outside corner of the last. To achieve this, riser material may need to be "ripped" along its length. Attach 1x material to the vertical portion of your stringer notches using 8d galvanized nails or stainless trim screws. For thicker material, such as 2x material, use 2 1/2" or 3" deck screws.

    Treads are installed with an overhang at their "nosing" (by code, between 3/4" and 1 ¼”). Ideally, we'll cut the treads long, roughly matching the overhang we have decided on for nosing. This means double your overhang and add this to the length of your tread when cutting.

    Typically your tread material will match the material installed on the deck. To make this work, material may have to be creatively fitted, and in cases, this will also require the use of rip cuts. Fit your treads around posts, by notch-cutting with a jigsaw or equivalent. Threads are fastened at minimum with two 3 1/2" deck screws per stringer surface. While most screws are "self-tapping" and can be sunk without, it is best to pre-drill at these locations.

    Take care when setting treads, aim to fasten exactly perpendicular to the surface and directly into the center of the stringer’s head. Ganged thread boards, threads requiring more than one board, can be installed such that they touch.

    12. Adding Rails

    Four or more risers in a stairway will require a handrail, independent from the deck's rail assembly.

    Railings should be kept roughly consistent with the rails installed on the attached deck. There are many acceptable ways in which to approach a deck stair rail, but your primary goal should be tying in seamlessly with the deck's main rail system.

    The simplest (and most utilitarian) option is to build a rail which employs two 2x4s laid in a T for the top rail, a 2x4 laid on edge for the bottom rail, and 2x2 material throughout for the vertical balusters, or guard. Important! Take care in the layout phase here as well. Rails must be 34”, but not more than 38” above the nose of any tread. The triangular area created between a tread, a riser, and the bottom rail may not allow for the passage of a six-inch ball.

    Lay a 2x4 on your now installed stairs and move it into contact with your posts. Using the posts as a guide, transfer the angle this creates to this 2x4. Doing this, not only establishes the angle but the length you'll need for your top and bottom rail. You’ll use this 2x4 as a template for the additional cuts in this installation. Using a circular saw or a 10” chop saw, set to the determined angle, cut your top and bottom (horizontal) rails to this length. Cut a third 2x4 (used for our cap) to these requirements, but in this pass, your material is laid flat.

    Locate your 2x4 standing on edge at the center point of your posts, and toenail into the inside faces of posts using 3 1/2" decking screws (yes, drilling pilot holes here is best practice). When locating rail height, it is a pretty safe option to measure up from base of posts, and each should receive the same rough marking. Once installed the bottom rail should be level with the treads, one to the next. The top rail should be parallel with the bottom rail. Use your deck's rail to determine proper spacing and placement of the top rail. In general, the top rail once capped should be held about two-inches below the finished post height.

    For the balusters, use a two-foot level to hold a piece of 2x2 material, plumbed, against both the top and bottom rails. Marking at the top edge of the top rail and the bottom edge of the bottom rail, transfer the angle(s) to this 2x2 material. This too becomes a cutting guide for us. Mark layout lines on the outside of top and bottom rails, such that balusters will fall between three and four inches apart. You may again need to employ math here, adjusting such that balusters are spaced evenly across the rail span.

    Pre-drill balusters and secure them with 8d finish nails to outside face of your rails. Alternatively, a classic option, though disallowed in some municipalities, has been to finish the baluster space using 1x6 laid flat and installed horizontally.

    Many local building departments will allow you to cap your top rail with a 2x4. This is by far your easiest option. By code, your rails must be made of a corrosion-resistant material and should be grippable. Grippability, by code, in many cases can only be achieved with a milled material either riding atop the rail or attached independently to the guard system.

    Center your 2x cap, flushing up with edges of your 4x4s, and attach to the top rail using 3” screws, 10d finish nails, or appropriate finishing screws.

    Check the flushness of post tops and trim to final height. Install, plastic caps, which may be decorative, at post heads to help minimize splitting and checking over time.

Apart from the need for a wide variety of tools, a set of deck stairs is a project that is very much in reach of a do-it-yourselfer. The most important aspect perhaps is planning. It is always best to engage in conversation with your local building authority regarding requirements for these types of jobs in your jurisdiction. Otherwise when working with decking, acquaint yourself with DCA 6 – Prescriptive Residential Deck Construction. It is a definitive guide for deck building, published by the American Wood Council.

Much of what you choose to do with deck stairs will already be dictated by the existing deck structure. Use this for a cue to elements in this project. Finish the underside of your stair set with lattice or other material. Paint or seal treads, along with the rest of the installation, with an appropriate flooring-rated product as required.

If you need a helping hand for your deck stair build project, don't hesitate to contact a qualified deck build pro.

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