Upgrading an exterior concrete stairway with a new wood deck and stair system is an excellent way to improve the appearance and functionality of your home entryway. By constructing a supporting wood framework and landing over the existing concrete, you avoid attaching wood materials directly onto the old masonry surfaces, which greatly reduces the risk of long-term moisture damage and rot. Success in this project relies heavily on precise layout calculations, secure structural connections, and proper footing placements.
Calculating Joist Height And Decking Layout
The first critical phase involves determining the exact height of your support wall and joists. This guarantees that your final decking surface transitions seamlessly into your interior floor. To find the top edge of your deck joists, subtract the exact thickness of your chosen decking material from the overall desired height. For standard two-by-six dimensional lumber, you must subtract a full one and one-half inches.
To achieve a professional appearance, calculate the total span of your decking before cutting the stair stringers. Lay out your boards on a flat surface, incorporating the required structural gaps of at least one-eighth of an inch between each board and a quarter-inch gap where the deck meets the exterior building wall. Dry-fitting the exact run of your decking allows you to position your stairway stringers perfectly, eliminating the need to rip cut a narrow, unsightly decking board at the very edge of your platform.
Installing Footings And Supporting The Structure
Because the new wood stairway extends past the old concrete, it requires a dedicated foundation. You must pour new concrete footings to support the base of the stair stringers. This allows you to position the bottom landing precisely where your decking layout dictates. If you live in a climate subject to freezing temperatures, you must dig these footings below your region's designated frost line. Shallow footings in freezing climates are highly susceptible to frost heaving, which will push the foundation upward and severely damage your framing.
Secure Ledger And Base Plate Attachments
Attaching the new wood structure to the existing concrete stairway and house framing requires specialized hardware. The base plates and deck ledgers must be anchored securely using proper concrete fasteners or framing anchors. This usually requires a rotary hammer drill to bore holes into the old concrete stairs to accept structural anchor bolts. Once the ledgers and plates are locked in place, the stair stringers should be attached using heavy-duty structural hardware and corrosive-resistant fasteners, such as hot-dipped galvanized sixteen-penny nails, to ensure the framework cannot shift under heavy foot traffic.
Three Key Construction Tips
Calculate Decking Spacing Before Digging: Always determine your exact decking layout, including all expansion gaps, before pouring your bottom footings. This allows you to position the base of your stringers perfectly so you finish on a full-width decking board.
Adjust Joists For Decking And Risers: When calculating the layout for your framing, always subtract the exact thickness of your tread materials from your total height, and subtract the thickness of your riser boards from the total width of the steps.
Reinforce Notched Joists: If your elevation requires taking a deep notch out of a supporting deck joist to clear the old concrete stairs, you must install additional structural blocking or sistered framing lumber alongside the notch to restore the lost load-bearing strength.
Bonus Questions And Answers
Transitioning from the structural layout techniques covered above, there are a few additional factors to consider to ensure your new stairway is safe, code-compliant, and built to last.
What Is The Best Way To Prevent Wood Decay Where The New Framing Meets The Old Concrete?
Moisture management is critical when building near existing concrete, as masonry absorbs and retains water like a sponge. Even when using pressure-treated lumber for your base plates and ledgers, you should install a capillary break between the wood and the concrete. Applying a heavy-duty self-adhering flashing tape to the back of your ledger boards, or placing a plastic standoff base under your bottom stringers, prevents the wood from wicking moisture out of the surrounding concrete and greatly extends the lifespan of your framing.
How Do I Ensure My Final Steps Meet Building Code For Height Consistency?
When building over existing concrete, the varying slopes and uneven settlement of the old stairs can throw off your measurements. The International Residential Code requires that the greatest riser height within any flight of stairs shall not exceed the smallest by more than three-eighths of an inch. To achieve this, use a laser level to establish a benchmark line across the entire work area. Measure down from this perfectly level line to calculate your stringer cuts, rather than measuring up from the uneven grade of the old concrete or soil.
Which Anchors Are Most Reliable For Attaching The Wood Base Plates Into Fifty Year Old Concrete?
Older exterior concrete is often much harder and more brittle than modern mixes, which changes how you should approach fastening. While light-duty masonry screws are popular, they can easily snap or strip out in aged concrete. For structural base plates, mechanical wedge anchors or heavy-duty screw anchors installed with a rotary hammer drill are the best choice. Wedge anchors expand deep inside the masonry to provide immense pull-out resistance, ensuring your new wall framing will never detach from the old stairway.
