How to layout and cut the solid & sawn deck stair stringers with diagrams and photos.
Table of Contents
- Planning and Building Wood Deck Stairs with Landing
- Tear Down Old Wood Deck Stairs and Landing
- Remove Wood Deck Stair Landing Support Posts and Concrete Footers
- Build Deck Stair Landing: Pour Concrete Footers and Install 6×6 Posts
- Deck Stair Landing: Saw Post-to-Beam Support Notches
- Deck Stair Landing Beam and Joist Framing
- Deck Stair Stringer Hanger Board and Simpson Strong-Tie LSCZ Stringer Connectors
- Install Wood Deck Stair Stringers and 4×4 Newel Posts
- How to Frame a Wood Deck Stair Landing
- Build Wood Deck Stairs – Layout Solid and Sawn Stringers (you are here)
- How to Install Deck Stair Stringers and Treads
- Build Wood Deck Stairs and Landing – Completed Job Photos
Build Wood Deck Stairs – Layout Solid and Sawn Stringers
The old stairs have been torn down. The new landing and lower stairs construction is basically complete. Now I can start work on the upper stairs:
The upper stairs are built per the dimensions in my design diagram:
The stair Rise & Run calculations are explained in the project introduction – Planning and Building Wood Deck Stairs with Landing.
This photo shows the solid and sawn stringer on the finished stairs to better understand the design:
Solid Deck Stair Stringer
The upper stairs are rather long and 15 feet high. It will be supported by with three 2×12 stringers – two solid and one sawn. Solid stringers are stronger because the saw tooth pattern steps aren’t cut out. The outer solid stringer design is illustrated in the following diagram:
Recall that only two solid stringers support the lower stairs because it’s much lower and has a shorter span.
Stringer Design Notes
- The State of Georgia 2015 Prescriptive Deck Code Amendments (page 5, Figure 33 “Stair Stringer Requirements”) allows maximum unsupported span of 13 ft 3 in for a solid stringer versus only 6 feet for a sawn stringer.
“Unsupported” means there are no intervening support posts under the stairs.
- My solid stringers span 10ft 8-3/4 inches (see the diagram below).
- Simpson Strong-Tie TA9Z-R ZMax staircase angles will support the 2×12 stair treads.
- The maximum allowed Riser height of 7-3/4 inches is necessary to fit within the constraints of the deck.
Recall the landing can’t be moved to make the stairs less steep because there’s a 6×6 main deck post in the way.
The solid stair stringer board dimensions are:
Sawn Deck Stair Stringer
The steps marked and cut out on the sawn stringer. This makes it weaker compared to a solid stringer because there’s only 5-1/4 inches of load bearing wood at the narrowest point of the notches:
The sawn stringer extends 3-5/8 inches lower than the solid stringers in the above diagram. Why? For two reasons:
- The Deck Code on Sheet 17, Figure 33 “Sawn Stringer” requires a 5 inches of load bearing wood at the narrowest point of the notched step. My stringer has 5-1/4 inches here:
- The sawn stringer fits under the stair treads and therefore cannot extend above the treads as with a solid stringer.
The 3-5/8 inches lower mounting position versus the solid stringers is due to the sloping geometry of the stairs and only valid for a 7-3/4 inch riser. The measurement will be different for lower risers.
You needn’t to worry about the sawn stringer positioning as it will fall out naturally during installation because the top step of the stringer must be level with the staircase angles on the solid stringers.
Layout Stair Stringer Steps
The stair steps must be laid out on the solid and sawn stringers with a carpenter’s square and stair gauges. Dave Osborne’s tutorial is excellent:
Stringer Construction Notes
- The stringers are cut from 2×12 by 16 feet long Number 1 Grade pressure treated boards.
- No. 1 Grade has fewer defects compared to No. 2. I bought my boards at a lumber supply yard because the big box home improvement stores only had No 2 Grade.
- The boards must be very straight and dry to limit shrinking and warping. I stacked them on spacer blocks to dry for a month.
- The steps must be traced on all stringers with a square and stair gauges in the normal way.
- The Simpson Strong-Tie staircase angles are mounted where each tread is marked on the solid stringers.
- Only the head and foot are cut on the solid stair stringers per this diagram.
- The sawn stringer steps cannot be traced on the solid stringers.
Normally the 1st sawn stringer is cut and used to trace the steps on the other stringers for a mirror image. Because the sawn stringer is offset lower than the solid stringers, the steps can’t be traced on the solid stringers.
The step pencil marks are highlighted in blue for clarity here:
Saw Stringer Step Notches
The sawn stringer steps are cut with a circular saw. Do not over cut the steps because you won’t meet the minimum 5 inches of load bearing wood required by Code. Sloppy contractors in a hurry will over cut the notches to save time, which weakens the board:
The circular saw cuts on the top side of the board don’t go all the way to apex of the notches:
The cuts are incomplete on the bottom side:
Finish the cuts with jigsaw or handsaw following the kerf made by the circular saw. This avoids over cutting the notch:
The sawn 2×12 stair stringer step notches:
Correct Bowed Sawn Stringer
There’s a problem with my sawn stringer because it bowed about 5/8 inch towards the right after sawing. You can see this near the middle where the step noses aren’t even with the right edge of bottom board:
I corrected the bow by:
- Bending the stringer in the opposite direction of the bow until it was straight, and beyond so it bowed in the opposite direction.
To bend the stringer:
- Set the one end of the stringer against a 6×6 deck post.
- Stack blocks about 8 inches high under the middle of the stringer to make a fulcrum (pivot point).
- Hold the stringer more or less level and screw the end to the 6×6 deck post. Use several screws so it won’t twist.
- My helper pressed down on the other end of the stringer to flex it in the direction opposite the bow.
There was a risk the stringer would break or split but no damage was done.
- Screw a pressure treated 2×4 to the bottom edge of the stringer for reinforcement.
Place the screws about 12 inches apart.
With the stringer pre-stressed/bent in the direction opposite the bow, it relaxed almost straight.
A second 2×4 can be fastened to the opposite side if the stringer needs more correcting. Any residual bowing will be taken out when the 2×12 stair treads are screwed to the sawn stringer, pulling it up and tight. A single stair tread probably isn’t strong enough to pull the stringer straight, but several stairs treads will:
The solid and sawn stringers are ready to be installed. A 24 foot extension ladder is needed to reach the main deck. You can see the 2-ply 2×10 hanger board secured with four 1/2″ galvanized bolts to 4×4 blocks (more on this in next project) at the top of the ladder:
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