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newSchoolWorks.com › VoTechWorks › Building & Construction › Carpentry › Stair Construction: Layout, Framing & Finishing › Lesson 7
BLD-CARP03-05 · Lesson 7 · 13 clock hours · lab

Installing Stringers: Attachment Methods and Plumb-and-Level Procedure

Objective. Students will fasten a three-stringer assembly between the header and a bottom plate, verifying that all stringers are plumb, parallel, and equal in height at top and bottom attachment points before final fastening.

Why Stringer Installation Quality Matters

The stringer is the structural backbone of any stair assembly. If stringers are installed out of plumb, unequal in height, or attached with inadequate fasteners, every riser and tread that follows will be wrong — and the finished stair will be unsafe. NCCER Carpentry standards and the International Residential Code both require that rise and run be consistent across the full flight. A stringer that sits even a quarter-inch higher than its neighbor creates an inconsistent unit rise, which is a leading cause of trips and falls on stairs. Getting the attachment right the first time is far easier than pulling nails after drywall or finish treads are in place.

Layout of Bottom Plate and Stringer Positions

Before you lift a stringer, establish its exact footprint on the pressure-treated bottom plate. Snap three parallel chalk lines representing the centerline of each stringer. Measure the spacing between lines carefully — the spacing must match the tread-width layout completed in earlier lessons. For a standard 36-inch-wide residential stair with three stringers, the outside stringers typically sit near each edge and the center stringer falls at the midpoint.

After snapping lines, tack a temporary 1×4 spreader across all three stringers at a convenient point near the top. This brace locks the spacing before you fasten anything permanently, preventing the assembly from racking while you work. Do not skip this step: without the spreader, stringers can lean toward each other as you nail, and correcting that after connectors are set is time-consuming.

Approved Attachment Hardware

Toe-nailing alone is not an approved method for attaching stringers in most jurisdictions. Metal connectors transfer shear loads that a few angled nails cannot reliably handle. Two hardware types are commonly used:

At the bottom, each stringer bears on and is toe-nailed to the pressure-treated bottom plate. Use approved corrosion-resistant fasteners with pressure-treated lumber — plain bright nails corrode rapidly in contact with treated wood preservatives and can lose significant strength over time. Structural screws rated for treated lumber are an acceptable alternative where your instructor or local practice permits.

Plumb-and-Level Procedure

A stringer must be plumb on its face — that is, the side face of the stringer must be perfectly vertical. An out-of-plumb stringer causes treads to slope sideways, which is both a code violation and a safety hazard.

Procedure for each stringer:

1. Set the stringer in position against the layout line on the bottom plate and rest the top cut against the header.

2. Hold a 4-foot level against the face (flat side) of the stringer.

3. Read the bubble. If the stringer leans away from plumb, slide a shim between the stringer bottom and the plate on the appropriate side until the bubble centers.

4. While a partner holds the stringer in position, fasten the stringer connector at the top and toe-nail the bottom — do not remove the level until at least two fasteners are set.

5. Recheck plumb after fastening, because driving nails can shift the member slightly.

Work from one outside stringer to the other, then do the center stringer last. Recheck all three after the center is fastened.

Verification Round

With all three stringers fully fastened, conduct the verification round before any risers or treads are installed:

Record every measurement on the stringer-inspection checklist. The checklist is a legal and professional document — write legibly, note the date, and sign your entry.

Safety on the Job

Key terms8

StringerThe inclined structural member of a stair that supports the treads and risers; also called a carriage.
Stringer connectorA manufactured metal hanger or bracket fastened to the header and stringer to transfer shear loads at the top attachment point.
Hurricane tieAn L- or T-shaped metal connector used to add lateral resistance at a framing connection; sometimes used at the top of a stringer where it meets the header.
PlumbPerfectly vertical, as confirmed by a level; a stringer face must be plumb so treads do not slope sideways.
Unit riseThe vertical height of a single step; it must be consistent across all stringers and all steps in a flight.
Pressure-treated bottom plateA piece of lumber chemically treated to resist decay and insect damage, used as the bearing surface for stringer bottoms where they contact concrete or are near grade.
ShimA thin wedge of wood or composite material inserted between framing members to make fine plumb or height adjustments before final fastening.
Stringer-inspection checklistA written form used to record height, plumb, and connector measurements for each stringer; serves as quality-control documentation before finish work begins.

Worked examples4

1. You measure the height from the subfloor to the top edge of the bottom cut on your three stringers and get these readings: Left = 3 1/2 in., Center = 3 5/8 in., Right = 3 1/2 in. Does the assembly pass the 1/8-inch tolerance, and if not, which stringer needs adjustment?
  1. Step 1: Identify the difference between the highest and lowest readings. Highest = 3 5/8 in. (Center), Lowest = 3 1/2 in. (Left and Right).
  2. Step 2: Convert to a common fraction. 3 5/8 in. − 3 4/8 in. = 1/8 in. difference.
  3. Step 3: Compare to the tolerance. The tolerance is 1/8 in. The center stringer is exactly 1/8 in. higher than the outside stringers.
  4. Step 4: Determine pass/fail. A difference of 1/8 in. is at the limit. Most inspection checklists treat 'within 1/8 in.' as the outer boundary, so this is a borderline pass — but best practice is to shim the outside stringers up by 1/8 in. or lower the center stringer by adjusting its bottom bearing to achieve equal heights and eliminate any risk.
Answer: The center stringer is 1/8 in. higher than the outside stringers — exactly at the tolerance limit. The center stringer should be adjusted (shimmed down at its bearing or refastened) to bring all three to equal height and ensure a clear pass.
2. Your 4-foot level shows the face of a stringer is out of plumb. The bubble is 1/4 inch off center, which represents a lean of 1/8 inch over the 4-foot length of the level. How much shim thickness do you need at the bottom of the stringer to correct it, and on which side?
  1. Step 1: Read the level result. The stringer face leans 1/8 in. over 4 feet (48 inches) as shown by the bubble position.
  2. Step 2: Determine the lean direction. If the bubble moves toward the top of the stair, the bottom of the stringer is leaning away from the wall; place the shim on the wall side of the stringer bottom to push the face back toward plumb.
  3. Step 3: Determine shim thickness needed. The out-of-plumb measurement at the level is 1/8 in. over the 4-ft level length. The correction shim goes at the stringer bottom, and a 1/8-in. shim at the base will translate to approximately 1/8-in. correction at the level contact point if the level spans from near the bottom. Insert a 1/8-in. shim on the appropriate side.
  4. Step 4: After shimming, recheck with the level before final fastening to confirm the bubble centers.
Answer: Insert a shim approximately 1/8 inch thick on the low/leaning side at the stringer bottom, then recheck with the 4-foot level to confirm the face is plumb before driving final fasteners.
3. You are filling fastener holes in a stringer connector rated for 10d × 1 1/2-in. nails. The connector has 12 holes on the header side and 8 holes on the stringer side. How many total fasteners are required to fully load the connector?
  1. Step 1: Count header-side holes: 12.
  2. Step 2: Count stringer-side holes: 8.
  3. Step 3: Add the two counts: 12 + 8 = 20 fasteners total.
  4. Step 4: Confirm fastener type. All 20 must be 10d × 1 1/2-in. nails as stamped on the connector — substituting a different size voids the rated capacity.
Answer: 20 fasteners of the specified size are required — 12 on the header side and 8 on the stringer side. Every hole must be filled to achieve the rated load capacity.
4. The unit rise on a stringer is supposed to be 7 1/4 inches. You measure the first four risers on the left stringer with a folding rule and get: 7 1/4, 7 1/4, 7 3/8, 7 1/4 inches. Does this stringer pass, and what is the error on the third riser?
  1. Step 1: Identify the designed unit rise: 7 1/4 in. = 7 2/8 in.
  2. Step 2: Compare each measurement to the design. Riser 1: 7 1/4 in. — matches. Riser 2: 7 1/4 in. — matches. Riser 3: 7 3/8 in. — does not match. Riser 4: 7 1/4 in. — matches.
  3. Step 3: Calculate the error on riser 3. 7 3/8 in. − 7 2/8 in. = 1/8 in. high.
  4. Step 4: Evaluate: a 1/8-in. deviation in a single riser creates an inconsistent unit rise. This must be corrected before treads are installed, as code requires consistent rise. The stringer does not pass as-is.
Answer: Riser 3 is 1/8 inch too high. The stringer does not pass — the third step cut must be corrected (by re-cutting or by adjusting the stringer height at that point) to restore a consistent 7 1/4-inch unit rise throughout.

The math in this lesson1

Learners compare stringer heights and riser measurements in fractions and convert a level bubble reading to lean.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Layout of bottom plate and stringer positions: students snap three parallel lines on the bottom plate for stringer centerlines, confirm spacing meets the tread-width requirement, and tack a temporary brace across the top to hold spacing during installation. · Attachment and adjustment: students fasten each stringer to the header with an approved metal connector (hurricane tie or stringer connector) and toe-nail the bottom to the pressure-treated bottom plate; use a level to check plumb on the face of each stringer and shim as needed before final fastening. · Verification round: with stringers fully fastened, students measure the height of each stringer at top and bottom, check that unit rise is consistent on all three stringers using a folding rule, and record results on a stringer-inspection checklist.
Materials: Pre-cut stringers from Lesson 5, stringer connectors and hurricane ties, structural nails and screws, pressure-treated bottom plate material, shims, 4-foot level, folding rule, tape measure, stringer-inspection checklist, drill/driver, hammer
Check: Stringer-inspection checklist reviewed by instructor: all three stringers within 1/8 inch of equal height at top and bottom, each stringer plumb within 1/8 inch over its length, all connectors fully fastened. Pass = all items on checklist signed off.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Carpentry — Stair Framing and Structural Connections
1. What is the primary reason metal stringer connectors are required at the top of each stringer rather than relying on toe-nails alone?
NCCER Carpentry — Stair Framing
2. During installation, why is a temporary spreader brace tacked across the top of the stringers before fastening?
NCCER Carpentry — Structural Hardware and Fastening
3. You are fastening a stringer connector that has 14 nail holes on the header flange. You fill 11 holes with the correct nail. What is the effect on the connector's load rating?
NCCER Carpentry — Stair Layout and Inspection
4. A carpenter measures the height at the top of three stringers and finds left = 5 1/2 in., center = 5 5/8 in., right = 5 1/2 in. below a reference line. What action is correct?
OSHA 10 — Personal Protective Equipment
5. Which PPE is most important to wear when handling freshly cut metal stringer connectors?
NCCER Carpentry — Materials and Fasteners
6. Why must corrosion-resistant or approved nails be used when toe-nailing stringers to a pressure-treated bottom plate?
NCCER Carpentry — Stair Framing and Layout
7. When checking a stringer for plumb using a 4-foot level, where should the level be placed?
NCCER Carpentry — Quality Control and Documentation
8. A stringer-inspection checklist is described as a 'legal and professional document.' In the context of construction work, what does this mean for the carpenter filling it out?
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