Introduction
You install a beautiful new floor and the homeowner loves it—until the first step feels “off.” That first or last riser jumped by half an inch and now you’ve got a safety issue, a code problem, and a callback you didn’t budget for. Here’s what’s happening, why it matters, and several ways to fix it fast without tearing apart the whole staircase. We’ll cover solid field methods, code guardrails, step‑by‑step options, and how to prevent it on your next job.
Table of Contents
Key Takeaways
- Code guardrail: In most residential codes (IRC), total riser variation stair‑to‑stair must be 3/8 inch or less, max riser 7‑3/4 inch, min tread depth 10 inch.
- Flooring changes commonly add 3/8 to 5/8 inch for LVP/engineered wood stacks; tile on membrane can add 1/2 to 1 inch—enough to fail the 3/8 inch variation.
- Diagnose before demo: measure risers, flooring stack, nosing, and landing flatness; choose the least invasive fix that keeps the whole run within tolerance.
- You’ve got options: rebuild the top tread, undercut the bottom nosing, add a tapered transition, overlay an entire run, or reframe select treads—pick based on access and finish.
- Prevent callbacks by planning: agree flooring build‑up and stair adjustments up front, and put it in writing.
The Stair Riser Jump Problem: Why It Happens
Problem
New flooring changes the height of the finished surfaces that your stairs connect to. If you add height at the top landing (or reduce height at the bottom), you create a non‑uniform riser at the first or last step.
- In general, LVP/engineered wood with underlayment adds about 3/8 to 5/8 inch.
- Tile over a decoupling membrane commonly adds 1/2 to 1 inch.
- Industry codes commonly limit riser variation across a flight to 3/8 inch. Many inspectors flag anything beyond that, even if only the first or last riser is out.
Why it matters: humans feel height change quickly. That odd step is a trip hazard and a liability. It’s also the most visible step—right where clients notice it.
Solution Approach
Treat stairs as a system. Any fix must bring the entire flight back within the 3/8 inch variation while staying under the max riser height and maintaining tread depth and nosing rules.
- Most residential codes (IRC): max riser 7‑3/4 inch, min tread 10 inch; nosing 3/4 to 1‑1/4 inch on open risers without uniform treads.
- Keep consistent: once you adjust one end, re‑check every riser in the run.
Example
You add 12 mm LVP plus 2 mm pad on the top floor (~9/16 inch). First riser becomes 8‑1/16 inch while the run averages 7‑1/2 inch. You either: lower the top nosing 9/16 inch (rebuild top tread) or raise all treads by ~9/16 inch (overlay) to bring uniformity back.
Diagnose Your Stair And Flooring Stack
Field Checks That Matter
- Measure all risers, bottom to top, finished surface to finished surface (or to a consistent reference if unfinished).
- Record the existing top landing and bottom landing build‑up (subfloor, underlayment, finish, membranes).
- Check nosing projection and tread depth—don’t fix height and accidentally violate tread/nosing.
- Confirm stringer condition and straightness—no point overlaying a twisted run.
- Look at skirt boards, balusters, and railing code clearances if you’ll add overlay thickness.
- Story pole with 1/16 inch marks for fast readouts.
- Digital caliper for build‑up and nosing projection.
- Laser line to check tread plane and landing flatness.
Common Findings
- It’s common for only the first or last riser to be out by 1/2 inch after tile installs.
- Contractors often report that fixing riser variation adds half a day to a day depending on finish and access.
Five Ways To Fix Riser Jumps (With When To Use Each)
1) Rebuild The Top Tread (Lower The Last Riser)
When
- Top landing got thicker and first step up is now too tall.
- You can access and modify the top tread without wrecking finished skirts or railing posts.
How
- Remove the top tread and riser.
- Adjust framing height or pack down to set new finished tread elevation equalizing risers.
- Re‑install tread and riser; maintain nosing projection within 3/4 to 1‑1/4 inch (typical IRC).
Example
Added 1/2 inch tile on membrane upstairs. You drop the top tread by 1/2 inch. Result: run returns to ~7‑1/2 inch uniform risers, nosing remains 1 inch.
2) Undercut Or Replace The Bottom Tread/Nosing (Raise The First Riser)
When
- Bottom landing got thicker (new floor at the foyer) and the first rise is now too short.
- There’s a replaceable starter tread/nosing detail.
How
- Remove the starter tread and riser.
- Shim up the bottom tread assembly by the landing build‑up (or add a prefinished starter block).
- Ensure the second riser does not exceed the 3/8 inch variance.
Example
New 3/8 inch LVP plus pad at the foyer. Shim and reset the starter tread by ~7/16 inch to match. First two risers now match within 1/8 inch.
3) Add A Tapered Transition Ramp At The Landing
When
- You need a minimal, non‑destructive correction and you have enough run at the landing.
- The delta is small (commonly less than 3/8 to 1/2 inch) and you can create a gentle slope.
How
- Fabricate a tapered filler under the finish at the top or bottom landing to “fade” height change over 24 to 36 inches (longer is better for comfort).
- This effectively reduces the riser jump felt at the first step while keeping landing uniform.
Example
Top landing increased by 3/8 inch. You feather 3/8 to zero over 36 inches using a self‑leveling compound or tapered underlayment, re‑install finish. First riser drops by ~1/8 inch; the remaining 1/4 inch is within tolerance across the run.
When
- Several risers are off or the delta is large (around 1/2 to 3/4 inch) and finishes allow overlay.
- Client wants a fresh look (new treads/risers) anyway.
How
- Install uniform overlay treads and risers (prefab kits or site‑made), maintaining tread depth and nosing.
- Re‑check headroom—overlay reduces it—and railing heights.
Example
Tile added 5/8 inch at the top landing. You overlay all treads/risers by 5/8 inch, preserving uniformity. Handrail still meets height rules; headroom remains greater than code minimum.
5) Selective Reframe (Adjust Multiple Treads Near The Offending End)
When
- Cosmetic overlay won’t cut it and you can open the stringer zone.
- Historic or high‑finish stairs where overlay changes reveals, skirts, or baluster bases.
How
- Remove several treads/risers near the top or bottom.
- Re‑cut stringer notches or add cleats to redistribute rise evenly.
- Re‑install with matching species/finish.
Example
Last two risers are out by 5/8 inch. You reframe the top three treads, spreading the height so each riser changes by about 3/16 to 1/4 inch—keeping total variation less than 3/8 inch.
Quick Comparison
| Option | Impact On Finish | Typical Time | Risk | Best For |
|---|
| Rebuild Top Tread | Low to medium | 2–6 hours | Low | Thickened top landing |
| Raise Starter Tread | Low | 2–4 hours | Low | Thickened bottom landing |
| Tapered Ramp | Very low | 1–3 hours | Low | Small deltas, long landing |
|
Prevention: Plan Stairs Before You Change Floors
What To Confirm Up Front
- Final flooring stack thickness at both landings (finish, pad/membrane, underlayment).
- Existing riser heights across the run.
- Whether top tread can be adjusted or bottom starter can be swapped.
- Any railing/baluster connections that could be affected by overlay.
Write It Down (And Get Buy‑In)
- Note the expected height change and the chosen mitigation (e.g., “Rebuild top tread by approx. 1/2 inch to maintain 3/8 inch max variation”).
- Include acceptance criteria: “Riser variation across flight not to exceed 3/8 inch; tread depth min 10 inch; nosing 3/4–1‑1/4 inch.”
- Set an allowance if the actual build‑up changes at install.
Timing Tip
- Sequence the stair fix right after landing finishes cure. That way, your final measurements are real, not guessed.
Proposal Language You Can Reuse
Here’s clear, plain‑English language clients understand and inspectors recognize:
- Scope: “Adjust stair geometry to maintain uniform risers after new flooring. Rebuild top tread by approx. 1/2 inch; verify final rise across all steps; confirm nosing projection and tread depth meet residential code.”
- Assumptions: “Final flooring build‑up at landings is between 1/2 and 5/8 inch. If different by more than 1/8 inch, additional adjustment may be required.”
- Exclusions: “Railing height changes, baluster rework, finish matching beyond the top three treads unless noted.”
On site, you can capture these details by voice, snap a few photos, and turn them into a clean proposal before you pack up. With Donizo, the voice‑to‑proposal workflow lets you record the stair measurements and chosen fix, then generate a branded PDF your client can e‑sign. Many contractors find this cuts the back‑and‑forth and commonly saves 1–2 hours a week on admin. Once accepted, convert the proposal to an invoice in one click and keep moving.
Frequently Asked Questions
How Much Riser Variation Is Allowed?
Most residential codes modeled on the IRC allow a maximum riser height of 7‑3/4 inch and require that the greatest riser height and the smallest riser height in a flight don’t differ by more than 3/8 inch. Keep tread depth at least 10 inch and nosing projection typically between 3/4 and 1‑1/4 inch.
Is A Tapered Ramp At The Landing Acceptable?
Often, yes—if it’s subtle, secure, and doesn’t create a trip hazard. Use long transitions (24–36 inches or more) and ensure thresholds remain accessible. Always re‑measure the new first or last riser to confirm the entire run stays within the 3/8 inch variation.
When Should I Choose A Full Overlay?
Use overlays when the delta is large (around 1/2 to 3/4 inch), multiple risers are off, or the client wants a cosmetic upgrade. Re‑check headroom, railing heights, and skirt reveals. Overlays typically take a day or two depending on finish work.
Do I Need To Touch The Railing?
Sometimes. If you add overlay thickness, rail height relative to tread can drop. In general, keep guard/handrail heights compliant after changes. Plan railing adjustments in the scope if overlaying more than a quarter inch.
What If The Landings Are Out Of Level?
Flatten them first. A crowned or dished landing can throw your measurements. Use a laser and correct with self‑leveling compound or underlayment before final stair adjustments.
Conclusion
Stair riser jumps after a flooring change are predictable—and preventable—once you treat stairs and landings as a single system. Diagnose the stack, pick the least invasive fix that keeps the whole run within the 3/8 inch variation, and write those acceptance criteria into your proposal. Want to close the loop= while you’re still on site? Talk your measurements and photos into Donizo, generate a professional PDF, get an e‑signature, and convert to an invoice without re‑typing. That’s fewer callbacks, faster approvals, and a safer stair every time.
