Construction Pro / Support / Stairwell Opening
Stairwell Opening

How to Size a Stairwell Opening correctly.

Stairwell opening size depends on total rise, required headroom, tread depth, and the riser height you are designing around. Construction Pro's Stairwell Opening tool turns those values into total risers, risers inside the opening, and a minimum opening length that is easier to discuss before framing starts.

By Construction Pro Team Last updated March 29, 2026
App Screenshot

Stairwell-opening screen

This screenshot is taken from the standard interior stairwell recording for this support page.

Construction Pro Stairwell Opening screenshot for a standard interior stairwell example.
Recorded Stairwell Opening screen showing total risers and minimum opening length.

Quick answer

  • 105 in rise, 80 in headroom, 10 in tread, 7.5 in riser: 14 total risers, 3 risers in opening, minimum 30 in opening length.
  • 120 in rise, 80 in headroom, 10 in tread, 7.5 in riser: 16 total risers, 5 risers in opening, minimum 50 in opening length.
  • 98 in rise, 80 in headroom, 10 in tread, 7 in riser: 14 total risers, 2 risers in opening, minimum 20 in opening length.
Field Use

Why this check matters before framing

Stair openings are easy to undersize when the framing crew focuses only on the stair run and not on the headroom relationship. This calculation helps early during layout, remodel planning, and any project where the opening competes with joists, landings, or upper-floor layout.

  • Use it when framing a new stair opening in a floor system.
  • Use it to sanity-check a remodel stair before demolition or reframing begins.
  • Use it alongside the Stair Calculator when the stair geometry and the opening geometry both matter.
Worked Examples

Three headroom-driven opening checks

These examples follow the exact Stairwell Opening formula currently used in Construction Pro.

Example 1

Standard interior stairwell

Inputs: 105 in total rise, 80 in headroom, 10 in tread, 7.5 in riser.

The app calculates 14 total risers. With 80 inches of required headroom, that leaves 3 risers in the opening, which turns into a minimum opening length of 30 in.

Example 2

Taller two-story stairwell

Inputs: 120 in total rise, 80 in headroom, 10 in tread, 7.5 in riser.

With a taller rise, the total riser count reaches 16. That pushes the opening requirement to 5 risers in the opening, which means a minimum opening length of 50 in.

Example 3

Tight remodel stair

Inputs: 98 in total rise, 80 in headroom, 10 in tread, 7 in riser.

A tighter remodel stair with a smaller riser height still needs the headroom check. Here the app shows 14 total risers, 2 risers in the opening, and a minimum opening length of 20 in.

Common mistakes

What makes openings undersized

  • Ignoring headroom and using total stair run as the opening number.
  • Using a riser assumption that does not match the stair layout.
  • Forgetting that remodel constraints can change the riser count and opening length together.
FAQ

Stairwell-opening questions

Does the app calculate the whole stair run too?

No. This tool is focused on the opening geometry. Use the Stair Calculator for the stair run and stringer layout.

Why is headroom entered in inches?

Because the app uses the same inch-based stair geometry throughout, which keeps the opening math consistent.

Is the minimum opening length the final framing dimension?

It is the minimum calculated by the current model. Real framing decisions may still add tolerance, finish buildup, or local code requirements.

Soft App CTA

Check opening length before the joists are cut

Construction Pro keeps the headroom calculation close to the stair inputs so layout decisions happen sooner and with less guesswork.

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