Open vs Closed (Housed) Stringers

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Open (Cut) Stringers

An open stringer is a 2x12 (sometimes 2x10) with triangular notches. Treads sit on the level cuts; risers bear on the plumb cuts. You see the notches from the side unless a skirt covers them. This is the production stair in most US houses: fast to lay out with a framing square and stair gauges, easy to clone from a pattern, and easy to inspect.

Use open when you want speed, a hidden or skirted side, a center carriage plus two outers, or a crew that already walks a square. Exterior deck stairs are almost always open (often 2x12 with treated stock and a wider remaining throat).

Do not use open when the remaining throat drops under about 3.5", when the side of the stair is a showpiece (the triangles read as unfinished), or when you need the treads housed for a furniture-grade quiet flight. A steep well that already flags FAIL on run will not be saved by switching to open — the math is the same.

Risk: overcutting the crotch and splitting the throat. The layout guide is written around this type because that is the cut people get wrong.

Closed / Housed Stringers

A housed (closed) stringer keeps a full-height outer board. Treads and risers are housed into dados — typically 3/8" to 1/2" deep — and wedged or glued. From the side you see a smooth stringer, not triangles. This is the stair you want in an open foyer where both faces show, and the stair that stays quieter if the dados are tight.

Use housed when the stringer is visible, when you want furniture-grade stiffness, when treads are hardwood that should not show brackets, or when you are matching an existing housed flight in a remodel.

Do not use housed when the crew has never cut dados on a pitch, when you are building deck stairs in the rain, or when you need to sister and recut in place next week. Housed is slower. A sloppy dado squeaks forever. Router jigs and a pitch board pay for themselves on the second flight, not the first practice board.

The rise/run math does not change. You still need legal unit rise and unit run. The calculator's throat readout becomes “N/A (housed)” because you are not notching triangles; you still should not hog the dado past about half the board thickness.

Basic Cut

Basic cut is the same triangular pitch-board layout as open, without housed grooves and without extra finish tricks (no routed nosing rebate, no false stringer). It is the “cut the notches and bolt it to the deck” option: garage stairs, basement utility flights, temporary access, some exterior carriages that will get a skirt later.

Pick basic in the calculator when you want the open-stringer throat warning but you are not building a housed show stair. Pick open when those notches are the finished structural look (or will get a skirt). The numbers on the page will match; the note on remaining throat is what you came for.

Which to Use When

You can mix: housed wall stringers and a cut center carriage is a common quality interior. Do not mix unit rise from one type with a different run on the other — one story pole, one calculator result, every board.

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