Stair Calculator: IRC Winders

Enter the numbers from your drawing. The app checks the stair against IRC R311.7 (2021), winders included, and draws the plan and the section.

■ Winders, measured the way the code does Winder treads must be at least 10 in at the walkline (12 in from the inside of the turn) and at least 6 in at any point, including the narrow end. Enter the depth at the narrow end and every winder is checked, together with winder uniformity (3/8 in), risers (7 3/4 in), treads (10 in), width (36 in, and 31 1/2 in or 27 in at handrail height), rise between floors or landings (12 ft 7 in) and handrails.

■ Feet, inches and sixteenths Type 9' 6 3/16", 9-6 3/16 or 114.1875 and they all mean the same. Results are shown to the nearest 1/16 in.

■ If your drawing numbers disagree, it says so first When riser × risers doesn't match the total rise, the app stops instead of giving a verdict and asks which number is right.

■ One riser more or less See how the riser, the angle and the straight run change with one riser more or less, and how much floor area that gains or loses.

■ Layout drawing and marking sheet as PDF (Pro, one-time purchase) The layout drawing puts the plan, section, check table and sources on one A4 page. The marking sheet lists each step's height, nosing position, winder angles and the upper floor edge. Keep as many named plans as you like, too.

■ Japan's Building Standards as well Switch the code to Japan in Settings: winders measured 30 cm from the narrow end (two methods), plus the housing performance Grades 3, 4 and 5.

This compares your numbers with IRC R311.7 (2021). It is not a plan review. Jurisdictions amend the IRC, so the final call is your local building official's. Headroom, nosing projection and landing depth are not checked. This app is not affiliated with the ICC or any government agency.

The drawing numbers you enter and your plan names stay on this device. They are not stored in iCloud, so they do not move to a new phone. Only usage records, crash reports (Google Firebase) and the messages you send to us are sent; your drawing numbers and plan names are never sent. No ads.

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