Stairs

Stairs Design

Why Stairs 1) Important consideration in a home 2) Accommodate flow traffic 3) Key to circulation—should be close to axis of plan

Stair Groupings Groupings by Material 1) Wood 2) Steel 3) Concrete

Stair Terminology KICKER

Stair Term Definitions Run (total run)--horizontal distance from end to end of the stairs Rise (total rise)--vertical distance from finished floor to finished floor Unit run--the design size of one horizontal step Unit rise--the design size of the vertical distance between each step

Stair Term Definitions Kicker Tread--complete horizontal size of the step, that is, the size of one unit run plus the nosing Riser--the back portion between each tread, it is equal to the unit rise Stringer, carriage, or stair jack--the saw tooth shape support for tread and riser Kick block or kicker--used to keep the bottom of the stringer from sliding on the floor when a downward load is applied

Stair Term Definitions Headroom--vertical distance measured from the tread nosing to the structure (wall or floor) above the stairs. Code required: 6’-8”min

Stair Term Definitions Handrail--the support on the sides of the stair that you grab with your hand to aid walking up and down the stairs. Code required: 34” Guardrail--the railing placed around an stair opening or balcony. Code required: 36”

Stair Term Definitions BALUSTER Elevation of stairs With newel post, Balusters, and handrail Newel post--the vertical post used to support the handrail at its end, also the post intersecting the handrail and guardrail Baluster--smaller vertical supports of the handrail or guardrail. Code spacing requirement: 4”-O.C. max 6” where a triangle is formed by the tread and riser.

Stair Terminology Nosing projection of tread beyond riser 3/8” or less

Stair Terminology Stringer Types Plain or Made On-Site Stringer Closed/Housed or Mill Made Stringer

Plain or On-Site Stringer Notched out 2x12 to support the treads and risers

Closed/Housed or Mill-made Stringer Stringer where ends of risers and treads are not exposed, usually routed so the treads and risers will fit into it

Types of Stairs Basic types straight run right angle or “L” double “L” reverse or “U” winder spiral

Type of Stairs--Straight Run Straight in design and does not change direction Typical minimum width 3’-0”, sometimes where space can be justified 3’-6” or more

Type of Stairs--Right Angle or “L” A 90 degree directional change occurs usually occurs near the center Platform at direction change intermediate landing between floors

Type of Stairs--Double “L” Same as L but with multiple platforms

Type of Stairs--Reverse or “U” A 180 degree directional turn occurs, usually near center Platform at direction change

Type of Stairs--Winder Steps continue in pie shape fashion at landing area Not desirable because steps are wedge shaped The arc at the winders is 12” and the tread design not less than 10” Handrail located where the tread is narrower EQUAL

Type of Stairs--Spiral Additional stair--not used as the main stairs Used for unique design requirements tight space aesthetics

Framing Stairs Note double header double trimmer stringers joist hangers

Design Considerations Stairs should be comfortable to climb 30 - 35 degree angle is optimum

Design Considerations Codes influence Sizes of Risers and Treads Maximum angle 7 3/4” riser with 10” tread Recommended (Common) Size Ranges riser = 7 to 7 1/2” tread = 10” to 10 1/2”

Design Rules When: Unit rise = R Unit run = T R+ T = 17” to 18” R (x) T = 70 to 75

Design Rule Example If unit run is unknown unit rise = 7” (low limit of recommended) (high) R + T = 18 (therefore) 7 + T = 18 (then) T = 11 (low) 2R + T = 24 (therefore) 2*7 + T = 24(then) T = 10 (high) 2R + T = 25 (therefore) 2*7 + T = 25(then) T = 11 (low) R (x) T = 70 (therefore) 7 * T = 70(then) T = 10 (high) R (x) T = 75 (therefore) 7 * T = 75(then) T = 10.7

Design Rule Example If unit run is unknown unit rise = 7.5” (high limit or recommended) (low) R + T = 17 (therefore) 7.5 + T = 17 (then) T = 9.5 (high) R + T = 18 (therefore) 7.5 + T = 18 (then) T = 10.5 (low) 2R + T = 24 (therefore) 2*7.5 + T = 24(then) T = 9 (high) 2R + T = 25 (therefore) 2*7.5 + T = 25(then) T = 10 (low) R (x) T = 70 (therefore) 7.5* T = 70(then) T = 9.33 (high) R (x) T = 75 (therefore) 7.5* T = 75(then) T = 10

Stair Calculations Necessary to determine exact riser height and total run 1. Determine vertical distance between finished floors 2. Divide vertical distance by approximate desired riser height to set approximate number of risers 3. Round to number of whole risers 4. Divide vertical distance by number of risers to get actual riser height 5. Number of unit runs = number or unit rise minus 1 6. Total run: use design rule to determine unit run size then multiply by the number of unit runs

Stair Calculations Example Given: vertical distance = 102”(Total rise) 1--Approx # unit rise = 102 / 7.5 = 13.6 2--Round 13.6 to 14 3--Unit rise height = 102 / 14 = 7.286” 4--14 unit rise (-) 1 = 13 unit runs 5--Design rule: R + T = 17.286 (therefore) 7.286 + T = 17.286(then) T = 10” 6--Total run = 10 * 13 = 130” = 10’-10” Solution: 14 R @ 7.286” and 13 T @ 10”

Stairs Layout Procedures 1) Calculate the how many and size of Risers and Treads 2) Create box showing total rise and total run Total Rise Total Run

Stairs Layout Procedures Divide the total rise into number of Risers (actual value of Riser) Example: R=14, T=13 Line at any angle divided Into equal Parts, points Transferred by Parallel lines

Stairs Layout Procedures Another approach to get equal risers 14 equal risers

Stairs Layout Procedures Divide the total run into number of Treads (actual value of calculated Treads) Line at any angle divided Into equal Parts, points Transferred by Parallel lines

Stairs Layout Procedures Another approach to get equal treads 13 Equal Treads

Stairs Layout Procedures Draw grid using riser and tread divisions determined previously

Stairs Layout Procedures Starting point: Head or Foot of Stairs Follow grid and mark the design of stairs Stair Design

Stairs Layout Procedures Add actual tread boards and riser boards Add stringer board Tread Thickness Stringer Size Material Sizes Riser Thickness Nosing Value

Stairs Section Complete (Your drawing should look like handout) Find the headroom location for structure Locate headers to determine stairwell dimension Add notes and dimensions Place title and scale below drawing

Class Lab Work on Stair Detail/Section Assignment