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Stairs Terminology and Design Rules. Why Stairs u Important consideration in a structure –design –function u Accommodate traffic flow from one level to.

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Presentation on theme: "Stairs Terminology and Design Rules. Why Stairs u Important consideration in a structure –design –function u Accommodate traffic flow from one level to."— Presentation transcript:

1 Stairs Terminology and Design Rules

2 Why Stairs u Important consideration in a structure –design –function u Accommodate traffic flow from one level to another u Key to circulation in a plan u Code requirements –based upon safety –established by occupant count

3 Stair Groupings based on Material u 3 Groupings 1--Wood 2--Steel 3--Concrete

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

5 Straight Run u does not change direction u typical width is 3’-0” to 3’-6” (residential) u typical width for commercial construction is set by code u simple u popular

6 Right Angle or “L” u Intermediate platform between floors u A 90 degree directional change occurs, usually near the center u Platform at directional change of stairs u Platform provides a resting area between flights of stairs Platform

7 Double “L” u Same as “L” but with multiple platforms Platform

8 Reverse or U u A 180 degree directional turn occurs, usually near center u Platform at direction change u Platform length is 2 (x) stair width Platform

9 Winder u Wedge shape steps u Steps continue in place of landing u Unsafe at the small of the wedge u The design: arc in the area of the winder is half the stair width and the tread design is 10” 10” tread width

10 Spiral and Curved u Spiral Stairs u Used as an additional stair--not used as the main stairs, follow code requirements u Used for unique design with requirements such as –limited or tight spaces –aesthetics –extra/addition stairs u Curved Stairs

11 Rise/Unit Rise (design rise) vertical distance between stairs/treads, vertical member Total Rise vertical distance between floors Total Run horizontal distance between first and last riser Stair Terminology Run Run/Unit Run (design run) horizontal distance from riser to riser, horizontal member Rise total rise total run

12 Stair Terminology landing headroom stringer Landing “floor” at the bottom and top of a flight of stairs Headroom vertical distance from outside edge of step (nosing) to ceiling Stringer/Carriage/Stair Jack member on which risers and treads rest, provides structural support for risers and treads

13 Stair Terminology u Nosing –projection of tread beyond riser –usually 1 1/8” u Tread –equal to unit run + nosing u Riser –equal to unit rise

14 Stair Terminology u Plain Stringer –notched out 2x12 to support the treads and risers u Closed/Housed Stringer –stairs ends at stringer and are not exposed, stringer usually routed so the treads and risers will fit into it

15 Stair Terminology at a glance Run (Unit Run) Rise (Unit Rise) Total run Total rise Tread Riser Nosing Stringer (carriage) Headroom Clearance Stairwell Landing (fin fl) Kick board

16 Stairs Framing Terms u double header u double trimmer u stringers u joist hangers u stairwell

17 Design Considerations u Stairs should be comfortable to climb u 30 - 35 degree angle is optimum to prevent fatigue u Max of 16 steps between landings u Design rules have been developed with years of study and experimentation

18 Design Considerations u Every step should be same size u Absolute minimum ratio of riser to tread –4” riser with 11” tread u Absolute maximum ratio of riser to tread –7” riser with no maximum tread u Optimum ratios –7” riser (unit rise) –11” tread (unit run) » includes nosing

19 Design Rules u Riser + Tread = 17” - 17 1/2” [book] (17”- 18” usually) u 2 (x) Riser + Tread = 24” - 25” u Riser (x) Tread = 70 - 75 sq inches

20 Design Rule Example u Normal conditions –If: Riser = 7 andTread = 10 7 + 10=17 (required 17 to 18) 2 x 7 + 10 = 24 (required 24 to 25) 7 x 10 = 70 (required 70 to 75) u All conditions conform to rules

21 Design Rule Example u A minimum condition –If: Riser = 5 and Tread = 14 5 + 14 = 19(required 17 to 18) 2 (x) 5 + 14 = 24(required 24 to 25) 5 (x) 14 = 70(required 70 to 75) Only two rules are satisfied, okay since at least one rule works

22 Stair Calculations u 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

23 Stair Calculations Example Given:vertical distance = 102” 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”

24 Example of a Wood Stair Section

25 Example of an Exterior Concrete Stair Section

26 Stair Section u A--Section View –Scale of sectional drawing (1/2” = 1’-0”) –Coordinate sectional view with details (notations) u B--Structural Connection Details –Scale of detail drawings: 1”= 1’-0” Details to draw –1) top of stair run –2) intermediate landings/platforms –3) bottom of stair run (More) B1 B2 B3 A

27 Stair Section View –Add height and width of platform –Add 2x4 kick board –Add 2x6 ledger @ platform (down steps area) –Determine number and size of Riser and Tread include on your drawing in a note –Show total run on each flight of stairs (More)

28 Structural Connection Details scale 1”=1’-0” u Detail at Top of Stair connection –note use of joist hanger

29 Structural Connection Details u Stringer to Landing connection –note use of ledger u Add platform joist spacing 16”OC u 2x6 Ledger u 2x4 ledger beyond (hidden lines) (More)

30 Structural Connection Details u Bottom of Stair connection –note 2 x 4 plate (kick board) & notched stringer u Joist are 2x8 @ 16” OC

31 ASSIGNMENT u On sheet A-7 create the stair cross section A/A-7 and B/A-7 u Develop a landing detail 1/A-7 u Develop a bottom of stair detail 2/A-7 u Develop a top of stair detail 3/A-7 u Include handrail information on any or all of the above

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