STAIR DESIGN 9.03 The dimensions of risers and treads in a stairway should be proportioned to accommodate our body movement. Their pitch, if steep, can make ascent physically tiring as well as psychologically forbidding, and can make descent precarious. If the pitch of a stairway is shallow, its treads should be deep enough to fit our stride. Building codes regulate the minimum and maximum dimensions of risers and treads; see 9.04–9.05. For comfort, the riser and tread dimensions can be proportioned according to either of the following formulas: • Tread (inches) + 2x riser (inches) = 24 to 25 • Riser (inches) x tread (inches) = 72 to 75 Exterior stairs are generally not as steep as interior stairs, especially where dangerous conditions such as snow and ice exist. The proportioning formula can therefore be adjusted to yield a sum of 26. For safety, all risers in a flight of stairs should be the same rise and all treads should have the same run. Building codes limit the allowable variation in riser height or tread run to 3 /8" (9.5 mm). Consult the building code to verify the dimensional guidelines outlined on this and the following page. • The actual riser and tread dimensions for a set of stairs are determined by dividing the total rise or floor-to-floor height by the desired riser height. The result is rounded off to arrive at a whole number of risers. The total rise is then redivided by this whole number to arrive at the actual riser height. • This riser height must be checked against the maximum riser height allowed by the building code. If necessary, the number of risers can be increased by one and the actual riser height recalculated. • Once the actual riser height is fixed, the tread run can be determined by using the riser:tread proportioning formula. • Since in any flight of stairs, there is always one less tread than the number of risers, the total number of treads and the total run can be easily determined. Ladders • R = 12" (395) o.c. typical Step Ladders • 12- 3 /4" (325) riser; 3" (75) tread • For private stairs only: • 7- 3 /4" (195) maximum riser; 10" (255) minimum tread • 7" (180) maximum riser; 11" (280) minimum tread • 4" (100) minimum riser • 1:8 maximum • 1:12 maximum when part of an accessible route or an emergency egress system • Maximum riser height; minimum tread depth for accessible stairs and emergency egress Stairs Ramps Riser and Tread Dimensions Riser Tread inches (mm) inches (mm) 5 (125) 15 (380) 5- 1 /4 (135) 14- 1 /2 (370) 5- 1 /2 (140) 14 (355) 5- 3 /4 (145) 13- 1 /2 (340) 6 (150) 13 (330) 6- 1 /4 (160) 12- 1 /2 (320) 6- 1 /2 (165) 12 (305) 6- 3 /4 (170) 11- 1 /2 (290) 7 (180) 11 (280) 7- 1 /4 (185) 10- 1 /2 (265) 7- 1 /2 (190) 10 (255)
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STAIR DESIGN 9.03
The dimensions of risers and treads in a stairway should be proportioned to accommodate our body movement. Their pitch, if steep, can make ascent physically tiring as well as psychologically forbidding, and can make descent precarious. If the pitch of a stairway is shallow, its treads should be deep enough to fit our stride.
Building codes regulate the minimum and maximum dimensions of risers and treads; see 9.04–9.05. For comfort, the riser and tread dimensions can be proportioned according to either of the following formulas:• Tread(inches)+2xriser(inches)=24to25• Riser(inches)xtread(inches)=72to75
Exterior stairs are generally not as steep as interior stairs, especially where dangerous conditions such as snow and ice exist. The proportioning formula can therefore be adjusted to yield a sum of26.
For safety, all risers in a flight of stairs should be the same rise and all treads should have the same run. Building codes limit the allowable variation in riser height or tread run to 3/8"(9.5mm).Consult the building code to verify the dimensional guidelines outlined on this and the following page.
• Theactualriserandtreaddimensionsforasetofstairsaredetermined by dividing the total rise or floor-to-floor height by the desired riser height. The result is rounded off to arrive at a whole number of risers. The total rise is then redivided by this whole number to arrive at the actual riser height.
• Thisriserheightmustbecheckedagainstthemaximumriserheight allowed by the building code. If necessary, the number of risers can be increased by one and the actual riser height recalculated.
• Oncetheactualriserheightisfixed,thetreadruncanbedetermined by using the riser:tread proportioning formula.
• Sinceinanyflightofstairs,thereisalwaysonelesstreadthanthe number of risers, the total number of treads and the total run can be easily determined.
Stairway design is strictly regulated by the building code, especially when a stairway is an essential part of an emergency egress system. Because an accessible stairway should also serve as a means of egress during an emergency, the ADA accessibility requirements illustrated on the next page are similar to those of an emergency egress stairway.
code allows exceptions for stairs in individual dwelling units.
• 34"to38"(865to965)heightabovetheleadingedgeofthestair treads or nosings.
• Handrailsshouldbecontinuouswithoutinterruptionbyanewelpost or other obstruction.
• Handrailsshouldextendatleast12"(305)horizontallybeyondthe top riser of a stair flight and extend at the slope of the stair run for a horizontal distance of at least one tread depth beyond the last riser nosing of the flight. The ends should return smoothly to a wall or walking surface, or continue to the handrail of an adjacent stair flight.
• Seethenextpagefordetailedhandrailrequirements.
Treads, Risers, and Nosings• Aminimumofthreerisersperflightisrecommendedtoprevent
tripping and may be required by the building code.• Seethenextpagefordetailedtread,riser,andnosing
• Guardrailsshouldbeabletowithstandaconcentratedloadapplied nonconcurrently to their top rails in both vertical and horizontal directions. Consult the building code for detailed requirements.
STAIR REQUIREMENTS 9.05
Handrails• Handrailsshouldbefreeofsharporabrasive
elements and have a circular cross section with anoutsidediameterof1-1/4"(32)minimumand2"(51)maximum;othershapesareallowable if they provide equivalent graspability and have a maximum cross-sectional dimension of2-1/4"(57).
• 1-1/2"(38)minimumclearancebetweenhandrail and wall
Nosings• 1-1/2"(38)maximumprotrusion• 1/2"(13)maximumradius• Risersshouldbeslopedortheundersidesofthenosingsshouldhavea60°angleminimumfrom the horizontal.
• Landingshouldbeaswideasthewidestrampleading to it.
• 60"x60"(1525x1525)minimumlandingwhere ramp changes direction
Handrails• Rampshavingarisegreaterthan6"(150orarungreaterthan72"(1830)shouldhavehandrails along both sides.
• Handrailrequirementsarethesameasforstairways.
• Extendhandrailsatleast12"(305)horizontally beyond the top and bottom of ramp runs.
ADA Accessibility GuidelinesAccessible stairs should also serve as a means of egress during an emergency, or lead to an accessible area of refuge where people who are unable to use stairs may remain temporarily in safety to await assistance during an emergency evacuation.
Risers and Treads• Treaddepth:11"(280)minimum• Riserheight:4"(100)minimum;7"(180)maximum• Uniformriserandtreaddimensionsarerequired.• Openrisersarenotpermitted.
RampsRampsprovidesmoothtransitionsbetweenthefloorlevels of a building. To have comfortable low slopes, they require relatively long runs. They are typically used to accommodate a change in level along an accessible route or to provide access for wheeled equipment. Short, straight ramps act as beams and may be constructed as wood,steel,orconcretefloorsystems.Longorcurvilinearramps are usually of steel or reinforced concrete.
with winders, as a circular or spiral stair. Quarter-turn and half-turn stairs may also use winders rather than a landing to conserve space when changing direction.
• Winderscanbehazardoussincetheyofferlittle foothold at their interior corners. Building codes generally restrict the use of winders to private stairs within individual dwelling units.
circular plan configuration. Even though a circular stair is constructed with winders, the building code may allow its use as part of the means of egress from a building if its inner radius is at least twice the actual width of the stairway.
Spiral Stair• Aspiralstairconsistsofwedge-shaped
treads winding around and supported by a central post.
• Spiralstairsoccupyaminimumamountof floor space, but building codes permit their use only as private stairs in individual dwelling units.
• See9.12fortypicaldimensions.
• Windersmusthavetherequired tread dimension at a point 12"(305)infromthenarrow end of the treads.
• 6"(150)minimumatthenarrow end of the treads
• 10"(255)minimumatthenarrow end of the treads
• Theinsideradiusshould be at least twice the actual width of the stair.
• 7-1/2"(190)minimumtread dimension at a point 12"(305)infromthenarrow end of the treads.
• 9-1/2"(240)maximum riser height
• 6'-6"(1980)minimumheadroom clearance
9.08 WOOD STAIRS
A wood stair is constructed of the following elements:
• Carriagesorroughstringersaretheprincipalinclinedbeams supporting the treads and risers of a flight of stairs. The number and spacing of carriages required for a stairway depend on the spanning capability of the tread material.
• Stringersaretheslopingfinishmembersrunningalongsidea staircase, against which the risers and treads terminate.
• Risersaretheverticalboardsthatcloseoffthestairspaceand help make the construction rigid; some stairs have no risers.
CSI MasterFormat™ 06 43 00: Wood Stairs and Railings
• Soffit,ifdesired• Fireblocking
• Carriage• Spacer
Closed-Riser Stair with Full Stringer
• Carriagesmaybeattachedtotheir supporting beam, header, or wall framing with metal hangers or a ledger.
• Kickplateanchorsandabsorbsthe thrust of an inclined stair carriage.
• Finishwoodflooringoverplywoodtreads and risers
• Fullstringer
• Rise• Run• See9.03–9.05forriser,tread,
and nosing requirements.
• Chamferedgesofplywoodtreads for carpeting.
• See9.04–9.05forhandrail requirements.
• Metalhandrailbracket
• Wallframing• Wallfinish
• Fullstringers
• Carriages• Spacers
• Blockingasrequiredforwall finish
WOOD STAIRS 9.09
• Facestringerreceivesriser at a mitered joint.
• Facestringeristheouterstringer of a staircase; it may be housed to form a curb or be open with its upper edge cut to the profile of the treads and risers.
• Balusters• Fillerbetweenbalusters• Shoerail
• Housedstringer• Tread
• Wedge• Blocking• Carriage• Wallfinish
Housed Stringer @ Rail
• Handrail;see9.04–9.05 for requirements.
• Fillerbetweenbalusters
• Balustersdovetailedintotreads
• Housedwallstringer• Tread• Treadreturn
• Wedge• Carriages• Blocking
• Facestringer• Wallfinish Open Stringer @ RailClosed-Riser Stair with Housed Stringer
Open-Riser Stair
• Housedstringerisroutedtoreceivetheendsoftreads and risers in a series of housings; wedges are used to assure a tight fit.
• Balusterslag-boltedtocarriage
• Treadsmaybesupportedeitherbysteel angles let into the treads or by letting the planks into the carriage 1/2"(13)minimum.
• Aboxstairhasahousedstringonboth sides so that it may be more or less completely finished before being set in its final location.
A concrete stair is designed as an inclined, one-way reinforced slab with steps formed on its upper surface. If the stair is constructed after the floor beam or wall supports, it acts as a simple beam. If it is cast with the beam or slab supports, it is designed as a continuous beam. Concrete stairs require careful analysis of load, span, and support conditions; consult a structural engineer for final design requirements.
Laddersareusedprimarilyinindustrialconstruction and in utility and service areas. They may also be used in private residential construction where space is extremely tight and traffic is minimal.
The drawings on this page illustrate ladders built with metal components. The ladder forms may be translated into wood construction.
• Itismoreconvenienttoaccessladder from the side rather than through the hand bars.
• 2'-0"(610) minimum width
• Supportangles@10'-0"(3050)o.c.maximum
• 1'-6"(455)minimum
• Rungsmaybe3/4"(19)roundbarsor1"(25)øpipes.
• Stringersmaybechannels,angles, or flat bars.
• Anglebracketsboltedtofloorstructure
• 3'-0"(915)highhand bars
• 12"to13-1/2" o.c. (305to345)
• 7"(180)minimum
• 12"(305)+/– to first rung
Vertical Ladders
Ship’s Ladder
• 1-1/4"(32)øpiperailing; secure to wall structure or return to stringer at top.
• 6"(150)todoorway
• 3"to6"(75to150)
• 10-1/2"to12" (265to305) rise
• 60°to75°
9.14 ELEVATORS
Elevators travel vertically to carry passengers, equipment, and freight from one level of a building to another. The two most common types are electric elevators and hydraulic elevators.
Electric ElevatorsElectric elevators consist of a car that is mounted on guide rails, supported by hoisting cables, and driven by electrichoistingmachineryinapenthouse.Gearedtractionelevatorsarecapableofspeedsupto350fpm(1.75m/s)andaresuitableformedium-risebuildings.Gearlesstractionelevatorsareavailablewithspeedsupto1200fpm(6m/s)andtypicallyservehigh-risebuildings.
• 16'-0"to20'-0"(4875to6095)
• Topfloor
• Hoistingcableisoneofthewirecablesorropesusedforraising and lowering an elevator car.
• Hoistwayistheverticalenclosedspaceforthetravelofone or more elevators.
• Travelingcableisoneoftheelectriccablesconnectinganelevator car to a fixed electrical outlet in the hoistway.
• Guiderailsaretheverticalsteeltrackscontrollingthetravel of an elevator car or counterweight; they are secured to each floor with support brackets.
• Counterweightsarerectangularcast-ironblocksmounted in a steel frame to counterbalance the load placed on the hoisting machine by an elevator car.
• Alimitswitchautomaticallycutsoffcurrenttoanelectric motor when an elevator car has passed a given point.
• Riseortravelistheverticaldistancetraversedbyanelevator car from the lowest to the highest landings of the hoistway.
• Bottomfloor
• 5'-0"to11'-6"(1525to3505)
CSI MasterFormat 14 20 00: Elevators
• Apenthousehousesthehoistingmachinery on the roof of a building.
• Acontrolpanelcontainsswitches,buttons, and other equipment for regulating the hoisting machinery.
• Thehoistingmachineryforraisingand lowering an elevator car consists of a motor-generator set, traction machine, speed governor, brake, driving sheave, and gears, if used.
• Heavysteelmachinebeamssupportthe hoisting machinery for an elevator.
• Landingistheportionofaflooradjacent to an elevator hoistway, used for the receiving and discharge of passengers or freight.
• Elevatorcarsafetyisamechanicaldevice for slowing down and stopping an elevator car in the event of excessive speed or free fall, actuated by a governor and clamping the guide rails by a wedging action.
• Hoistwaydoorbetweenahoistwayandan elevator landing is normally closed except when an elevator car is stopped atthelanding;7'-0"and8'-0"(2135and2440)heightsaretypical.
• Bufferisthepistonorspringdevice that absorbs the impact of a descending elevator car or counterweight at the extreme lower limit of travel.
• Elevatorpitistheportionoftheshaft that extends from the level of the lowest landing to the floor of the hoistway.
ELEVATORS 9.15
Hydraulic ElevatorsHydraulicelevatorsconsistofacarsupportedbya piston that is moved by or moves against a fluid under pressure. A penthouse is not required, but the hydraulic elevator’s lower speed and piston length limit its use to buildings up to six stories in height.
• Guiderail
• Hoistwayoffire-resistiveconstructionmustextend to the underside of a fire-resistive roof, or atleast3'(915)aboveanon-fire-resistiveroof.
• Hydraulicpiston
• Machineroomhousesthehoistingmachinery,control equipment, and sheaves for raising and lowering an elevator car; a location at or near the bottom landing is preferred.
• Elevatorpit
• Pistoncylinderwell; depth equals rise or travel+4'to7'(1220to2135)
• Thesedimensionalguidelinesareforpreliminaryplanning only. Consult the elevator manufacturer for specific sizes, capacities, and dimensional and structural support requirements.
• 3"to1'-6"(75to455) depending on elevator operation
Limited Use/Limited Access ElevatorsLimitedUse/LimitedAccess(LU/LA)elevatorsaresmallhydraulicelevators designed for installation in new or existing low-rise structures.LU/LAelevatorsarelimitedto25'(7620)oftravelataspeedof30fpm(0.55km/h),aloadcapacityof1400lb.(635kg),andacabfloorareaof18sf(1.67m2).Theycanoperateonsingle-phase power and require less pit depth and overhead space than do regular commercial elevators.
9.16 ELEVATORS
Elevator LayoutThe type, size, number, speed, and arrangement of elevators are determined by:• Typeofoccupancy• Amountandtempooftraffictobecarried• Totalverticaldistanceoftravel• Round-triptimeandspeeddesired
• Banksorrowsofelevatorsinahigh-risebuildingarecontrolledbya common operating system and respond to a single call button.
• Elevatorsshouldbecentrallylocatednearthemainentrancetoabuilding and be easily accessible on all floors, but also be placed off of the main circulation path.
• Consultelevatormanufacturerforrecommendedtype,size,layout, controls, and installation requirements and details.
• Consultthebuildingcodeforstructuralrequirementsandshaftway requirements for fire separation, ventilation, and soundproofing.
ADA Accessibility Guidelines• Visibleandaudiblecallsignalsorlanternsshouldbecenteredatleast72"(1830)abovethefloorateachhoistwayentranceandbe visible from the adjacent floor area.
• RaisedcharactersandBraillefloordesignationsshouldbeprovided on both jambs of elevator hoistway entrances and be centeredat60"(1525)abovethefloor.
• RaisedandBrailledesignationsshouldbeplacedimmediatelytothe left of the button to which the designations apply.
• Audibleandvisiblecarpositionindicatorsshouldbeprovidedineach elevator car.
• 1.5xcardepthor 10'(3050)minimum
• 1.75xcardepth
• 2xcardepthor 12'(3655)minimum
• Eightcarsper row maximum
• 68"(1725)minimumwidth for cars with side opening doors; 80"(2030)minimumforcars with center opening doors
• 51"(1295)minimumclear car depth
• 36"(915)minimumcleardoorway opening
ESCALATORS 9.17
Escalators are power-driven stairways consisting of steps attached to a continuously circulating belt. They can move a large number of people efficiently and comfortably between a limited number of floors; six floors are a practical limit. Because escalators move at a constant speed, there is practically no waiting period, but there should be adequate queuing space at each loading and discharge point. Escalators may not be used as required fire exits.
• 2"(51)
• Escalatorsrequiresupportsat both ends; intermediate supports may be required whentheriseexceeds18'(5485).
• Thesedimensionalguidelines are for preliminary planning only. Consult the escalator manufacturer for specific sizes, capacities, and dimensional and structural support requirements.
CSI MasterFormat 14 30 00: Escalators and Moving Walks
• 7'-6"(2285) • 1.732xrise • 8'-0"(2440)
• 7'-6"(2285) minimum headroom
• Rise
• 3'-2"(965)• 2'-8"(815)
• Atrusssupportstheescalator and provides space for the necessary mechanical equipment.
• Movingsidewalksarepower-driven,continuouslymovingsurfaces, similar to a conveyor belt, used for carrying pedestrians horizontally or along low inclines.