Lecture 8 - Stairs Design [Compatibility Mode]

7/22/2019 Lecture 8 - Stairs Design [Compatibility Mode]

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Lecture 8: Stairs Design

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Topics

Definition, functions and functional requirements

of stair Stair terminology

Types of stair

Stair design pursuant to UBBL 1984

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References

Chudley, R. and Greeno, R., ConstructionTechnology

Part 7.4 Timber Stairs

Chudley, R. and Greeno, R., Building ConstructionHandbook

Part 6 Internal Construction and Finishes

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Stages of building construction

1. Preliminary works including site exploration, soilinvestigation, excavation and setting out

2. Foundations or footings including ground beamsand column stumps

3. Ground floors4. Frames (columns & beams) and upper floors

5. Stairs

6. Walls and internal partitions with door and windowframes in position

7. Roofing4


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Definition, Functions &

Functional Requirements of Stair

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For access between floors anddifferent levels in buildings, aladder, stair or ramp is used.

Lifts and escalators are alsoused for verticalcirculation.

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Uniform Building By-Laws 1984

Part VI Constructional Requirements

By-law 124: Lifts

For all non-residential buildings exceeding4-storeys above or below the main access level,

at least one lift shall be provided.

For all residential buildings exceeding 5-storeys above or below the main accesslevel, at least one lift shall be provided.

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Building services for vertical circulation

Lift Escalator

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How to differentiate among ladders, stairs andramps?

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1. Ramps

A surface sloping uniformly as an inclinedplane linking different levels.

Constructed at a slope ofat least 1 in 20.

The pitch oframpsvaries between 0 to 20.

Because of the comparatively shallow slope, itoccupies a considerable area.

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1. Ramps

Must be considered earlyin design process sothat enough room is allowed.

It allows relatively easy and safe access forwheelchairs and pushchairs.

May be less daunting to people with mobilitydifficulties.

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Ramps

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3. Stairs

A set of steps constructed to pass to another level.

The pitch of stairs varies between 20 to 75.

May be formed as a straight f light of steps. More usually formed as two or more flights of steps.

Two flights help to limit the number of steps ineach flight for a safer stairway.

It occupies a considerable space in small houses.

Access forwheelchair users and less mobile persons maybe facilitated with stair lifts fixed to the side.

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Stairs

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Stair lifts

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The primary function of a stair is: -

To allow vertical movement safely from one levelto another.

Other functions of any stairway are: -

To provide a suitable means of escape in event offire.

To provide a degree of sound insulation.

Other functions of stair ??? 21

Storage staircase Spiral staircase with slide

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Bookcase stair

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It is an alternating step design that rises

twice as steeply as conventional stairs,turned into an extraordinary librarystaircase.

The functional requirements of any stair include: -

Strength

Stability

Durability

Sound insulation

Fire resistance

Aesthetics

Safety in use

How to design and construct a staircase tomeet these functional requirements ???

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Aesthetics of stairs

No rails concept

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Floating Stair by Jordi Vayreda

Beautiful or Dangerous ???

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Steep vs. shallow stairs

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Stair Terminology

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Stair

A number of steps leading from one level toanother.

Staircase

The complete assembly of f lights, landings andbalustrades in a single stair.

Stairwell/stairway

The space in which the stairs and landing arehoused.

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Tread

The horizontal surface of a step on which the foot isplaced.

Riser

The vertical or near vertical surface of a step betweenthe two consecutive treads.

Nosing

Projection of tread beyond the face of the riser toprovide as wide as surface of tread as practicable.

Going

The horizontal distance between two consecutive risers.

Rise

The vertical height between two consecutive treads. 30

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Step

Riser plus tread.

May be constructed as openriser/tread stair or enclosedsteps.

Flight

A series of steps without alanding.

Landing

Platform between two flights.

The level space that breaksup the vertical incline of aflight of stairs. 32


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Enclosed steps

A stair which is constructed with a vertical face,i.e. riser between the treads.

Open riser/tread stair

A stair which is constructed with horizontaltreads with a space between the treads.

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Pitch

Angle of inclination of the stair to the horizontal.

Domestic stairs are pitched at not more than 42.

Pitch line

A line connecting the nosings of all treads in any oneflight.

Also known as line of nosings.

Strings

The side support for a flight of steps.

Called wall or outer strings according to their position.

Newel post

Post forming the junction of flights of stairs with landingsor carrying the lower end of strings.

Handrail

Protecting member usually parallel to the string and

spanning between newel post. Either fixed to a wall or supported on a balustrade.

Baluster

The vertical infill member between a string and handrail.

Balustrade

The protection erected on the outer edge of a staircase toprevent anything or anyone falling off the edge. 35 36


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Handrail

Wall string

Outer string

Newel post

Baluster

Balustrade = Handrail + Baluster +Newel post + Outer string

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Exercise: Identify the stair terminology.

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A: Handrail H: Riser

B: Newel pos t I: Tread

C: Baluster J: Wall string

D: Outer string K: Flight

E: Rise L: Landing

F: Nosing M: Balustrade

G: Going

Exercise: Identify the stair terminology.

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Lecture 8: Stairs DesignTypes of Stair

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There are 3 basic ways inwhich stairs with parallel treads areplanned: -

Straight flight stair

Quarter turn stair

Half turn stair

A straight flight of stair is the mostsimplelayout.

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If the flight changes direction between levels,

then need toprovidea landing.

Thedegreeof changein directiondeterminesthesizeof thelanding: -

A90 turn needs a quarter-spacelanding

A 180 turn needs a half-spacelanding

Stair incorporating landings to economisewith the space required to accommodate thestairs.

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1. Straight flight stair

A stair rises from floor to floor in one direction with or without anintermediate landing.

The most economical use of stair.

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Staircase layout plan

2. Quarter turn stair

A stair rises to a landing between two floors, turns through90, and then rises to the f loor above.

Offeringgreat economy in compact planning.

The landing is described as a quarter space or quarterturn landing.

The quarter space or quarter turn landing was often replacedwithwinders for further economy in the use of space.

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2. Quarter turn stair

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3. Half turn stair

A stair rises to a landing between floors, turns through 180,and then rises parallel to the lower flight to the floor

above.

Thelandingisdescribedasa half space or half turn landing.

Often described as a dog leg stair because it looks somewhatlikethehind legof a dog.

The mostcommon arrangement of stairs.

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3. Half turn stair

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4. Open well stairs

Stairs are sometimes described as open well stairs, which refers to aspace orwell between the flights.

As the term open well does not describe the arrangement ofthe flights of stepsin a stair, itshould only beused inconjunctionwith themoreprecisedescriptionstraightf light, quarteror half turnstair.

E.g. half turn stairwith open well, quarterturnstairwith openwell.

A half turn or dog leg stair can be arranged with no spacebetween thef lightsorwitha spaceor well betweenthem.

A quarter turn stair can also be arranged with a space or wellbetweenthe f li hts. 48


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4. Open well half vs. quarter turn stairs

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Staircase layout plans

5. Tapered steps

Tapered steps orwinderswere frequently used by designerstoeconomise on space.

Donot need a landing and use less space.

More dangerous to usebecause thereduction in the inner edgemakeswalking difficult.

Not recommended forusein means of escape stairs orstairsin public buildings.

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5. Tapered steps

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5. Tapered steps

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5. Tapered steps

Disadvantages of tapered steps are: -

Hazard to the aged andvery young because of the verysmall

treadlengthator near the newel post.

Difficulttocarpet, requiringmanyfolds orwasteful cutting.

Difficult to negotiate with furniture due toa rapid rise ontheturn.

Difficult and expensive to construct.

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6. Geometrical stairs

Constructed withtreads thatare tapered onplan.

With the tapered treadsarounda centre support.

There are two types ofgeometrical stairsavailable.

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6A. Spiral stair (a.k.a. helical stair)

With the treads tapering to a central vertical support.

The most economical way of planninga stair.

Ittakesup little floorarea.

It is diff icul t to use and may be dangerous to youngchildren and people withlimited mobility.

Used where space is limited for access to an intermediatefloorofoneroom.

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6A. Spiral stair

(a.k.a. helical stair)

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6B. Elliptical stair

(a.k.a. open well circular stair)

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Constructed around a generous open well with the treadshaving a shallow taper towards the well.

Extravagantin the

use of space.

Used as a feature for grand means of access in large buildings.

7. Open riser/tread stair

A stair which is constructed with

horizontal treads with aspacebetweenthem.

Consi sts of strings withtreads and no risers.

Should not be used whenstairs provide disabledaccess.

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Various materials and forms of construction areused for open riser/tread stairs.

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7A. Closed string

Treads are tightly housed intothe stringswhich are tied togetherwith long steel tie bars underthe first, last and every fourthtread.

Nuts and washers can behoused into the strings andcoveredwithtimberinserts.

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7A. Closed string

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7B. Cut string

Used to support cantilevertreads.

Upper end ofthecarriage can

be housed into the stairwelltrimming member withpossible additional supportfrommetal brackets.

Foot of the carriage ishoused in a purpose mademetal shoe or fixed withmetalangle brackets.

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7B. Cut string

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7C. Mono-carriage

Employs a single central carriagewithdouble cantilever treads.

Often of a tapered section toreduce the apparent bulkyappearance.

Foot of the carriage is secured witha purpose made metal shoe inconjunction with timberconnectors. 65

7C. Mono-carriage

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7D. Alternating tread stairs

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Have a pitch of about 60 and paddle-shaped treads.

Make economic use of space.

Frequently applied to loft (attic) conversions. Additional requirements: -

Non-slip surface

Handrails both sides

Minimum going of 220mm Maximum rise of 220mm

A gap between treads of no more than 100mm

A loft or attic is an upperstorey in a building, directly underthe roof.

Amezzanine or entresol is anintermediate floor betweenmain floors of a building, andtherefore typically not counted

among the overall floors of abuilding.

Often, a mezzanine is low-ceilinged and projects in theformof a balcony.

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7D. Alternating tread stairs

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Case study: Staircase for long house

Stair that lead to longhouse in Sarawak, it has been

carved from one log only.It is so functional andsimple.

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Exercise:

Identify the following types of stair.

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Architectural drawings:

stair layout plan & section details

Stairsare shown on the floor plans withbasic widths andnumber oftreads and risers.

The plan also shows the run with an arrow indicating whetherthe stairs go up or down from that level.

A separate enlarged plan is also prepared for the stairwayand cross-referenced to the floor plans.

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Architectural drawings:

stair layout plan & section details

The enlarged plan of a stairway shows the dimensions of thelandings, thewidths and the run of each stair, risers,treads and other details.

Stair sections are often drawn to detailed out theconstructionand finish components, which are notshown in plan views.

Stair sections will show the stair rise and going,handrails and other details, cross-referenced to the plan view.

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Floor plans

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Stair layout plans

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Stair layout plans

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Stair layout plans

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Stair section details

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Stair section

details

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Lecture 8: Stairs DesignStair Design Pursuant to UBBL 1984

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Part VI Constructional RequirementsBy-law 106: Dimensions of staircases

1 . In an y st ai rcase, t he rise of any staircase shall be not more than180mm and thetread shall be not less than 255mm and thedimensions of the rise and the tread of the staircaseso chosen shall be uniformand consistent throughout.

2. Thewidthsof staircaseshall be in accordance withby-law 168.

3. The depths oflandings shall be not less than the width ofthestaircases.

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Dimensions of steps

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Landing depth vs. Stair width

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Depth of landing must be

at least width of stair


Part VI Fire RequirementsBy-law 168: Staircases

1. Except as providedfor in by-law194, every upper floor shall havemeans ofegressvia at least twoseparate staircases.

2. Staircases shall be of such width that in the event of any onestaircase not being available for escape purposes, theremaining staircases shall accommodate the highestoccupancyload of anyonefloordischarging into itcalculated in accordance with provisionsin the Seventhscheduleto theseBy-laws.

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Part VI Fire RequirementsBy-law 168: Staircases (Cont)

3. The required width of a staircase shall be the clear widthbetween walls but handrails may be permitted to encroach onthiswidth to a maximumof 75mm.

4. The required width of a staircase shal l be maintainedthroughout its length includingat landings.

5. Doors giving access to staircases shall be so positioned thattheir swing shall at no point encroach onthe required widthofthe staircase or landing.

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Part VI Constructional RequirementsBy-law 107: Handrails

(1) Except for staircases of less than 4 risers, all staircasesshallbe providedwithat least one handrail.

(2) Staircases exceeding 2225mm inwidth shall be providedwith intermediate handrail for each 2225mm ofrequiredwidthspaced approximatelyequally.

(3) In building other than residential buildings, a handrailshallbe provided on each side of the staircasewhen thewidthof thestaircase 1100mmor more.

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Handrails for stairway

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Greater than 1.1 mLess than 1.1 m Greater than 2.225 m

Stairs less than 1.1 m

require only one

handrail

Stairs greater than

1.1 m require a

handrail at each side

Stairs of width greater

than 2.225 m must be

divided by a handrail

825mm

to

900mm


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Part VI Constructional Requirements

By-law 107: Handrails (Cont)

(4)

All handrails shall project not more than 100mm from theface of the finished wall surface.

Shall be located not less than 825mm and not more than900mm measured from the nosing of the treads provided

that handrails to landing shall not be less than 900mm fromthe level of the landing.

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Handrails for stairway

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Max. 100mm

825 900mm

Not less than 900mm


Part VI Constructional RequirementsBy-law 108: Maximum flights

(1) In residential buildings, a landing ofnot less than 1.80min depth shall be providedin staircases at vertical intervals ofnotmore than 4.25m and in staircases in all other buildings thereshallbe not more than sixteen risers betweeneach such landing.

(2) No part in any flight of any staircase shall have less than tworisers.

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Landing not less than

1.8m depth

Riser not more than 16

Vertical interval not more

than 4.25m

Maximum flights

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Headroom means the clear vertical distance between thefinished floor level and the soffit of the lowest projectingmemberor surface above that point.

A minimum headroom of 2m measured vertically isrecommended between the pitch line of stair and the undersideof stairs, landings, and floors above the stair.

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Part VI Constructional RequirementsBy-law 109: Winders

(1) Subject to the provisions of Part VII and VIII of these By-laws, spiralstaircases may be permitted as a secondary staircase inbuildings where the topmost floor does not exceed 12.2m inheight. (Assume:- One flooris 3.00m (h));(12.2m/ 3.0m= 4 storeyheight)

(2)Winding staircasemay be permittedwhere they are not used asa required means of egress.

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Part VI Constructional RequirementsBy-law110: No obstruction instaircases

(1) There shall be no obstruction in anystaircase between thetopmost landing thereof and theexit discharge onthe groundfloor.

(2) There shall be no projection, other than handrails in

staircases, in any corridor, passage or staircase at a level lower than 2mabove thef looror above anystair.

By-law111: Lightingand ventilationof staircases

All staircases shall be properly lighted andventilated accordingtothe requirementsof thelocal authority.

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Design calculations of stair Stair is oftendesignedbytrial and error.

To setout a stair, it is necessaryto select a suitable rise andadjustit, ifnecessary.

Thenselecta suitable going.

Before standards were set for the rise and going of steps, it was practice todeterminetheconvenienceof steps fromthe simple formula:-

2 Rises + 1 Going = between 550 and 700mm

It is important to note that in any one flight, there will be one moreriser than treads. Sincethe last tread isin factthe landing.

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Number of treads & risers

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Example

The floor height of a building is 2750mm and thedepth of the stairwell is 3900mm.

Recommend the total number of steps to the stair.

Calculate the dimensions of steps and landing (ifrequired) to the stair.

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Solution

1. Divide the floor height by the rise to find thenumber of risers: -

2750/180 = 15.28 risers

Consider 16 risers

2. Find the exact rise by dividing the floor heightwith the number of risers: -

2750/16 = 172mm

3. Find the going to suit the stairwell depth: -

3900/15 = 260mm104


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Solution (cont)4. Use the formula 2 Risers + 1 Going to see if this

design is comfortable: -

(2 x 172) + 260 = 604mm

i.e. between 550 and 700mm

5. Does the design come within the allowable limits?

6. If YES, use staircase with 16 risers and 15 treadswith 172mm rise and 260mm going.

7. If NO, repeat from step 2 with 15 risers.

8. If this still does not fit, increase the stairwell depthand repeat from step 3.

9. Only 16 risers, hence no need to provide landing. 105

Exercise

The floor height of a building is 2600mm and thedepth of the stairwell is 3600m.

Recommend the total number of steps to the stair.

Calculate the dimensions of steps and landing (ifrequired) to the stair.

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Solution

1. Total number of steps required: -

UBBL 1984: Rise not more than 180mm

2600/180 = 14.44 risers

Consider 15 risers, hence 14 treads

There will be one more riser than treads

2. Dimensions of steps: -

2600/15 risers = 173mm for risers

3600/14 treads = 257mm for treads

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Solution (cont)

3. Simple checking: -

2 (173) + 257 = 603mm

2 Rises + 1 Going = within 550 to 700 mm

4. Only 15 risers, hence no need to provide landing.

Maximum number of risers in any f light is 16,after which a landing must be provided.

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Any questions ???

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Lecture 8 - Stairs Design [Compatibility Mode]

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