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Presentation 36:

STAIR RISE AND RUN

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Rise and Run

• Stairs have a rise and run.

Un

it R

ise

Unit Run

Total Run

Un

it R

ise

Unit Run Un

it R

ise

Unit Run

To

tal Rise

• Similar to rafters, rise is vertical and run is horizontal.

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Rise and Run

• Unit rise and unit run do not include the tread nosing.R

iser

Tread

NosingU

nit

Ris

e

Unit Run

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Stair Design

• Building stairs involves several options.

First Floor

Second Floor • In this design there are three treads and four risers.

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Stair Design

• Another set might have four treads and five risers.

Which is best?

• Deciding which to use depends on stair usage.

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Rise/Run Rule

• A formula is used to keep the stairs at a safe and comfortable angle.

• Rise + Run = between 17″ and 18″• Run + two Rises = between 24 and 25 may

also be used.• The first one will be used for this

demonstration.• 7 ½″ rise and 10″ run are numbers that fit the

formula.• 7 ½″ + 10″ = 17 ½″

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Starting Information

• Total rise must be measured.

First Floor

Second Floor

To

tal R

ise• Assume for now there

is ample room to land the stairs on the first floor.

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Number of Risers

• Unit Rise = Total rise ÷ # of Risers

• # of Risers = Total Rise ÷ 8 (Rounded up)

(8 is used as a starting point)

e.g., If the total rise is 30″, then:

# of risers = 30 ÷ 8 = 3.75

Rounding up gives 4 risers.

Note that 5 risers may also work.

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Number of Risers

• Then the unit rise could be either

30″ ÷ 4 = 7 ½″ with 4 risers

or

30″ ÷ 5 = 6″ with 5 risers

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Determining Unit Run

• Tread width may be found from the Rise/Run rule.

7 ½″6″

11″–12″ 9 ½″–10 ½″

• 17″ – 7 ½″ = between 9 ½″ and 10 ½″

• 17 – 6 = between 11″ and 12″

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Example

• What are the possible unit rises and runs for a stair with a total rise of 102″?

# Risers Unit Rise Unit Run

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Example

• 102 ÷ 8 = 12.75 13 risers.

# Risers Unit Rise Unit Run

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Example

• Also 14 or possibly 15 risers.

# Risers Unit Rise Unit Run

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14

15

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Example

• 102 ÷ 13 = 7.86 7 7/8″ unit rise.

# Risers Unit Rise Unit Run

13 7 7/8″

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15

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Example

• 17 – 7 7/8″ = between 9 1/8″ and 10 1/8″ unit run.

# Risers Unit Rise Unit Run

13 7 7/8″ 9 1/8″ & 10 1/8″

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15

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Example

• 102 ÷ 14 = 7 5/16″ unit rise.

• 17 – 7 5/16″ = 9 11/16″ and 10 11/16″ unit run.

# Risers Unit Rise Unit Run

13 7 7/8″ 9 1/8″ & 10 1/8″

14 7 5/16″ 9 11/16″ & 10 11/16″

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Example

• 102 ÷ 15 = 6 13/16″ unit rise.

• 17 – 6 13/16″ = 10 3/16″ and 11 3/16″ unit run.

# Risers Unit Rise Unit Run

13 7 7/8″ 9 1/8″ & 10 1/8″

14 7 5/16″ 9 11/16″ & 10 11/16″

15 6 13/16″ 10 3/16″ & 11 3/16″

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Design

• Deciding which to use depends on the intended use and available total run.– 7 7/8″ steep

• Check local building codes for more guidance.

– 7 5/16″ medium

– 6 13/16″ gentle

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Conclusion

• Stairs have a rise and run.• Unit rise = total rise ÷ # of risers.

• Unit run may be found using

Rise + Run = between 17″ 18″