1. Stair Design Weekend Cabin Retreat Project
Sacramento City College
EDT 51
Kenneth Fitzpatrick, P.E.
EDT 51-Stair Design

2. Objectives Define common stair terminology.
Discuss the appropriate use of various stair designs.
Design a stairway for a residential structure.
Draw structural details for a main stairs.
Perform stair calculations for a residential stairway.
EDT 51-Stair Design

3. Definitions
A stairway is a series of steps with or without landings or platforms which is installed between two or more floors of a building.
A house may have main stairs and service stairs.
Main stairs are generally of much better quality than service stairs
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4. Definitions Six general types of stairs Straight run L Stairs
Double-L stairs
U Stairs
Winder stairs
Spiral stairs
Circular stairs
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5. Straight Run Stairs Most common type used in residential construction.
Straight run stairs, obviously have no turns.
Least costly type.
Require a long open space in which to construct.
This may be difficult to accommodate in the floor plan
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6. Straight Run Stairs
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7. L Stairs Have one landing at some point along the flight of steps.
If the landing is near the top or the bottom of the stairs, they are called a long L stair.
These stairs are used when the space required for a straight run stair is not available.
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8. L Stairs
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9. Long L Stairs
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10. Double L Stairs These stairs require two 90o turns along the flight.
Used when insufficient room exists for a straight run stair or an L stair.
Double L stairs are not frequently used in residential construction.
They are expensive to build and break up the floor plan.
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11. Double L Stairs
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12. U Stairs Can be constructed as either wide U or narrow U stairs
Both have two flights of steps parallel to each other with a landing between.
The difference between the wide and narrow U is the space between the flights.
Narrow U stairs have little or no space between the flights; wide U have a well between the flights
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13. U Stairs
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14. U Stairs
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15. Winder Stairs
Have “pie-shaped” steps which are substituted for a landing.
Used when space is insufficient for an L shape.
The triangular shaped steps should be as wide as a standard step.
Are not very safe.
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16. Winder Stairs
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17. Spiral Stairs Used when little space is available.
Most are made from steel and welded together.
Not very safe; have wider steps.
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18. Spiral Stairs
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19. Spiral Stairs
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20. Circular Stairs
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21. Circular Stairs
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22. Stair Terminology
Baluster: vertical members that support the handrail on open stairs.
Bullnose: the first step on an open stair, which has been extended out forming a semicircle and often receiving the newel post.
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23. Stair Terminology
Carriage: the rough structural support (usually 2" x 12") for treads and for risers of wood stairs, sometimes called string or stringer that has been routed or grooved to receive the treads and risers
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24. Stair Terminology
Enclosed stairs: stairs that have a wall on both sides (also known as closed, housed, or box stairs)
Headroom: the shortest clear vertical distance measured between the nosing of the treads and the ceiling.
Housed stringer: a stringer that has been routed or grooved to receive the treads and risers
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26. Stair Terminology
Landing: the floor area at either end of the stairs and possibly at some point between, as in the case of L stairs.
Newel: the main posts of the handrail at the top, bottom or at points where the stairs change direction.
Nosing: the rounded projection of the tread which extends past the face of the riser.
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28. Stair Terminology
Open Stairs: stairs that have no wall on one or both sides.
Plain stringer: a stringer that has been cut or notched to fit the profile of the stairs.
Rise: the distance from the top surface of one tread to the same position on the next tread.
Riser: the vertical face of a step.
Run: the distance from the face of one riser to the face of the next.
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31. Stair Terminology
Stringer: a structural member, also called the carriage that supports the treads and risers.
Total rise: the total floor-to-floor vertical height of the stairs.
Total run: the total horizontal length of the stairs.
Tread: the horizontal member of each step.
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32. Stringer Types
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33. Proper Stair Design Means
The stairs will support the required weight
The stairs are wide enough to provide ease of passage and movement of furniture.
The stairs slope between 30 and 35 degrees.
The stairs are not less than 3’-0” wide.
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34. Stringer Design
The main supporting members of the stairs are the stringers.
Plain stringers and housed stringers are the two types.
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35. Plain Stringers Are generally cut from 2 x 12 straight-grain fir.
Treads and risers are nailed directly to the stringers.
This type of construction is generally used for service stairs and occasionally for main stairs if they will be carpeted.
Are sturdy, but tend to squeak.
Do not look “finished”
Treads are 2” fir; risers are 1” white pine
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36. Housed Stringers Constructed from finished lumber
Generally purchase pre-cut or pre-assembled
May, however, be cut from 1 x 12 or 2 x 12 lumber
1/2” deep grooves are usually routed in the stringers to hold the treads.
The bottom and back sides of the grooves are wider than the thickness of the treads and risers so wedges may be driven in to hold them in place
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38. Housed Stringers
The treads, risers and wedges are glued and nailed into place.
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39. Stringers
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40. Other Stair Components
A stairway must provide a handrail for support while ascending and descending the stairs.
One rail is sufficient unless the stairs are very wide
Handrail height should be between 30 and 34 inches.
Note that the height is greater at a landing than along the incline.
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41. Handrails
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42. Other Stair Components
Standard Treads
1-1/4” thick oak
10-1/2” wide
11-1/2” wide
A tread width of 10” is the most popular choice.
Risers
the ideal riser height is between 7” and 7-1/2”.
Are usually 3/4” thick.
Usually made of clear white pine.
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43. Treads and Risers Every step must be the same size and proportion
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44. Rules for Stair Design
Rule #1: the slope of the stairs should be between 30 and 35 degrees.
Rule #2: The sum of two risers and one tread should equal 25 inches.
Rule #3: the product of the riser height multiplied by the tread width should equal approximately 75 inches.
Rule #4: the sum of one riser and one tread should equal 17 to 18 inches.
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45. Stair Calculations - Step 1
Determine the distance from finished floor to finished floor.
This is the total rise of the stairs.
Add
the distance from the finished lower floor to finished ceiling,
the thickness of the ceiling material
width of the floor joists
thickness of the subfloor and finished floor.
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46. Stair Calculations - Step 1
Finished lower floor to 8’-0” finished ceiling
The thickness of 1/2” the ceiling material
Width of the floor joists 9-1/4
Thickness of the subfloor 1/2” and finished floor.
Total 8’-11 1/4”
Convert total to inches = 107 1/4”
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48. Stair Calculations - Step 2
Determine how many risers will be required
First, divide the total rise by 7
7 is an ideal riser height and is the logical place to start.
107 1/4” / 7 = risers
The number of risers must be an exact number, so 15 or 16 risers will be required.
107 1/4” / 15 = 7.15 inches; use this height
Remember: each riser must be exactly the same height !
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50. Stair Calculations - Step 3
Determine the tread size and total run which will yield a stair slope between 30 and 35 degrees.
Remember, there is always one less tread than the number of risers. The floor serves as the top tread.
Using Rule #2, the sum of two risers and one tread equals 24.80”
This is very close to the required sum of 25.
This indicates this combination will be acceptable.
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52. Stair Calculations - Step 3
For comparison, use Rules #3 and #4
#3: the product of the riser height and tread width should be approximately 75 inches.
7.15 x 10.5 = 75.1
#4: the sum of one riser and one tread should equal 17 to 18 inches.
7.15” /2” = 17.65”
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53. Stair Calculations - Step 4
Darken the tread and riser lines
Draw the bottom edge of the stringer
Locate stairwell rough opening size.
This dimension is determined with the headroom dimension.
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55. Stair Calculations - Step 5
Remove construction lines and add notes.
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