Types of Stairs
The staircase in a building is one means whereby one may travel from the level of one floor to another. The ease with which a stairway can be traveled depends upon the proper proportioning of the riser and tread of each step and the number of steps in one series or flight. The design of the building and the space allowed for stairs will control the type of staircase which may be built. Geometrical Stairs. The most complicated and most expensive stairways are those that are curved, commonly known as the geometrical stairway. The geometrical stairway is a winding stairway, but it is so designed that the tread at the line of travel of all steps is the same width. These staircases may be circular as shown at A, or elliptical as at B, Fig. 73, and often are designed with landings to insure ease in ascending them.
Safety Precautions in Stairway Building
Statistics compiled by the National Safety Council show that stairways are the cause of the greatest number of accidents in the home, These accidents can be attributed to various factors; some, of course, are beyond the control of those who design and build the stairways. However, there are far too many accidents due directly to faulty construction.
The carpenter can make a worthwhile contribution toward accident prevention if he plans and does his work well.The Safety Engineering Department of the National Workmen’s Compensation Service Bureau has set up the following standards as suggestions to stair builders to help remove some of the causes responsible for many accidents.
1. Stairways should be free from winders.
2. The dimensions of landings should be equal to or greater than the width of stairways between handrails (or handrail and wall).
3. Landings should be level and free from intermediate steps between the main up flight and the main down flight.
4. All treads should be equal and all risers should be equal in any one flight.
5. The sum of one tread and one riser, exclusive of the nosing, should not be more than 18 inches nor less than 17 inches. (Stair ratio.) Tread and Riser Relationship
Stairs must be adapted to meet many special requirements to fit into a particular building and rules have been established to make stairs as comfortable to use as possible. Unfortunately, rules must be overlooked occasionally at times in order to solve a problem. This is particularly true in remodeling work, but is also true when a house has not been well planned. However, a carpenter should know how to make choices which will result in the best stairs under the circumstances. He should be familiar with the building code which applies locally and should bend every effort to build stairs accordingly.
The stair ratio is a relationship between the tread run (width) and the riser height so that as one increases, the other decreases, and vice versa. A minimum tread run and a maximum riser height keep the stairs from exceeding the critical angle of the whole stair. See Fig. 74 and Table II. The economical use of material is also a factor. Good design often requires wider boards for treads than the carpenter would like to use if economy were the main consideration. Some fundamental ideas on tread-riser relationships:
The stair ratio is a relationship between the tread run (width) and the riser height so that as one increases, the other decreases, and vice versa. A minimum tread run and a maximum riser height keep the stairs from exceeding the critical angle of the whole stair. See Fig. 74 and Table II. The economical use of material is also a factor. Good design often requires wider boards for treads than the carpenter would like to use if economy were the main consideration. Some fundamental ideas on tread-riser relationships:
1. All risers in the same flight must be equal.
2.All treads in the same flight must be equal.
3. For residences, the maximum height of a riser shall be eight inches. (F.H.A. permits 8¼ inches.)
3. For residences, the maximum height of a riser shall be eight inches. (F.H.A. permits 8¼ inches.)
4. For residences, the minimum tread run shall be nine inches exclusive of nosing.
5. The stair ratio: The height of a riser plus the width of a tread shall equal not less than 17 inches nor more than 18 inches.
Minimum R + T = 17”
Maximum R +T = 18”
5. The stair ratio: The height of a riser plus the width of a tread shall equal not less than 17 inches nor more than 18 inches.
Minimum R + T = 17”
Maximum R +T = 18”
The formula T + R = 17 to 18 is used by many carpenters because the calculations can be made mentally. Local building codes may have other tread and riser limitations and ratio requirements.
Treads. Material for treads is generally 2 x 10 or 2 x 12 inches (actual size 1½ x 91/2 or 1½ by 11½ inches). See Fig. 75. The run of the tread is the distance from the face of one riser to the face of the one which follows it and is the same dimension as the cut on the stringer. When a 9 inch tread run is required, only ½ inch is left for nosing. When a larger tread run is required (either by the code or by the use of the stair ratio formula) a board wider than a 2 x 10 will be necessary. The stringer is the most important of the stair parts. This is the cut out support for treads and risers. If the carpenter has made the correct layout and made the proper deductions, the stairs will he perfect when installed. The material used is usually a 2 x 10 or a 2 x 12 in order that 31/2inches are left to carry the load after the cuts are made. Deductions must be made at the top and at the bottom of the stringer so that the bottom rise and the top rise of the finished stair may be equal. The thickness of the tread material must be deducted at the bottom and is added at the top unless the flooring and tread thickness are not the same. Further additions and adjustments are required, depending on the problem. See Fig. 76.
Treads. Material for treads is generally 2 x 10 or 2 x 12 inches (actual size 1½ x 91/2 or 1½ by 11½ inches). See Fig. 75. The run of the tread is the distance from the face of one riser to the face of the one which follows it and is the same dimension as the cut on the stringer. When a 9 inch tread run is required, only ½ inch is left for nosing. When a larger tread run is required (either by the code or by the use of the stair ratio formula) a board wider than a 2 x 10 will be necessary. The stringer is the most important of the stair parts. This is the cut out support for treads and risers. If the carpenter has made the correct layout and made the proper deductions, the stairs will he perfect when installed. The material used is usually a 2 x 10 or a 2 x 12 in order that 31/2inches are left to carry the load after the cuts are made. Deductions must be made at the top and at the bottom of the stringer so that the bottom rise and the top rise of the finished stair may be equal. The thickness of the tread material must be deducted at the bottom and is added at the top unless the flooring and tread thickness are not the same. Further additions and adjustments are required, depending on the problem. See Fig. 76.
Adequate bearing (4 inch minimum F.H.A.) against the header must be provided so that the stringer may be well fastened.
Using The Story Pole to find the Unit Rise. PROCEDURE
1. Take a story pole (any piece of lumber 1 X 2 preferred straight with square ends) and set it on the finished floor in the stairwell on the basement floor. Mark the location of the finished floor above, or first floor, as shown at 1, Fig. 77. The distance 1 —x will be the total rise of the stair, in this case 8 feet 4 inches. Then place the story pole on two horses.
Note: If the finished floor has not been laid when the measurement is taken, a block of wood should be placed on the rough floor to establish the line of the finished floor, or allowance can be made for the thickness of the finished floor.
2. Set a pair of dividers to 7 inches (a permissible unit rise per step) and step off the total rise on the story pole, dividing the distance 1—X into equal parts. If upon the first trial you find there is a remainder, adjust the dividers and try again. If the remainder is less than 3 inches set the dividers to a setting larger than 7 inches. If the remainder is more than 3 1/2 inches, set the dividers to a setting smaller than 7. Continue adjusting the dividers and stepping off the distance on the story pole, until the last unit is the same as all of the others. The dividers are now set to the unit rise which should be within the allowed
1. Take a story pole (any piece of lumber 1 X 2 preferred straight with square ends) and set it on the finished floor in the stairwell on the basement floor. Mark the location of the finished floor above, or first floor, as shown at 1, Fig. 77. The distance 1 —x will be the total rise of the stair, in this case 8 feet 4 inches. Then place the story pole on two horses.
Note: If the finished floor has not been laid when the measurement is taken, a block of wood should be placed on the rough floor to establish the line of the finished floor, or allowance can be made for the thickness of the finished floor.
2. Set a pair of dividers to 7 inches (a permissible unit rise per step) and step off the total rise on the story pole, dividing the distance 1—X into equal parts. If upon the first trial you find there is a remainder, adjust the dividers and try again. If the remainder is less than 3 inches set the dividers to a setting larger than 7 inches. If the remainder is more than 3 1/2 inches, set the dividers to a setting smaller than 7. Continue adjusting the dividers and stepping off the distance on the story pole, until the last unit is the same as all of the others. The dividers are now set to the unit rise which should be within the allowed
riser height requirements. Be careful not to disturb the divider setting.
Using Mathematics to find the Unit Rise. The unit rise per step can also be obtained by dividing the total rise in inches by 7 to find the number of risers (drop the fraction if any), then divide the total rise by the number found, to obtain the exact unit rise per step.
Using Mathematics to find the Unit Rise. The unit rise per step can also be obtained by dividing the total rise in inches by 7 to find the number of risers (drop the fraction if any), then divide the total rise by the number found, to obtain the exact unit rise per step.
Total Rise 8’-4” or 100 inches, 100 — 7 = 14 2.8 risers.
We must choose either 14 or 15 risers:
100 /14 = 7.143 inches or 7 1/8 inches.
Finding the Unit Tread. The stair ratio is used to find the unit tread. There is a little leaway permitted the ‘carpenter because he should choose a tread width which falls between the limits of the ratio:
T + R 17 to 18.
The riser height has been determined as 7 1/8 inches.
Minimum tread ratio: T + 7 1/8 = 17, T = 9 7/8 inches.
Maximum tread ratio: T + 7 1/8 = 18, T 10 7/8 inches.
A midpoint would be 10 3/8 inches.
Referring to Table II it will be noted that these dimensions, R = 7 1/8, T 10 3/8, fall within the range of preferred angles.
A midpoint would be 10 3/8 inches.
Referring to Table II it will be noted that these dimensions, R = 7 1/8, T 10 3/8, fall within the range of preferred angles.