Basic Stair Anatomy
There are three main components in a typical staircase: stringers, treads and risers. Stringers, typically cut from 2 x 12s, are the sloped boards that support the other components and carry the weight of people walking on the stairs. They’re typically spaced 16 in. on center. When determining the staircase width, remember that wider is better. “Wide staircases are more comfortable and safer to walk on. seldom build one less than 4 ft. wide, and prefer them a bit wider.
Treads form the top surface of each step, and risers are installed directly under the front lip of each tread. Some stairs don’t have risers, but that’s a mistake, according to many builders. “Risers protect the exposed endgrain of the notched stringers from the weather,” explains award-winning deck builder Scott Padgett, of Idyllwild, Calif. “Without risers, stringers will crack or split much sooner.
Geometrical staircase refer to the staircases having treads that taper in their plan. They maybe helical (spiral staircases), open well circular staircases, or even elliptical staircases.
Creation of Space
– These staircases do not occupy as much space as normal staircases. The more gradual the climb, the more space it will occupy, but the space utilized is much less than say a straight flight staircase or maybe a open-well staircase.
Difficult to Climb
– If you’re hoping for a comfortable climb, then these staircases are best avoided. The continuous change of direction and tapering treads are not the easiest to man oeuvre.
1.Calculating Rise and Run
The first step in building stairs for a deck is finding the total rise or overall vertical height the stairs have to cover. Lay a straight board on top of the deck, extend it from the edge, then measure down to the landing location. Let’s say the total rise is 57 in. The next job is to find the rise of each step. Divide 57 by 7 in. (the typical rise per step) to get 8.14. Round down to get the steps: eight. To then determine the actual rise, divide the 57 in. by the eight steps to get 7 1/8 in. per step.
You can use that information to find the total run of the staircase–or how much horizontal distance it will cover as it climbs. Multiply the number of steps by the run, or horizontal depth, of each step. The optimum run of each step is no less than 10 in., which is enough space to accept two 2 x 6 treads. In our example, the staircase has eight steps, so the total run is 80 in.
There is one wrinkle in the math, however: If you are working with a tall deck, it’s a good idea to break up the staircase with intermediate landings. “As a practical matter you’re limited to about 14 steps because that’s the most you can cut [in a stringer made] from a 16-ft.-long 2 x 12,” says Andy Engel, author of Building Stairs, “but I prefer adding a landing after every seven or eight risers.”
Before laying out the steps on a 2 x 12, decide how the stringers will join the deck. They’re either attached directly to the rim joist so the top step is flush with the deck top, or to the framing under the deck, which is the way we did it (see drawing on previous page). When mounted under the deck, the stringers are either attached to the joists or to blocking placed between joists, and the stringer ends are cut long to reach the framing.
Mark the tread notches using a framing square fitted with stair gauges. These small brass fixtures clamp onto the square, providing an accurate way to mark several identical notches. Clamp one stair gauge on the square’s tongue directly at the rise dimension. Attach the other gauge to the body of the square at the run dimension. Then, lay the square on the 2 x 12 with the gauges pressed against the board’s edge and mark the tread and riser. Slide the square down, align it with the previously drawn notch, and add the next one.
Cut the notches using a circular saw, being careful not to go beyond the lines. Finish the cuts with a jigsaw or a handsaw.
Next, trim the bottom of the stringer an amount equal to the tread thickness. For example, if you’re installing 2 x 6 treads, cut 1 1/2 in. from the bottom of the stringer. Use the first stringer as a template to mark the remaining stringers.
We screwed each stringer to the deck-frame blocking, which was spaced 16 in. on center. With the stringers in place, check that each step is level, and use a block plane to shave down high spots.
3.Installing Treads and Risers
Cut the risers to length and fasten them to the stringers with 2 1/2-in. trim-head decking screws. Note that we cut the risers and treads to overhang the outer stringer by 1 1/4 in. Later, a 1 x 12 cedar trim board will be nailed to the stringer, giving the staircase a more finished look. This detail isn’t always necessary.
After installing the risers, fasten the treads with screws. Leave a 1/8- to 1/4-in. space between the treads. Continue installing treads, working your way up the staircase. The 4 x 4 posts used to support the stair rail are typically bolted to the stringers before installing the treads. However, we completed the stairs first, and then attached the posts and built the handrail that codes usually require.
Some stairways are easier to ascend than others, and there are reasons for that. The parameters of stair design are set by building codes, and there are also recommended configurations based on average human proportions.
There are, for example, tread-width-to-riser height relationships that make stairs more comfortable for the average person to traverse. Building codes set a minimum for staircase width, but wider dimensions are often necessary. Other important considerations are head clearance, railing dimensions and landings.
The length of the run is the total dimension the treads must occupy to complete the required rise. Staircases use significant square footage by the time all the steps are in place, landings are located and headroom has been cleared.
Consider that if a tread is 12 inches and you need 19 of them, that is 19 feet for the length of the steps alone. Now add at least 3 ft. on each end for landings, and you have 25 ft. in which to place that stairway path, at minimum. When you multiply the 25-ft. length times the 4-ft. width, which includes the railing and the wall, you have a 9 square metres (100 square foot) area that is required for that staircase. Double those figures to account for the hall or path to go around the staircase, and you have 18 square metres (200 square feet) for one staircase. This is the size of a single-car garage.
Since they require so much space, efficient staircases must be designed. The trick is a balance of comfort and efficiency that satisfies the building code and enhances the architecture of the space.
Risers and treads
Critical to stair design are the height of each riser and the width of each tread.
All risers should be exactly or nearly the same height. Varying riser heights feel awkward and are difficult to ascend, because we need rhythm when we climb steps. Building codes also mandate equal heights, though slight variations (less than ⅜ in.per step) are acceptable.
There are some rules of thumb when planning stairs. One is: “Two risers plus one tread should equal 25 in. This works well in most circumstances. For example, you could have stairs with 7-in. risers and 11-in. treads (7 + 7 + 11 = 25), or you could have stairs with 7½-in. risers and 10-in. treads (7½ + 7½ + 10 = 25).
Those with generous budgets and space, however, may build steps that have 12-in.treads and 6-in. risers, and that equation is 6 + 6 +12 = 24. This configuration provides a gentler ascent and broader steps that feel easier on the body; however, it uses considerably more space.
The traditional architecture seen here shows a staircase that makes a gentle ascent with lower risers, wider treads and landings.
For many years the maximum rise allowed was 8 in. coupled with a 9-in. minimum tread. Newer codes mandate 7¾-in.-maximum risers with 10-in.-minimum treads.
This simplified illustration calls out the key elements that must be considered in staircase design. Two extremes are presented: A very steep stair with 8-in. risers and a gentle stair with 6-in. risers. Critical is the run of the stairs. Clearly shorter risers will require much more space.
Most staircases fall somewhere between these two extremes. For example, a staircase with 7-in. risers and 11-in. treads creates a comfortable ascent for most people.
The total height of the rise of a staircase depends on the height of the ceiling and depth of the upper-floor structure. With a taller ceiling, such as the one pictured, more risers and treads are needed to make the staircase function.
For example, if your risers are 6 in. each and your ceiling is 9 ft. high with a 1-ft. upper-floor-structure depth, you will have to ascend 10 feet. It will take 20 6-in. risers to make it all the way up. If we can increase the risers to 8 in. each, we will need only 15.
So, when you have 20 6-in.risers, you will need 19 12-in.treads for a total stair run of 19 feet. When you have 15 8-in. risers, you will need 14 treads of only 9 in. each. Now your stair run needs to be only 10 ft., 6 in. The run is significantly shorter and takes up much less square footage.
There are many other minor but important details in stair design. The nose of the tread, which overhangs the face of the riser (or not), is one; limitations on it are set by building codes.
Stairs can be fully supported by walls from underneath or the sides, or they can seem to float in space by the assistance of steel structural elements.
1. STRAIGHT STAIRS
These are the stairs along which there is no change in direction on any flight between two successive floors. The straight stairs can be of following types.
Straight run with a single flight between floors
Straight run with a series of flight without change in direction
Straight stairs can have a change in direction at an intermediate landing. In case of angle stairs, the successive flights are at an angle to each other. Scissor stairs are comprised of a pair of straight runs in opposite directions and are placed on opposite sides of a fire resistive wall.
2. QUARTER TURN STAIRS
They are provided when the direction of flight is to be changed by 900. The change in direction can be effected by either introducing a quarter space landing or by providing winders at the junctions.
3. HALF TURN STAIRS
These stairs change their direction through 1800. It can be either dog-legged or open newel type. In case of dog legged stairs the flights are in opposite directions and no space is provided between the flights in plan. On the other hand in open newel stairs, there is a well or opening between the flights and it may be used to accommodate a lift. These stairs are used at places where sufficient space is available.
4. THREE QUARTER TURN STAIRS
These types of stairs change their directions through 2700. In other words direction is changed three times with its upper flight crossing the bottom one. In this type of construction an open well is formed.
5. CIRCULAR STAIRS
These stairs, when viewed from above, appear to follow circle with a single centre of curvature and large radius. These stairs are generally provided at the rear of a building to give access for servicing at various floors. All the steps radiate from a newel post in the form of winders. These stairs can be constructed in stone, cast iron or R.C.C.
6. SPIRAL STAIRS
These stairs are similar to circular stairs except that the radius of curvature is small and the stairs may be supported by a center post. Overall diameter of such stairs may range from 1 to 2.5 m.
7. CURVED STAIRS
These stairs, when viewed from above, appear to follow a curve with two or more centre of curvature, such as ellipse.
8. GEOMETRICAL STAIRS
These stairs have no newel post and are of any geometrical shape. The change in direction in these stairs is achieved through winders. The stairs require more skill for its construction and are weaker than open newel stairs. In these stairs the open well between the forward and the backward flights is curved.
9. BIFURCATED STAIRS
These stairs are so arranged that there is a wide flight at the start which is subdivided into narrow flights at the mid-landing. The two narrow flights start from either side of mid landing. Generally these stairs are more suitable for modern public buildings.
10. COMBINATION OF DIFFERENT TYPES
Depending upon the requirement of a building or as per owner’s demand few of the types as mentioned above can be combined to design a new stair.