Design Factors Affecting Stair Costs

The interests of all concerned are best served when the stair is so designed and specified as to properly fulfill its intended purpose, yet provide maximum value received per dollar of cost. The following suggestions are offered as ways of avoiding unnecessary costs without sacrificing essential values. They deserve careful consideration, especially in the design of commercial and service class stairs in multi-storied buildings.

Stair Flight Construction

Especially on flights of relatively short run or narrow width, the load carried by the stringers should be checked to see that stringers are not oversized. On many stairs a 10" channel weighing 6.5 lb./ft. may be adequate, in place of one weighing 8.4 lb./ft.

The use of plate stringers may sometimes effect savings, but in evaluating this possibility, the method of providing rail connections must be considered. Open channel stringers are generally cheaper than boxed stringers, and, for obvious reasons, straight stringers cost much less than curved stringers.

The welding of treads and risers directly to stringers (unit construction) will eliminate the need for carrier angles or bars and will sometimes reduce costs, but such construction should be used only when practically feasible. As welds are made on the upper side of a pan type tread, they are covered by the tread fill. The use of floor plate or tread plate for treads and risers usually results in maximum economy, as the need for tread fill is eliminated.

Platform Construction

The provision of a base or curb around platforms by exposing the upper part of the stringers above the platform floor increases costs. A structural frame with platform pan construction and fill on top of it is less expensive and often provides a satisfactory construction. Still further economy can be achieved by the use of a floor or tread plate platform, rather than pan construction and fill, where this type of construction is acceptable.

Railings

An economical type of rail for a stair is a steel pipe or tube rail connected at the ends by standard terminal castings to a square or rectangular tube newel. This construction provides rigid support at both ends of a flight, yet permits minor installation adjustments, where necessary, at floors and platforms.

The use of square or rectangular tube for the railing, in place of pipe, provides an alternative at slightly higher cost.

The use of continuous rails without interruption by newel posts or other obstructions, along the flight of the stairs and at floors and platforms between flights, as presently required by codes for most types of construction, increases the cost. However, it does improve the safety of stairs and facilitates their use by persons with certain physical handicaps.

Often, on relatively short flights, the need for intermediate posts on pipe rails can be eliminated by substituting a larger size pipe. This also reduces cost.

Connections and Finishing Work

The use of hex head bolts in place of flat or oval head bolts eliminates the necessity of counter-sinking and speeds stair assembly. Where appearance is not critical, welding neatly done but not ground smooth, provides maximum rigidity at minimum cost. The use of flat or oval head bolts, the grinding of welds and the complete removal of all sharp edges and burrs only on the travel surface and wherever they may be a hazard to stair users will result in some savings.

Expediting Installation

Metal stairs can usually be installed earlier in a steel framed structure than in one having a concrete frame. Because the erection tolerances in the steel framing around the stairwell are minimal, the stairs can be detailed, shop drawings can be prepared and approved and the stairs can be fabricated before the building frame is erected. In conventional practice the metal stairs can then be installed as soon as the frame is in place. Or, if some of the larger pre-assembled units are used, the stairs may be installed in place, completely self-supporting, before erection of the building frame. In any case, delays to subsequent construction are eliminated and overall construction costs are minimized.

If the building has a concrete frame, the stair fabricator can supply the contractor with the necessary detail drawings showing critical dimensions to be maintained, and if maintenance of these dimensions is guaranteed, he can proceed with fabrication so that the stairs can be installed as soon as forms are removed and the stairwell is cleared. Because of the probability of greater dimensional variations in a concrete frame than in a steel frame, consideration should be given to using tube newel railing construction which permits installation adjustments.

When stairs cannot be installed until walls are in place, the contractor should locate and set all anchors and anchor bolts, provide recesses and pockets in floors and walls, and fill in such recesses and pockets after the stairs are installed, all in accordance with the approved shop drawings. Of course it's his responsibility, too, to see that stairwells are cleared of all debris and interference before the installation begins.

When considered individually, these potential ways of reducing stair costs may not seem very significant, and the savings on a small job may not be very large. But collectively, and especially when applied to installations in multi-storied buildings, they can result in substantial economies.