9.02 SPECIAL CONSTRUCTION 17 This chapter discusses those elements of a building that have unique characteristics and that therefore should be considered as separate entities. While not always affecting the exterior form of a building, they do influence the internal organization of spaces, the pattern of the structural system, and in some cases, the layout of heating, plumbing, and electrical systems. Stairs provide means for moving from one level to another and are therefore important links in the overall circulation scheme of a building. Whether punctuating a two-story volume or rising through a narrow shaft, a stairway takes up a significant amount of space. The landings of a stairway should be logically integrated with the structural system to avoid overly complicated framing conditions. Safety and ease of travel are, in the end, the most important considerations in the design and placement of stairs. Multistory buildings require elevators to move people, equipment, and freight from one floor to another. For accessibility to multistory public and commercial facilities by persons with disabilities, federal regulations mandate their installation. An alternative to elevators is the escalator, which can move a large number of people efficiently and comfortably between a limited number of floors. Fireplaces and woodburning stoves are sources of heat and visual points of interest for any interior space. The placement and size of a fireplace or stove in a room should be related to the scale and use of the space. Both fireplaces and stoves must be located and constructed to draft properly. The damper and flue sizes should correspond to the size and proportions of the firebox and precautions should be taken against fire hazards and heat loss. Kitchens and bathrooms are unique areas of a building that demand the careful integration of plumbing, electrical, and heating/ventilating systems with the functional and aesthetic requirements of the spaces. These areas also require special fixtures and equipment, as well as durability, ease of maintenance, and sanitary surfaces and finishes. The dimensions of risers and treads in a stairway should be proportioned to accommodate our body movement. Their pitch, if steep, can make ascent physically tiring as well as psychologically forbidding, and can make descent precarious. If the pitch of a stairway is shallow, its treads should be deep enough to fit our stride. Building codes regulate the minimum and maximum dimensions of risers and treads; see 9.04-9.05. For comfort, the riser and tread dimensions can be proportioned according to either of the following formulas: Tread (inches) + 2x riser (inches) = 24 to 25 Ladders • R= 12" (395) o.c. typical Step Ladders . 123/4" (325) riser; 3" (75) tread For private stairs only: 73/4" (195) maximum riser; 10" (255) minimum tread STAIR DESIGN 9.03 • Riser (inches) tread (inches) = 72 to 75 Exterior stairs are generally not as steep as interior stairs, especially where dangerous conditions such as snow and ice exist. The proportioning formula can therefore be adjusted to yield a sum of 26. For safety, all risers in a flight of stairs should be the same rise and all treads should have the same run. Building codes limit the allowable variation in riser height or tread run to 3/8" (9.5 mm). Consult the building code to verify the dimensional guidelines outlined on this and the following page. Stairs Ramps 7" (180) maximum riser and 11" (280) minimum tread 4" (100) minimum riser 1:8 maximum 1:12 maximum when part of an accessible route or an emergency egress system . • • . The actual riser and tread dimensions for a set of stairs are determined by dividing the total rise or floor-to-floor height by the desired riser height. The result is rounded off to arrive at a whole number of risers. The total rise is then redivided by this whole number to arrive at the actual riser height. This riser height must be checked against the maximum riser height allowed by the building code. If necessary, the number of risers can be increased by one and the actual riser height recalculated. Once the actual riser height is fixed, the tread run can be determined by using the riser:tread proportioning formula. Since in any flight of stairs, there is always one less tread than the number of risers, the total number of treads and the total run can be easily determined. Tread Riser and Tread Dimensions Riser inches (mm) inches (mm) 5(125) 15 (380) 514 (135) 1412 (370) 51/2 (140) 14 (355) 534 (145) 132 (340) 6(150) 13 (330) 614 (160) 122 (320) 61/2 (165) 12(305) 634 (170) 112 (290) 7(180) 11 (280)- 714 (185) 1012 (265) 71/2 (190) 10(255) Maximum riser height; minimum tread depth for accessible stairs and emergency egress 9.04 STAIR REQUIREMENTS 12' 0" (3660) maximum rise between landings • 6'8" (2030) minimum overhead clearance- . Guardrails • . . . Guardrails are required to protect the open or glazed sides of stairways, ramps, porches, and unenclosed floor and roof openings. Guardrails should be at least 42" (1070) high; guardrails in dwellings may be 36" (915) high. Guardrails protecting the open or glazed side of a stairway may have the same height as the stair handrails. A 4" (100) sphere must not be able to pass through any opening in the railing from the floor up to 34" (865); from 34" to 42" (865 to 1070), the pattern may allow a sphere up to 8" (205) in diameter to pass. Guardrails should be able to withstand a concentrated load applied nonconcurrently to their top rails in both vertical and horizontal directions. Consult the building code for detailed requirements. 34" to 38" (865 to 965) height above the leading edge of the stair treads or nosings. Stairway design is strictly regulated by the building code, especially when a stairway is an essential part of an emergency egress system. Because an accessible stairway should also serve as a means of egress during an emergency, the ADA accessibility requirements illustrated on the next page are similar to those of an emergency egress stairway. Stairway Width The occupant load, which is based on the use group and the floor area served, determines the required width of an exit stairway. Consult the building code for details. 44" (1120) min. width; 48" (1220) minimum between handrails for accessible means of egress stairways; 36" (915) min. for stairways serving an occupant load of 49 or less. Handrails may project a maximum of 41/2" (115) into the required width; stringers and trim may project a maximum of 11/2" (38). Landings •Landings should be as least as wide as the stairway they serve and have a minimum length equal to the stair width, measured in the direction of travel. Landings serving straight-run stairs need not be longer than 48" (1220). Door should swing in the direction of egress. Door swing must not reduce the landing to less than one-half of its required width. • When fully open, the door must not intrude into required width by more than 7" (180). Handrails Handrails are required on both sides of the stair. The building code allows exceptions for stairs in individual dwelling units. Handrails should be continuous without interruption by a newel post or other obstruction. Handrails should extend at least 12" (305) horizontally beyond the top riser of a stair flight and extend at the slope of the stair run for a horizontal distance of at least one tread depth beyond the last riser nosing of the flight. The ends should return smoothly to a wall or walking surface, or continue to the handrail of an adjacent stair flight. ADA standards require an additional 12" (305) of horizontal extension at bottom of stair flight. • See the next page for detailed handrail requirements. Treads, Risers, and Nosings ⚫ A minimum of three risers per flight is recommended to prevent tripping and may be required by the building code. See the next page for detailed tread, riser, and nosing requirements. See 9.03 for tread and riser proportions. STAIR REQUIREMENTS 9.05 ADA Accessibility Guidelines Accessible stairs should also serve as a means of egress during an emergency, or lead to an accessible area of refuge where people who are unable to use stairs may remain temporarily in safety to await assistance during an emergency evacuation. Handrails Handrails should be free of sharp or abrasive elements and have a circular cross section with an outside diameter of 11/4" (32) minimum and 2" (51) maximum; other shapes are allowable if they provide equivalent graspability and have a maximum cross-sectional dimension of 21/4" (57). 11/2" (38) minimum clearance between handrail and wall Risers and Treads . Tread depth: 11" (280) minimum - Riser height: 4" (100) minimum; 7" (180) · 30° maximum maximum . Uniform riser and tread dimensions are required. • Open risers are not permitted. Nosings 11/2" (38) maximum protrusion 1/2" (13) maximum radius Risers should be sloped or the undersides of the nosings should have a 60° angle minimum from the horizontal. Ramps Ramps provide smooth transitions between the floor levels of a building. To have comfortable low slopes, they require relatively long runs. They are typically used to accommodate a change in level along an accessible route or to provide access for wheeled equipment. Short, straight ramps act as beams and may be constructed as wood, steel, or concrete floor systems. Long or curvilinear ramps are usually of . steel or reinforced concrete. . 1:12 maximum slope- 30" (760) maximum rise between landings 36" (915) minimum clear width between curbs or guardrails Ramp surface should be stable, firm, and slip-resistant. Curbs, guardrails, or walls are required to prevent people from slipping off of the ramp; 4" (100) minimum curb or barrier height. Landings •Ramps should have level landings at each end with a 60" (1525) minimum length. Landing should be as wide as the widest ramp leading to it. • 60" x 60" (1525 × 1525) minimum landing where ramp changes direction Handrails Ramps having a rise greater than 6" (150) or a run greater than 72" (1830) should have handrails along both sides. Handrail requirements are the same as for stairways. Extend handrails at least 12" (305) horizontally beyond the top and bottom of ramp runs. 9.06 STAIR PLANS Straight-Run Stair • A straight-run stair extends from one level to another without turns or winders. Building codes generally limit the vertical rise between landings to 12' (3660). . . . A stairway may be approached or departed either axially or perpendicular to the stair run. Quarter-Turn Stair A quarter-turn or L-shaped stair makes a right-angled turn in the path of travel. The two flights connected by an intervening landing may be equal or unequal, depending on the desired proportion of the stairway opening. . Landings that are below normal eye level and provide a place to rest or pause are inviting. Half-Turn Stair • A half-turn stair turns 180° or through two right angles at an intervening landing. ⚫ A half-return stair is more compact than a single straight-run stair. The two flights connected by the landing may be equal or unequal, depending on the desired proportion of the stairway opening./n• Follow USA codes • Use the pdf file to answer the questions • Typed answers ⚫ For Ques 14 and 15 detailed answer is required/nFrancis D K Ching Stairs-2.docx✓ Some questions require research and not Google to answer questions on the assignment.

Fig: 1

Fig: 2