Chapter 12 Stair Design Flashcards
Minimum width of any stair (per IBC) is?
36”, and 44” when occupancy load exceeds 49
Handrails Code Requirements?
may project maximum of 4-1/2” on both sides of stairway
U Shaped Stair Layouts require what adjustments?
U-shaped stairs requires adjustment of relationship between lower and upper flights in order for center railing to make smooth switchback.
- first riser of upper flight is offset from last tread of lower flight by one tread at landing. This allows handrail to turn back smoothly at landing.
- If last riser of upper flight ends one tread dimension short of opening, handrail can be extended required 12” without intruding into upper level
T/F… Winding stairs are only allowed in dwelling units per IBC?
True
T/F… Spiral stairs are usually not allowed for egress, and are usually only allowed in dwelling units
True
T/F Curved stairways cannot have inside arc less than 2x width of stair; otherwise, considered winding stair, which limits use to dwelling unit
True
T/F evacuation assistance space (also called areas of refuge in some codes) inside enclosure; these areas are usually required, and normally provided in building exit stairways
True
IBC requires maximum riser of ______ for residences), minimum tread of ____
7” (7-3/4”) and 11”
Tread considered horizontal projection of distance from edge of one nosing to the next – does not include part of tread under nosing
Vertical Layout code requirements
- Handrails must be provided on both sides of stairs (except in dwellings), and must run continuously for full length of stair
- Stairs consisting of just one or two risers are dangerous because people have a difficult time recognizing the level change – use minimum 13” tread, use riser lights or other warning strips, etc.
- Handrails should also be used as visual cue to indicate level change & give people support traversing steps
For L-shaped stairways.
first riser of upper flight should also begin one tread distance from nosing of last riser of lower flight so handrail makes direct 90-degree turn without vertical offset rise
Vertical Layout Maximum horizontal dimension between landings is?
12’-0”
Handrails must be placed inside guards, ___ - ___” above leading edge of treads and must be placed ___” from wall.
34”-38” above leading edge of treads, and 1-1/2” from wall
IBC requires stairways and ramps not adjacent to a wall and more than 30” above floor to have guardrails as well as handrails; guards must be __” above leading edge of tread, measured vertically.
42”
Wood Stair Construction:
Basic, straight-run and other simple stairs with little decoration
usually site-built by finish carpenters; more elaborate/complex designs built in mill shop, assembled on site
Wood Stair Construction:
Wood stairs can be constructed in almost unlimited styles and details
- Basic, straight-run and other simple stairs with little decoration usually site-built by finish carpenters; more elaborate/complex designs built in mill shop, assembled on site
- Typical site built stairway uses double joist members to form opening, and 2x12’s cut to form carriages (sometimes also called stringers) to form supports for treads & risers
-Narrow stairs usually have three carriages, one at each side and one in center; wider stairs require more carriages
If carpeting is used, treads/risers finished with plywood; for exposed hardwood, prebuilt treads with rounded nosing or strip flooring can be applied over underlayment
-Open stairs can have any type of railing/baluster configuration as long as code requirements are met
most codes require one handrail in residences, two for other building types
True
Steel stairs are prefabricated assemblies made to fit the dimensions required by opening in building
- Constructed with preformed steel risers and treads welded to supporting framework of steel channels (sometimes other sections, such as rectangular tubes) and angles
- Utility stairs use stringers of channels with flanges pointing away from stairs
-Landings constructed of steel plate supported on channels and stiffening angles
Treads and landings usually filled with 1-1/2-2” concrete
-Finishes can be applied over supporting framework, studs can be attached below to allow attachment of finishes as needed
three risers are sufficient for most people to notice existence of level change; stairs consisting of just one or two risers are dangerous because people have a difficult time recognizing the level change.
True
Tread Design
- Critical components of tread design include depth, material, and nosing design
- Tread depth must be sufficient to provide safe footing for ascending and descending
- Material should be nonslip surface, but not so rough as to catch feet upon descending; nonslip materials added to tread should be level with the rest of tread
- Coefficient of friction should be .5-.6
- Can be many materials: carpet, hardwood flooring, vinyl tile, concrete, ceramic tile, terrazzo, glass, special glass block, steel plate
Handrail purpose
Handrails are provided in stairways for many purposes: to help users prevent loss of balance, to maintain stability in case of a fall, to guide people with visual or balance impairment, and in some cases, to help users pull themselves up when climbing stairs
IBC requires handrails with ___” min., ___” max. diameter.
1-1/4” min to 1-1/2” max Dia.
Handrail material
should have enough friction to allow proper grip, without abrading skin
Guards (or guardrails) purpose?
- protect people from falling into a floor opening
- Must be high enough to resist center of gravity of majority of people
- Top portion of guardrail should be designed to discourage people from sitting on it, where this might be a likely occurrence; high school students might be more likely to do so vs. elderly people
- If space below top rail is open, it must be filled to prevent small children from climbing through; most codes require maximum spacing that prevents 4” sphere from passing through rails
-Toe boards or raised edges used to prevent objects falling through gaps, if needed
Guards should be designed to reduce likelihood of people climbing; bottom rails should be avoided
IBC Req. for Guardrails?
- IBC requires 42” minimum height; some residential codes allow 36” height
- Most codes (including IBC) do not require guards if level change is less than 30”
