Patent Publication Number: US-9422726-B2

Title: Stair system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Benefit is claimed of U.S. patent application Ser. No. 61/407,336, filed Oct. 27, 2010, and entitled “Stair System” and U.S. patent application Ser. No. 61/430,700, filed Jan. 7, 2011, and entitled “Stair System”, the disclosures of which are incorporated by reference herein in their entirety as if set forth at length. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to construction. More particularly, the invention relates to staircases. 
     In many construction situations, temporary staircases are needed. For example, architectural plans may call for an ornate staircase which might be damaged during construction. Also, plans may call for a staircase fabricated off-site which may not be available in early phases of construction. In such situations, it is common for builders to fabricate a temporary staircase. Because the dimensions of stringers will depend upon the height difference between floors, they may not be easily re-used if the height of the next location differs. Additionally, increasing safety requirements increase the complexity and costs of temporary staircases. 
     SUMMARY OF THE INVENTION 
     A stair system comprises: a first length-adjustable stringer; a second length-adjustable stringer; and a plurality of tread assemblies installable to the first and second stringers. Each tread assembly has an adjustable pitch tread. 
     In various implementations, there may be at least one handrail and a plurality of balusters attached or attachable to the tread assemblies and handrail. The stringers may be telescoping stringers. Each stringer may have a longitudinal array of first engagement features. Each tread assembly may have one or more left engagement features and one or more right engagement features respectively mountable to the first engagement features of a respective left said stringer and a respective right said stringer. 
     In various implementations, there may be means for adjusting a vertical registration of the first and second stringers with the upper floor (e.g., registration with a top plate assembly). 
     Another aspect of the disclosure involves a tread assembly for mounting to a first stringer and a second stringer. The tread assembly comprises a tread. There are means for removably and reinstallably mounting the tread to the first and second stringers. There are means for adjusting a pitch (pitch angle) of the tread. 
     The means for adjusting the pitch of the tread may effectively adjust a rise of the tread. The means for removably and reinstallably mounting may include respective left and right engagement features. The left and right engagement features may comprise downwardly-open channels for receiving the stringers. The engagement features may comprise keying projections for mating with holes on the stringers. A riser may be rigidly connected (e.g., via welding) to the channels. 
     Another aspect of the disclosure involves a stair system for spanning between a lower floor and an upper floor. The system includes first and second length adjustable stringers. A plurality of tread assemblies are installable to the first and second stringers. There is means for adjusting a vertical registration of the first and second stringers with the upper floor. 
     Other aspects of the disclosure involve methods for using such systems and components. The system may be installed between a lower floor and an upper floor of a building. The installation may comprise determining a length setting for the stringers based upon a height of the upper floor above the lower floor. This determining may be done by first determining a tread count based upon the height. The tread count or other determined length may be used to adjust the stringers to the length setting. The stringers may be attached to the upper floor and the lower floor. Tread assemblies may be attached to the stringers. In various implementations, at least some of the tread assemblies may be installed after the stringers are attached to at least one of the upper floor and lower floor. The attaching/mounting of at least some of the tread assemblies may include lowering the tread assemblies onto the stringers so that upper portions of the stringers (e.g., of the stringer cross-sections) are received in respective channels of the tread assemblies. The tread assemblies may be longitudinally shifted so that the features shift to a locked condition wherein direct translatory removal of the tread assembly is prevented or otherwise resisted. A pitch (pitch angle) of at least some of the tread assemblies may be adjusted. The pitch adjustment may comprise relative rotation of respective left and right jack screws and nuts (e.g., rotating a nut relative to a rotationally captured jack screw). A vertical registry of the stringers with the upper floor may be adjusted. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show exemplary stair systems with exemplary dimensions corresponding to an exemplary US installation situation in view of exemplary US code requirements. 
         FIG. 1  is a cutaway partial side view of upper and lower portions of a staircase. 
         FIG. 2  is a cutaway view of a stringer assembly of the staircase of  FIG. 1 . 
         FIG. 3  is a partially exploded view of a tread assembly on the staircase of  FIG. 1 . 
         FIG. 4  is a cutaway view of a tread assembly on the staircase of  FIG. 1 . 
         FIG. 4A  is an enlarged view, designated by numeral  4 A in  FIG. 4 , of a tread hanger region of  FIG. 4 . 
         FIG. 5  is a view of a top plate assembly. 
         FIG. 6  is an exploded view of the top plate assembly of  FIG. 5 . 
         FIG. 7  is a side view of the top plate assembly of  FIG. 5 . 
         FIG. 8  is a cutaway view of a telescoping stringer. 
         FIG. 9  is a bottom view of the stringer of  FIG. 8   
         FIG. 10  is a view of a second staircase. 
         FIG. 11  is a view of a tread assembly and baluster pair of the staircase of  FIG. 10 . 
         FIG. 12  is a view of a second baluster used in the staircase of  FIG. 10 . 
         FIG. 13  is a view of stringers and top and bottom plates assembled for forming the staircase of  FIG. 10 . 
         FIG. 13A  is an enlarged view, designated by numeral  13 A in  FIG. 13 , of a stringer joint. 
         FIG. 14  is a cutaway partial side view of upper and lower portions of the staircase of  FIG. 10 . 
         FIG. 15  is an exploded view of a tread assembly. 
         FIG. 16  is a longitudinal vertical sectional view of the tread assembly of  FIG. 15 . 
         FIG. 16A  is an enlarged view, designated by numeral  16 A in  FIG. 16 , showing adjustment indicia. 
         FIG. 17  is a view of a bottom plate assembly. 
         FIG. 18  is an exploded view of a top plate assembly and safety barricade combination. 
         FIG. 19  is a cutaway view of a stringer-to-top assembly joint. 
         FIG. 19A  is an enlarged view, designated by numeral  19 A in  FIG. 19 , showing adjustment indicia. 
         FIG. 20  is an exploded view of a stringer-to-base plate assembly joint. 
         FIG. 21  is a transverse sectional view of an intra-baluster joint. 
         FIG. 22  is a transverse sectional view of a stringer. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A temporary stair system  20  is used in a building  22  having a lower floor  24  and an upper floor  26 . The lower floor has a floor surface  28  and may have an opening  30  at a header  32  (e.g., likely the case if there is a series of stairways one above the other). The header has a surface/face  33 . Similarly, the upper floor has a floor surface  34  and has a header  36  having a header surface/face  38 . The exemplary stairway has a first length-adjustable stringer  40 A and a second length-adjustable stringer  40 B. The exemplary stringers are identical to each other. The exemplary stringers are mounted off-horizontal by an angle θ. When viewed from the perspective of a user ascending the staircase, the first stringer is a left stringer and the second stringer is a right stringer. The exemplary stringers are extensible/contractible. Exemplary extensibility/contractibility is via telescoping. Exemplary telescoping is via a single inner member within a single outer member. In exemplary implementation, the outer member is the lower member whereas the inner member is the upper member. The upper member extends from a lower end  60  to an upper end  62 . Similarly, the lower member extends from a lower end  64  to an upper end  66 . Exemplary upper and lower members have an essentially rectangular tubular cross section. The upper member cross-section defines upper  70 , lower  72 , left  74 , and right  76 , sides. Similarly, the lower member cross-section defines upper  80 , lower  82 , left  84 , and right  86 , sides. 
     At its upper end, the upper member includes means for mounting to the upper floor. Similarly, at its lower end, the lower member includes means for mounting to the lower floor. Both exemplary means are hinges  90  and  92 , respectively. The hinges have first portions  94 ,  96  secured to the associated member (e.g., via welding) and second portions  98 ,  100  hinged thereto for rotation about respective axes  510 ,  512 . The exemplary upper hinge second portion will normally be secured to the upper floor along the upper surface thereof. Exemplary securing is by fasteners such as screws. Alternatively, however, the upper hinge second portion may be screwed against the face of the upper floor header. 
     To cover any gap between the uppermost riser and the upper floor, the exemplary system further includes a tread-like cap  106  which mounts to the floor surface of the upper floor and extends over the uppermost riser to form an uppermost nosing. The exemplary cap may be formed of the same or similar profile to the treads (e.g., formed of the same alloy extrusion). The cap may have screw holes for screwing into the upper floor. In the exemplary embodiment, the stringer upper hinges have underside rabbets  108  into which edge portions of the cap may be slid after installation of the uppermost tread assembly. Thereafter, the cap may be screwed down. 
     Exemplary upper hinges have axes offset away from the upper member extrusion. This allows for the change in pitch angle while avoiding bottoming against the header. The exemplary offset is provided by having the proximal/lower plate (portion)  98  of the hinge bent with a first portion  110  secured (e.g., welded) to the extrusion and an offsetting portion  112  extending to the axis. The offsetting portion is essentially horizontal when installed. 
     Similarly, the lower member hinge second portion may be screwed to the surface of the lower floor or to the exposed surface of the lower floor header (the latter position being shown as  100 ′). The upper sides/walls  70 ,  80  of the upper and lower members have a linear array of engagement features  120  for mating with the tread assemblies. Exemplary features  120  are keyholes having a relatively wide upper portion  122  and a relatively narrow lower portion  124  extending from the upper portion to an end  126 . An exemplary keyhole spacing is shown as S 1 . 
     Each stringer may similarly include means for locking the stringer at a series of specific lengths. An exemplary means comprises a linear array of holes  130  in the lower side/wall of the inner member which may be mated to a complementary engagement feature of the outer member. An exemplary complementary feature comprises a spring-loaded pin  132 . The exemplary holes  130  have a central enlarged area and a pair of diametrically opposite legs extending therefrom. The central area is complementary to a shaft of the pin. The pin further includes a pair of diametrically protruding arms. The arms may be inserted through the arms of the hole and the pin then rotated to lock the pin in place. The pin passes partially through a hole (not shown) in the outer member. Other pin arrangements are possible. An exemplary spacing of these lower wall features is S 2 . An exemplary spacing S 2  is the same as the spacing S of the installed tread assemblies  148 . This combined with the particular registration of the array of features may insure that an integral number of tread assemblies will exactly fit along the stringers at each possible length of the stringers. The upper features may, more easily, be formed otherwise (e.g., as an array of pairs of longitudinally spaced-apart features (e.g., with a pair-to-pair spacing the same as S 2 )) or the like. 
     The stringer may bear indicia indicating a particular state of extension. For example, the inner member may bear an array of marks which correspond to the nominal floor-to-floor height at the target nominal angle θ. An exemplary specific nominal θ is associated with a 7.5 inch rise and 10.0 inch run (e.g., 37 degrees) and an exemplary range for nominal θ would be associated with a rise of 6.5-8.25 inch (code range for rise) with a 10 inch run. An exemplary adjustment range might be at least that large. Each marking could, alternatively, identify a range of heights associated with such marking Alternatively, the user could be provided with a chart indicating what length setting is associated with what range of floor-to-floor height. 
     Each exemplary tread assembly  148  comprises a first side portion  150 A for engaging the first stringer and a second side portion  150 B for engaging the second stringer. The exemplary side portions are formed as downwardly-open right channels each having an outboard wall  152 , an inboard wall  154 , and an upper base wall or web  156 . Depending from the channel inboard surface  158  along the base/web  156 , each exemplary side portion has engagement features complementary to the engagement features of the stringer. Each exemplary engagement feature  160  comprises a pair of upper and lower projections  160 A,  160 B and an intermediate projection  160 C. Each exemplary projection has a shaft  162  depending from an upper end at the web to a lower end. At the lower end, the projection has a head or protuberance  164 . An exemplary head is formed as a flat feature. An exemplary flat feature is circular and slightly smaller than a similarly circular upper portion of the stringer engagement features. This allows the tread assembly to be installed by a downward (or particularly normal to the stringer longitudinal direction) insertion with the head  164  passing through the keyhole upper portion  122  followed by a downward longitudinal translation so that the shaft  162  passes into the keyhole lower portion  124  with the underside of the head becoming captured by the periphery of the keyhole. With the shaft abutting the lower end  126  of the keyhole, further downward longitudinal movement is prevented. The capturing prevents movement normal thereto. The exemplary tread assembly  148  comprises a riser  170  extending transversely between the two side portions and rigidly connected thereto (e.g., such as via welding). 
     The exemplary tread assembly also includes a tread  180  having an upper surface  182 , a lower surface  184 , a proximal end  186 , a distal end  188 , and left and right edges  189 A and  189 B. Near the proximal end, the exemplary tread is mounted relative to the side portions and riser via a hinge  190 . An exemplary hinge  190  has a transverse pivot axis  520 . The exemplary hinge may have respective portions secured to the riser and tread (e.g., via welding) or unitarily formed therewithin. 
     The exemplary tread is pitch-adjustable within a range of rotation about the hinge axis  520 . The pitch adjustment allows the system to accommodate floor-to-floor heights which differ from a height exactly corresponding to the target angle θ (given the discrete adjustments associated with only having the option of integral numbers of fixed height and separation assembling). 
     For example, if the exact floor-to-floor height is slightly greater than the height associated with a given number of treads, then θ will be slightly greater than the target θ. If the treads are in an initial neutral position (e.g., in the middle of their range of rotation about the axis  520 ) they will be pitched slightly downward (so that the upper surface descends from the hinge outward). This may be compensated for by adjusting the pitch in the opposite direction. An exemplary pitch adjusting mechanism comprises a screw (bolt) and nut combination at left and right ends of the tread (left and right sides of the assembly). In an exemplary implementation, a screw  200  has an upper end  202  (e.g., a head) engaging the underside of the tread and secured against rotation about the screw axis  530 . The head may be mechanically captured (e.g., in a recess or by brackets or may be otherwise secured). A threaded shaft  204  depends from the head. A nut  210  (e.g., a star nut) is axially/vertically captured by the associated side portion of the stair assembly (e.g., between upper and lower flanges  212  and  214 ) which may be welded to the associated side portion. Rotation of the nut (e.g., via fingers or a wrench) in one direction causes the pitch to increase; whereas in the opposite direction causes the pitch to decrease. Alternative implementations may involve capturing the nut against rotation and allowing the screw to rotate. 
     The exemplary system may also include one or more handrails  268 . Exemplary handrails are provided by individual handrail members associated with individual tread assemblies. Depending upon the situation, one, two, or no handrails may be installed. For example, if a given side of the stair is against a wall, installing the handrail may be optional. If a side of the staircase is open, installing a handrail may (under safety code or regulation) be required. For mounting each handrail member, each side portion includes mounting features. Exemplary mounting features comprise one or more upward projections from the web of the side portion. Exemplary upward projections are formed in a pair of upper and lower projections  270 A and  270 B. Exemplary projections are tubular bosses extending vertically upward (i.e., at the nominal angle θ relative to the web). These may be short stubs secured to the web  156  via welding. Each exemplary handrail  268  includes a respective upper vertical member (upright or baluster)  280 A and lower vertical member  280 B each extending from a lower end  282  to an upper end  284 . The exemplary upper ends are formed at respective upper and lower ends of a rail portion  286 . The uprights  280 A,  280 B and rail  286  may be formed from a single tubular piece by bending. The exemplary rails are dimensioned to receive the bosses  270 A,  270 B when the rails are installed. The uprights may be secured to the bosses via pins  290  (e.g., extending through diametric through holes in the bosses and uprights). The exemplary handrails include means for filling the gap between each upper upright and lower upright (e.g., longitudinal crossbars  292  welded therebetween). The cross bars may be positioned to satisfy the relevant code for maximum allowable gap. Similarly, the uprights may be positioned so that the gap between a given upper upright and the lower upright of the next tread assembly above is no greater than the maximum allowed under code. 
     As noted above, in operation the floor-to-floor height may be measured or otherwise determined. This may be used to determine the appropriate length of each stringer. The stringers may be set to such length and installed (although not necessarily in that order). For example, the stringer may be secured at one end in an initially extended or contracted condition and then relatively contracted or extended to the final length and then secured at the other end. At some point during this process, one or more transverse spacer bars may be secured across the two stringers to maintain their predetermined separation to allow tread installation. Exemplary spacers are aluminum bars with predrilled holes corresponding to associated predrilled holes near an upper end of the upper members and a lower end of the lower members. The spacers may be secured to the members via screws, pins, or the like. After securing the stringers to the floors, the tread assemblies may be installed. Exemplary tread installation is one-by-one starting from the bottom. After tread installation, the rails (if any) may be installed (if not already installed). Removal may be via a reverse of this process with the tread assemblies being removed from top-to-bottom by an initial upward longitudinal shift which brings the mating features of tread assembly and stringer into a removal orientation (e.g., aligns the projection head  164  with the upper end portion  122  of the associated keyhole). The tread assembly may then be removed via an upward extraction normal to the longitudinal direction. After the tread assemblies are removed, the stringers may be unsecured from the floors. Optionally, such a system may be used on a more permanent basis if it meets code for a permanent installation. 
     Although exemplary English dimensions are shown for the typical US installation in view of typical US codes, other dimensions are possible and would be likely in other jurisdictions with other codes and other standard sizes of component. 
     Other variations replace the upper hinge with a single bracket that mounts to the upper floor .The stringers then have hooks to engage this fixture. This can remove the need for a separate upper spacer bar. Similarly, a lower fixture may replace the lower spacer bar. For example, a lower fixture may have pockets that receive the distal portions of the lower hinges. After such reception, the stringers can be rotated down to mate the upper hooks with the upper fixture. 
     Other variations involve use of some or all of the foregoing system components and features in a free-standing staircase. A subset of free-standing staircases involves movable (i.e., as a unit) staircases. One example includes a frame for supporting the stringers at the desired nominal angle θ. Among variations, the frame may be equipped with wheels (e.g., lockable or stowable for stability). The frame may also carry an upper platform/landing at the upper end of the stringers in place of the upper floor previously described. 
     Exemplary materials for the major structural pieces are aluminum alloys (e.g., aircraft aluminum 7075 for lightness). Exemplary hardware such as hinge pins, locking pins, screws/bolts, nuts, springs, and the like are of stainless steel. This can facilitate indoor/outdoor use. Exemplary stringer inner and outer members are extruded from such exemplary aircraft aluminum or 6061 aluminum alloy. Similarly, exemplary treads may be extruded (e.g., to provide a nosing feature along the tread front). A traction coating or applique may be applied to the treads. The side portions may also be extruded in channel form or may be assembled (e.g., welded of sheet/bar/strip stock). An exemplary system allows use with a floor-to-floor height of up to 144 inches. 
     The second embodiment (staircase)  300  ( FIG. 10 ) has several differences in construction/operation involving telescoping handrails  302 A,  302 B and upper  304  and lower  306  mounting fixtures in place of upper and lower pairs of individual hinges. Otherwise, materials and manufacture and use methods may be the same or similar to those above. For purposes of reference, gross features include left  308 A and right  308 B stringers (stringer assemblies) shown in  FIG. 13 . Each stringer assembly comprises an upper/inner member  310  extending from an upper end  312  to a lower end  314 . Each stringer assembly further comprises an outer/lower member  316  extending from an upper end  318  to a lower end  320 . The inner and outer members include tread assembly attachment features  322  ( FIG. 13A-e .g., holes/slots along stringer upper surfaces having wide upper portions  324  and narrow lower portions  326 ).  FIG. 12  shows the upper member  310  cross-section as defining upper  330 , lower  332 , left  334 , and right  336  sides. Similarly, the lower member cross-section defines upper  340 , lower  342 , left  344 , and right  346 , sides. An individual tread assembly is shown as  350  in  FIG. 11 . 
     There are several noteworthy differences in construction relative to the staircase of  FIG. 1 . 
     First, at each side, there is a single continuous (no vertical gaps) handrail  302 A,  302 B (e.g., an assembly of aluminum outer ( 352 )/inner ( 354 ) extrusions- FIG. 21 ) that telescopes similarly to the stringers. In one embodiment, the outer extrusion or member  352  is an upper member and the inner member or extrusion  354  is a lower member. This provides a smoother perceived transition if one is descending the stairs with hands sliding along the handrail. The exemplary outer/upper member  352  extends from an upper end  355  to a lower end  356  and the exemplary lower/inner member  354  extends from an upper end  357  to a lower end  358 . The cross-section (of each extrusion  352 ,  354 ) is downwardly open and has a bulbous closed upper end for hand gripping. 
     At each side, each overall tread assembly or stair unit comprises the basic tread assembly  350  plus at least one baluster attached to each side for connecting to the handrail. The baluster upper ends are received through the open lower end of the handrail cross-section and secured via fasteners such as pins, or screws. In the exemplary implementation, there is a single left side baluster and a single right side baluster each formed of a rectangular box cross-section (e.g., extruded aluminum) identical to each other. In the exemplary implementation, there are two different types of baluster. One type of baluster  360  is of said rectangular sectioned extrusion of the exact width to fit within the inner handrail extrusion  354  ( FIG. 21 ). A second type baluster  362  ( FIG. 12 ) is otherwise the same as the first  360  but, near its upper edge/end is flared outward on both side surfaces to create a respective upper and lower widened areas  364  and  366  of width to more closely and stably fit within the outer extrusion  352 . Both the balusters  360  and the balusters  362  are otherwise similar to each other and extend from a lower end  370  to an upper end  372  and have first and second lateral sides  374  and  376  and upper and lower cross-section ends or baluster edges  378  and  380 . Near the lower end  370 , a fastening hole  382  extends through both sides of the cross-section (inboard and outboard sides of the baluster) for securing to the tread assembly  350 . Similarly, near the upper end  374  a hole  384  extends through both sides for securing to the associated handrail extrusion(s).  FIG. 21 , for example, shows one of the balusters  360  at the junction between handrail extrusions wherein a pin  390  (e.g., a flat-head, spring-loaded, ball detent pin) extends through apertures  392  on both sides of the outer extrusion and apertures  394  on both sides of the inner extrusion. Such detent pins may be provided in two lengths: a shorter length for attaching to the balusters  360  along the inner extrusions  354  only; and a longer length for attaching the balusters  362  to the outer extrusions  352  and attaching the one or more balusters  360  along any overlapping region of the baluster extrusions. 
     In alternative implementations, each side of each tread unit may have a pair of balusters/posts (e.g., aluminum tubing) joined by a sheet metal web. 
       FIG. 5  shows the basic tread assembly  350 . This includes a tread member (e.g., aluminum alloy extrusion)  400  and a riser member (e.g., aluminum alloy extrusion)  402 . The exemplary tread extrusion  400  is extruded with traction ribs  403  along its upper surface. The tread extrusion  400  and riser extrusion  402  are formed with an integral hinge  404 . The exemplary hinge  404  is formed by a generally circular sectioned protrusion  406  on one of the members (e.g., a rearwardly projecting protrusion  406  along a rear edge of the tread extrusion  400 ) received within a complementary circular sectioned socket/channel  408  in the other (e.g., a forwardly open channel along an enlarged bottom edge portion of the riser extrusion  402 ). The exemplary tread extrusion comprises a forward end/edge  410  formed along a laterally closed channel  412  which provides a box structure for strength and also a bull nose feature for convenient ergonomic tread functioning. The exemplary traction ribs  403  extend along at least an upper portion of the bullnose. Behind the bull nose is a downwardly open channel structure  414  defining a channel  416  for receiving bolt heads  418  of height adjustment bolts  420  (functioning as jack screws) having downwardly extending threaded shafts  422 . The channel structure  414  captures the bolts against rotation and may have slightly inwardly projecting rim lips  424  capturing undersides of the bolt heads to vertically retain the tread relative to the bolts. 
     Each basic tread assembly  350  ( FIG. 15 ) includes a respective left side member  430 A and right side member  430 B for mounting to the respective stringer. These may be formed of aluminum extrusions and may represent the same extrusion merely cut at different angles. Each exemplary extrusion  430 A and  430 B comprises an upwardly open upper channel portion  432  and a downwardly open channel portion  434  joined at their shared base web  436 . The upper channel comprises an inboard wall  438  and an outboard wall  440  and the channel  434  comprises an inboard wall  442  and an outboard wall  444 . The upper channel walls are extruded with ribs  445  for gripping the balusters. 
     The upper channel  432  receives a lower end portion of the associated baluster and has a hole  446  through both its walls  438 ,  440  to, in turn, receive a detent pin or other fastener which also extends through the baluster bottom hole  382  ( FIG. 12 ). The lower channel  434  receives the associated stringer with the channel base resting along the stringer top. In the exemplary implementation, each side member further includes a key  450  secured within the channel  434  for engaging an associated hole in the top of the stringer. The exemplary key  450  is of inverted T cross-section and may be welded in place (e.g., with a rebated base of the leg of the T being received in a machined slot in the web  436  prior to welding thereto). The head of the T is dimensioned to just fit through the slot upper portion  324  and be captured beneath the slot lower portion  326  upon installation of a tread assembly in similar fashion to that described above. 
     For height adjustment, each side member further includes a clevis  452  (e.g., of aluminum alloy extrusion) which may have a base welded to the inboard face of the inboard wall  442 . Each of the clevis arms includes a hole through which the associated bolt shaft  422  freely passes. A height adjustment nut  454  is closely accommodated between the clevis arms and receives the shaft  422 . Rotation of the nut  454  in opposite directions respectively raises or lowers the bolt, and therefore the front end of the tread extrusion, causing the tread extrusion to rotate about its transverse hinge axis. Thus, the underside of the tread along the bolt-receiving channel structure  416  transfers weight to the bolt head  418  which, in turn, transfers weight through the bolt to the nut  454  and, therefrom, to the lower arm of the clevis  452  and, therefrom, to the inboard wall  452  of the channel  434  and therethrough to the web  436  and the stringers. 
     To physically/structurally connect the two side members  430 A,  430 B, the edges of the riser extrusion (ends when measured along the direction of extrusion) are welded to the adjacent inboard walls  442  of channels  434  along the rear end of the walls  442  and side members. At the front, a transverse brace  460  (e.g., aluminum alloy bar stock) may also be welded below the tread extrusion with respective ends welded to the respective walls  442 . 
     As is discussed further below,  FIG. 16A  shows inboard faces of the walls  442  as bearing indicia (e.g., hash mark indicia  470  and alphanumeric indicia  472 ) for height/angle adjustment of the tread. The exemplary alphanumeric indicia are for actual tread rise in inches. 
     One alternative indicia would be a delta value from a nominal tread rise. Other variations of such indicia include angles. The other indicia are non-descriptive (e.g., A, B, C, and the like each indicating one of the nominal tread heights). 
     To mount the stringer upper ends, the upper floor mounting fixture (top mounting plate assembly- FIG. 18 ) has left and right pairs of upper  600  and lower  602  mounting features protruding in front of the upper floor header. The exemplary features  600  are hooks (upwardly open) whereas the exemplary lower features  602  are merely projections that are received in the open stringer upper ends (open portions of the upper ends of the stringer inner extrusions). Alternative embodiments may involve upper and lower hook pairs. Each hook  600  is received in the associated open upper stringer end and engages/receives a transverse rod/pin (e.g., aluminum alloy rod  604  ( FIG. 19 ) welded to the stringer upper member) within the stringers to hang the stringers from the upper floor. The exemplary members  600  and  602  each comprise an aluminum alloy extrusion welded to the vertical plate  608  of the top mounting plate assembly. The exemplary top mounting plate assembly comprises the combination of this vertical plate  608  and a tread  610  which may be formed of an extrusion similar to the tread extrusion  400  of the tread assemblies. An upper edge of the vertical plate  608  abuts an underside of the tread  610  and is welded thereto. In an initial stage of installation, these may be respectively screwed to the joist face and floor surface ( FIG. 18 ). Additionally, at the initial assembly, a safety barrier/barricade/gate  612  may also be secured in place (e.g., atop the tread  610 ). The barrier  612  may be removed upon completion of installation and reinstalled at the beginning of a disassembly/removal process performed as a reverse of the assembly/installation process. 
     After the stringers are initially hung in place, to prevent their removal, a slider  618  (slide lock —e.g., aluminum alloy strip stock) at each side of the top mounting plate assembly slides through the open end of the associated stringer upper member and over the upper hook and pin.  FIGS. 18 and 19  show the slider in its retracted/unlocked condition. The exemplary slider slides via a pair of elongate apertures cooperating with rivets, screws, or other fasteners extending into the tread  610 .  FIGS. 18 and 19  also show each slider as having a small upwardly protruding handle (e.g., an aluminum alloy rod welded to the strip stock). 
     Means for vertical height adjustment of the stringers is also provided. Exemplary means vertically adjusts the height of the stringer upper ends relative to the upper floor while not effecting position of the stringer lower ends. Exemplary means comprises a bolt  630  having a threaded shaft extending within a threaded bore in the base of the channel  600  so that the end of the threaded shaft engages the underside of the rod  604 . Tightening of the bolt  630  thus raises the rod and associated stringer whereas loosening lowers. The exemplary vertical plate  608  also includes registration indicia  620 ,  622  ( FIG. 19A ) for indicating the relative height adjustment. These may be of similar form to the combined hash mark and alphanumeric indicia of  FIG. 16A . 
     To mount the stringer lower ends, the stringer lower ends are provided with a combination of hinged feet  640  and features for mating with the lower floor mounting fixture  306 . The exemplary hinged feet  640  are similar to hinged feet used on extension ladders and the like (having webs extending upward along either side of the stringer and secured thereto with a hinge pin for rotation about a hinge axis  541 ). The lower floor mounting fixture (bottom mounting plate assembly) has a hinged riser portion  650  (hinged relative to a base portion  652  screwed to the lower floor) which has mounting holes  654  that receive pins  656  protruding from ends of the stringer lower members. Each stringer has a pair of upper and lower pins  656  (e.g. aluminum alloy pins welded to end plates of the stringers) The holes have enlarged lower portions for passing the pin heads during installation/removal and narrower upper portions for capturing the pin shafts/shanks in installed conditions. This allows the stringers to initially be put into an approximate position with the feet  640  on the floor. Thereafter, the riser  650  may be inserted and dropped into place during which process, the stringer separation may be adjusted to fit the spacing between the holes  654 . Thereafter, the plate  652  may be screwed to the floor holding the stringers laterally, vertically, and front-to-back (with the shanks of the pins  656  trapped in the narrower upper portions of the holes  654 ). An exemplary cooperation between the plates  650  and  652  is via a hinging similar to that of the tread assembly tread extrusion and riser extrusion. In the exemplary embodiment, the lower edge of the plate  650  has a downwardly open circular sectioned channel receiving a complementary upwardly-protruding circular sectioned protuberance along the rear edge of the plate  652  to create the hinge having a transverse hinge axis  540 . With the stringers secured to the top and bottom mounting plate assemblies, the stringer separation is fixed, thereby facilitating installation of the tread assemblies. 
       FIG. 20  further shows a lower safety bar  660  which complements the upper safety barrier/gate  612  of  FIG. 18 . During assembly, the lower safety bar  660  may be installed on the lowest completed tread assembly/baluster assembly. This prevents someone from walking up an incompleted series of stairs and falling through a gap. During disassembly of the system, the lower safety bar  660  may be installed upon the next lower tread assembly below that being removed at any given time. The exemplary safety bar  660  is formed of welded aluminum alloy comprising a transverse bar (e.g., square sectioned tubing)  662  and having downwardly open right channels (e.g., extrusions)  664  at opposite ends with inboard walls of the channels welded to adjacent ends of the bar  662 . One or more vertical bars  666  may have an upper end welded or otherwise secured to the bar  662  and depending therefrom to extend between the balusters. The channels  664  have apertures in their adjacent walls for receiving detent pins  668  or other fasteners going through the channels and through the upper holes  384  of the associated balusters. 
     In the  FIG. 10  embodiment, each stringer is lockable via a transverse pin  670  ( FIG. 13A ) through sides of the members rather than through the bottoms of the rectangular cross-sections of the members. 
     An exemplary process for using the system (described relative to the second system  300  but also applicable to the first system) involves first calculating the number of tread assemblies required. The floor-to-floor height H is obtained such as by physical measuring or from prints or a computer model. H is then divided by the nominal rise R and the result rounded to the nearest full number to provide the nominal rise count. The number of tread assemblies needed is, therefore, one fewer than the nominal rise count. The inner stringer extrusion may be marked with hash marks and corresponding numerical indicia indicating the number of steps. For example, the hash marks may align with the open end of the outer member that receives the inner member. The stringers may be adjusted to length (e.g., via gradations marked to correspond to tread count) and secured via the aforementioned pin ( 670 ) or other fastener going through the single pair of holes in the outer member and whatever pair of holes in the inner member is associated with the particular tread count. 
     H is then divided by the nominal rise count to obtain a target actual rise. The target actual rise can then be used to adjust the top plate setting and the treads. For example, the adjusters associated with both may be marked with gradations (the indicia above) identifying either the target actual rise or a deviation from the nominal rise. In the exemplary implementation, the nominal rise in accordance with standard US building codes is 7.5 inches. Both the individual treads and the top plate have a marked range of adjustment of three-quarters of an inch. On the top plate, this is marked merely with the actual target rise values (from seven and one-eighth to seven and seven-eighths holes). For compactness, the exemplary tread assemblies mark only the deviation plus or minus from the nominal height (from −⅜ inch to +⅜ inch). In the US-standard example, the gradations are in eighths of an inch. The calculation of the target actual rise may involve rounding to the nearest eighth of an inch in such a situation (or, alternatively, sixteenth of an inch). This may be used to generate tables associating the tread assembly count and adjustments with the floor-to-floor rise. The top plate may be installed to the upper floor along with the barricade as noted above. For convenience, the height adjustment of the top plate may be performed before this installation. 
     After the stringers are adjusted to length, they may be hung from the top plate and the locks shifted forward to lock the stringers in place. Before installation of each tread assembly, the tread assemblies may be adjusted to height as discussed above. 
     The first/lowest tread assembly may be installed (e.g., without balusters). This may help stabilize/align the stringers. Thereafter, the bottom plate assembly ( 306 ) may be installed as discussed above. The first pair of balusters may be assembled to the first tread assembly via the pins as discussed above. The safety bar may be installed to the first set of balusters via pins as discussed above. In alternative implementations, the first set of balusters and safety bar may be installed prior to installing the bottom plate assembly. 
     The second tread assembly may then be installed followed by installing the second set of balusters thereto. Thereafter, the safety bar may be removed from the first set of balusters and installed to the second set of balusters whereafter the next tread assembly may be installed and the process repeated. If the baluster inner and outer members are of the same length as the stringer inner and outer members, then once one has passed the region of overlap (which is seen by looking into the holes in the tops of the stringers to see whether there is two layers or one layer) one can switch over to using the widened top balusters). Once all the stair assembly and balusters have been installed, the handrails may be installed pinned or otherwise fastened to each associated baluster. Thereafter, the barricade may be unscrewed or otherwise removed. 
     Alternative variations may be used in situations where there is not need for one or both handrails or balusters (e.g., wherein there are walls on either side). 
     In an exemplary kit for forming the staircase  300 , there are the two stringer assemblies including inner and outer members, feet, and pins ( 370  or other fasteners). There is also the top plate assembly and bottom plate assembly. There is also the two handrail assemblies including enough detent pins of the two respective sizes to address the maximal extension/height situation. An exemplary kit involves providing eighteen basic tread assemblies  350  plus ten pair of the regular balusters  360  and eight pair of the widened balusters  362 . The kit further includes detent pins to secure all such balusters to their associated tread assemblies. The kit further includes the safety barrier  612  and bar  660  and associated pins (if different from pins used otherwise) and associated screws. Different sets of screws may be provided for screwing into different surfaces such as wood or concrete or one common type of screw fastener may be used for all. There may be spares of the pins, screws, and the like, a paper and/or digital media manual, and any other accessories. The various fasteners and manual may all be in a bag or other container. The system may be shipped in a carton or several associated cartons. 
     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, particular regional building codes may influence particular implementations. Additionally, particular fields of use may influence particular configurations (e.g., use in the wood frame housing industry versus use in a more industrial setting). Accordingly, other embodiments are within the scope of the following claims.