A metal stairway stringer with horizontal slots at each tread level, into which the treads are inserted laterally for supporting them at one end, the other ends of the treads being similarly supported in like manner by a second stringer. The slots for the treads each taper from adjacent the open end at the edge of the stringer toward the back, so that the treads must be wedged into position and are therefore held rigidly by the stringer.

BACKGROUND OF THE INVENTION 
The present invention relates to stairway constructions and it relates more 
particularly to stairway stringers having slots for receiving and 
supporting the stair treads. 
It is known to use pre-formed metal stringers of various types for 
receiving and supporting wooden stair treads, in order to facilitate 
on-site construction of a stairway in a bluiding. In most instances the 
stringers are designed simply to support the treads, and separate 
fastening means such as nails are relied upon to retain the treads in 
place or to prevent rocking of the treads relative to the stringers. 
It is the object of the present invention to more effectively secure the 
treads on and to prevent any wobbling or rocking of the treads in the 
stringers, without increasing the cost of the stringer or the work 
involved in installing the treads. 
SUMMARY OF THE INVENTION 
The invention resides in providing paired pre-formed stringers having slots 
in confronting faces which slots are disposed horizontally in the 
installed position of the stringers. The slots are open at their forward 
ends adjacent the front edge of the stringer, but are closed at their rear 
ends adjacent the rear edge of the stringers. Furthermore the slots are 
tapered from front to rear so that they are wide enough at their front 
ends to readily receive a wooden tread of standard thickness, but narrow 
down toward the rear to something slightly less than the thickness of the 
tread adjacent their closed ends. Consequently, in assembling the stairs, 
each tread is placed in the open end of each slot, but must be forced to 
the closed end of the slot due to the taper of the slot. In this way the 
tread becomes wedged in the slot so that it can not rock.

Referring to the drawings two metal stringers 10 are mounted in spaced 
relation to each other in an outside stairwell for a basement. Stringers 
10 (only one of which is shown in the drawings) may be mounted directly on 
the concrete side walls of the stairwell by means of suitable masonry 
anchors as shown in FIG. 2. 
Stringers 10 are each provided with a raised central portion 14 and 
mounting flanges 16, 16 extending the full length of the stringer. The 
flanges 16, 16 mount flush against the side wall of the stairwell with the 
central portion 14 projecting inwardly toward the opposite stringer. 
Basement stairways usually have seven or eight treads 18, each of which is 
held at its ends in horizontal slots 20 in the central portion 14 of each 
stringer. Each slot 20 opens forwardly at the upwardly inclined edge 21 of 
the central portion 14 of the stringer, and extends rearward across the 
stringer at a predetermined angle, so that it is horizontal when the 
stringer is in place. The back ends of slots 20 are closed for positioning 
the treads in that direction. 
Each tread 18, which may be a standard 2".times.10" wood plank, is inserted 
edgewise into the open ends of the appropriate slots 20 in the two 
stringers 10 and moved rearward until its back edge rests against the 
closed ends of the slots, where it is secured in place by driving spikes 
22 into it through holes 24 in both stringers. 
Proposal has been made to employ slots which are uniform in their vertical 
dimension from front to back, this dimension being approximately the same 
as the thickness of the plank 18, so that the plank can be inserted into 
it. However, due to variations in thickness of planks, as well as to 
shrinkage and wear of the planks during use, the planks can become loose 
within the slots, so that they rock slightly when a person steps on them. 
This would not only be annoying, but would also give the person a feeling 
of instability when he walks up or down the stairs. 
The present invention therefore involves tapering the slots 20 inward 
toward their closed ends, so that the plank 18 must be driven rearward 
against the end of each slot, thereby deforming the plank between the 
upper and lower edges of the slot, and effectively preventing the treads 
18 from loosening in the stringers once they have been locked in the slots 
by the spikes 22. It should be noted that spikes 22 are driven into planks 
18 at an angle toward the rear of each tread, thereby urging the plank 
toward the tapered end of each slot 20. 
As illustrated in FIG. 4, the vertical dimension of each slot 20 at its 
open end is approximately equal to the thickness of the tread 18. However, 
the upper edge 26 of the slot is tapered downward, beginning at the point 
A located a short distance in back of its open end. The degree of taper is 
relatively gradual, but is sufficient to ensure that the vertical 
dimension W at the closed end of the slot is less than the thickness of 
the tread. Thus, for nominal 2" planks which are usually used as treads 
for cellar stairs, the vertical dimension of each slot 20 should be 15/8" 
at the open end and 11/2" at the closed end, with the point A where the 
taper begins located about 11/2" from the point at which the edge 26 
intersects the upper edge 21 of the stringer 10. 
In this instance, the lower edge 28 of each slot 20 is straight and is 
disposed to the edge 21 of the stringer at an angle which is the 
complement of the angle at which the stringer is inclined to the vertical, 
so that the lower edge 28 is horizontal when the stringer is installed. If 
desired, however, the upper edge can be made horizontal throughout and the 
lower edge inclined upward, or both the upper and lower edges can be 
inclined toward each other at substantially the same angle to the 
horizontal. 
From the foregoing, it will be seen that an extremely simple, but effective 
means is provided for preventing loosening of stair treads in metal 
stringers.