Modular tread and riser unit

An element for use in constructing a stairway, said element comprising a body in a right-angled triangle configuration, one side of said body being the hypotenuse of two adjacent sides, a first of said adjacent sides being longer than a second of said adjacent sides, said first adjacent side and said hypotenuse forming a first acute corner of said body, said second adjacent side and said hypotenuse forming a second acute corner of said body, a flange extending in at least one direction from each of the said sides at an approximate right angle to said body, said second adjacent side having a portion in which the flange is absent, said absent flange portion proximal to said second acute corner of said body, said absent flange portion dimensioned to receive said first acute corner of an adjacent element such that in use adjacent elements can be used to fabricate a self-supporting stairway stringer by interlocking consecutive abutting elements together, the flanges of the adjacent sides providing a mounting portion for a stair tread and/or riser.