|Carpentry for Vocational Schools - A Teachers Handbook|
For interior stairs, treads and risers are usually joined to the stringers by housing joints which are chiselled 12 mm into the stringer. This job has to be done with accuracy in order to achieve a good result and prevent the steps from creaking.
On the bottom of the tread you have to glue and nail timber battens in the size of 50 mm x 20 mm to support the riser. When assembling, join the riser to the tread by nailing the riser to the support timber.
Where stringers are not restrained by walls, the stringers must be bolted together with long iron bars, 10 mm in diameter and a thread cut on both ends. These iron bars must be placed at least two to three times in a stair.
Drill 10 mm holes in the stringers directly underneath a tread. When assembled, all treads and risers with the stringers, place the bars into the holes, put washer and tighten the stringers together with two spanners.
Overlength of bars can be cut and covered with a piece of timber to improve appearance.