Scotia molding – Imperial, standard sizes.
The scotia molding is used to soften the junction and add a decorative detail, under the tread nosing where it sits on the stringer and riser.
There are 2 main sizes, to suit the 2 standard tread thicknesses, that most heritage or traditional imperial dimensioned stairs would have been made too.
The scotia for 1 3/8″ tread thickness is 3/4″ X 5/8″
The scotia for 1 1/8″ tread thickness is 5/8″ X 1/2″
The scotia curve.
The curves to the 2 different size scotias are slightly different, this is due to the fact they do not scale and each curve will be drawn to suit its own proportians.
Allthough the scotia will reduce in size by 1/8″ in both directions, the quirk lines at top and bottom reamain the same, a standard 1/8″ on both sizes and do not scale down therefore the curve changes in proportions. These would have been hand drawn and thus drawn to suit the dimensions of each size.
The cutters used to mould the scotia would have also been hand shaped, so allthough these are very close in size, when matching to an existing scotia if reparing older stairs then some dressing in may be required.
Alternative scotia design.
This design I came across while working on a listed building in the Kensington area of London.
The property was built circa 1880.
The scotia is traditional in size for a 1 3/8″ tread thickness, the only difference being they have added a 1/8″ bead detail to the bottom of the scotia curve and extended the curve with an additional 1/8″ quirk line.