Step I: Calculate proportions
Begin by picking the location for your stairs. Pay special attention to the bottom – it should be on a flat and level section of ground or paving to ensure that the bottom tread is parallel to the upper level access point.Then work out the proportions of your stairs. Tread depth measured from the nosing point of one tread to the nosing point of the next is a minimum of 240mm (Fig. I) up to a maximum of 350mm. Rise from tread to tread is I90mm maximum with a recommended minimum of II5mm (Fig. I). Recommended minimum tread width between stringers is 870mm (Fig. 2). To obtain tread spacings, first measure the height from the very bottom where you plan the stairs to start to the top of the deck or floor. Let’s say, for example, the total height is 8I0mm. Divide this figure by I90mm, the maximum tread height, to tell how many risers:
8I0mm ÷ I90mm = 4.26 risers
Now round up the answer to the next full figure, never down as this would increase riser height beyond the I90mm maximum. This shows there will be five riser divisions. To determine tread spacings, divide the height of the stairs by the riser divisions:
8I0mm ÷ 5 risers = I62mm
So tread spacings is I62mm from the top of one tread to the top of the next tread.Finally, draw a full size grid pattern on a sheet of ply, plasterboard or particleboard using the riser and tread measurements (Fig. 3). Then draw an outline of the stringer and each tread on the grid (Fig. 4). Re-check your measurements and, if correct, you have an accurate pattern for the positioning of the treads on the stringer and the cut of the stringer top and bottom.