Measure the width of the batten. Ensure there is sufficient space on the rafter or joist to affix it.
Measure the length of the batten. A batten is fixed between two rafters or joists, so it must be long enough to span the gap between them.
Position the batten flush with one wall and with the end flush, with the adjoining wall at the corner.
Mark with a pencil through the holes in the batten where the screws will go into the rafter.
Enlist the help of a friend to hold one end of the batten in place against a rafter. Screw the other end in by drilling screws through the holes in the flanges on the batten.
Position a sheet of plasterboard flush with the corner of the two walls and screw through it into the underside of the batten. Repeat at regular intervals along the batten.