|Carpentry for Vocational Schools - A Teachers Handbook|
When a stairway is required from the ground floor to the first floor we have to cut out one or more ceiling joists to allow space for the stair cases. To hold the remaining ceiling joists in the correct places, we use "trimmers". Trimmers are placed from the first ceiling joist on either side of the space for the stairway. To join trimmers to the ceiling joists, we use a halving joint.