|Carpentry for Vocational Schools - A Teachers Handbook|
a) Strengthening the house construction:
- If there are no ceiling joists, the weight of the roof will tend to spread the walls.
- Through the ceiling joists exist a triangle construction which is immovable This means the pressure of the roof is straight downwards.
Ceiling joists are fixed across the narrow way of the house. Every second or third ceiling joist has to be placed near a rafter and connected to that rafter, so the ceiling joists act as ties to the bases of the rafters.
b) carrying the ceiling material: - Plywood, masonite etc. is nailed onto the ceiling joists. Depending on the ceiling material being used, the distance between each ceiling joist will vary from 500 mm - 700 mm. When plywood is used, the distance from the centre of one ceiling joist to the centre of the next ceiling joist is 610 mm.