Floor Joists

  • Description

Common Domestic Floor Joists Sizes

When sizing the timbers within the floor it is important that the correct size of joists are used. The tables below give some of the standard timber sizes and their spans.

Strength Class C16 Suitable for Joists laid at 400mm centres

Span in meters Joist Size mm (depth x width)
2.08 97x50
2.48 122x38
2.72 122x50
3.27 147x50
3.77 170x50
4.31 195x50
4.79 220x50
5.06 220x63
5.27 220x75

Strength Class C24

Span in meters Joist Size mm (depth x width)
2.20 97x50
2.58 122x38
2.83 122x50
3.39 147x50
3.91 170x50
4.47 195x50
4.93 220x50
5.20 220x63
5.42 220x75


All structural timbers are to be Kiln Dried Note: Floor joists under a bath location must be doubled. Strutting to floor joists: between 2.5m and 4.5m spans provide 1 strut at mid span, over 4.5m span provide 2 struts at 1/3 span positions .Permitted positioning of Notches and Holes

Please check with your local building control department before using information contained in these tables to ensure that they comply with your local building codes.