• Description

Notches and Holes in Joists

Notches and holes are often required to be made in timber floor and roof joists to accommodate waste pipes from sanitary fittings, pipes for central heating installations or pipes and cables for other types of appliances.

If not made correctly, notches and holes can weaken the strength of the joists and ultimately result in collapse.

The guidance suggests an accepted approach for normal domestic loads on joists in single family houses of not more than 3 stories. In the interests of your own safety any proposed notches or holes outside the limits shown in the diagram below or in other types of building or loading conditions should be checked out by a qualified structural engineer.

Holes or notches too close together, holes drilled near joist ends or off the central axis and notches badly made or near the centre of the span can weaken joists so that they become unreliable for supporting loads.

Notches and Holes in Joists


- Should only be made in the top edge of the joist.
- Should be no deeper than 0.125 times the depth of the joists.
- Should be no closer to the support than 0.07 times the span and no further away than 0.25 times the span.


- Should only be drilled on the centre line of the joist.
- Should have a diameter no greater than 0.25 timesthe depth of the joist.
- Should be no closer together than 3 times the largerdiameter.
- Should be no closer to the support than 0.25 timesthe span and no further away than 0.4 times the span.

Notches and Holes in Joists

Maximum Notch Depth

125mm JOIST – 15mm
150mm JOIST – 18mm
175mm JOIST – 21mm
200mm JOIST – 25mm
225mm JOIST – 28mm

If the above requirements cannot be met within the limitations shown, then increase the joist depth by the depth of notches or diameter of holes.

Please check with your local building control department before using information contained in this page to ensure that they comply with your local building codes