Hole cutting in floor joists

[ranzor]

Hello!
I have a question regarding making holes in the floor joists on the upper floor of a house from the 1920s. I am setting up a bathroom in a former attic. The house has a mansard roof, and the wall between the attic and the rest of the living area is load-bearing and supports the rafters. This wall then stands on the floor joists that the plumber wants to make holes in for the shower's drainage. The distance from the outer wall to the load-bearing wall is about 125cm. The total span of the floor joists is 3.5m. In two floor joists, 75mm holes are needed for the drainage as well as two smaller holes for water pipes. Can these holes be made in the floor joists without reinforcement, or should construction plywood or metal be applied to the floor joists?

Floor joist dimensions: 230x75
Span: 3.5m

 

[jonaserik]

It's fine to make holes for the drainage; reinforcement under the hole/notch is done with a 45X95 beam, approximately 0.5 meters long. It can advantageously be done on both sides of the ridge if there is any uncertainty. Holes for the water pipes, which are a maximum of about 25 mm, are made in the center of the timber, where there is zero tension. Reinforcement can also be applied if notching is done.

 

[Karl-Ove Qvarfordt]

If you are going to drill a hole in a floor joist, make sure to make the hole in the middle, preferably just above, as this will weaken the least. Reinforcements will probably also be needed.