Cutting into 7" deep joists

[TicklyT]

Consider the spacing and the span of the joists, not just the depth.

IIRC a 7/8" notch in 7" deep joists at 18" centres spanning less than about 10 feet is permissible, but if the span is more, or the joist spacing is greater, they should not be notched at all.

Have a look at the table at the bottom of the page electronicsuk linked to.

 

[Cambridge Mum]

Tickly T, the span is more. A structural engineer is doing the calculations. They also notched joists that run from the front of the house to the back; my house is pretty small, but I suppose the full depth is between 22 and 25 feet.
The engineer found one notch that was 5cm deep - completely unnecessary for a 22mm pipe. I am wondering whther this may end up in court; I do hope it doesn't come to this.

 

[bengasman]

Thats how pipes are run in almost every single house in the uk!

That doesn't automatically make it right.

 

[bengasman]

Thank you everyone for your replies - and for the link to that paper. Looks as though the Building Regs man may have been wrong.

They usually are.

 

[bengasman]

O dear, I just measure the joist and the cut out part. The joist is 17cm deep, the cut out 4 cm deep - so they've taken out nearly 25% of the depth. I shall definitely be asking them to reinforce the joists now.

It is probably even a bit worse; the bit that counts is the deepest part of the notch, which is usually one of the bits where they sawed through.
The reason you feel movement in the floor is that the "strength" of the floor is the square of the height of the joist. In other words: 1 cut of 30% of the height will reduce the strength of the joist to half of what it used to be.