Cutting Holes in Joists for Pipes - Strengthening

[It's me]

We are planning to fit a shower tray in our upstairs bathroom, but to reach the waste, I would need to drill through the joists. I am concerned that this would weaken the joists and lead to problems in the future. I have seen that in America, you can buy steel reinforcing plates that have a hole bored in them. I have not been able to find these here: does anyone know whether they are available here anywhere? Alternatively, is there another sound way to reinforce the beams? I am not sure what size they are, but the house was built in the early 50s.

Thank you.

James.

 

[freddiemercurystwin]

What size are the joists, their centres, what size hole, how high up the joist is the hole, how close to the end of the joist is it?

 

[conny]

You could source your own steel plates here in the UK.
Measure the height of your joists, find a local engineering workshop and ask them for a price to make a couple of plates up with the required hole in the centre. 6mm, (1/4"), would be sufficient and make it at least 9"-12" longer on each side of the hole. Drill 2 holes in each end and another 2 holes about 3" each side of the pipe hole. Drill your hole in the joist first, then you can line up the pipe hole by inserting a short length of your pipe to hang the plates on. If you're are bolting right through you can line one plate up, drill through and hang your plate on the opposite side. If screwing from each side, without going all the way through, make sure the screws don't hit each other.

 

[It's me]

What size are the joists, their centres, what size hole, how high up the joist is the hole, how close to the end of the joist is it?

I cannot check until I lift the bath panel off again, but I think that they are about 290mm by 75mm. I intend to put the holes are near the centre of the beam. The hole will be 400mm from the end of the joist which is 2,400mm long.

 

[It's me]

You could source your own steel plates here in the UK.
Measure the height of your joists, find a local engineering workshop and ask them for a price to make a couple of plates up with the required hole in the centre. 6mm, (1/4"), would be sufficient and make it at least 9"-12" longer on each side of the hole. Drill 2 holes in each end and another 2 holes about 3" each side of the pipe hole. Drill your hole in the joist first, then you can line up the pipe hole by inserting a short length of your pipe to hang the plates on. If you're are bolting right through you can line one plate up, drill through and hang your plate on the opposite side. If screwing from each side, without going all the way through, make sure the screws don't hit each other.

I had considered that, but buying a commercial product, if available, would be quicker. Thank you for the suggested dimensions if I do pursue that route.

I had wondered about using 18mm plywood either side of the beam. Would this be adequate?

 

[freddiemercurystwin]

I cannot check until I lift the bath panel off again, but I think that they are about 290mm by 75mm. I intend to put the holes are near the centre of the beam. The hole will be 400mm from the end of the joist which is 2,400mm long.

They can't be 290x75.

 

[freddiemercurystwin]

If you can get your holes to work so they meet the criteria in here then happy days: https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists

 

[It's me]

They can't be 290x75.

Quite probably. I do need to get the bath panel off again to check.

 

[It's me]

If you can get your holes to work so they meet the criteria in here then happy days: https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists

Thank you for this, which is helpful and frustrating. For the length of the beam that we have, the hole should be at least 600mm from the wall, but we would need them at about 400mm or so.

Back to the drawing board.

 

[John D v2.0]

If the span is only 2.4m then the load would be relatively smaller, if you're taking out 50mm or so,I would say as long as the joists are 170mm or more it would be fine. But you can't sue me if your house falls down.
Ply is quite good for making things feel stiffer but it won't affect the official calculations for shear strength in your case.

 

[It's me]

Thank you all for your replies and suggestions. I have now been able to measure the joists which are 55mm by 165mm with a 2,400mm span. They are at approximately 450mm spacings: they are not consistent, but all in that region.

 

[conny]

Thank you for this, which is helpful and frustrating. For the length of the beam that we have, the hole should be at least 600mm from the wall, but we would need them at about 400mm or so.

Back to the drawing board.

The only way I can see you getting round that is to run the pipe between the joists to the 600mm line, right angle band across as far as you need to go, then right angle bend back down between the joists to where it will exit.

 

[John D v2.0]

The reason you can't go too close to the end is that the shear load is greatest there.
If they are 55mm wide that's an odd size but it will help with the shear strength.
You could go to a structural engineer and get them to calculate if you're worried

 

[It's me]

The only way I can see you getting round that is to run the pipe between the joists to the 600mm line, right angle band across as far as you need to go, then right angle bend back down between the joists to where it will exit.

A

 

[It's me]

Thank you for all of the advice and suggestions. Sadly, I need to find another way to get the drain out as I discovered a steel utility pipe right in the way. I am not sure whether the pipe is still in use, but I do not want to find out the hard way.