Reinforcing floor joists when running pipes through the beams?

[Nizztos]

This has been brought up a bit, but I don't really think I've seen the answer to my question.

I will want to run quite a lot of VP conduits for electricity across the existing floor joists. 9" x 2" with cc about 600mm (floor level above basement in a house from the 1930s).
I have seen recommendations about where to make the holes (but have also read contradictory info). Typically in the middle or closer to the support.

If I choose to put a sheet of plywood, screw-glued, on each side where I make holes (quite a lot of conduits that need to go through in some places), can I then "ignore" the recommendations about where to make the holes? Or is this reinforcement not good enough?

The holes will be about 20mm, and there is some rule about the distance between the holes that I don’t remember but will follow. Holes in the center of the beams, not at the edge. I will have lots of circuits for my new kitchen so there will be quite a lot of conduits to run, so many holes it will be....

 

[huggan]

Here you can read about the recommendations for hole cutting:

https://www.traguiden.se/konstruktion/konstruktiv-utformning/stomme/bjalklag/barformaga--bjalklag/


Here you can read about how to make a reinforcement:

https://www.traguiden.se/konstrukti...lag/bjalklag--generellt/forstarkning-vid-hal/

 

[Nizztos]

Thank you, unfortunately, I'm not getting any wiser. I've seen recommendations before, and the reinforcement didn't seem applicable in my case with many small holes. But it might be that I can't interpret what's written correctly.

 

[Robert-san01]

Can't you run the pipes through the studs to the basement ceiling?

 

[huggan]

How many pipes are involved?

 

[Nizztos]

Can't you run the pipes in the furring to the basement ceiling?

No furring. Rough boarding, so would need to mill grooves in that case. Feels a bit cumbersome. Absolutely don't want to lower that ceiling either.

 

[Nizztos]

How many pipes are we talking about?

Haven't actually calculated it yet. Guessing about 10 groups. Will have quite a few fixed consumers in the kitchen and then there will be lights and sockets etc.

 

[huggan]

No spars. Raw boards, so I would need to mill grooves in that case. Feels a bit troublesome. Absolutely don't want to lower that ceiling either.

You don't have to mill, you can just leave a gap or two where you pull your lines.

 

[Thomas_Blekinge]

I would screw-glue long strips of plywood on both sides. The beams must have smooth sides. Then you can drill the holes through both the plywood and the beam. 17 mm diameter should be enough. Every mm counts in weakening.

 

[Nizztos]

You don't need to router, you can just leave a space or two where you draw your strokes.

Ahh, maybe it was unclear. This is a renovation/rebuilding, so the raw wood is in place. Replacing the entire floor on the upper floor in conjunction with moving the kitchen, which opens up and gives me access to the joists.

 

[Nizztos]

I would screw-glue long strips of plywood on both sides. The beams need to have smooth sides. Then you can drill the holes through both the plywood and the beam. 17 mm diameter should be enough. Every mm counts when it comes to weakening.

That's exactly what I want to do but I'm unsure how much it will help.

How smooth is smooth? They're not planed beams but also not hacked with an axe. I realize as you write this that it could become a problem. That is, the gluing won't be strong enough, and it will only be the screws handling the load (to use layman's terms).

Nailed raw boards on the underside and later screw-glued particle board on the top should also help a bit, I hope.

 

[farbror j]

As a layman's know-it-all, I intuitively say that the sheathing on the underside, across the beams, doesn't bear a thing. Imagine a crack appearing in a beam, on the underside of course, how is it supposed to be relieved by your sheathing? The sheathing just splits apart there. Or cracks between two nails. But of course, there will be a "hammock effect" sideways, so your beam won't collapse. Silly, I watched a YouTube film a long time ago with a "rambling rant" by an American who showed how such relief should be done. But that doesn't help you, here and now.
In the past, one might have made nail joints with two planks, half the beam thickness, length: half a meter on each side of the hole. And then nail from alternating sides in a grid pattern so the nails don't meet.
Short answer: Think "nailed joint with wooden lash" https://www.traguiden.se/konstrukti...xempel/bostadshus/spikad-skarv-med-tralaskar/

 

[Anonymiserad 173289]

If you make the cutouts in the upper part and then screw-glue the floorboards, it should not weaken significantly. The greatest stress is on the underside of the beams when pressure is applied from above.

 

[Staffans2000]

Well.
It will probably be just as much strain on both sides.
With such small holes, I would have drilled in the middle with scattered holes without reinforcing. I am convinced it holds up well anyway.

Staffan

 

[huggan]

You should absolutely not make holes in the bottom or top edge since the most forces are there. Consider why HEA and IPE beams have their shape? It is because the greatest forces are at the top and bottom of a beam, hence the wider flanges to take up forces while the web can be narrow.