Notching joists

[bernhund]

What's the score with notching joists these days? I've got two 8x3 joists side by side & need to run a 40mm waste pipe through them. The trap dictates the pipe is only just below the top of the joists, so can't see I can avoid notching.

[Tom_C76]

So do you need a 10mm notch (base of pipe just below top of joist) or 50mm notch (top of pipe just below top of joist)? And how far out from the bearing?

[barryrs]

Notches and holes in simply supported floor and ceiling joists should be within the following limits:

Notches should be not deeper than 0.125 times the depth of a joist and should not be cut closer to the support than 0.07 of the span, nor further away than 0.25 times the span.

Holes should have a diameter not greater than 0.25 times the depth of a joist and should be drilled at the joist centreline. They should be not less than 3 diameters (centre to centre) apart and should be located between 0.25 and 0.4 times the span from the support.

[bernhund]

Thank you people. I'm looking at a 50mm deep notch that's around 300mm from the bearing. The span is looking like 5800mm.

[bernhund]

So am I looking at max 25mm deep and 400mm off the bearing? If so, can I plate each side of the joists with 4 coach bolts through 6mm steel? (50mm hole in centre of plates)

[Andehh]

For what it's worth when we had a new boiler fitted in our Loft, the plumbers went to town on our joists, with zero regard for regulations.

Does make me concerned about selling in future & someone lifting up the loft floorboards and seeing 6-8 joists each with 3 notches cut out to comfortably routing the 22mm pipes (feed, return & gas) - some 1/3 of the way through the joist.

Didn't realise until 18months later when I was laying extra insulation up there and wanted to route some CAT6 cable under said board.

''Professionals....''

Edited by Andehh on Tuesday 31st January 11:43

[Bristol spark]

Andehh said:

For what it's worth when we had a new boiler fitted in our Loft, the plumbers went to town on our joists, with zero regard for regulations.

Does make me concerned about selling in future & someone lifting up the loft floorboards and seeing 6-8 joists each with 3 notches cut out to comfortably routing the 22mm pipes (feed, return & gas) - some 1/3 of the way through the joist.

Didn't realise until 18months later when I was laying extra insulation up there and wanted to route some CAT6 cable under said board.

''Professionals....''

Edited by Andehh on Tuesday 31st January 11:43

Thats standard practice for most plumbers!

[Lesgrandepotato]

Plumbers Chisel

[roofer]

bernhund said:

So am I looking at max 25mm deep and 400mm off the bearing? If so, can I plate each side of the joists with 4 coach bolts through 6mm steel? (50mm hole in centre of plates)

Yes.

[andy43]

18mm ply strips full length either side of the joists works well too, bolted or screwed.
Always check your plumbers toolbox for woodworms. Big buggers, usually with 25mm teeth...

[bernhund]

andy43 said:

18mm ply strips full length either side of the joists works well too, bolted or screwed.
Always check your plumbers toolbox for woodworms. Big buggers, usually with 25mm teeth...

Lol.

I can't believe it, it turns out there was already a 50mm deep notch right where I needed it. Silly me.....

[Ahbefive]

I wouldn't think about notching 50mm out of a joist. Find another solution.

[Renovation]

Personally I'd move the trap around and use a bend so I could lower the pipe then drill rather than notch.

However as others have mentioned most plumbers regularly cut this amount out.

More likely to cause bounce / squeak than outright failure.

[bernhund]

Relocating the shower waste is not an option nor is drilling the joist, because the pipe will run uphill to the stack. Raising the shower tray means the enclosure touches the ceiling as it's in a dormer. Notching & supporting the notch appears to be the only way without major expense and disruption to other rooms.

[andy43]

Cheapest and easiest may be to just run it vertically via the room below.
I've found a suitable technical drawing if it helps...

[Ahbefive]

bernhund said:

Relocating the shower waste is not an option nor is drilling the joist, because the pipe will run uphill to the stack. Raising the shower tray means the enclosure touches the ceiling as it's in a dormer. Notching & supporting the notch appears to be the only way without major expense and disruption to other rooms.

Good luck with that. Hope you don't need to get NHBC, building controls or a surveyor to ever look at it.

Get a different shower screen and raise the shower tray or drop the ceiling/box in in the room below.

Edited by Ahbefive on Wednesday 1st February 21:38

[TA14]

Ahbefive said:

bernhund said:

Relocating the shower waste is not an option nor is drilling the joist, because the pipe will run uphill to the stack. Raising the shower tray means the enclosure touches the ceiling as it's in a dormer. Notching & supporting the notch appears to be the only way without major expense and disruption to other rooms.

Good luck with that. Hooe you don't need to get NHBC, building controls or a surveyor to ever look at it.

Get a different shower screen and raise the shower tray or drop the ceiling/box in in the room below.

Yes, a major re-think is required on routing the waste, esp in a listed property.

bernhund said:

Our house is a grade 2 old stone school circa.1820. There's a central section with 3 rooms upstairs, the 2 wings are single level.
As it's listed,

[paulrockliffe]

Ahbefive said:

I wouldn't think about notching 50mm out of a joist. Find another solution.

Have you worked out the effective point loading required to snap an 8" x 3" joist that's been notched down to 6"? It's not going to snap! It might be against regs, but it's not going to snap or flex appreciably. If the floor is well screwed to the joists then they will allow some transfer of load around the weakness as well.

[Ahbefive]

paulrockliffe said:

Ahbefive said:

I wouldn't think about notching 50mm out of a joist. Find another solution.

Have you worked out the effective point loading required to snap an 8" x 3" joist that's been notched down to 6"? It's not going to snap! It might be against regs, but it's not going to snap or flex appreciably. If the floor is well screwed to the joists then they will allow some transfer of load around the weakness as well.

Have you done the calcs? Do you know the exact job, the condition of the joists, the centers, the loadinga on top etc etc. You are putting a shower tray, a person and no doubt lots of tiles and adhesive on top of that joist.

It may never cause an issue, it could ens up with minor issues with tiles/grout cracking or it could in time cause a big issue. If it were me I'd look for an alternative solution.

[paulrockliffe]

Ahbefive said:

paulrockliffe said:

Ahbefive said:

I wouldn't think about notching 50mm out of a joist. Find another solution.

Have you worked out the effective point loading required to snap an 8" x 3" joist that's been notched down to 6"? It's not going to snap! It might be against regs, but it's not going to snap or flex appreciably. If the floor is well screwed to the joists then they will allow some transfer of load around the weakness as well.

Have you done the calcs? Do you know the exact job, the condition of the joists, the centers, the loadinga on top etc etc. You are putting a shower tray, a person and no doubt lots of tiles and adhesive on top of that joist.

It may never cause an issue, it could ens up with minor issues with tiles/grout cracking or it could in time cause a big issue. If it were me I'd look for an alternative solution.

No, I've not done the calcs, but the loading is very low. If the joist is in poor condition or under-sized for the span to the extent that a 50mm notch near one end causes a problem then there's a bigger problem. There's more than enough contingency in the specification of a joist.

All those things you list are heavy, but not on a per unit area basis. The regs are designed to take into account all possible use of the room, so there's enough contingency for you to use the room as a storage room for heavy stuff. They also make allowance for dynamic loading, ie someone jumping up and down or whatever. The maximum loading for the use of a bathroom is inevitably much lower than that.