Wastes through joists

[Nat]

Hi all,

Thought I'd ask this in the Arms cuz if you follow building regs to the letter I don't think you can do this but...

Can you run an inch and a half waste through normal floor joists with a fall for a shower tray? It's probably only a couple of metres from the proposed shower trap to the stack and the tray needs to be as low as possible for accessibilty hence the need to run it through the floor.

Looking at the official guidelines for notching and drilling joists it says you can only drill in the centre of the joist so you wouldn't get a fall. I have done this before but on those new type engineered joists with the large web in the middle and that hasn't been a problem but this isn't new build and they (although I haven't taken the floor up to look) are bound to be the solid timber ones. I haven't been able to measure the depth of them either.

Has anyone done this before?

Cheers

Nat

 

[Mike Jackson]

I've not done it but I've been involved with the remedial works after a DIYer did it. We had to take the ceiling down, prop the ceiling with acrows and bolt steel plates either side of the joists to reinforce them. Total cost was over a grand without the structural engineers costs.

IMHO it's not worth the risk.

 

[dontknowitall]

Only in certain circumstances, where the joists are really deep (e.g. large Victorian house). Even then, you have to strengthen the joists.

I'd never do this without consulting expert help (e.g. a decent construction engineer).

I've only done this the once (on said advice). All other times I've simply told the customer that it's not possible but with built a platform you overcome this.

 

[Nat]

Thanks for your response guys.

According to the guidelines though you *can* drill a 40mm hole through a 9 inch joist it's just getting the fall thats the problem.

Really didn't want to go down the platform route. F#*k!

 

[SimonG]

Can you go out an adjacent wall and run external, or drop below by the wall and box in below?

I'd be going this route than messing with building structure.

 

[Mike Jackson]

You can only drill a holes on the centre axis from .25 to .4 of the span of the joist up to a maximum of 1/4 of the depth. In a 9" joist this is around 57mm so a fall is achievable. This is only if there are no other notches in the area.

The job I attended the holes were bored through the centre of the joists about half way across.

 

[Nat]

Can you go out an adjacent wall and run external, or drop below by the wall and box in below?

I'd be going this route than messing with building structure.

The bathroom is inbetween two bedrooms and the stack is actually internal in the bathroom. Running outside would be a very long route and it would have to drop a lot by the time it got back to the stack. Don't really think this is an option. Dropping by a wall below might be worth looking at though, thanks Simon.

 

[Nat]

You can only drill a holes on the centre axis from .25 to .4 of the span of the joist up to a maximum of 1/4 of the depth. In a 9" joist this is around 57mm so a fall is achievable. This is only if there are no other notches in the area.

The job I attended the holes were bored through the centre of the joists about half way across.

Thanks for clarifying Mike. As I remember there was a solid wall below that the joists could be resting on so it's possible that the area i need to cut holes in would fall within 0.25 and 0.4 of the span.

I am obviously not a structural engineer but it's funny how you are OK to go within 0.25 and 0.4 but not as far as 0.5! The tolerances are quite exact.

 

[dontknowitall]

You need to clear your back with this one, imho.

If you get a structural chappie in you can then pass all the blame on to him (wording this as necessary on your invoice/receipt).

It will save you the worries in the future.

 

[Mike Jackson]

Have a look at http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Pipework-in-suspended-flooring.pdf . Although it's about copper the dimensions given in the diagram obviously apply for whatever the hole is drilled for.