Joist notching and over spec joists.

[DIY_Disasters]

Hi,

I am in the middle of a bathroom refit where we want to put wall mounted taps for the bath and basin. The joists are running parallel to walls where the basin and bath is situated. To facilitate altering the pipework so the pipes can run inside the walls I need to notch the joist closest to the wall on both sides (bath and basin on opposite walls). For the basin side, it's not a problem as the notching location is within the first 25% of the joist and past the first 7% from the support wall. On the bath side, the location is around 40% along a 3.6m span, which is outside of the safe zone. But my joists are well over spec for this span because of much greater spans elsewhere in the house (210x72 @ 400mm centres). Looking at the span tables, for a 3.6m span with 72mm widths, I would need 145mm height joist at a minimum.

With all this in mind, if I was to notch 20mm depth to allow the 15mm pipe to travel into the wall, would this still be safe, as the overall height of the joist would still fall well above the span tables in the notched area?

Thanks

 

[cjcoffin]

In a word, yes. But as 40% is close to the point of maximum bending moment (which is at mid-span) then it would be even better to put the pipe through a hole in the middle of the joist, 15mm plastic pipe is helpful for this. But many ppl would use 22mm pipe for bath taps.

 

[DIY_Disasters]

Unfortunately a hole is not possible because the joist happens to be in the centre of the house, so it's actually sistered with another of the same size and bolted together, the plans show this too, so it's not a repair job. If I drilled through both joists, I would end up going too far and the pipe will simply end up in the floorspace of the bathroom next door. The sparky when installing the wiring 20 years ago has drilled holes further up again, which I would say is around the 50% mark. In his case though, every joist all the way through the house, I'm sure he had other options .

There is a 22mm hot and 15mm cold capped off, but the previous owner had a booster pump installed with a new supply running to the bath, these are both 15mm. I have since had the pump removed because it was too bloody noisy. It's an unvented system and the plan is to have the entire house cold water boosted with a pump like the Ezybox housed outside which should then deliver a constant 3 bar pressure, but not for a while yet. Do you think it's worth re-instating the 22mm hot for the bath? It also means my notch for the hot will need to be closer to 25mm too.

Thanks

 

[cjcoffin]

Hard to say. When they fitted our pressurised system they put in 22mm hot and cold for the bath as I was expecting. The supply was an old lead 1/2 in pipe but in the middle of a town the pressure is good and it was OK. I subsequently replaced the 15mm copper CW feed to the tank with 22, and the lead with 20mm MDPE because I had a big length of it. I was nervous I should have used 25 but it all works fine in practice.

If you know you are going to need a 3 bar booster for other reasons then 15mm probably adequate. Personally I have had a lot of trouble with pumps elsewhere on a rainwater harvesting system (Stuart Turner - rubbish) and would go to some lengths to avoid them on a mains-fed system. Your joist is so oversized the extra 7mm dia is trivial. If it worries you there are the thin steel plates you can get to protect pipes with which would give a little bit of extra strength at the top of the joist, but it is in compression there anyway so will tend to close the notch not open it.

 

[DIY_Disasters]

The supply is 25mm MDPE but come to think of it, the 22mm to the bath will be pointless because the internal cold feed to the unvented is 15mm. The gravity fed tank used to have 22mm from the loft which is now disconnected. I'm not going to increase the flow rate anymore than the 15mm internal cold feed. 15mm it is. Appreciate the input on the joists.