Connect new Soil/Waste pipe from New Attic Bathroom to Existing Soil Vent Pipe in a Bungalow

TimHorton · 02-01-2022 01:50PM #1

As per the title, I am considering adding a bathroom in my attic, Can I add new waste/soil pipe to the existing Vent pipe if I bring a new soil/waste pipe out via the soffit adjacent to the existing vent pipe.

chooseusername · 02-01-2022 06:30PM

That looks like a vent pipe only, ie. no toilet discharging into it.

If so, it's unlikely to have the correct bend connection to the soil pipe underground for toilet waste.

C. Eastwood · 02-01-2022 06:42PM

https://www.boards.ie/discussion/2058225458/connect-new-soil-waste-pipe-from-new-attic-bathroom-to-existing-soil-vent-pipe-in-a-bungalow

TimHorton.

Yes you can do that.

The attached photos shows how this can be achieved.

3687E385-E383-4517-9D46-91E5C453F38D.jpeg

20B5C628-3FB6-40CD-B34E-BE2CA3533BE9.jpeg

One of these photos shows the 100 mm pipe from the Attic WC, and the wastepipe from the WHB and the wastepipe from the Shower. Both wastepipes coming down through the soffit and connected on to the RHS of the 100 mm Soil & Vent pipe ( the original Vent pipe), which was extended up through the soffit and in to the attic to connect to the Attic WC

On the LHS is a 40 mm PVC Vent pipe which discharges the gasses from the sewage system above the gutters. (Plumbers will tell you that you must have a 100 mm vent pipe) which is not correct. A 40 mm vent pipe is fine, it allows gasses out and fresh air in to prevent siphonage

Remove the top 2 Nr bends on your Vent pipe. Cut a 100 mm dia hole in the soffit and feed up a pipe and connect it to a bend in the attic above the wallplate. This can be connected to your proposed WC in the attic.

If your WC is far from this 40 mm vent pipe, you may have a problem with Siphonage, which may cause the level of water in the water-trap in the WC to drop down. It will therefore be necessary to fit an AAV - Air Admittance Valve to prevent self-siphonage. See - https://cdn-5ba91903f911c8155452f22e.closte.com/wp-content/uploads/2021/08/Air-Admittance-Animation-low.gif

You may also need one of these AAV on the WHB waste and also on the shower waste , depending on the length of the wastepipe from 40 mm vent pipe, again this is to prevent siphonage and prevent gargling noises from the wastepipes when water is being discharged.

TimHorton · 02-01-2022 08:29PM

https://www.boards.ie/discussion/comment/118406570#Comment_118406570

So how risky is not having the correct Bend ? House was built with Attic Renovation in mind,

TimHorton · 02-01-2022 08:32PM

https://www.boards.ie/discussion/comment/118406639#Comment_118406639

Thank you for the comprehensive reply. Excellent Information. If you don't mind I will digest the same and come back with some follow-up questions.

Still stihl waters 3 · 02-01-2022 09:15PM

It all depends on what bend you have at the bottom and which way its turned

C. Eastwood · 02-01-2022 09:20PM

https://www.boards.ie/discussion/comment/118407264#Comment_118407264

TimHorton.

The 2 Nr bends at the top of the Vent Stack are the correct type bends.

There should be one of these bends at the bottom of the Vent Stack (under ground) and in should be flowing down-stream in the direction of flow of the underground sewer pipe.

chooseusername · 02-01-2022 10:22PM

Tim,

looking at your photo in your op, does the underground sewer pipe run L to R, or R to L

and are toilet/s discharging into it to the left or right of this vent pipe?

"House was built with Attic Renovation in mind,"

Do you know what the underground connection looks like,

A vent connection is different to a toilet discharge connection.

That vent pipe is more likely to be at the end of the sewer pipe

and you need the connection to be a "slow bend" to connect to it.

https://www.screwfix.ie/p/floplast-push-fit-87-5-double-socket-rest-bend-110mm/12719?gclid=Cj0KCQiAt8WOBhDbARIsANQLp97F_nCMeWpT_Uv8qbBqyGIvkM4yMBzqM8fkxzUcH43eu0MpOiierOoaAtRJEALw_wcB&gclsrc=aw.ds

If the bend is like the ones at the top of the vent pipe in your photo

then I would suggest a "NO SOLIDS" notice in your attic toilet!

C. Eastwood · 03-01-2022 11:43AM

https://www.boards.ie/discussion/comment/118407281#Comment_118407281

TimHorton. Building Contractor use the fitting in the photos below for foul sewers in domestic dwellinghouse. They do not use the Wide radius bend on the photo above.

6ADBF012-307D-4B31-94BB-A9E07F90078D.jpeg

23197C78-47B9-4B43-AB68-39594B8D0F37.jpeg

Bear in mind that the Watertrap in a WC is a very small radius bend which allows all solids to pass through the WC Bend.