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Solid Core PVC vs Cast Iron Sanitary Risers

Solid Core PVC vs Cast Iron Sanitary Risers

Solid Core PVC vs Cast Iron Sanitary Risers


For a high rise building, and a sanitary riser that serves for example 12 stacking levels - is it acceptable to use solid core PVC in lieu of cast iron for a bathroom group riser? Obviously the potential concern would be noise. However, the project is adamant that they want to use PVC. Same question goes for storm risers.

Would it help to have riser pipe offsets every so many floors (or example every 4-5 floors)? This would slow down the slug of waste potentially.

This leads to another question, is there any requirement to have sanitary riser offsets every so many floors? There is obviously the requirement to have relief vent every so many floors, but have not heard of any requirement for an actual sanitary offset. This bathroom group riser would have a 4" sanitary riser, and a 3" vent riser.

Any offset requirement would not make sense either, as waste stack vent would not be possible as it can not have offsets (waste stack vent obviously not being used for bathroom group riser, but just for sake of argument for the offset discussion).

Thanks for any feedback

RE: Solid Core PVC vs Cast Iron Sanitary Risers

Residential buildings are not my field but I do work with some requirements related to fire control. On that note, CPVC is the only material that can substitute for metal in certain applications due to its inherent resistance to burning.

RE: Solid Core PVC vs Cast Iron Sanitary Risers

Ductile iron pipe has historically been used in high-rise DWV systems because it is stronger, quieter, and fire resistant.

Your choice of pipe material will be defined by the local plumbing code that was adopted where your project is located. It is very difficult to make changes to the plumbing codes and it takes years to make any changes.

If PVC is not listed as an acceptable product in the plumbing code, it will not be an option for your building developer.

Terminal velocity of flow is well understood. In a 100 mm to 150 mm stacks the water will flow at terminal velocity of 3-6 m/s and with solids up to 15 m/s and it reaches this between 3-6 meters from entering the stack, so the requirement to slow the flow is not needed. In high-rise designs, it is generally understood that offsets should be avoided,

RE: Solid Core PVC vs Cast Iron Sanitary Risers

Hello John_187 (Mechanical),

Some of the codes which i am familiar do not allow the use of plastic pipes for risers.. moreover, the use of plastic material which can emit toxic gas during fire is inside the building restricted .

IMO, for multistorey bldgs, the use of cast iron or ductile iron pipes for risers the best options.. However, the branch laterals could be CPVC..

Pls check the applicable code at your region...

RE: Solid Core PVC vs Cast Iron Sanitary Risers

For sound/acoustic purposes, we have specified insulation (usually fiberglass) around PVC pipes. PVC is generally acceptable for non return air plenum areas. But, as mentioned before, ask the local AHJ.

If you can, do not offset stacks. There is no requirement in the IPC to offset - but again check your local code. Early experiments indicate the annular flow in a stack reaches a terminal velocity and does not increase. Putting an offset in will likely require venting on both sides of the offset. Also an offset will require two "chases" or "shafts" for the piping, which will eat up valuable floor space.

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