It is my understanding that flexible PVC couplings (e.g. Fernco) meet the definition of Mechanical Joint in the international residential code. The 2015 IRC prohibits the use of Mechanical Joints on PVC couplings above ground "unless otherwise approved". I am having trouble finding the right terms to help me identify where else they are approved.

Where else are flexible PVC tees/wyes/elbows allowed (if anywhere) for use in PVC to PVC joints?

2015 International Residential Code

P3003.9 PVC Plastic Joints between PVC plastic pipe or fittings shall comply with Sections P3003.9.1 through P3003.9.3.

P3003.9.1 Mechanical Joints Mechanical joints on drainage pipe shall be made with an elastomeric seal conforming to ASTM C 1173, ASTM D 3212 or CSA B602. Mechanical joints shall not be installed in above-ground systems, unless otherwise approved. Joints shall be installed in accordance with the manufacturer's instructions.

2015 International Residential Code

Section R202 Definitions


  1. A connection between pipes, fittings or pipes and fittings that is not welded, brazed, caulked, soldered, solvent cemented or heat-fused.

  2. A general form of gas- or liquid-tight connections obtained by the joining of parts through a positive holding mechanical construction such as, but not limited to, flanged, screwed, clamped or flared connections.

  • I wonder if they can be used for vents? Nov 27, 2017 at 18:12

3 Answers 3


Fernco (Rubber) fittings are not approved in wall framing unless they have a metal sheathed hose clamp assembly covering the entire fitting as part of the design, Which limit them to straight couplings or reducing couplings. The reason is that vermin can chew through the rubber. They are suitable for underground but are more expensive than standard no hub couplings or regular pvc fittings. So the reason for wanting to use them for that is questionable unless there is some sort of access issue.

  • I have seen Fernco-style 1 1/4” p-trap fittings used under bathtoom sinks by the unwitting home owner. Before I was aware of this section of code prohibiting their use above ground, thiat application seemed like a logical place to use one to get a little flex as you move things into place and to easily remove for cleaning. Also, could you please provide code references for your statements about being approved with metal sheath hose couplings? Thank you Mar 15, 2019 at 1:37

Reading the first point of the Mechanical Joint definition it would apear that if you caulked your Fernco fitting, it would no longer quality as a mechanical joint.

That should be relatively easy to remove, yet still comply with P3003.9.1


If the fitting isn't rated for above ground use, it is probably rated for direct burial. Usually the kind with the steel shield around it is able to be used above ground.

As far as the flexible tees and elbows, those would be fittings, not joints. Many local codes forbid them for sewer completely. They may be acceptable for drainage applications though.

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