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