Replacing tub with shower - 2" drain code

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Old 12-14-18, 08:17 PM
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Replacing tub with shower - 2" drain code

I've broken out the concrete floor and exposed the cast iron trap with a 1-1/2" ABS elbow that was set with lead. It looks to me that with the ABS and lead removed that a 2" ABS will probably not fit into the cast iron opening. My understanding is that a shower requires a 2" drain so that the water will drain without pooling. I'm assuming a bathtub doesn't pool and drains easily with a 1-1/2" drain because the air from the overflow vent allows the water to drain quickly. If that's the case then if I have to use 1-1/2" ABS and the opening of the trap is behind the wall then why can't I just use a "Y" and vent straight up behind the wall to allow air into the mix like an overflow does in a tub? I would run the vent above the height of the shower curb. Also, no matter the size of the ABS what do I use to attach the pipe to the cast iron?
 
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Old 12-15-18, 08:05 AM
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Showers require a 2" drain to ensure they don't back up and overflow.

Underground, you should use a rubber coupling to transition from ABS to Cast Iron. But you may need to replace the wye that you're connecting to.

Can you add a picture or two? Maybe we can help with exactly what you need?
 
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Old 12-15-18, 01:48 PM
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Rubber couplings, also often called Fernco do work, but to comply with code you need a shielded no hub coupling. It's basically a rubber boot with a corrugated stainless steel band around the exterior to provide support and protection for the rubber.

You do have to properly vent the fixture but that does not remove you from the requirement to use 2" minimum for the entire drain length. At no point can it be 1 1/2". If your cast iron or whatever is only 1 1/2" you have to go back further until you hit larger drain pipe and connect there with 2" to your shower.
 
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Old 12-16-18, 01:50 PM
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@Pilot Dane
to comply with code you need a shielded no hub coupling
Something I've been a bit hazy about... Since it's an underground connection, my understanding is a rubber coupling is code compliant. Above ground, it would need a shielded no-hub connector. Can a no-hub coupling be used both above and below ground?
 
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Old 12-16-18, 03:33 PM
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With my inspectors it seems to depend on the weather and their mood. I've had non-shielded couplings approved above and below ground in new construction and repairs and other times had an inspector require shielded. It's most often a issue when connecting to cast iron. They don't seem to mind as much when it's PVC to PVC. So, shielded is a safer bet but the non-shielded type are very reliable especially if the pipes are properly aligned and not putting strain on the coupling.
 
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