Kitchen islands have come a long way from the "permanent table with doors" that were common in older kitchens. Today’s kitchen island is often an appliance warehouse, housing cooktops, ranges, trash compactors, sinks, and dishwashers. But contractors need to be aware that when a sink is added to the island mix, the designer’s dream can become a plumber’s nightmare. Running the supply lines to an island sink is seldom a problem; it’s equipping the sink with a code-approved drainpipe that often presents the challenge.

Plumbing vents are an essential part of a properly designed drainage system. The vent does two things: It allows makeup air to enter the system as the sink drains and enables sewer gases to escape outdoors. A plumbing vent must be located within an acceptable distance of the island sink. The maximum allowable distance will vary depending on your...

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