How to Vent a Kitchen Island

Consumers’ desire for an island in the kitchen remains high, and today’s larger kitchens can easily accommodate one. These islands vary greatly in size, shape, and usage and may include multiple levels. The island may be used solely as a prep area or contain a variety of appliances and fixtures, including a cooktop, sink, or microwave oven. One portion may also serve as an eating bar for snacks and informal meals. Double islands—two islands with each serving a different purpose in the kitchen—are also growing in popularity for larger, multi-cook kitchens that support many different activities.

A separate work area or island can be incorporated into most kitchen configurations, provided there is room for the proper clearances in the work and traffic aisles. Island kitchens can be arranged in many different ways. The island is usually a workspace and may be combined with another activity area, such as dining. At least one side of the island faces a work area with a work aisle in between. The other side is more likely to be a traffic aisle or seating area, but it could be a work aisle as well.

Three ways to vent an island fixture are discussed next. Each method chosen should be verified by the local plumbing inspector.

Single-fixture Wet Vent

In a wet vent, the P-trap from the sink runs horizontally into a larger vertical pipe in the sink base cabinet and discharges into a 3- or 4-inch (76- or 102-mm) drain line located in the floor. The drain line must have a cleanout upstream from the entry tee. This system works because oversizing the drain lines beyond the P-trap increases the drain’s free-air capacity, allowing the sink to drain without siphoning out the water in the trap.

Bow Vent

Another approach is to connect the P-trap outlet to a vent, as if it backed up to a wall. But instead of the vent continuing up through the countertop, the portion above the trap loops back down to connect with a remote vent that is in a wall. The portion of the vent below the P-trap connects to a drainpipe below the floor. The main drawback of this arrangement is the large amount of space inside the cabinet consumed by the bow vent.

Automatic Vent

The simplest way out of the dilemma may be a simple device that works as a one-way check valve to let makeup air into the system as the sink drains. Automatic vents (bladder vents) typically are glued to the end of the short vertical vent pipe that rises above the P-trap. But if the mechanical valve fails, the room will be suffused with sewer gas.
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This article is excerpted from the NKBA Professional Resource Library volume: Kitchen Planning, Second Edition by Kathleen Parrott, PhD, CKE, Julia Beamish, PhD, CKD, JoAnn Emmel, PhD, and Mary Jo Peterson, CKD, CBD, CAPS, CAASH. Copyright: 2013 National Kitchen & Bath Association; published by John Wiley & Sons Inc. This material is reproduced with the permission of John Wiley & Sons Inc.

Three ways to vent an island fixture are discussed, each method chosen should be verified by the local plumbing inspector.