They are the two ways to prevent backflow and get good drainage between a dishwasher and the drain connection at the sink tailpiece or disposal. It’s your choice of which one to use, but the code requires one or the other. 

   The Residential edition of the Florida Building Code, at 802.1.1.6, states that “the waste line of a domestic dishwashing machine discharging into a kitchen sink tailpiece or food waste disposer shall connect to a deck-mounted air gap OR the waste line shall rise and be securely fastened to the underside of the sink rim or counter.” The International Residential Code (IRC) has a similar citation.

    The high drain loop is the simplest of the two options. It’s easy: just attach the drain line to the underside of the counter before it descends to the drain connection under the sink. Here’s a diagram from a GE installation manual.

    The air gap (shown at top of page) is a device that is installed at the kitchen counter surface, usually to side of the sink faucet. It’s an unobtrusive, but not especially stylish, countertop detail. Some jurisdictions around the country (not Florida) require an air gap and will not accept a high drain loop. Because an air gap is not required in Florida, we rarely see one.

    The most common dishwasher defect we find during a home inspection is lack of a high drain loop, which is sometimes referred to as an air gap loop.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of some of our other blog posts about APPLIANCES: 

• What are the building code requirements for installing an appliance (furnace, air handler, water heater) in the attic?

• Which house appliances need a dedicated electrical circuit? 

• Is a washing machine drain hose required to be secured at the standpipe?

• When was GFCI-protection for kitchen dishwasher receptacle outlet first required? 

• Why does venting a clothes dryer into a garage, attic, or crawl space cause problems?

• Does a refrigerator water supply line require a shutoff valve behind it? 

• My spa tub stopped working. What's wrong?

• What is the maximum recommended height above the floor for an above-the-range microwave?

• Why would a home have natural gas appliaces but no gas meter? 

• Is a hot water faucet required at a washing machine?

• Can I remove a 240-volt range receptacle and hard-wire the range? 

• Can a dishwasher be wired to a kitchen counter small appliance receptacle circuit?

• Why is it bad to have a clothes dryer vent near an air conditioning condenser (outdoor unit)? 

• Do home inspectors test the appliances?

• What are the most common defects with over-the-range microwaves?

• Are a range and refrigerator required kitchen appliances for a house to pass FHA inspection? 

• What are the code requirements for an outdoor dryer vent cover?

• What is the maximum length for a clothes dryer vent? 

• Why are my ceiling fan blades drooping?

• How do you inspect a dryer vent? 

• Why is there a water hose connected to the back of the clothes dryer?

    Visit our APPLIANCES and PLUMBING pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.