Q: A client wants to enlarge her existing deck, but a whole-house air-conditioning unit is located directly beneath the proposed addition. There seems to be plenty of clearance, so is it okay to build the deck above it?
A: Glenn Mathewson, a building plans analyst in Westminster, Colo., responds: An air-conditioning unit contains both a compressor—a hefty motor that draws a lot of amps—and a condenser, which cools the refrigerant and exhausts warm air. So there are a couple of issues to consider.
With any piece of electrical equipment, you should always start with the installation instructions (this is actually a code requirement: 2012 IRC E4101.2). If they aren’t with the unit or the owner, they’re usually easy to find on the Internet using the make and model number found on the equipment nameplate. You need to build the deck in compliance with the manufacturer’s requirements for clearance around the equipment.
To illustrate, here is an excerpt from Carrier’s installation instructions for an Infinity Series A/C unit:
When installing, allow sufficient space for airflow clearance, wiring, refrigerant piping, and service. Allow 24 in. (610 mm) clearance to service end of unit and 48 in. (1219.2 mm) above unit. For proper airflow, a 6 in. (152.4 mm) clearance on 1 side of unit and 12 in. (304.8 mm) on all remaining sides must be maintained. Maintain a distance of 24 inches (609.6 mm) between units. Position so water, snow, or ice from roof or eaves cannot fall directly on unit.
For this unit (and probably many others), providing at least 12 inches of clearance around the sides and 48 inches above it should be sufficient to allow it to function properly.
But clearances for maintenance and worker safety—governed by electrical codes—also need to be considered. For example, code often requires a minimum 30-inch by 30-inch level working space on the service side of electrical equipment (generally the side with a removable panel). Other provisions for equipment under floors are primarily intended for the inside of buildings (in crawlspaces). However, an inspector may deem it appropriate to enforce all “under floor” provisions of the IRC and require, for instance, a path to the equipment that is no longer than 20 feet (unless head clearance is more than 6 feet), as well as a light (with a switch at the start of the path) and an electrical outlet near the equipment.
Another thing to keep in mind is the location of the means for disconnecting the unit. This could be the overcurrent protection at the main panel, or it could be a supplemental device located adjacent to the unit. To avoid a detailed explanation of electrical code provisions, I’ll just give some general advice: Working back from the A/C unit, find the first means of disconnecting the power. Whatever it is (switch, fuse, breaker) and wherever it is, don’t build a deck, or skirt the sides of a deck, in any way that would block the line of sight between that switch and the equipment. This code provision is intended to prevent anyone from restoring power to the unit while someone else is working on it.