Mechanical equipment on a commercial roof

Roof or unit: where the water comes from

Some common causes belong to the mechanical system, not the roof.

• The unit's condensate drain is clogged and overflowing.
• A poorly insulated duct inside the building is covered in condensation.
• An access panel that was not closed properly lets rain into the unit.

Have the cause established before ordering a repair. A preventive maintenance program devotes a large part of each inspection to the areas around equipment.

A waterproofing detail at each unit

Near a unit, the membrane has to climb up a base, wrap around a pipe or end against a piece of metal. Waterproofing then relies on flashings, pieces cut by hand and sealants.

Units vibrate. From one season to the next, the metal and the membrane each move at their own pace. Sealants often harden long before the membrane reaches the end of its life.

Four points we examine

1. The unit curbs. The unit sits on a raised base whose sides are covered by the membrane. This upturn must go high enough, hold firmly and run under a counterflashing.
2. Plumbing and electrical penetrations. Each one passes through a sleeve or a pitch pocket filled with sealant. If that sealant cracks, water follows the pipe.
3. Supports set on the roof. Wood or concrete blocks carry pipes and ducts. Without a protective pad, their movement wears the membrane.
4. Fasteners. Antennas, signs, guardrails: anything anchored by drilling through the membrane.

Before installing a new unit

The arrival of a unit is a risky moment for a roof that was watertight until then. Every opening and every fastener that goes through the membrane belongs to a roofer, who seals it with products compatible with the system in place. Three precautions are taken in advance.

• Reread the roofing warranty, which sometimes reserves this work to an authorized roofer.
• Submit the load to a structural engineer when the unit is heavier or changes location.
• Put the roofer on the HVAC contractor's schedule from the start.

Technicians leave traces

Those who service the equipment know units, not membranes. A sharp panel laid flat, a forgotten screw, and the membrane is cut.

The countermeasures are known: protective walkways between the roof door and the units, and an instruction to contractors to pick up screws and scraps before coming down.

Equipment and section 380

Section 380 of the Code de l'urbanisme (Laval's urban planning code) requires a flat roof to be green, white or made of a material with a solar reflectance index of at least 78. It provides an exception for buildings and equipment authorized on a roof. The Code does not say what applies to an existing roof redone identically. The City's Service de l'urbanisme (urban planning department) can answer for a specific project.

Frequently asked questions