Problem Roof or Scapegoat

by: Steve Nelson, RRC

Occasionally "roof" leaks just won't go away. After facility staff have searched for the problem, and roofing professionals have conducted a thorough visual examination of the roof system, leaks often remain elusive. Eventually, a moisture scan or flood test may even be performed to find the leaks.

What to do when there are no conclusive answers and the roof still leaks? The first thing may be to ask yourself if the cause of the leaks is even roof related. Following are examples of common sources of water entry that sometimes masquerade as "roof" leaks.

Rooftop Equipment

Mechanical equipment can take in water at poorly sealed joints, or rust damaged areas of the cabinet or ductwork. Vent stacks with excessive clearance between the storm cap or collar and the bottom sleeve are susceptible to moisture penetration from wind driven rain.

Windows and Skylights

The most obvious leak source at glass walled monitors and skylights is broken panes and panels. Window glazing materials can dry out with age and shrink or crack, allowing moisture to penetrate. Skylight gaskets can also shrink and split with age, or become displaced with the same results. Certain skylight designs rely on weep holes in the framing for drainage. When weeps become clogged with debris or even blocked by air flow from negative building air pressure, water can back up and overflow the drainage channel, causing leaks at the skylight curb.

Walls

Deteriorated mortar joints, damaged masonry and unsealed wall penetrations above the roof level can allow wind driven rain to penetrate masonry walls. Moisture may collect in sufficient quantities to migrate down through the wall materials and into the building interior, or behind wall flashings and into the roof system. The same result can occur with heavy rains against a porous wall material such as concrete block or EIFS (Exterior Insulating and Finishing System)applications that have insufficient waterproofing protection. Even tilt-up concrete panels are susceptible to moisture penetration when sealant dries out and shrinks, creating gaps at joints between panels.

Plumbing

Leaking sprinkler or water lines can stain ceiling tiles and are often mistaken for roof leaks. Fortunately, they are one of the easiest non-roofing leak sources to detect. Defective seals in roof drain lines also fall into this category, but can be somewhat more elusive. Often the drain flashing is blamed for water entering where the drain bowl and drain line connect.

Condensation

Under certain environmental conditions both inside and outside a building, moisture vapor will condense to a liquid that can form within a roof system, or on a surface below the roof system. The lack of a barrier membrane to prevent the free flow of moisture vapor allows this to occur, typically when there is a contrast between interior and exterior temperatures and relative humidity levels. As a result, water may saturate the roof insulation or drip into the interior with no apparent visible means of entry.

Problems may be seasonal or vary with changes in building operations. Identifying these leaks takes knowledge of how the roof assembly is constructed and environmental readings used to determine vapor drive and dew point dynamics.

As part of a thorough investigation, identifying and resolving non-roofing leak sources may also require a detailed history of roof performance. To aid the investigation, building occupants should keep records that describe leak activity, including the following:

• Location

• Whether leaks repeat

• Whether leaks occur with every rain or only heavy rains

• Whether leaks are dependent on wind direction

• How soon after rain begins do leaks appear?

• How long after rain stops do leaks continue?

• Whether leaks appear independent of precipitation, and if so, under what environmental conditions (i.e., temperature, humidity, time of year)

These clues will dictate the focus of a leak investigation and enable those providing professional assistance to expedite the process, and hopefully absolve the roof of blame . . . this time.