Roof Failures

The life of any roofing system is finite. Most low-slope roofing materials begin to exhibit water infiltration within 20 years after installation. Distress conditions and leaks on low-slope roofs are more likely to emerge at certain predictable areas, such as at punctures or seams in single-ply membranes. Roofing materials are subject to damage from strong winds and flying debris. Generally, roofs are not designed to withstand winds of hurricane and tornado intensity.

Leaks also often occur where pipes or vents penetrate the roof membrane, as well as at roof perimeters where roofing systems transition to other materials. By identifying areas that are prone to developing problems, maintenance and engineering managers can take steps that will prevent roof problems cost effectively. Less preventable source of roof leaks is roofing failure—that is, the structural failure of roofing materials. To make repairs in the most common roofing material—asphalt shingles—use the following approach:

  1. Go into the attic space during a rainstorm and inspect all the rafters or trusses with a flashlight. Look for damp or wet areas and mark them with a black felt marker.
  2. When the rain stops, look for any holes in the roof next to the leaking areas you marked. If you see sunlight coming through, you’ve found a hole. Push a small nail through each hole to mark these spots.
  3. Go onto the top of the roof and find your projecting nails. Push the nails back through the sheathing and fill the holes with plastic roof cement. Use cement that’s packaged in a caulk tube for easy application.
  4. If you see leaks around flashing for chimneys, plumbing pipes, or roof vents, fill these holes with plastic roof cement. Chip out the old sealant first with a hammer and cold chisel, and brush away any dust.

Every roof system can tolerate an optimum level of ponding water, after that it causes cracks on the roof surface. All roofs face any of the two conditions;

1. Every additional quantity of rainwater will cause a deflection that is bigger than the thickness of the rainwater layer causing this deflection. This means that the rainwater falling on the roof will flow towards the deflection, the additional weight of the water increasing the deflection further and so on and so on. Rainwater flowing over the edges of the roof will not take place. This will continue until either the rain stops, or the ultimate bearing capacity of the roof will be reached and the roof will collapse.

2. Every additional quantity of rainwater will cause a deflection that is smaller than the thickness of the rainwater layer causing this deflection. This means, that at a certain moment, provided that the ultimate load bearing capacity of the roof is not reached, equilibrium takes place, the deflection does not increase anymore and the additional rainwater falling on the roof flows over the roof edges.

Generally speaking, roof failures have common causes for all roofing systems.

  • Open laps: in the field membrane, but especially in the flashings, is another problem. Open laps are just carelessness on the part of the installer. Usually it means that the installer has failed to apply adhesive to the entire lap. Sometimes it is caused in built-up and modified bitumen systems when the bitumen is applied too cold. The laps appear to be closed, but open up as the roof ages.
  • Splitting: Splits occur frequently in expansion joints. The most common splits occur when a metal accessory is flashed with a membrane material. As the temperature changes, metals and membranes expand and contract at very different rates. Because the membrane generally cannot move as much as the metal, it will eventually fatigue and crack when it is adhered to metal. This problem is not as common with single-ply membranes with better expansion and contraction capabilities, but it is common in asphalt and coal tar systems.

Penetrations: Another common failure location is penetrations. Of particular concern are pitch pans. There are three failures common to pitch pans: the sealer itself, the container in which it sits and the penetration to which the sealant is supposed to adhere. Almost all sealers used in pitch pans will crack eventually due to loss of plasticizer or aging. If the penetration is not stabilized, vibration or movement of the penetration can cause the sealant to crack around the penetration. If a penetration is not thoroughly cleaned of asphalt before installing pourable sealers, the sealer will not adhere to the penetration.

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