Case 6
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
Splitting, Ridging, and Wrinkles
Splitting, ridging, and wrinkles are results of movement of the roof assembly, loss of physical properties of the membrane as it ages, low fatigue resistance and may be accelerated by vapor drive. Many of these causes can be addressed with expansion joints, proper securement of the roof insulation, tightly butted or double layered insulation and vapor retarders where required.
Standard asphalt and fiberglass felts have limited elongation properties and no recovery characteristics. As standard asphalt ages due to exposure to ultraviolet aging and water, it loses what minor elongation properties it did possess. After aging and associated loss in physical properties, movement induced by daily and seasonal thermal cycles results in splitting and ridging of the membrane and ultimately, fatigue failure.
The roofing material’s initial physical properties, severity of the elements, installation procedures and design elements all have an impact on when this phenomenon occurs. Membrane splitting occurs more often on large roof areas, with widely spaced contraction-expansion joints. Like Ridging , membrane splits almost parallel to the longitudinal direction of the felts.
Membrane splitting has many causes [1], acting singly or in combination of:
- Thermal contraction
- Insulation movement
- Water absorption on felts
- Drying shrinkage of wet felts
- Shrinkage cracking of roof decks
- Movement of roofing elements
- Roof deck deflection
- Stress concentration factor.