Inspecting an old felt roof requires careful attention to common signs of wear and degradation. Cracking, often referred to as ‘alligatoring’ due to its distinctive pattern, is a major issue that can affect both the appearance and performance of the roof. Understanding the causes of cracking can help in identifying potential problems early and taking appropriate action.
UV Radiation and Loss of Protective Layers
One of the primary causes of felt membrane cracking is prolonged exposure to ultraviolet (UV) radiation. Felt roofs are not inherently UV-stable, and without adequate protection, the bitumen within the membrane can become brittle over time. Older roofing systems typically relied on protective measures, including:
- Mineral granules: These absorb UV rays and protect the bitumen but can erode over time, exposing the surface to further damage.
- Solar reflective coatings: Often applied to sanded membranes, these coatings help deflect UV rays but require regular maintenance to remain effective.
- Stone chippings: These were traditionally used to protect felt membranes but can be displaced by wind and foot traffic, leading to exposure and cracking.
Material Composition
In addition to UV exposure, the material composition of the roofing membrane also plays a crucial role in its longevity. Older felt roofs often contain unmodified or oxidised bitumen, which lacks flexibility and is more prone to cracking under stress. Modern roofing systems now incorporate materials such as Styrene-Butadiene-Styrene (SBS) or Atactic Polypropylene (APP), which offer improved flexibility, UV resistance, and longevity. When inspecting an older felt roof, it is important to assess the material composition to determine its susceptibility to cracking.
Thermal Movement and Ageing
Temperature fluctuations cause roofing materials to expand and contract daily. Over time, this continuous movement can lead to stress within the membrane, resulting in fatigue and cracking. Ageing further exacerbates this issue, as materials naturally degrade and lose their ability to accommodate movement. Many older felt roofs are now approaching or have exceeded their expected service life, making them more vulnerable to damage.
When inspecting an old felt roof, it is essential to check for signs of cracking, UV damage, and material degradation. Regular maintenance and timely repairs can help prolong the roof’s lifespan and prevent costly issues in the future. Engaging a professional for regular inspections can ensure potential issues are identified early, extending the life of the roof and avoiding unnecessary costs. For severely aged roofs, considering modern replacement solutions or upgrades may offer better durability and efficiency.
We’re here to help
If you have concerns about a flat roof or need expert advice, contact our team. As specialist commercial flat roofing contractors, we provide tailored solutions for commercial and large residential properties. With a commitment to quality, our experienced team combines traditional craftsmanship with modern techniques to deliver outstanding results.
