Penetration flashings play a vital role in preventing water leaks around vulnerable areas of metal roofs. Whilst it is ideal to keep roof penetrations to a minimum, they are sometimes unavoidable, particularly on large commercial roofs. In this blog, we will explore the significance of metal roofing penetration flashings and the best practices for their installation.
Some common types of roof penetrations include:
1. Chimneys
2. Skylights
3. Vents and Pipes
4. Roof Access Hatches
5. Solar Panels and Solar Hot Water Systems
6. Antennas and Satellite Dishes
7. Roof-Mounted Facilities - HVAC units, condensers, etc.
8. Lightning Protection Systems - Metal rods or conductors used to protect structures from lightning strikes
9. Walkways and Fixed Harness Points
10. Structural Supports – For flyover patio roofs, plant platforms, etc.
Roof penetrations are potential weak points in any roofing system and whilst they are generally required for a functional purpose, they are susceptible to water intrusion. Penetration flashings provide these vulnerable areas with protection from the weather by creating a watertight seal around these openings. They prevent water from seeping into the roof structure, protecting the building against leaks, moisture damage to internal components, and mould growth. Well-designed and properly installed penetration flashings are essential to ensure the long-term performance of a metal roof.
When deciding how to flash penetrations it is important to consider several key aspects to ensure the chosen method provides suitable protection from the elements, without jeopardising the lifespan of the roof.
Materials: Choose flashings made of materials that are compatible with the roof material used, as well as compatible with the materials of the specific roof penetration. For example, condensation drainage from roof mounted AC units can cause accelerated corrosion to Zincalume and Colorbond roofs. AC condensation pipes should be discharged directly into a PVC pipe that extends to the nearest gutter or downpipe.
Proper Sizing: Ensure that the flashings are properly sized to match the specific penetrations. A precise fit is crucial for creating an effective seal and preventing water entry.
Sealants: Before application, ensure surfaces are clean to allow for a strong bond. Apply sealants which are compatible with both the metal roof and the material penetrating the roof. As roofs are typically exposed to high amounts of direct sunlight, it also critical to use UV resistant sealants.
Environment: Consider the environment of the area and choose materials that are compatible with the environment and climate. For example, black rubber dektite flashings are not suitable for use in bushfire rated areas, or with hot penetrations such as chimneys. In these situations, red silicone dektites are required.
Drainage: When designing flashing systems around new or existing roof penetrations, it is critical to consider how this will affect the roofs drainage capability. When flashing around roof penetrations such as large ductwork, ensure you choose a roof profile with increased capacity. It is highly recommended to consult with a hydraulic engineer to assist with the roof and flow design to ensure it meets the requirements of the National Construction Code and relevant Australian Standards.
Metal roofing penetration flashings are critical elements in a watertight roof structure. By effectively sealing vents, chimneys, and skylights, these flashings will minimise the risk of water ingress and subsequent damage. Whether you are installing a new metal roof or addressing existing penetrations, following best practices, and relying on professional expertise will ensure a durable and secure roofing system that stands the test of time.
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