Flat roofs are a common feature in many modern buildings, offering practical advantages such as cost-effectiveness and easy access for maintenance. However, one of the most significant challenges flat roof owners face is the issue of ponding water. If left unaddressed, ponding water can lead to a host of problems, including structural damage and leaks. In this blog, we'll explore the causes and effects of ponding water on flat roofs and provide practical solutions for mitigating its impact.

A roof is categorised as flat when its pitch falls within the range of zero to ten degrees. As per BS 6629-2018 guidelines, it is recommended to maintain a minimum 1:80 finished fall for both the entire roof surface and any internal gutters. To accommodate potential inaccuracies on-site and slight deck deflections, designers aim for a fall of 1:40 in the design of flat roof surfaces.

Understanding ponding water

Ponding water refers to the accumulation of water on a flat roof surface that does not drain or evaporate within 48 hours after precipitation. This standing water can form due to various factors, including inadequate drainage systems, improper roof slope, debris buildup, or structural defects.

Regardless of the cause, ponding water can pose a significant threat to the integrity of flat roofs and requires attention to prevent damage.

Effects of Ponding Water

1.    Structural Damage: The weight of ponding water places excessive stress on the roof structure, leading to sagging, deflection, and even collapse in severe cases. Over time, this can compromise the structural integrity of the building and necessitate costly repairs or replacement.

2.    Leakage: Ponding water creates prolonged exposure to moisture, increasing the risk of roof leaks and water infiltration into the building interior. This can result in damage to ceilings, walls, insulation, and electrical systems, as well as potentially condensation and associated risks

3.    Waterproofing Membrane Degradation: Dependent on the type of flat roof membrane, some are susceptible to deterioration when exposed to standing water for extended periods. For these, ponding water accelerates membrane aging, leading to cracks, blisters, and degradation of waterproofing properties, compromising the roof's ability to repel watereffectively.

4.    Increased risk of pedestrian slips and falls: Flat roofs house a number of facilities, plant and equipment that requires routine maintenance. Safe access is required for personnel which can be compromised if ponding water is present. Particularly of concern in winter, when icy patches are hazardous, ponding water needs to be addressed to prevent falls.

Solutions for Ponding Water

1.    Improve Roof Drainage: Ensure that the roof is equipped with adequate drainage systems, including gutters, downspouts, and internal drains, to facilitate the efficient removal of water from the roof surface. Regularly inspect and clean drainage components to prevent clogs and obstructions.

2.    Correct Roof Slope: Address improper roof slope by implementing tapered insulation systems or installing crickets and saddles to redirect water flow towards drainage points. Consulting with roofing professionals can help determine the most effective slope modifications for your specific roof configuration.

3.    Repair Roofing Defects: Identify and repair any structural defects, such as low spots, depressions, or damaged roofing materials, that contribute to ponding water. This may involve patching leaks, replacing deteriorated membranes, or reinforcing roof supports to ensure proper load distribution.

4.    Install hydrolysis resistant waterproofing membranes: It’s not always possible to negate ponding water when refurbishing roofs. Advanced technological PMMA resins such as those from Triflex are inherently hydrolysis resistant. This means that they will not break down in water, providing long lasting waterproofing protection. They also offer the advantage of the ability to overlay existing membranes negating the need for strip up and offer minimal disruption.

5.    Consult Roofing Professionals: Seek guidance from experienced roofing professionals such as Triflex Authorised Contractors or our Business Development Managers to assess the extent of ponding water issues and develop tailored solutions to address them effectively. Professional expertise can ensure proper diagnosis, implementation, and appropriate means of mitigation.

In conclusion, ponding water may pose significant risks to the performance and longevity of flat roofs, necessitating proactive measures to mitigate its impact. 

By understanding the causes and effects of ponding water and implementing appropriate solutions, flat roof owners can safeguard their properties against water-related damage and maintain a watertight and structurally sound roofing system for years to come.

Contact us today to find out more.