Why Do They Put Rocks on Roofs? Understanding Roof Ballast
The practice of placing rocks on roofs, known as roof ballast, isn't a random act. It serves several crucial purposes, primarily for flat roofs but sometimes also appearing on sloped roofs in specific circumstances. Let's delve into the reasons behind this seemingly unusual construction technique.
What are the main reasons for using roof ballast?
The primary reason for using roof ballast is to secure and weigh down the roofing membrane. This is especially important for flat roofs, which are more susceptible to wind uplift and damage from extreme weather. The weight of the rocks prevents the membrane from being lifted by strong winds or torn by debris. Think of it as a giant, heavy blanket holding everything in place.
What types of roofs use ballast?
Ballast is most commonly found on flat roofs, often those made of single-ply membranes like EPDM or TPO. These membranes are relatively lightweight and flexible, making them vulnerable to wind damage without additional weight. While less common, you might see ballast on sloped roofs in areas prone to high winds or where the roof design necessitates extra stability.
What kind of rocks are used for roof ballast?
The type of rock used for ballast varies depending on availability and cost. However, the ideal rock is durable, weather-resistant, and relatively uniform in size and shape. Common choices include river rock, crushed stone, or specifically manufactured ballast. The size and weight are carefully considered to ensure adequate weight distribution and prevent damage to the underlying roofing membrane.
Are there any disadvantages to using roof ballast?
While highly effective, roof ballast does have some drawbacks:
- Weight: The added weight can put extra stress on the building's structure, requiring a stronger foundation and potentially increasing construction costs.
- Maintenance: While relatively low-maintenance, regular inspections are needed to ensure the ballast remains evenly distributed and that no rocks have shifted, potentially damaging the membrane. Over time, some rocks may need to be replaced.
- Drainage: Proper drainage systems are crucial to prevent water accumulation under the ballast, which could lead to leaks and damage. This often requires careful design and installation.
- Aesthetics: Some find the appearance of a rock-covered roof less aesthetically pleasing than other roofing options. However, architects are increasingly incorporating ballast into contemporary designs, finding ways to integrate it into the overall building aesthetic.
Is roof ballast environmentally friendly?
The environmental impact of roof ballast depends largely on the source of the rocks and transportation methods. Using locally sourced materials reduces the carbon footprint associated with transportation. Moreover, the weight and insulation properties of ballast can contribute to energy efficiency in some cases.
How is roof ballast installed?
The installation process typically involves spreading a layer of ballast over the roofing membrane, ensuring even distribution and sufficient weight. This layer is often several inches thick and carefully planned to accommodate drainage and avoid overburdening the membrane.
In conclusion, while the sight of rocks on a roof might seem unusual at first, it's a practical and effective method for securing roofing membranes and protecting buildings from wind damage. The decision to use ballast involves careful consideration of various factors, including climate, building design, and budget.
