All about Green Roofs

Green roofs refer to layers of vegetation grown on rooftops of buildings to help in reducing surface runoff and in effect boost your water mitigation efforts. These rooftop gardens can be applied on a wide variety of buildings including residential buildings, educational facilities, church buildings, multi-office blocks, and industrial complexes among others. The size and type of green roof can range from a simple 2-inch vegetation cover to complex mix of vegetation that includes trees.

Benefits of Green Roofs 

• Efficient storm water mitigation and management: The urban environment is particularly susceptible to flooding during storms. With a rooftop garden in place, it is easy to slow down storm water runoff and thus reduce chances of flooding. On the other hand, the vegetation helps to filter pollutants from rainwater.
• Energy Conservation: Vegetation cover on the rooftop helps in curbing energy loss by absorbing heat and/or insulating buildings. As such, property owners require less amounts of energy for heating/cooling, leading to lower energy bills.
• Enhanced health and Comfort: Rooftop gardens make the interior living spaces more comfortable and habitable by controlling the amount of heat transfer that occurs through the roof. With a green roof, there are lower risks of heat stress which is usually caused by heat waves.
• Aesthetic appeal: Vegetation on your rooftop increases the beauty of your building, and at the same time increases the value of your property. 

The Significance of Green Roofs In Water Mitigation

Green roofs play a crucial role in water mitigation by reducing not only the peak flow rates, but also the total volume of rainwater runoff. Green roofs are ideal in water mitigation, especially in the urban environment, due to the fact that most of the area comprises of impervious surfaces. During a storm, these surfaces channel all the rainwater into storm sewers, thereby overburdening the existing drainage systems.

How a Green Roof Works in Water Mitigation  

The plants and substrate trap rainwater on the roofing and releases the water back into the atmosphere via evapo-transpiration. The absorption process is very crucial in delaying the runoff from the roof. The amount of rainwater that a green roof can store depends on the type of vegetation, depth of substrate, and type of drainage layer, among other factors.Usually, increasing the depth of the substrate increases the average annual water retention. A properly constituted green roof can retain almost all of the incoming rainwater.

Types of Green Roofs

There are two main categories of rooftop gardens, namely; shallow and intensive roofs. The choice of green roof usually depends on the following factors: 

Regional weather – the weather patterns in your area determine the kind of vegetation to grow on your rooftop for either water mitigation or energy conservation purposes.

Intent of installation – do you need a roof garden for storm water mitigation, or insulating your home, or aesthetics? 

1. Shallow Green Roofing- These roofs are built using a minimal amount of soil substrate, usually less than five-inches thick. The shallow soils cannot allow for the growing of oversize shrubs and plants. In addition, the variety of vegetation that can be supported is quite limited. These roofs are usually left undisturbed and only accessed occasionally for maintenance.

2. Intensive Green Roofing- These are rooftop gardens with more than a foot deep of soil substrate and can support a wide variety of vegetative cover, including large plants and trees. Some of the intensive roofs are designed as extensions of buildings or accessible parks, where people can visit and relax.

Flat roof vs. Sloping Roof Gardens in Water Mitigation

A common dilemma for property owners is whether to go for a flat or sloping green roof: which of these two is ideal for installing a rooftop garden and which option is ideal for water mitigation purposes?

Flat roofs, though more efficient in storm water mitigation, are unsuitable for green roofing owing to the fact that they require an additional layer to act as drainage in the root zone.

Sloping rooftops, on the other hand, do not require this additional layer since gravity works to drain any excess water naturally. However, if the slope is too steep, you require a mechanism for holding the soil substrate in place – usually a wooden lath grid – until a thick vegetation mat forms to hold the soil together.

Aaron’s Restoration is a water damage restoration company serving Macomb, Oakland, Wayne, St. Clair, Lapeer, Washtenaw, Monroe, and Livingston counties. A veteran-owned business, Aaron’s Restoration has been helping Michigan residents with home restoration for over 15 years.

From Michigan Insurance Group:

Although we are very supportive of the concept of a Green Roof, careful consideration must be given before adding this feature to your home. This is outside the obvious concerns of structure, design, and functionality. I am talking  about insurance concerns.  For example:

• Most property policies either exclude landscaping or have a tiny sub limit. To avoid arguments about what is a roof and what is shrubbery, specific coverage ought to be purchased or an endorsement manuscript.

• The cost to replace a Green Roof is generally going to be more than the cost of a standard asphalt roof. You want to make certain you have enough coverage for replacement cost.

• A Green Roof provides heating, cooling  and storm water management  benefits. Will your extra expense coverage pay any extra heating or  cooling  costs  while the  roof  is being repaired and the vegetation regrown or replanted?

These are just a couple of concerns that might arise when trying to insure a Green Roof. Fortunately, some insurance company are developing products to address green construction, green renovation and green re-building and provide coverage through endorsements. The bottom line, if you are going to cover your home with a green roof, make sure your policy covers the green roof as well.