Waterproofing for Green Roofs

It seems that every construction industry event and publication these days is bursting at the seams with “green” building advertisements and articles. Could it be that our society is turning into an eco-friendly, tree hugging Utopia? ….Not likely. However it is hard to deny the negative impact that building construction has on the environment. The evidence is so strong that several years ago this roofing industry enthusiast set out to learn more about the benefits of green roofing. I have to admit that I was skeptical at first, but I quickly began to see the benefits attainable through rooftop vegetation. In addition to the obvious aesthetic improvements, many physical, psychological and  sociological benefits can be achieved. We will discuss more on that topic in an upcoming newsletter for now we will stick to the topic at hand: waterproofing for green roofs.

As a waterproofing consultant and an engineer I would be remiss not to state the importance of ensuring that proper design and construction methods are followed for all building renovations; but particularly when a new element is added to an existing building. Before even considering installation of a green roof; a structural assessment of the existing roof must be performed to see what type of green roof system, if any, can be installed. After the allowable saturated wei ght of the green roof system is identified; the intended use. desired benefits, expectations of the final product and Owner’s budget should be considered to identify the options available for vegetation. There are three primary categories of vegetative roof systems:

Extensive

Extensive green roofs are typically the least expensive, require the least maintenance and are relatively light weight (10–50 psf saturated weight)

Intensive:

Intensive green roofs are typically the most expensive, require more maintenance and range considerably in weight (80–300 psf saturated weight)

Semi-Intensive:

Semi-Intensive green roofs fall between the Intensive and Extensive categories.

On more than one occasion I have heard potential green roof consumers say that they are going to “save money” by leaving there existing “new” (10 year old) roof in place and install the vegetation over it. It pains me to think that just as their vegetation begins to fully develop they will be removing it to address leaks resulting from a roof that was not designed to accommodate the overburden stresses of the vegetation not to mention the constant presence of moisture and the destructive roots attacking the seams. Don’t get me wrong I am all for greening rooftops, where appropriate, I just don’t want to see it happen at the expense of the occupants of the buildings top floor.

To ensure proper green roof design, an expert should be consulted from the start. Green Roofs for Healthy Cities, the leading industry organization in North America, has establish and accreditation process to establish industry experts known as Green Roof Professionals (GRP’s). By receiving this accreditation the GRP’s have successfully completed a thorough multi-disciplinary exam encompassing five areas of concentration including pre-design, design, contract management, quality assurance and support, and maintenance. As an accredited Green Roof Professional, I can assist in all aspects of green roof development, if you have any questions or would like to discuss a potential green roof project please feel free to contact me at bsullivan@sullivanengineeringllc.com.

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