Considering a Green Roof

Written by Andrew Morrison

Green Roof
Green Roof in Auckland, New Zealand

Have you considered a green roof for your straw bale project? You may think that they seem intimidating or even risky, but the truth is they are not only beautiful, but also a smart investment. There are a lot of myths out there which I hope to dispel in this article so that you can make an informed decision as you develop the design of your home. Please know that if properly designed and built, a green roof, often referred to as a living roof, can add longevity to your home and even reduce your annual costs. These are just two examples of benefits this roof style can provide. Let’s take a look at more of the benefits of a green roof, and the ONE potential drawback that you should consider.

Benefits of a Green Roof

As I mention above, there are a lot of benefits and only one real potential drawback. We will get to the drawback a little later on, but first, let’s get to the good stuff! You may be surprised by some of the benefits, although most are obvious once you spend some time considering them. Let’s jump in.


Flowers on a green roof can create biodiversity
A biodiverse planet is a healthy and resilient planet.

This may be the all time most important aspect of life on our planet, and our ability to survive as a species. I say that in all earnest. It is easy to see the damage that mono-crops create. In other words, when we reduce the biodiversity of the crops we grow, we see that those crops become far more susceptible to damage and even total loss. It has also been scientifically shown that when gardens, fields, forests, and other areas are allowed to grow with a multitude of different species, both flora and fauna, they are much more resilient to disease.

I believe that we need to do whatever we can to increase the levels of biodiversity on our planet. Most of us are not in a position to raise large varieties of wild animals for release into nature; however, we are capable of planting gardens that attract a wide range of insects and animals from honey bees and bumble bees to birds, tree-frogs and more. One way to do this is to add a green roof to your home and make sure that the plants in that garden represent a wide range of flora. Even better: make sure that the plants you select are native to your area.

Rainwater Storage Capacities of Green Roofs

Green Roof
A simple green roof with gutters to handle overflow.

I think it’s safe to assume that you know just how vital water is to life: your own and to every living thing on this planet. You most likely also know that we humans do a pretty crappy job (hint, hint) of taking care of our water. One obvious example of this is the fact that we rely on flush toilets. Consider it this way: one of the most important elements on the planet for our survival is water and yet we choose to use it as a vehicle to remove waste from our homes. And we get upset with pigs for how they handle their poop!? I’ll save the flush toilet conversation for another day, but consider that a green roof can help store water on your site. This not only helps bring life to your land, but also reduces the risk of damage from stormwater runoff.

A green roof is like a personal water storage facility on your property. The Green Roofs in the New York Metropolitan Region, Research Report” by Rosenzweig, et. al found that a conventional roof has an average rainfall retention of 24%. A green roof has an average retention of 80%. That’s a huge difference and one that you can benefit from in many ways. During “peak runoff”, the numbers change slightly showing a retention of 26% and 74% respectively. So what to do with the water that isn’t retained? You can install gutters, downspouts, and filtration to direct that water to storage tanks. The water will have spent some time in the “on roof filtration system” too (i.e. the soils) before heading down the pipes, so it will be naturally cleaner than water from a conventional roof.

Temperature Regulation (inside and out)

A green roof provides a layer of thermal insulation on top of your house. It lowers the level of heat absorption into your home through the roof, and as a result, lowers interior home temperatures. This is especially important if you live in a hot climate. Don’t worry that you’re missing out if you live in a cold climate. The same roof can help you retain heat inside your home, acting once again as an insulation layer on your roof to help lock in that comfortable climate your passive design and/or heating system have created.

There’s another impact on temperature that a green roof provides: neighborhood regulation. In other words, if you live in a more urban or even suburban location, there is likely a lot of asphalt and concrete around your home. Those “hardscapes” absorb and store heat and can have a significant impact on the health of your neighborhood’s climate. It’s not uncommon for areas with lots of hardscape materials to have temperatures as much as 40 degrees F above nearby areas of primarily natural landscapes. Nature does an amazing job of regulating temperatures and a green roof is an additional team member in that fight. It not only provides that regulation to your home, but also provides it to your immediate community.

Sound Insulation

I love the sound of rain, but I like peace and quiet even more.

I love the sound of rain on a roof, to a certain extent. It can get overwhelming though if that roof is not well insulated. You know what else can get annoying when a roof is not well insulated? All kinds of neighborhood noises. You may be surprised how much noise travels through a roof structure, even when it is well insulated. This is because the sound can travel through the framing members that make up the roof. With a green roof, you have a solid, thick layer of sound insulation to keep your home quiet and cozy in the form of soil and plants. Add that to the sound qualities of a straw bale wall system, and you’ll be in a house as comfortable as a womb!

Green Roof Aesthetics

Green Roofs in Norway
Green roofs in Myrkdalen, Norway. Who wears it better?

Green roofs are beautiful. I could probably leave it there, but I think saying a little more may actually be beneficial. Green roofs create a soft and elegant style on any structure, from urban skyscrapers to humble homes in the country. The type of plants used can add emphasis or contrast to your design, depending on what you’re looking for. You may choose to use flowering plants, which change the look of the home along with the seasons. Perhaps you prefer year-round consistency in your landscape/roof design. No problem either way. A well designed and executed green roof will provide a beauty that no other roof can, unless of course your neighbors are into green roofs too!

Fire Resistance

Wildfires are an ever growing threat to our environment, our homes, and our lives.

Unfortunately, wildfires are becoming more and more of an issue the world over. We in the western United States have seen massive fires year after year. Some places, the entire state of California, for example, officially no longer have a “fire season.” Instead, the risk of wildfire is now a 12 month, 365 days a year problem. That’s a major shift and a scary one. A green roof can help protect against wildfires, depending on the landscaping materials used. Long stalk grasses that can dry out as the climate heats up would not be the best choice; however, succulents and other low profile, high water content plants are a great idea. In addition, the soils in which the plants live provide another layer of fire resistance to the home. This roof system, when used in conjunction with other fire-safe building practices, including straw bale wall assemblies, can reduce your risks of flame spread and can help save your home in a wildfire event.

The Downside of Green Roofs

stack of money on top of plansThere are not many downsides to green roofs at all. In fact, the only potential downside, assuming that the roof is well designed and built, is the price-tag. In direct comparison with conventional roof systems, a green roof will be more expensive every time. This is not only because of the labor involved, but also due to the upgrades that you’ll need to make to the structural system of the roof. The weight of a living roof is much more than a conventional roof, so the rafters, beams, and even the lateral shear systems will likely need significant upgrades in order to support it.

Of course, you can’t just look at a dollar to dollar comparison of the construction costs. You need to consider the lifecycle costs of the roof. In other words, take a wider view of the roof choice, its impacts on other aspects of the home, and the overall interconnectedness of the roof and all other components of your build during and for the life of the project. For example, how long will the green roof last you? How long will a conventional roof last? What savings will you experience in your heating and cooling costs as a result of having the green roof? Will the water storage be financially beneficial in some way? All of the more global impacts of your roof choice must be considered when making your decision.

What’s Next?

Be sure to get the plans right. The details matter.

The key to the success of a green roof, as it the case with anything else, lies in the design and execution. Now that you’ve taken the time to consider building a green roof, be sure to take the time to research the proper execution of that roof on your project. Don’t cut corners. Build it right the first time and it will last you a lifetime. It’s not brain surgery or rocket science, but there are details that you want to get correct to ensure the roof’s success. As a primer, you want to consider the general make up of the roof system. A green roof consists of a waterproofing layer (some type of membrane), a root barrier to stop the roots (and even vermin) from damaging the waterproof membrane, a drainage system so that you don’t build up excess moisture levels which can make the roof heavier than the engineering had planned for, and a growing medium for the plants, ie.e soil or perhaps perlite and other lightweight materials. Of course, there’s a lot to it, so do your research and get help from an expert if that fits the budget.

4 Responses

  1. Looking into the Green Roof the theory is — The blades of the vegetation absorb the heat developed by the sunlight. This heat is dissipated by the breeze blowing over the grass and dispersed in the air rather than to the solid roof system. Which means the Heat of Radiation does not penetrate to the structural system. As in the winter the vegetation system creates a thermal barrier providing an obstruction the penetration of the cold. The coldest it will normally get below the grass layer will be 32 degrees, a far cry better than having 0 degrees penetrating. Cold absorbs cold.

  2. We hope to include a green roof in the house we’re planning to build, but the structural change was a deal killer for the new roof we need on our existing house and garage.

  3. On Vancouver Island they had a shopping center/ tourist attraction that had hosts living on their roofs. I have always thought that was the only way I could. Have goats, cute but afraid they eat everything and too many get out and I guess their not so fast.
    anyway, I remember that was the first time I had seen a glass building and a tire building and a year before I participated in building a strawbale house, and became secretly obsessed.

    The shopping area as I recall reminded me of an ole west wooden street strip of stores, so the goats were able to move a distance. I have one design I’ve thought of incorporating like the main SB house with an overhang to my garage then using 2 container buildings that carry the wait better had planned to have that as my studio/ guest house but with a sitting area with the goats to hangout with a view, visit and feed the goats, and just chill in the feel of nature. Bunnies could be cute too

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