A house that grows
Adding plants to walls and roofs can create a better space to live
Look deep into nature, and then you will understand everything better. — Albert Einstein.
Intro
I spent a lot of time flying as a consultant. Looking down across the US I noticed a lot of bare roofs where forests once stood, like the image below from Google Maps of a Seattle area suburb.
These roofs could be transformed into solar farms or living farms. In my last post, I shared a view of the solar roofs. One of the challenges with solar roofs is that it can create a lot of heat. In this post, I’ll discuss green roofs where plants are growing on the roof and absorbing the energy and creating a natural insulation barrier. For many parts of the US and the world, solar is not a great investment due to the cloud cover or angle to the sun. Green roofs, like the one on the Gates Foundation below, can provide insulation, reduce heat island effects, and clean the air.
Green Roofs
I love being out in nature and thus love the idea that I could be in a city and see green roofs and walls to feel more connected to the natural environment. The reality is that our cities are getting denser and natural spaces are harder to see in your daily life. Living roofs and walls bring us closer to the natural spaces that many of us crave as humans.
The basics
A green roof is a system designed to grow living plants. This is more complicated than a typical roof in that you’ll have additional layers to ensure the roof is waterproof and that plants can grow.
The costs of a green roof
The average cost for a basic green roof — including the design, permitting, and installation — will typically run between $18 and $22 per square foot. A deeper or more specialized roof can cost more, between $30–50 per square foot. A traditional roof is $5–10/s.f. and a solar roof can be as high as $22/s.f. These green roofs currently face a high-cost barrier.
Cost-Benefit Analysis:
A recent study on the costs of green roofs by the GSA (Government Services Administration), a part of the government that controls our built infrastructure, has evaluated the cost-benefit of a green roof vs. a typical black roof in the commercial sector. Compared to a black roof, a 3-inch to 6-inch green roof covering 10,000 feet has a Net Present Value of $2.70 per square foot per year, Payback of 6.2 years and an Internal Rate of Return of 5.2% nationally. One of the challenges is that the benefits come through other systems, mostly in stormwater infrastructure ($14.10) and energy savings ($6.60). These benefits are real, but given the indirect nature may be harder to justify vs. the $12.60 cost premium per s.f. to install the green roof.
How to maintain a green roof:
Most green roofs are designed with local plants that don’t need much if any maintenance. It is advised that you do some fertilizing and weeding throughout the year to ensure that other plants don’t grow and that your plants are healthy. This additional concern is another reason that green roofs are less likely to be adopted. A traditional shingle roof or solar roof in comparison requires very little maintenance.
Living Walls
There is also a growing movement to have plant walls. These walls create natural spaces and can help filter the air quality (inside and outside). These walls when used outside a building create an additional insulation layer that will lower the costs of energy to heat and cool the building.
Below is an example of an interior wall design. It can be much easier to build an exterior wall as the house already has a waterproof layer.
The idea of integrating the natural and built world continues to be a desire for humans. The majority of the installations at this point are seen in multi-family and office spaces to create a connection with nature that is normally lacking in the city.
This last year Amazon opened their Spheres, a biodome working space for employees. Amazon’s Spheres are a popular place for people to work in a weather controlled, natural environment.
The Future of Green Roofs
I love the idea of seeing green roofs cover the warehouses and flat roofs around the US. I find it hard to believe that this reality can come without strict regulations and/or large changes in the cost to build a green roof. The idea of lowering costs to build a green roof is harder to predict given the low tech solutions that are in use.
Germany provides the best hope that we can see lower prices and thus increased adoption. The market is larger and more competitive in Germany which has resulted in costs that are 1/3 that of a green roof in the US (according to Green Roof Service). Technology can play a role if there can be an easy mixture that can be sprayed onto the top of a roof quickly. This will help to lower costs and increase demand.
In Closing
In researching this article Green Roofs peaked in interest around 2008, which during this period sustainability had very strong interest. It was also a time where there was a lot of new construction being built. Following the Great Recession, these “extra features” have been harder to justify. This can be seen in the orange line below that represents searches for LEED building certification, the standard used for green buildings. Search volume and articles around Green Roofs is much lower now (see the blue line below). Plant Walls (red line below) is on the rise and is almost equivalent in search to green roofs.
I am optimistic of a green future, but the current trends point towards the status quo, with some potential for more solar. It is more likely you’ll see a plant wall near you as new products emerge to make it easy to manage plants inside the office and outside the walls.
