With rising energy prices, saving money is top of the agenda for many a facilities manager. So DO green roofs save energy? And if so, how do they do it?
- Insulation against heat – reduces air conditioning (AC) costs and makes AC units more efficient.
- Insulation against cold – reduces heating costs
- More efficient Photovoltaic (PV) panels – allows buildings to become more self-sufficient in energy production
Most people will agree that it’s important for the human body to be at a comfortable temperature for most of the time. We none of us perform particularly well if we’re too hot or too cold. And for some demographics (the elderly, the infirm and the very young) extreme temperatures can be highly dangerous. As a society we have become very good at controlling the climate inside our buildings. Heating in winter and air conditioning in summer enable us to keep fairly constant conditions. However, temperature control comes at a price. It uses energy. Energy that not only costs money, its production is associated with climate change.
Green roofs have many benefits to the wider environment, to the buildings that support them and to the people who use those buildings. One of those benefits is an improvement of the thermal performance of a building.
Living roofs are well known as a great way to support biodiversity net gain (can you see the goldfinch in this picture?). But did you know that they also have the potential to reduce energy usage in buildings?
Green Roofs Help To Insulate Against Heat And Cold
How can we minimise energy consumption? Well, the design and construction of any building can make a huge difference.
Architects and property developers are very good at designing buildings that are well insulated, carefully orientated, and have energy efficient heating systems. But there is still an opportunity to make buildings even more energy efficient – by topping them off with a living green roof.
Once established, a living roof harnesses the energy of the sun to help cool the building and the surrounding environment on hot days.
In winter, the additional thermal mass of a green roof provides an extra layer of protection against the cold.
Studies at Nottingham Trent University show a considerable difference in the average temperature beneath the waterproofing on a green roof compared to a conventional roof in winter AND in summer
- Air temperature 0 oC/18.4 oC
- Temperature under membrane of conventional roof 0.2 oC/ 32oC
- Temperature under membrane of green roof 4.7oC / 17.1 oC
This reduction in temperature also helps to make AC units more efficient. As AC units will receive cooler air, they will have to use less energy cooling air down. In real life results will vary from roof to roof and will potentially be influenced by aspect, height, weather, depth of substrate and plant coverage. But you can see how the costs of running a building can potentially be reduced by installing a living roof. Plus, of course there’ll be a wealth of accompanying benefits such as SuDS compliance, biodiversity net gain and great PR.
Green Roofs And PV Panels
Aside from reducing energy usage. It is possible to cut energy costs and reduce carbon emissions by generating your own electricity. Green roofs are surprisingly helpful at this. No, we’ve not yet developed the technology to somehow harness plant physiology. But, evapotranspiration, that wonderful system that plants use to cool themselves, also cools the air around them and this can maximise the productivity of PV panels.
Diagram showing how the output from PV panels changes according to the ambient temperature.
Image credit to Kare Lohse writing on Quora.com
Photovoltaic panels are far more efficient when ambient temperatures are below 30 degrees celsius. Logically, therefore, by surrounding PV panels with actively transpiring plants, they will be more productive. Surely it’s better to harness the combined power of plants and PV panels on our rooftops rather than use agricultural land that would be better utilised for food production?
The team at Bridgman and Bridgman installing a biosolar green roof atop a childrens’ hospice
Designing and Specifying Green Roofs For Energy Saving
Designing and specifying a living green roof that can help reduce energy usage involves a collaboration of several skills sets. Fortunately, the team here at GRO has access to the expertise you need to bring your project to life.
Start by downloading the GRO green roof code. It has been written by a collaboration of experts in order to help architects, designers, planners and developers to maximise the benefits of green roofing. In this document, you’ll find all of the information you need in order to understand the principals of green roofing.
Armed with the relevant knowledge, you can contact the right green roof designer, specifier or installer for your project. Read our blog on choosing a green roof company for guidance on who to contact at each stage of the project.