19 Feb Building A Garden Pergola With A Green Roof
We had the pleasure of adding a living green roof to one of our bespoke garden pergolas. Learn all about it in this blog.
For ages now I’ve been longing for the opportunity to add a living green roof to a garden building. And so when our client agreed to top her pergola with plants, I couldn’t wait to get started.
If you’re not familiar with green roofing, it’s an ancient method of insulating a building that goes back as far as the vikings. It’s been largely overlooked for hundreds of years but began to increase in popularity in the mid 20th Century. Today, green roofing is hailed as a valuable tool in the fight against climate change and biodiversity loss. So much so that it has become common practice on commercial buildings. I’m also hearing of more and more homeowners who are adding plants to flat roofed extensions, sheds, garden offices and even bin stores.
Leeds Skelton service station sports a fine example of a living green roof.
What Is A Green Roof?
In a nutshell, a green roof (or living roof) consists of a layer of living plants on top of a structure. There are several types of green roof including extensive green roofs, intensive green roofs, blue roofs and biosolar roofs. The green roof pergola we’ve built is classified an extensive green roof. Here’s why.
Extensive Green Roofs: Low maintenance, drought tolerant, and only accessed one or twice a year for essential tasks such as feeding and tidying. Compared to intensive green roofs they are relatively light weight.
Intensive Green Roofs: These are like roof gardens and are often used for leisure or for food production. A deep layer of growing medium supports a wide variety of plants. Intensive green roofs may also have landscaped features such as paths, patios and lawns.
Blue Roofs: Also known as blue green roofs, these are increasingly being used on developments in areas where there is a risk of flooding. Rainwater is collected from the roof and stored in large tanks before being used inside the building eg for flushing toilets, or released slowly back into the natural environment. This is a great way to manage the pressure on our already overworked drainage and sewerage systems.
BioSolar Roofs: These are green roofs, or green-blue roofs that also sport solar panels for generating electricity. PV panels are much less efficient in temperatures over 30 degrees celsius and as you can imagine ‘normal’ roofs get much hotter than that. Surrounding the panels with plants helps to keep the cool which means they work at maximum efficiency all year round.
This sturdy hand made pergola with a living sedum roof was built by the Holland Landscapes team. Once the sedum plants have settled in, this will look amazing from the first floor of the property.
Why Is Green Roofing Important?
Plants play a vital role in the cycle of life, and the more of them we can fit into our gardens the better for everyone. But, in many modern gardens, plants are squeezed out by the hard landscaping features that are an important part of our lifestyles. Popping a green roof on top of a garden structure such as a pergola, shed, bin store or summerhouse allows us to have the best of both worlds. But did you know that green roofs do an awful more than just look pretty?
- Insulation – that layer of growing material and plants keeps the cold at bay in winter and helps cool the building in summer. Which is probably why the Vikings liked them so much.
- Protects the waterproofing. Waterproofing cracks when it is subjected to temperature changes. A green roof will protect against that meaning that the waterproofing lasts longer and less of it gets sent to landfill.
- Creates wildlife habitat: That undisturbed area of planting on top of your building can provide food, shelter and resting places for all kinds of creatures.
- Absorbs rainwater: Up to 80% of the water that falls onto a living roof can be retained. It will drain off slowly meaning that less water floods into the sewerage system during heavy rainfall.
- Helps a building blend into its surroundings. Your garden office or pergola will be much easier on the eye. Especially when viewed from above.
The top of our bespoke made green roof pergola.
What Can You Grow On A Green Roof?
The choice of plants depends on the depth of growing medium that your building can support, the microclimate on the roof and the amount of maintenance you want to do every year.
Our client’s pergola has a sedum roof. It was created using sedum matting which is effectively a carpet of living plants that is unrolled onto the roof and anchored in place. Alternatives could include wild flowers, herbs, spring flowering bulbs, alpine strawberries, heathers – the list is endless.
Can You Put A Green Roof On An Existing Building?
You can retrofit a green roof but only if the building is robust and well waterproofed. For a lightweight sedum roof like the one on our pergola, the building needs to be able to support at least 150Kg per square metre. A wildflower roof needs more growing medium and can weigh in excess of 250Kg per square metre.
Be careful with slopes too. It’s important to have a slight fall so that excess water can drain away but if the roof is too steep, rainwater will run off before the plants benefit from it. Plus – you will need to devise a way to stop the green roof build up from slipping or slumping.
Our pergola was purpose built with a very gently sloping roof which was supported by a very sturdy structure. We added a timber fascia to prevent the wind lifting the sedum matting and to stop the plants drying out. We also incorporated drainage so that excess water can escape easily. Sedum plants hate wet environments.
Would You Like A Green Roof In Your Garden?
Talk to the team at Holland Landscapes for help to build a garden building with a living roof. Or visit the Green Roof Organisation website to download their free guide to specifying and building living roofs.
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