You’ve doubtless seen them on programs like Grand Designs but have you ever wondered how they’re made. Here’s how to make a living green roof of your very own.
Hints for Making a Living Green Roof
In this article we’re going to be looking at light weight sedum green roofs. These are the ones you often see on TV. They’re easy to install, simple look after and don’t need a lot of fuss. Sedums are by no means the only plants that like living on green roofs. However if you’re a newby, or if your building hasn’t been specifically designed to support a living roof, Sedum is a good choice for you.
First select your building carefully
You can’t just plonk a layer of soil and plants onto a roof and expect everything to be wonderful. The plants must be happy with the conditions they’re growing in. More importantly, the building must be able to take the weight.
If you want to grow a sedum green roof, choose a building that gets lots of sunshine. If the roof is in the shade for more than half a day, sedum plants won’t survive. They need lots of light.
Steep slopes make green roofing into a real challenge. A slope of over 20 degrees isn’t at all practical. For a start, it will be difficult to anchor the plants and not have them slump and slide off. Also rainwater will run off before the plants have a chance to drink it. A steep slope might look good to start with, but trust me, in 6 months or a year you’ll wish you never thought of it.
Slopes between 10 and 20 degrees show the plants off nicely. You can see them from the ground and the visual effect is great. However, you will need to irrigate them in dry weather because just like super-steep slopes, rainwater tends to runoff before the plants can benefit from it.
Slopes between 3 and 10 degrees are lovely, as are flat roofs. Those are what the Enviromat green roof system was designed for.
Weight bearing capacity
Each green roofing system is different in weight so consult the supplier and be sure of what you are buying. The Enviromat build up weighs around 42Kg per square metre when saturated BUT… you will need to walk on it to install the Enviromat and to maintain it. Your roof needs to be able to support 120Kg per square metre.
Prepare the roof
The green roof buildup isn’t a substitute for waterproofing. Before you start to add green roofing components to any building the roof must be watertight and the waterproofing in excellent condition.
Soak the roof with a hosepipe before ordering any green roofing materials. If a puddle sits on the roof for ages – you may have problems with the plants later on. Be confident that there are no pockets of poor drainage before you start work.
Next, add an edging. If your roof has an upstand you’re fine. Otherwise use timber to make your own upstand or buy a purpose-made green roof edging. This will keep everything neat, prevent the vegetation blankets becoming dry at the edges and it will stop wind uplift. If you’re making your own edgings, make sure that water can drain freely under or through them and please don’t put nails through your waterproofing.
Do you need a drainage layer?
For a flat roof – that is one with a slope of 3 degrees or less – you will need a layer of drainage matting. Sedums hate having wet feet and this is insurance against slow drainage. It’s very light. Doesn’t cost much and could save you a lot of heartache in a wet season.
Add the plants
Enviromat is easy to install. The plants are already growing in the mat. All you need to do is unroll it onto the prepared roof.
Be aware that it’s heavy and you might need help to lift it onto the roof. Another useful tip is to measure each piece and cut it to size before you put it on the roof. That way you reduce the risk of accidently puncturing the waterproofing.
This video takes you through the green roof installation process. Since this video was made, the water retention layer you see being installed has been stitched onto the Enviromat – cutting out one of the processes and saving you time.
Water well – but not too well
The plants need water to help them settle in. As soon as everything has been installed, water the plants to the point of runoff. They shouldn’t be allowed to dry out in the first few weeks so keep an eye on them – particularly in hot or windy weather. Bear in mind though, that lots of water will encourage weeds to grow so try to get the balance right.
The first few weeks
Keep an eye on watering. Keep drainage outlets clear and don’t allow any fallen leaves (or other debris) to sit on the roof for more than a few days at a time. Feed in spring or early summer. Most importantly – enjoy!