building the green roof
The green roof is up! It was a fairly straightforward process in the end. It cost about £40 in the end. I used leca, pond felt and liner and some arris rails and batons.
First things first, I checked the structure that I was putting the green roof on (if in doubt, consult an expert – it needs to be safe). Our posts were concreted in and the back half was well supported, but I added an arris rail on the front to give extra support (it bows a bit, but it’s solid. I jumped up and down to see if it was…you might want to find a safer way!)
I checked the drainage too, it needed to have a slope otherwise the water would sit on the roof, making it very heavy and potentially drowning the plants. The original roof was felt, held down with batons. The felt was in good condition, so I just moved the batons to the front and side edges, leaving the back for drainage.
I’d intended to use arris rail for this, but I thought this would make the planting area too deep and heavy. Instead I opted for 3x2cm baton. Sedum should work well at this depth, though you’d need to investigate depths for other plants.
Once the batons were in place I added pond felt (stapled to the batons) and pond liner. These are cheap to buy and are available in lots of sizes. I used more batons to secure the liner in place just by screwing them n top of the others.
For drainage at the rear of the roof I used small logs, held in place by a board screwed across the back of the structure. I used these for two reasons. Firstly, being uneven, the logs gave natural drainage holes, and secondly they will give homes to lots of creatures and fungi. They’re easily replaced if they rot.
Next, leca (expanded clay) was added, mixed with sand and compost. 60 litres gave me enough for 2.2mx1.2m at 2cm depth. Leca is light and well suited to sedums. I didn’t want a rich compost as it would be unsuitable for sedums and potentially very heavy. I added some more logs and rocks as bug homes then planted up with sedums taken from around my dad’s garden and my own. I faced the batons just to make it look nice from the front and sides.
So far the garden’s taking well. The sedums are all growing well and it seems to be draining as intended. I’ll post some photos as it progresses.