green roofs

building the green roof

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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.

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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!)

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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.

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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.

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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.

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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.

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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.

project green roof

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It’s been pretty quiet in the garden over the last couple of weeks, mainly just just keeping on top of the growth with all the rain followed by sun, followed by rain, followed by sun…. The veg patch is a mass of things to eat – radishes, peas, purple broccoli and rhubarb, and the red currants, blackcurrants. gooseberries and strawberries (including some lovely wild ones) are all ripening fast.

A week or so ago we added some rigging and a balcony to the ‘pirate ship’ using one of the crates we bought off eBay for £10:

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I’ve been intending to add a green roof too, so now seems a good time to start. A lot has been written about the benefits of green roofs, and we need more of them. They are a great way of replacing some of the green spaces we lose each day through building, deforestation and pollution, to name a few causes. There are lots of websites showing you how to do simple ones, have a go! Start on your bird table if you like, or go straight to the shed. http://www.bbc.co.uk/gardening/basics/techniques/gardenstructure_greenroof1.shtml

Green walls are an option too – maybe not as grand as this one at the Rubens Hotel, London: http://www.theguardian.com/environment/picture/2013/aug/21/london-largest-living-wall-big-picture but you can buy pockets to go on walls at home: http://www.woollypocket.co.uk

I should say at this point that I’m making a green roof on a garden structure, which is a lot different to building a green roof on your house! Get an expert in if you’re considering doing one on your house, you don’t want it collapsing. Green roofs can get very heavy, especially when it rains, and a structural engineer will advise you on specific loads for a house. Even for a garden roof there are things to consider:

  • Is the structure strong enough to support it?
  • Will you need to reinforce it?
  • Will the plants get too much/too little water?
  • Is the soil likely to slip off when it’s wet?
  • What sort of plants do you want/have access to?
  • How can you stop the wood rotting or roots penetrating?

This is our roof as it stands:

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As you can see, it bows a bit at the front, so I’m going to reinforce it with some metal angle bars. I’ll use arris rail to create a ‘cradle’ (with drainage at the back), then put a liner down for insulation/protection against the existing asphalt, with a pond liner on top. The growing medium will be leca mixed with compost, keeping it light and suitable for sedum, which I’ll plant on top. Sedum are pretty robust, come in lots of different colours, flower at different times, and we have lots in the garden already that I can split, keeping the cost down. Here’s the plan, you can download it if you like:

Green roof plan

Green roof plan

We’re just waiting for the materials to come, so I’ll post again when it’s being built…