One of the first people to buy the DIY Guide available on the site, Michael Thompson’s earth rammed Eco shed now has a developing green roof shed. Bought in august last year Michael used the guide to construct a living roof green roof on a rammed earth shed he constructed in his garden over the winter. He is using the shed as a focal point for courses on rammed earth.
Michael had never built a green roof before and like everything else at the Eco-shed it had to be achieved on a very tight budget! So instead of using a pond liner he decided to got hold of some regular builder’s plastic, saving about a thousand pounds on our 66m2 ’grand piano’ shaped roof.
The roof was topwith sub soil from a friend’s kitchen extension, which was going to be dumped! The soil was processed it using Sid the Soil Sifter before carrying it up onto the roof in 400 bucket loads, two at a time – all six tons of it. The resulting depth was three to four inches all over.
And then it rained…and Michael points out ‘
… to my despair I noticed the roof had sprung a couple of leaks. At first I assumed the builder’s plastic must’ve been damaged somehow, but after several days of fruitless searching for a tear or a puncture I realized I’d been barking up the wrong tree altogether. The leak was occurring because of the way I’d overlapped the plastic sheeting (the roof’s so wide that I couldn’t do it in one piece) – although I’d allowed well over one metre of overlap the rainwater was by capilliary action travelling up the 5 degree slope and finding its way through the plywood sheets into the shed below. My only option was to move three tons of soil from the lower half of the roof so I could peel back the geotextile layer to reveal the join. I then used some DPC Jointing Tape at a cost of £8.80 but the real cost was the ten days I had wasted by not sealing the joint in the first place! It only took five minutes to apply the tape – isn’t hindsight is a wonderful thing!
We’d had a quote to cover it with sedum matting which came to over £3k so we paid a visit to a local garden centre where we bought a couple of sedum ‘mother’ plants (Golden Acre and Alba). Bridget lovingly took around 400 soft cuttings that she started off in the greenhouse and as soon as they were big enough transplanted them out into a nursery bed where the plants proceeded to thrive. Six months later they were on the roof and flourishing! She has since gathered more sedum bits and bobs from various sources – including a neighbour’s gravel driveway… For a bit of variety and to attract a wider range of wildlife we also planted grass, wild flowers and most recently thyme – all of which are taking longer to get established and need more care but will hopefully prove to have been worth the effort by this time next year.
Quite a talking point are a couple of old horses skulls up there (each with a neat bullet hole in the top) that we salvaged whilst cleaning out a redundant cess pit in the garden which we now use for rainwater harvesting. Along with some gnarly decaying logs Bridget has used them to create a ‘skull-pture’ which will hopefully provide the perfect habitat for all sorts of mini beasts!’
You can’t skimp on the quality of the Waterproofing – building plastic is not a roofing material.
BBA certification and the FLL guidance should be the recommended standard for all roofs – commercial or domestic.
John Ruskin said; “It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little money — that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do.”
Would have been better to follow the guidelines set out by GRO as per the extracts below taken from livingroofs.org:-
Waterproofing:
The waterproofing system beneath any green roof MUST be root resistant in the long term preferably to the German FLL standards. If the waterproofing is not root resistant then the green roof system must include a root barrier. The installation of the waterproofing and its detailing to perimeters, outlets, protrusions through the roof etc., MUST take into account the depth of the green roof build up. The waterproofing should always be 150mm above soil level at internal upstands and protrusions, and at least 50mm at external perimeters. The waterproofing system must be leak tested and certified as such IMMEDIATELY before the installation of the green roof.
Green Roof System:
No matter what species of plants are specified, for them to flourish the green roof system MUST provide them with:
◦Moisture
◦Drainage
◦Aeration to the plants root systems
◦Nutrients
To achieve this, a successful system must basically replicate nature but within a very compressed build up. The build up should ideally consist of:
◦Moisture retention/protection layer
◦Drainage layer
◦Filter layer
◦Manufactured/Recycled Growing medium
◦Appropriate components i.e. outlet inspection chambers etc. The type, size, and design of each layer will depend on the proposed vegetation; as will the need or otherwise for irrigation
◦In the absence of a British Standard, green roof systems should conform to the German FLL standards. This standard is generally recognised as the benchmark for green roof quality, certainly within Europe