The completed storage space. Photo by Jonathan Leach
Oxford, United Kingdom • Owner and designer: Liz Hodgson • Context. Bicycle shed in residential front garden • Size: 1.3 × 2.1 m (4.3 7 ft) • Main purpose of green roof: Aesthetic, horticulture, stormwater management
WHILE LIVING in Tours, France, in the 1970s, Liz had seen the Troglodyte houses along the cliffs in the Loire Valley, with chimneys coming up through the grass above. She had also seen a green roof in a front garden on the route to her allotment, and this gave her the idea of trying one of her own.
The bicycle shed is sited along the sidewalk of Liz’s small terraced house. It is a very prominent feature in the front garden of the property and quite visible to passers-by. Liz wanted to improve the look of the shed and to create a different growing space for another range of plants in her garden. The green roof was also intended to soak up a little rainwater in a street where front gardens were becoming increasingly paved over, shedding rainwater runoff into a road with inadequate drains.
Liz had seen a turf roof at the Centre for Alternative Technology at Machynlleth in Wales in 1997 and had been inspired by it. She obtained the plans of the turf roof she had seen at the centre. The dimensions were determined by the existing shed and the materials at hand. Liz chose the plants herself, designing the planting during the execution, not in advance, and then planted new ones that made sense over the next few years.
In the summer, gaps fill in with Dianthus, annual Linaria, and Sisyrinchium. Photo by Jonathan Leach
The green roof is very visible to passers-by. In spring, blue grape hyacinths (Muscari) are prominent, together with emerging irises, sempervivums, and sedums. Photo by Liz Hodgson
During a kitchen remodelling in 2006, the builder needed to demolish the bicycle shed temporarily. It was put back retrofitted with the green roof space ready for filling and planting, using leftover materials from the construction.
The builder worked from the Centre for Alternative Technology plans, putting heavy-duty plastic sheeting over the original roof and creating the frame from leftover rafter lengths. The shed had turned out to be very robust and capable of supporting plenty of additional weight. The substrate comprises garden soil left over from reshaping the back garden plus two sacks of John Innes no. 3 (a gritty, free-draining soil-based horticultural compost), with gravel underneath, plus a layer of horticultural grit on top which is renewed periodically.
The plants used were the annual Linaria maroccana ‘Fairy Bouquet’ and the perennials Achillea millefolium, Anthemis tinctoria, Arenaria balearica, Campanula poscharskyana, Delosperma congestum, Geranium dalmaticum, Helianthemum nummularium ‘Golden Queen’, Phlox douglasii ‘Boothman’s Variety’, Saxifraga callosa, seven Sedum cultivars, three Sempervivum cultivars including ‘Black Knight’, and Sisyrinchium ‘Californian Skies’. Bulbs included four species of Crocus, Iris reticulata ‘Gordon’, Iris danfordiae, Muscari, and Tulipa tarda. Plants which come in regularly as self-sowers are Cotoneaster horizontalis, Laburnum, violets, dandelions, and grasses.
Liz didn’t anticipate the pleasure the roof would give her, ‘The slowing down to look instead of dashing in and out of the house, the fun of watching people inspecting it. Passers-by take photos, hold up little children to look, especially at crocus time, and stop me to say how they love it.’
The roof is simply constructed over the bicycle shed. Photo by Liz Hodgson
After three and a half years, the green roof is much more of a horticultural success than Liz ever imagined. It’s a manageable size, which is great for Liz as she has health issues that prevent her from working on a large scale, and the roof is easily weeded in passing. Although she enjoys rising to the challenge of the shallow substrate and exposed position, problems consist of worrying about whether plants will survive and keeping others under control. Successes are manifold and various, especially over-doing the crocuses, irises, and muscari, with spectacular results. Working out that Linaria would thrive and self seed was very satisfying.
The roof reminds Liz of the hours spent with her grandfather in his potting shed fiddling about with alpines and enjoying tiny plants. ‘The geranium was rescued from his last garden in 1979 and has survived ever since, and the phlox is named for the nurseryman Stuart Boothman, who taught him about alpines. The grape hyacinths remind me of the big garden at my uncle’s farm, where they grew under the old fruit trees. So there’s nostalgia and family history all bound up with something quite trendy!’
If Liz were to start again, she might have made the substrate deeper to allow for a wider range of plants, but the challenge of how shallow it is has become part of the fun. It has not experienced a really hot summer yet, so that may not last. She would not have planted Campanula poscharskyana, as it is running halfway across the roof already. This species would be ideal for a roof where no varied planting or aftercare is planned or only in combination with bulbs and other rampant plants.
NIGEL’S NOTES
Liz nicely describes the everyday delight and fascination that having a green roof can produce. But the project also highlights an important point: not only does a green roof provide benefits to the owner, but it also gives pleasure to others. These may be people living nearby who overlook the roof, or, as in the case of Liz’s project, to people who pass by in the street.
Upperthorpe, Sheffield, United Kingdom • Owner and designer: Dan and Kate Cornwell • Context: Garden building and bicycle shed • Size: 2 m2 (22 sq ft) • Main purpose of green roof: Aesthetic, horticulture, biodiversity
DAN AND Kate have a very small urban garden in Sheffield and three young children. ‘I have a great interest in horticulture, but no space for plants in my garden,’ says Dan. The family needed a small storage area in the garden and this seemed a perfect opportunity for a low-maintenance garden that fitted in with their busy lifestyle. With the kitchen window overlooking the roof, this was something they could see up close every day. Dan says, ‘It was my chance to have my own two square metres of unspoiled, child-free garden to enjoy.’
The completed shelter. Photo by Dan Cornwell
Dan works for Green Estate Ltd. in Sheffield, a social enterprise that works with innovative landscape techniques, and one of their areas of work is as green roof contractors. Dan therefore had access to a lot of knowledge and personal experience of green roof design and installation. He planned and designed the roof himself by looking at other green roof constructions. Dan came up with the final approach through trial and error by testing out different ways of strengthening small garden sheds. He bought an inexpensive timber bicycle shed that could be easily modified, changed the roof from a double to single pitch, and used local inexpensive building materials.
The shed is internally strengthened with batons. Photo by Dan Cornwell
To alter the pitch and to strengthen the shed, Dan used 100 × 25 mm (4 × 1 in) joists to span the roof at the back and 50 × 25 mm (2 × 1 in) joists at the front. He used 18-mm (0.7-in) external-grade plywood for the roof deck. The interior was reinforced with 30 × 20 mm (1.25 × 0.75 in) batons fitted diagonally across the sides. Plastic sheeting was used for root and waterproofing on to the deck. On this 100 × 20 mm (4 × 0.75 in) boards were used as edges and made a frame to sit on top of the deck. This frame was then screwed from underneath. Inside the frame sat a commercial drainage board (ZinCo FD25) for water retention, with landscape fabric over the top. Green roof substrate was placed at a depth of 100 mm (4 in) and sown with Pictorial Meadows Green Roof seed mix (developed in association with The Green Roof Centre, University of Sheffield) with additional plug planting of herbs and bulbs as a later addition. Subsequently, Dan has added buckets full of substrate turned upside down on the roof to sow new plants into and create more diversity as required.
The green roof serves as a small garden right outside the window. Photo by Dan Cornwell
The roof is low maintenance. Dan says, ‘I really enjoy seeing the planting change through the seasons and watching the birds and insects visiting the flowers as I do the washing up. It was well worth the effort considering the enjoyment we get from it.’ Spring bulbs such as dwarf narcissus give a real seasonal highlight, and the family grow culinary herbs such as thyme, coriander, chives, and parsley. ‘The planting is quite diverse on the roof and very wild looking, which I really like,’ says Dan, ‘but Kate thinks it is quite scruffy and should be tidied up with more flowers.’
London, United Kingdom • Owner and designer: Joe Swift • Context. Bicycle shelter • Size: 4 × 1.2 m (13 × 4 ft) • Main purpose of green roof: Aesthetic, horticulture, biodiversity
JOE WANTED to have somewhere to keep his family’s bicycles, but space was very limited in his London front garden, with only a few metres from the front door of the house to the sidewalk and road. There was no room to put in any major structures. As a garden designer and a presenter of the United Kingdom’s main gardening television programme, Joe had a good amount of knowledge and experience of green roofs and was very enthusiastic about innovative ways to incorporate biodiversity into the built structures of a garden.
Outhouses, structures, and buildings in front of the house usually require planning permission in the United Kingdom. Joe’s solution was to conceal the bicycles from the street and to have them securely fixed by incorporating a lock-up area within a new wall along the front edge of the garden alongside the street. The wall was built in the traditional style, and it looks no different from any other townhouse front garden wall.
The completed storage space. Photo by Joe Swift
The area below where the bicycles would be was dug out to increase the depth available for the bicycles. Drainage was incorporated to allow water to runoff. The wall was built up, and as the roof deck purpose-fabricated galvanized metal trays were fixed into the wall, with a supporting middle leg. Drainage holes were drilled into the trays, and a lightweight polystyrene sheet was put in the base for drainage. The trays were then backfilled with regular horticultural compost, with added perlite to increase drainage.
From the front, the bicycle shelter is invisible. Photo by Joe Swift
Foxes immediately started digging up the trays every night, so Joe had to put some chicken wire over the top of the compost to put a stop to it. The bicycle shelter is in a shady, north-facing position and hardly gets any sun. Joe says, ‘I’m just seeing what turns up and leaving bits in that can cope so it fills out well.’ He sowed some shady wildflower seed, and he planted in some garden cast-offs such as Salvia nemerosa ‘Ostrfriesland’ and some pinks (Dianthus). He also I put in some sunflowers, which did flower even though the site is shady. ‘The red campion (Silene dioica) has gone a bit mad, but after flowering I’ll thin it out,’ says Joe. He also put in some annual and biennial seeds (cornflowers and verbascums) and will plant some bulbs in the autumn. The roof does get dry, so Joe waters it occasionally if things look desperate.
NIGEL’S NOTES
Joe’s structure is a very simple and clever low-tech solution for hiding away a storage area in a small space. The idea of setting a green roof into a boundary wall in this way can be modified and adapted using a wide range of materials.
