The green house effect: Anna Pavord explores the possibility of planting on her shed roof

Does this count as a green roof, I wondered, looking at the corrugated asbestos that tops my hut? The hut is where I work; it's a wooden building with a room big enough to hold all my books, a bathroom, an overflow bedroom and a kitchen. It faces south, and both the south and the north face of the roof are mottled with orange lichen and spotted with firm humps of bright green moss. It's slightly greener on the north face than the south and the richest seams of moss run along the lines where the asbestos panels overlap. But will any green credentials the moss might give me be outweighed by the fact that they are sitting on asbestos? Asbestos is all right though, provided you leave it alone. It's when you try to remove it that it becomes dangerous, releasing its fibres.

Parallel to my hut there's another wooden building, a workshop and store, which has a corrugated tin toof. Nothing grows on that. It's smoother, more slippery, not so porous as the asbestos. It is more difficult for growing things to get a foothold. I'm cheered to learn from Ron Porley and Nick Hodgetts' book Mosses and Liverworts (Collins 25) that corrugated asbestos roofs - they have a special section on them - "provide a highly calcareous habitat, mimicking natural limestone, and may support a variety of species" including my green pincushions, Syntrichia ruralis. Hooray! I have a habitat, not a hazard.

Thatch is good for mosses too, though not so good as it once was. Thatched roofs tend to be replaced wholesale now, not patched up bit by bit, as they used to be. Mosses get chucked out just as they are really beginning to settle in. Fire retardants don't help. Nor does the use of chicken wire on thatch to stop birds burrowing into it. Mosses hate the zinc that gradually leaches out from galvanised wire. Only the orangey-red moss Bryum pallescens can tolerate it. It's the one you sometimes see colonising the ground under motorway crash barriers.

But I don't think that Nigel Dunnett, the Sheffield-based King of the Green Roof, would be impressed by our mosses. His concept of a green roof is a much more complicated construct, with proper load-bearing beams underneath and what the green roofers call "substrates" on top supporting a complex, self-sustaining colony of plants to trap rainwater, provide a habitat for insects and invertebrates and a pleasant view for those fortunate enough to look down on it.

A green roof, though, does not need such serious underpinning as a full-blown roof garden, where you want to grow trees and shrubs and pick your own veg. For that, you need a load bearing of at least 200kg per square metre. Covering the roof of a garden shed with a mat of sedums is a less complicated affair. The loading goes down to 70-80kg per square metre because you only need 5-10cm of substrate under your plants. The sedum mats are sold like strips of carpet, a mixture of low-growing types such as S. album, S. kamtschaticum, the vigorous evergreen S. spurium and S. rupestre (now naturalised in Britain). The substrate won't be plain earth - it's too heavy - but can be made up from recycled materials such as crushed breezeblocks, bricks and tiles, expanded clay granules or lightweight materials such as perlite and vermiculite. Typically, there'll also be compost in the mix, but not usually more than 10-20 per cent of the whole.

The simplest thing to do is to buy the whole concept off the shelf; you can do that through Taylors Garden Buildings, Ashwellthorpe Industrial Estate, Norwich NR16 1ER. They make wooden sheds on site at Norwich, with roofs ready to take mats of sedum, which they can supply and fix. A typical sized shed (8ft x 6ft) costs 387; you'll pay another 277.34 to get the green roof in place. Delivery is extra. A bigger shed (12ft x 10ft) costs 1,217 plus 550 for the roof. For more information call 01508 489260 or visit www.taylorsgarden buildings.co.uk. If you just want the sedum matting, then look for Enviromat at www.enviromat.co.uk or call 01842 828266.

Nigel Dunnett customised his own shed, supporting the green roof on 4in x 4in posts sunk into the ground a few feet from its corners. For extra strength, the posts were braced to the shed structure. He draped a heavy duty pond liner over the sloping roof (it must be root-proof as well as waterproof) and rested a grid framework of wood on top of the liner, to make 10 separate compartments, each the same size. separate council tax for it.

Discover more property articles at Homes and Property
Arts and Entertainment
Lou Reed distorted the truth about his upbringing, and since his death in 2013, biographers and memoirists have added to the myths
musicThe truth about Lou Reed's upbringing beyond the biographers' and memoirists' myths
News
people
News
Ed Miliband received a warm welcome in Chester
election 2015
Life and Style
Apple CEO Tim Cook announces the Apple Watch during an Apple special even
fashionIs the iWatch for you? Well, it depends if you want for the fitness tech, or the style
Property search
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Project Implementation Executive

£18000 - £23000 per annum: Recruitment Genius: They work with major vehicle ma...

Recruitment Genius: Chiropractic Assistant

£16500 per annum: Recruitment Genius: A Chiropractic Assistant is needed in a ...

Recruitment Genius: Digital Account Executive - Midlands

£18000 - £26000 per annum: Recruitment Genius: They work with major vehicle ma...

Recruitment Genius: Web Developer

£28000 - £30000 per annum: Recruitment Genius: This company provides coaching ...

Day In a Page

NHS struggling to monitor the safety and efficacy of its services outsourced to private providers

Who's monitoring the outsourced NHS services?

A report finds that private firms are not being properly assessed for their quality of care
Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

The Tory MP said he did not want to stand again unless his party's manifesto ruled out a third runway. But he's doing so. Watch this space
How do Greek voters feel about Syriza's backtracking on its anti-austerity pledge?

How do Greeks feel about Syriza?

Five voters from different backgrounds tell us what they expect from Syriza's charismatic leader Alexis Tsipras
From Iraq to Libya and Syria: The wars that come back to haunt us

The wars that come back to haunt us

David Cameron should not escape blame for his role in conflicts that are still raging, argues Patrick Cockburn
Sam Baker and Lauren Laverne: Too busy to surf? Head to The Pool

Too busy to surf? Head to The Pool

A new website is trying to declutter the internet to help busy women. Holly Williams meets the founders
Heston Blumenthal to cook up a spice odyssey for British astronaut manning the International Space Station

UK's Major Tum to blast off on a spice odyssey

Nothing but the best for British astronaut as chef Heston Blumenthal cooks up his rations
John Harrison's 'longitude' clock sets new record - 300 years on

‘Longitude’ clock sets new record - 300 years on

Greenwich horologists celebrate as it keeps to within a second of real time over a 100-day test
Fears in the US of being outgunned in the vital propaganda wars by Russia, China - and even Isis - have prompted a rethink on overseas broadcasters

Let the propaganda wars begin - again

'Accurate, objective, comprehensive': that was Voice of America's creed, but now its masters want it to promote US policy, reports Rupert Cornwell
Why Japan's incredible long-distance runners will never win the London Marathon

Japan's incredible long-distance runners

Every year, Japanese long-distance runners post some of the world's fastest times – yet, come next weekend, not a single elite competitor from the country will be at the London Marathon
Why does Tom Drury remain the greatest writer you've never heard of?

Tom Drury: The quiet American

His debut was considered one of the finest novels of the past 50 years, and he is every bit the equal of his contemporaries, Jonathan Franzen, Dave Eggers and David Foster Wallace
You should judge a person by how they peel a potato

You should judge a person by how they peel a potato

Dave Hax's domestic tips are reminiscent of George Orwell's tea routine. The world might need revolution, but we like to sweat the small stuff, says DJ Taylor
Beige is back: The drab car colours of the 1970s are proving popular again

Beige to the future

Flares and flounce are back on catwalks but a revival in ’70s car paintjobs was a stack-heeled step too far – until now
Bill Granger recipes: Our chef's dishes highlight the delicate essence of fresh cheeses

Bill Granger cooks with fresh cheeses

More delicate on the palate, milder, fresh cheeses can also be kinder to the waistline
Aston Villa vs Liverpool: 'This FA Cup run has been wonderful,' says veteran Shay Given

Shay Given: 'This FA Cup run has been wonderful'

The Villa keeper has been overlooked for a long time and has unhappy memories of the national stadium – but he is savouring his chance to play at Wembley
Timeless drama of Championship race in league of its own - Michael Calvin

Michael Calvin's Last Word

Timeless drama of Championship race in league of its own