The Shed Roof Project – part 2

Several months ago we started work on the new Shed Roof, carted away the rubbish (too awful for words) and constructed a new roof surface that would be suitable as a base for a living roof – something just as beautiful but more controlled than the ivy that had previously been there. It was all very exciting and I could see exactly how I wanted it to look and then came to a bit of a halt because I couldn’t achieve the results I wanted with the materials I’d been given for the purpose.

plastic lattice

At the start of the project, I wanted to see exactly what we could do with recycled materials. I’d been given 6 square metres of plastic lattice usually used to contain stones in a driveway and the idea was that we would fill the lattice with a soil mix and then plant the gaps with drought tolerant plants, some of which I already had in the garden. But although I’m a keen gardener, I don’t have enough knowledge to be able to gamble with soil compositions and to know that the weight of the soil wasn’t going to be too heavy for the roof structure – even though Richard had made it very robust indeed. So after investigating soil compositions to find a mix that would have sufficient water retention, but still be lighter than topsoil, I decided to bin that idea. I just didn’t know enough for it to be practical.

weather tight

Back to the drawing board as it were. I had to admit that without specialist help – which I didn’t want to pay for – I wasn’t going to be able to use the recycled materials after all. Frustrating, but a decision had to be made because the roof was just sitting there, weather tight, but unfinished. So, after a few sessions online I came up with a solution that seemed practical and achievable – a two part process involving a base layer of highly absorbent board topped with a sedum wildflower turf.

green roof composition
sedum wildflower turf

The boards are a pulped fibre, containing plant food for slow release, which starts out a bit like Ryvita and ends up a bit like Weetabix, nicely plumped up with moisture and even better, it retains the moisture for months at a time. For my south facing roof, this is going to be the biggest challenge, giving the plants a steady supply of food and water. The sedum turf sits on top of the boards and over time the roots work their way into the fibrous composition and completely mesh with it, so that the two really become one the same way they would in a garden bed.

Because of this the roof surface has to be prepared without roofing felt, so Richard coated the plywood boards he used to make the roof with bitumen and then applied a polythene membrane much like a DPC membrane. This will inhibit the roots from growing into the roof material, protect the structure and be low in toxicity for the plants.

an established green roof

an established green roof

I asked lots of questions of the companies supplying both components – because even though it is the plants that will be visible, I wanted to make sure I was using something that I could manipulate easily when it arrived on site – I didn’t want to have to use a fitter to get the boards in place.

The boards can be cut with a sharp knife. They’re great at insulating the internal space and they actually increase the lifetime of the roof structure because of the protection from the elements. And because of the nutrients impregnated in the boards, the sedum covering gets more established over time. Even better, a green roof absorbs CO2 emissions, which is logical but never articulated, so replacing my shed roof has now become my little bit of sustainability. The local wildlife will have seeds to eat, the shed will be well insulated and I can use the space for my business, the roof will become a feature of my garden and the maintenance will be organic rather than toxic.

This weekend the boards arrive and next Tuesday the sedum turf makes its appearance. So excited.

To be continued…

Photographs taken from riefa green roofing solutions and sedum supply – with thanks

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