The first time I saw a living roof, I wanted one. A meadow on the top of your house? Who wouldn’t want that? I discussed with friends how I’d grow fruit up there, and imagined myself laying in the lush green grass plucking strawberries. I forgot of course I was living on Turkey’s Mediterranean where it doesn’t rain for five months a year. Green roofs are perfect for cool, wet climates. But for the hot and the dry?
Unfortunately, I’m a stubborn sort, notorious for paying zero attention to advice or practicalities. The benefit of such a character is that occasionally you come up with new ways of doing things. My living/dead roof is one of them.
My roof is constructed the same way as a conventional living roof, with one small adjustment. Half of the year it’s dead.
Before you do anything at all, make sure your joists are strong enough. Earth roofs are heavy, and depending on how much soil, water, plants and what type of membrane you’ve used, it could weigh anywhere between 100-250 kg/square metre. You can check these figures in more detail here.
Also make sure you have the correct incline, (mine is 10 cm from front to back on a roof about 7 metres diameter, and I’d say that’s perfect). If there’s no incline, the water can’t drain away leaving you with a pond sitting on your roof. If the incline is too steep, you may have erosion issues.
A living roof is constructed with the following layers:
1. Plywood or OSB nailed to your roof joists.
2. A layer of thick (I used 4mm) waterproof roofing membrane. This is often made of rubber or modified bitumen.
3. A root barrier (greenhouse plastic works fine here). You need the barrier to stop plant roots burrowing into the membrane.
4. A drainage layer. Gravel and pumice are the least expensive and most natural options. Pumice may be preferable, because it’s lighter. Alternatively, you could purchase a synthetic drainage layer, such as a dimple mat.
5. A layer of blankets stops the soil clogging up the gravel/pumice. This layer may not be necessary if you use a synthetic drainage layer which has a soil barrier within it.
6. Earth mixed with compost. If you are worried about the weight of your roof, consider adding perlite or coconut husks to lighten the load, as well. Alternatively, leave a space in the middle of the roof, like I did, so the weight is concentrated on the supporting walls.
7. Plants. What you want is quick spreading, short plants like grass. Succulents can also work well. What you don’t want is a tree.
You also need to frame the sides of the roof to stop the soil falling out. I used wood. You could also use mesh guttering.
I made my roof back in 2012. How happy I was when I planted my flowers and succulents. Three months later, I had lost my smile, and so had my roof. There is no rain for five months of the year where I live, and of course the top of a roof is blazing hot. Everything died. So I came up with another plan: the semi-dead roof.
In summer, I cover the soil in dry grass cut from my garden. I have learned it’s easy to shape the straw by spraying water over it. The straw effectively insulates the house from the furnace-like heat. When winter comes, the dry grass rots and seeds, creating a lovely green roof. The fresh green growth prevents the earth from eroding in the heavy rain, too.
There seem to be a lot of preconceptions about living roofs, most of which are wrong. Here’s some myths you may have heard.
1. Living roofs are hard to maintain. A living roof requires very little maintenance. The grass and earth protect the waterproof layers from sun damage, so the roof lasts indefinitely. And you never have to paint it or replace tiles.
2. Living roofs will leak. As long as your waterproof membrane is laid correctly, and you have a decent root barrier, all is well. This is the driest roof I’ve ever lived beneath in all my life.
3. Expensive and tricky to make. I had no money and no building experience when I built my house. The living roof is probably the most inexpensive and easiest roofing option going, especially if you use a basic pumice/gravel and blanket system.
1. Flood prevention. Living roofs slow surface run-off and reduced flooding around your property.
2. Camouflage. I admit, my roof, with its huge straw flower, wouldn’t fool a spy plane. But most green roofs blend into their environment making them less obvious from the air.
3. Sound proofing. If you’ve ever lived under a tin roof, you know how noisy rain can be. Tiles are not much better. A living roof is quiet.
4. Fireproofing. Living roofs, when they’re wet and alive, are not going to burn. Obviously, the semi-dead option, comes with no such guarantee. Though don’t forget, there is 15-20 cm layer of earth under the straw to slow a fire down.
5. Wildlife habitat. This is my favourite part of the roof. It’s a haven for birds, lizards, squirrels, and other creatures.
Atulya K Bingham is an author and sustainable building addict. She lives semi off-grid in Turkey in her beloved earthbag house. Her days are spent growing her own food, experimenting with natural building techniques, and writing. For a limited time you can download her ebook Mud Mountain, The Secret Diary of an Accidental Off-Gridder for free!You can also find a free earthbag building PDF and other natural building tips from her website, The Mud Home. Read all of Atulya's MOTHER EARTH NEWS posts here.
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