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Chapter 4

Greenroof

The green roof system reduces heating inside the home or building by up to 30-40% making it a natural air conditioner. Green roofs are found in 20% of the homes in Germany. Recently, the home made green roof system developed by John Wilson has been upgraded to include swale’s for water collection where we are starting to grow some herbs. 

Insulation

 The award winning Wilson Natural Home above uses a green roof to both cool in the summer but also to improve insulation levels for improved warmth in the winter. The six inches of soil and several layers of membranes significantly increase the insulation levels in the roof which is a major contributer to heat loss.

Environment

The use of green roofing replaces soil that is displaced during construction. The return of native plants to the construction site returns the health of the local environment. Green roofs have been proven to significantly reduce the heating effect typical of homes, buildings, cities and towns caused by their dark roofing materials that absorb and then radiate heat into the local environment.

Design Overview

The basic design and construction of a green roof can be quite simple and inexpensive. Given the additional loads that a green roof requires engineering will be required to ensure the correct level of support structure. The basic design of a green roof is as follows:

1. Plywood layer on top of roof trusses or joists (some slope is required for drainage, too much slope may be difficult to cultivate due to erosion).
2. Apply a synthetic rubber membrane on top of the plywood roofing structure. Up to this point you have basically created a common industrial roof.
3. In order to retain the soil the roof must provide a containing edge from four to eight inches high, also covered by synthetic rubber. Don't forget to leave some drainage scuppers.
4. Once the base roof water proofing system is in place the additional green roof components can be added when ready.
5. The first layer of the green roof is typically a foundation membrane (a dimpled "Delta" membrane or something similar that can catch and retain some water in the little cups.
6. Add a landscaping root barrier membrane. Apply the all membranes from bottom to top and ensure layers overlap with upper (higher) layers on top of lower layers. (The same way you shingle a house).
7. Around the drainage zones create a drainage area as you would around the foundations of a house, with gravel and drainage tubing.
8. Fill in with soil from four to six inches.
9. Use straw mats tucked under the soil to reduce erosion as the soil begins to grow plants in it.

Green Roof 101 Video

The video demonstrates the home made construction technique for a green roof that was built starting in 2001. Featured in the video is the voice of the award winning sustainable building architect Martin Liefhebber.  Both narrating and working on the rooftop over several years is John Wilson, the author of this book. Of particular interest is the quite substantial slope of the roof which is unusual for a green roof. Normally green roofs have only a very slight grade, just enough to allow for water drainage. In the case of the roof in the video, the roof is at an angle of approximately 20 degrees.

The video shows the techniques and materials as they were actually implemented over a three year period. All of the soil was moved from the delivery point at the base of the ramp up onto the roof using a wheel barrow piloted many thousands of times by, again, your’s truly, John Wilson. Of course, in the first few weeks there was a lot of cheerful help from Ian and Lynn Wilson (the authors parents) as well as the authors children Ian and Claire.

Now that you’ve seen how easy it is, make sure to incorporate some type of green roof into your next building construction or renovation.

Greenroof 101 Video

Greenroof Resources

Solar Village Open Source Greenroof 101

Greenroof 101 PDF Free Download

Greenroof 101 ePub Free Download

Environmental Design & Construction, Feature

Check out www.GreenRoofs.com for more information.