rooftop growing
Getting Started
Despite some manageable drawbacks , any nearly flat roof can be gardened . Also , there ’ s no best way to go about it . Each good solution is unique to your goals and the local situation . Whatever you decide to do , start with a budget . Then check building codes and local laws . Seek out those who have roof gardens near you for valuable advice and a chance to see what ’ s working . Read a lot . The best book out there is The Rooftop Growing Guide by Annie Novak . Get clear about what you want to achieve . Scale drawings provide a reality check and help others envision your ideas . There are a few things to focus on , however :
Ownership
If you don ’ t own the rooftop , have interested parties — owners , managers , and tenants — buy in . Including an outdoor relaxing area gives non-gardeners a stake in the project . Talk about your plans . Present your drawings and budgets . Offer assurances or signed agreements .
Weight Issues
A damaged building really kills your budget . Have a knowledgeable person check the structure beneath the roof . The lowest-risk area to add weight to is near perimeter walls . There , forces transfer straight down through walls with high compression strength . Check engineering tables for density of different materials . Soil is heavy . A 20-square-foot bed with growing medium 10 inches deep weighs between 1,300 and 1,800 pounds . To lighten , loosen , and increase water-holding of any grow mix , add up to half perlite or vermiculite . Study your mix options to select the right one for your project .
Waterproofing
The essential waterproof layer is also a plant barrier , protecting the structure from determined roots . Heavy-duty black pond liner and thermoplastic membrane products are two options . Use quality materials . Compromises will cost you . Also , a soft layer of acoustic insulation placed below it reduces damage from boots and tools .
Good Drainage Without Soil Loss
Whether planting all over or in grow boxes , you need to drain off rain , melt , and irrigation water . However , you don ’ t want to lose your soil or growing media . A raised rim at the upper edge and sides of your sloped rooftop garden prevents soil loss . The lower edge is trickier . To contain the soil on the bottom edge , some simple designs include a built up or spread out barrier of gravel or rocks . We used commercialgrade landscape cloth over the rim of treated lumber . This creates an edge-strainer that allows excess water to escape under the soil-holding rim of treated lumber .
Irrigation
If you want to go automated , go for buried drip systems , perforated hoses , or , for the ambitious , a computercontrolled precision method . Overhead spray systems , on the other hand , are inefficient at getting water to roots . While hand watering isn ’ t automated , it has the advantage of allowing you the time to observe your plants more closely so you catch problems early .
You ’ ve talked with people who know , checked out a number of books , websites , and other resources for design ideas . You ’ ve done all the prep and preliminaries to get the roof ready , have your plans drawn and approved , borrowed a truck , and have a crane or friends lined up to carry stuff . You ’ ve chosen the grow mix and gotten starter plants and seeds . Now , it ’ s time for action .
Have fun !
“ Whether planting all over or in grow boxes , you need to drain off rain , melt , and irrigation water .”
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