Building a Hitched Green Roof

Start With a Strong Base

• Regardless of whether a green roof is hitched or flat, it begins with a waterproof surface with sufficient load-bearing capacity. The waterproofing material must also be root resistant, since over time roots can seriously damage waterproofing materials and roof construction. There are more than 70 products on the market that will provide root protection to waterproofing material. Besides the roof itself, the upstands, perimeters, joints and roof edges must also be protected from potential roof damage.

Pitched Green Roofs Are Different

• Green roof systems for pitched roofs are substantially different than those on flat roofs. The root barrier that needs to be installed, for example, increases the risk of slippage. Consult a structural engineer to determine the design for shear barriers and the eaves to cope with the heavy load and the weight of snow in the winter.

High Slopes Increase Problems

• While it is technically possible to build a hitched roof with a 45 degree slope, most designers suggest 30 degrees is the optimal pitch for reasonable upkeep and maintenance. Even then, plastic grid elements must be added to protect the substrate from erosion and the selection of appropriate plants is of paramount importance. The most popular method of creating a hitched green roof includes using pre-cultivated vegetation mats to allow for rapid coverage. The plant Sedum is popular because it retains water admirably. Complicating the hitched green roof project is the need to incorporate an additional irrigation system for watering the plants during dry periods.

Consider Load-Bearing Capacity

• A key consideration when building a hitched green roof is calculating its load-bearing capacity. To do that, calculate the water-saturated weight of the green roof, including vegetation. A simple flat green roof system, for comparison's sake, weighs between 13 lbs. and 30 lbs. per square foot, depending on the thickness of the roof buildup. Also add heavy construction elements on the roof, like bushes, benches, air conditioners or even snow, into the calculation.