County Building Green Roof Measures its Own Effectiveness

You may think of the Allegheny County Office Building, 452 Forbes Ave., Pittsburgh, as the place to go if you have a question about your property assessment.

But this historic building is also the site of a beautiful, functional and productive green roof, designed with the help of Pashek Associates. Green roofs benefit the local environment by reducing storm water runoff; keeping buildings warmer in winter and cooler in summer; evening out daily temperature swings; and helping to mitigate the heat island effect.

The County Office Building green roof, completed in 2010, is now growing into its role as a powerful tool for protecting the environment.

A network of sensors embedded in the soils monitor performance of this roof compared with a conventional “control” roof. The sensors measure roof temperature, soil moisture, water flow and water retention, with data collected every 15 minutes. Over time, this information will demonstrate the valuable role that green roofs can play in easing some of the damaging effects that development has on our environment.

Here is an example of the data that can be seen by visiting the monitoring website. This example compares temperatures in a one-month period on the control roof (top line) with temperatures recorded by two sensors on the green roof (bottom two lines).

The green roof includes four different types of growing conditions, and over time it will also be possible to learn through the monitoring system how each type performs compared with the others. They are:

1. Intensive – 8 to 12 inches of soil and growing shrubs and plants needing the soil depth.
2. Semi-intensive - 6 inches of soil and able to grow plants and shrubs.
3. Roll out Mat – set on 4 inches of soil, this pre-grown sedum mat provides instant cover.
4. Tray system – easy to install, pre-grown sedum and lightweight.