A conversation with the designer

Yesterday I had the chance to bend the ear of Peter Philippi, the designer of the Alice Paul and Kemp Hall green roofs. Peter Philippi of Green Roof Service discussed how the design of Kemp Hall’s green roof is different from the Alice Paul design. Kemp Hall green roof will be an extensive and semi-intensive green roof.

Extensive green roofs, like Alice Paul and the majority of Kemp Hall, usually include a thin layer of soil media and a vegetative cover over a synthetic membrane that will protect the roof. The vegetation needs to be adapted to moisture and drought and because of the media’s depth, it will not include shrubs and trees. Intensive roofs usually include a fairly thick growing media of a foot or more and may contain trees and shrubs.

Kemp Hall will feature semi-intensive sections with a layer of growing media eight to ten inches thick planted with grasses and perennials throughout the lowest level of the five-level roof. This area will be viewed from a third floor lobby and several dorm rooms in Kemp Hall. Tour participants will also be able to view this part of the roof from a paver area accessible through the small door access point to the roof.

I questioned Peter about his favorite species to plant on green roofs. He recommended Dianthus carthusianorum and the grass, Calamagrostis xacutiflora ‘Karl Foerster’ (credit bonthrone). He described them as his favorites because the Dianthus blooms with attractive flower heads and Calamagrostis displays handsome grass seedheads which play beautifully in the wind. These plants add a different texture and dimension to sedum varieties covering the majority of the roof.

Both these plants are also featured on the Alice Paul green roof and are favorites of mine. When I must choose an image of the roof to distribute to the press, I always choose the image with Dianthus blooming and the grass reaching for the sky in the background.