August 25, 2009

Letter to the Editor

Fire does not need to be an issue with green roofs

Re: Fire safety issue raised for green roofs, DCN July 13, 2009

Although I agree with the general sentiment of the comments, I do have a few issues with comments suggesting there isn’t one green roof that will pass the test and the vegetation will burn

The attached video is of some testing done on the LiveRoof system in 2007. It was done unofficially by a lab in Chicago which we cannot name as it was a developmental study. As you will note, the vegetation is scorched under the flame, but there is no fire spread, the modules and the growing media are untouched.

To us, this proves that fire spread does not need to be an issue on green roofs. There are those who want to impose minimum watering requirements to solve the issue. That could prove impractical and difficult to police. Instead minimum standards need to be set for the type and quality of growing media and the plant selection and mixtures on green roofs as well as the implementation of fire breaks on roofs that don’t meet these standards. An FLL standard growing mix is primarily mineral based with 6-10 per cent organic matter by dry weight. (FLL is the German Landscape Research, Development and Construction Society, an independent non-profit organization founded in 1975 by eight professional organizations for the improvement of environmental conditions through the advancement and dissemination of plant research and its planned applications.) Even when bone dry, it does not contain enough fuel to propagate a fire. This standard can easily be tested by the green roof media testing facility at Penn State University (the only accredited independent FLL lab in eastern North America.) As it stands, FLL standard mixes are the preferred growing media on green roofs because of longevity, lack of consolidation and oxidation and a good growing environment for the plants generally selected for extensive green roofs. FLL standard mixes have a track record of more than 30 years in Europe and well over 10 years in North America.

Plants likewise can be tested for fire propagation. Individual plants can be tested fully saturated, after 15 days of drought, after 30 days of drought etc. And the same can be done for mixtures of plants. In that process, succulents such as Sedums, Alliums, Sempervivum and similar plants will come out as the clear winners, where grasses and lush perennials will be the clear losers. That doesn’t mean that all extensive green roofs from here on in will only be succulents. There is no reason why grasses and perennials (fire propagators) cannot be integrated into mixtures of succulents (fire retarders) to come up with a successful green roof with minimal flame spread (quite possibly capable of passing ULC S107-03). However with the use of a non-combustible growing media, combustibility of the plants is much less of an issue, as the building envelope is protected below the growing medium.

Currently there is no testing protocol in place for fire testing to test green roof assemblies against and obtain the UL or ULC listing. As a green roof supplier in Ontario with a North America-wide affiliation we are waiting for test protocols to prove our point officially. We have no issue with the 10 minute open flame test as it stands.

Regards,

Kees Govers, BSc(Agr)

General Manager

Caradoc Green Roofs

Strathroy, Ontario

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