The issue of root penetration is known to most in the green roofing industry. The relatively complex world of roofing membrane compounds and organic chemistry has resulted in most green roof professionals defaulting to local instructional manuals, which default to FLL testing records. But just because a material is effective does not mean it is not harmful, e.g. lead in paint.
In 1997, Bayer Aktiengesellschaft was the assignee of Patent US 5672568 A titled “Root growth inhibitors for building materials comprising monohydric alcohol esters of mecoprop.” Root-resistant bitumen mixtures were soon marketed.
This past week the Berlin Senate’s Department for Urban Development and Environment and the Berlin State Office for Health and Social Affair published a series of recommendations for the prevention of environmental pollution due to the release of the herbicide Mecoprop from root-resistant bitumen membrane sheets.
The statement reads:
Investigations at the Swiss Federal Institute for Water Resource and Conservation (EAWAG) on behalf of the Swiss Federal Office for the Environment (FOEN) have shown that Mecoprop under natural weather exposure is released from the bitumen sheets and the precipitate is washed out.
Rain water contaminated with Mecoprop can pollute combined sewers or surface waters. Due to the low rate of elimination in sewage treatment plants results in a particularly high risk potential. In a decentralized rainwater infiltration system there is a risk of soil and groundwater contamination. (Translated from the German)
The report goes on to make simple recommendations. The first says the use of bituminous membranes impregnated with Mecoprop should not be used unless absolutely necessary for structural reasons. Second, they should never be used in protected water areas.
Since the issuance of Patent US 5672568 A, there has been a series of scientific papers published reporting the leaching of biocides from bitumen waterproofing. They can be found here, here and here.
Green Roof Technology is against any use of herbicides in green roof construction or maintenance. For more information on how to protect your building against root penetration without the use of poisonous herbicides please contact our office.