Vegetative roofing systems have added a whole new level of complexity for the roofing contractor, even though the market for these products in the U.S. remains small. Part of the reason for this may be the disproportionate level of expertise required for a successful installation.
The following tips come from a highly respected industry expert with a strong background in single-ply and asphalt-based roofing. This is important because vegetative roofing is merely the aesthetic overburden for the “real” waterproofing system underneath.
1. Vegetative roof systems have requirements beyond a traditional low-slope installation that must be considered by the roofing contractor. The load bearing capacity of the existing roof is just one example.
2. Some vegetative roofs do not require long-term irrigation, but must be watered intermittently for the first few years after installation. How this will be accomplished may require the advice of a consultant who is familiar with the site conditions and location of the building.
3. Poor timing and construction sequencing can literally kill a project. Planting vegetation close to the onset of winter in northern climates is a risky proposition.
4. Vegetative-free zones will be required for access to equipment and base flashings. They will also be needed to meet most wind uplift and fire codes and standards.
5. Pre-bid, pre-job and job close-out meetings are even more important when considering a vegetative roof installation.
6. The property owner must be made aware of his or her responsibilities in the care and feeding of a vegetative roof.
7. The growing medium for a non-tray type vegetative roof requires more than just garden soil or “dirt” to root successfully.
8. Water testing of the roof prior to installation of the vegetative overburden should be a requirement, not an option.
9. Like it or not, vegetative roofs have special needs. Root barriers, water retention layers and irrigation systems are often required.
10. Roofing professionals need to remind the building team that everything is secondary to keeping water out of the building.
It is the responsibility of the roofing contractor to stand firm and be the advocate for the waterproofing integrity of the installation. While vegetative roofs can be aesthetically pleasing, they will not keep water out of the building.