Problems With Green Roofs

Roof Capacity Overload

• If the roof has not been properly assessed for the weight that it can bear, or if that weight limit is not heeded, the roof can be damaged or even collapse from the combined weight of plants, soil holding water, drainage systems and other green roof construction materials. A certified structural architect should be consulted before the construction of a green roof, and the weight of all materials to be used plus weight from water considered before a green roof is installed.

Improper Drainage and Leaks

• Drainage from a green roof is crucial. If excess water is not properly directed off the roof, or if the system is improperly designed and becomes clogged, this adds far more weight to the green roof than it is supposed to hold. The excess water can become stagnant or drown the plant roots. Leaks in a green roof arise from poor design or inadequate root barriers. Root barriers are specific materials designed to inhibit the slow but inexorable dig of roots, which can break apart even sturdy roof materials in search of nutrients. Leaks also occur from holes or improper installation of the waterproof lining layer of a green roof.

Improper Plant Species

• Plants must be chosen with regard to the amount of care they need and that the owner can provide, their mature size and the wind conditions on the roof. Plants that are oversized may suffer in shallow green roof soils and become uprooted in high winds if there is no shelter. Plants must be able to bear the harsh climates often found on roofs, as they're more exposed to temperature and other weather extremes.

Considerations

• Most problems with green roofs are foreseeable and can be avoided with careful planning, consultation with green roof specialists and by ensuring that the green roof project is executed properly. There are several books, professionals and websites with green roof advice and guidance to help prevent problems with green roofs down the line.