Greenroofs  - Maintenance
 

Designing for Low Maintenance

Once a properly installed green roof is well established, its maintenance requirements are usually minimal.  However, of the two basic types of green roofing systems, extensive and intensive, the latter due to its increased weight and more intensive plantings tends to have higher maintenance requirements.  These maintenance requirements include inspection of the roof membrane, the most crucial element of a green roof, as well as routine inspection and maintenance (as needed) of the drainage layer flow paths. 

Typical extensive green roof material
(Source: Optima Planungs-Unterlage 9/97)

Typical intensive green roof material
(Source: Optima Planungs-Unterlage 9/97)

Regardless, for any kind of green roof initial watering and occasional fertilization are required until the plants have fully established themselves.  Supplemental irrigation in addition to natural precipitation at least once a week may be required in the first six months or so depending upon the type of roof membrane and water requirements of the planting material.  Plants for green rooftops must be selected with care if the roof is expected to stay more or less maintenance free. 

Extensive green roofs sometimes rely on a permanent drip tubing system which directly targets the root zone, and that can be put in place during the green roof installation process.  Once the plants are healthy and well established extensive green roofs no longer need to be irrigated except in cases of extreme drought.

Green roofing systems can vary in thickness from two to inches (5 to 18 centimeters). The term “extensive” is used to describe the lighter roofing systems, while the term “intensive” is used to describe the heavier roofing systems.  While a roof’s effectiveness in managing runoff generally increases with the thickness and weight of the roofing system, so do the maintenance requirements.¹  Key maintenance activities are described below.

Watering and Fertilizing

For any kind of green roof, initial watering and occasional fertilization are required until the plants have fully established themselves.  Supplemental irrigation in addition to natural precipitation at least once a week may be required in the first six months or so depending upon the type of roof membrane and water requirements of the planting material.  Extensive green roofs sometimes rely on a permanent drip tubing system which directly targets the root zone, and that can be put in place during the green roof installation process.  Once the plants are healthy and well established, extensive green roofs no longer need to be irrigated except in cases of extreme drought. Regular fertilization with a slow release fertilizer twice a year will prevent acidification of the thin soil layer.

Trimming and Weeding

If properly designed and established, a typical green roof does not need to be cut.  A thin soil layer does not support tall vertical growth, and the vegetation mat will tend to spread horizontally.¹  Occasional weeding of the rooftop, especially in the establishment phase, will remain necessary.

Inspection for Drainage

Because of the severe consequences of drainage backups, inspection of the drainage flow paths (or channels) is crucial, especially on extensive roofs.  If drainage routes become blocked, green roofs can cause some flat roofs to leak due to continuous contact with water or wet soil.  With insufficient drainage, the plants will also be susceptible to the impact of wide degrees of variability in the moisture content of the soil.  If too much water is present the soil will be adversely affected and the plants will drown or rot.⁴

Inspection for Leaks

Roofs can leak from drainage backups or root puncture or if the correct waterproofing membrane system, root barrier, and/or drainage layer are not selected.  Areas where occasional inspection for leaks is advisable include possible such as abutting vertical walls, roof vent pipes, outlets, air conditioning units, perimeter areas, etc.³  Most roofing companies, including those that install green roofs, will provide a warranty for the waterproofing integrity of the roof membrane(s) they have installed, including green roof membranes. 

Roof Replacement

Green roofs are generally more effective than conventional roofing systems in protecting the roof membrane.  This reduces regular maintenance costs and extends the life of the membrane itself. According to a study in Germany, a vegetated roof on average can be expected to prolong the service life of a conventional roof by at least 20 years (ZVG, 1996).

When the savings associated with deferred maintenance and reduced energy consumption are taken into account, vegetated rooftops are comparable in cost to conventional roofs.²

Once a properly installed green roof is well established, its maintenance requirements are usually minimal.  However, of the two basic types of green roofing systems, extensive and intensive, the latter--due to its increased weight and more intensive planting--tends to have higher maintenance requirements.  These maintenance requirements include inspection of the roof membrane, which is the most crucial element of a green roof, as well as routine inspection and maintenance (as needed) of the drainage layer flow paths. 

Initial and Long Term Maintenance Issues 

Green roofs are generally more effective than conventional roofing systems in protecting the roof membrane.  This reduces regular maintenance costs and extends the life of the membrane itself. According to a study in Germany, a vegetated roof on average can be expected to prolong the service life of a conventional roof by at least 20 years (ZVG, 1996).  When the savings associated with deferred maintenance and reduced energy consumption are taken into account, vegetated rooftops are comparable in cost to conventional roofs.²

In some cases green roof maintenance may involve re-waterproofing of the roof membrane.  However, if designed and installed properly, the waterproof characteristic of a green roof will be maintained for at least as long as a conventional roof.  Most roofing companies, including those that install green roofs, will provide a warranty for the waterproofing integrity of the roof membrane(s) they have installed, including green roof membranes.  Roofs can leak from drainage backups or root puncture or if the correct waterproofing membrane system, root barrier, and/or drainage layer are not selected.  Areas where occasional inspection for leaks is advisable include possible such as abutting vertical walls, roof vent pipes, outlets, air conditioning units, perimeter areas, etc.³

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