The only Sedum that might be considered invasive is Sedum sarmentosum also known as Star Sedum, Gold Moss, Stringy Stonecrop, or Graveyard Moss. It has green spearhead-shaped leaves, lemon yellow flowers, and long tendrils and is not recommended.
Leaks in the waterproofing layer are less likely when it is protected from the elements by a green roof. If a leak does occur, it can readily be located through new electronic technology which can rapidly and accurately pinpoint even minute holes. These systems are more reliable than the older testing method and can even be used on steeply-sloped surfaces. Repairs to the waterproofing are quick, and disturbance of the green roof is minimal.
Green roofs can be designed in conjunction with solar panels and in combination with other ‘low-impact’ development measures, such as infiltration beds, rain gardens, bio-retention systems, cisterns and rain barrels.
Generally, green roof systems are not deep enough for growing vegetables and the tools of traditional gardening would damage the green roof and the underlying waterproofing. However, incorporating container gardens or modular elements can accommodate an owner’s horticultural or agricultural desires.
Reducing the use of virgin materials is an important goal if the green roof industry is to be sustainable in the long run.
It is always advisable to contact a Structural Engineer, however if you have discussed the design with Building Control and they are satisfied that the nature of the work does not require additional strengthening it is your choice whether to ask structural engineer.
It is always advisable to contact your local planning department and explain what you are aiming to do, especially if it is on a permanent structure such as an office, dwelling or garage. They will advise you on what your next steps should be, they will also ask you to speak to Building Control who will be interested in the technical nature of the installation i.e. building loading etc.
There are several methods for starting green roof plantings. From April through October, Sedums may be established from fresh cuttings. Broadcast on the growing media, these cuttings will quickly form roots and affix themselves. Alternatively, Sedums may be started in May-June or September-October from 72-cell plugs, planted a foot apart. Perennials can be seeded, except during the summer months. A bio-or photo-degradable wind barrier fabric or hydro mulch is required while the plants are being established.
Roofs contribute to a greener urban environment and quality of life for communities in high density areas.
Research from around the world indicates that Green Roofs reduce annual run-off roofs by at least 50% and more usually by 60-70%, contributing to urban drainage and flood alleviation schemes. Moreover, the rate of release following heavy rainfall is slowed, reducing the problems associated with storm surges. With an increasing need for developments to have limited water run off the Environment Agency now highlights the use of Green Roofs in their May 2003 publication ‘Sustainable Drainage Systems’ and introduction.
New developments lead to a loss of habitats. Green Roofs can contribute to biodiversity and address local biodiversity action plans. In particular they have been to favour many rare invertebrates found on brown field sites, as well as ground nesting birds such as skylarks.
Green Roofs reduce the temperature inside the building they are on during increasingly hot summer months. The UK currently spend more money (uses more energy) cooling buildings than heating them in winter. Green Roofs reduce the need for air conditioning in the summer and as a result reduce CO2 emissions and keep the building cool.
One of most important benefits of green roofs is protection for the underlying waterproofing membrane and can be expected to double or triple the life of the underlying conventional roof by protecting from human activity and wind-blown debris; shielding from UV radiation; and buffering temperature extremes, thereby minimizing damage from daily expansion and contraction.
The ‘conventional’ approach to green roof design focuses on covering 100% of the waterproofing materials. In particular, conventional green roof detailing focuses on covering and protecting the most vulnerable parts of the roofing system: its flashings, penetrations, terminations and drains. One example is the use of enclosed drain access chambers to protect drains and scuppers and to eliminate the potential for clogging by blowing trash or vegetation. Green roofs, provide 100% protection by incorporating vegetated or stone margins, drain access chambers, etc.
Generally, a green roof that is planted correctly will reach maturity in two growing seasons, or less. Occasionally, reduced sun or rain may slow the process. If more rapid maturity is desired, pre-grown Sedum mats, can be used.
Cost per square foot depends on many factors: the size and slope of the roof, depth and complexity of the system, height and accessibility from the ground, cost of labour, and need for specialised elements, such as drains, railings, pavers, slope stabilization measures, etc.
Green roofs vary greatly in weight, depending on their depth and the materials used. The important measurement is ‘wet’ weight — fully-saturated fabrics and plants. Weights are about 60-150kg square metre. Any calculations must take into account the weight of water held in the soil and any snow loading.
The maximum slope recommended for conventional green roofs is 30 degrees, pitch. A variety of methods utilizing meshes, slope stabilization panels, cribbing, or battens can be used to secure the green roof and prevent media shifting and erosion.
Roofs with pitches greater than 30 degrees can be greened; however, special techniques are required.
Green roofs have been built most widely in temperate climates, but special techniques allow them to thrive in semi-arid, tropical, and even windy coastal areas and have been installed from hot, moist to the cold, windy locations.
Plant roots bind the layers of media and fabrics to create a unified cover, and the plants themselves create enough surface wind turbulence to foil potential uplift. If your green roof will be located in an unusually high wind area, such as a high rise building or coastal area you may need to use appropriate ballasts which should withstand winds of up to 94 mph using concealed ballasts.
With thoughtful planning irrigation is rarely necessary. When irrigation is required, the water should be delivered deep under the surface—where the roots will seek it and it will not be lost to evaporation. Surface irrigation systems are wasteful and require more maintenance than subsurface irrigation methods.
