Not everyone is so lucky. Most rooftop gardeners will have to stay strictly within the weight limits of the building. If there are no such specifications, a structural engineer will have to be hired to determine the amount of weight the roof can support. In addition, the roofing contractor who installed the waterproof membrane that protects the building from water damage, has a specific set of requirements to ensure that the warranty provisions are not violated. The building management company may have this information available.
Landscape designers and related professionals will not undertake a project of any size without weight allowance information. The liability for damages can be enormous for everyone.
Having said all this, the weight of planters can be manipulated through various methods to lighten the load. Everything from lightweight planters to increasing drainage levels to manipulations of the soil mix. The general rule is to stay within 40 to 60 lbs per square foot. But this is just an average. Some buildings will specify a lesser weight amount. This includes the weight of the planter, the soil, and the plant. Some specifications calculate the amount of weight the entire roof can sustain, while others differentiate areas of the roof that can sustain heavier weights because of load bearing beams.
If you would like all the calculations to determine weights, please email me and I'll send them out to you.
Visit the website: http://www.bonusgardens.com/
Planter Resource in New York City
28th Street betw 6th & 7th Avenues
(closer to 7th)