We have recently had a rooftop deck constructed on the third floor of our MN home, and since we have virtually no yard, are considering using some of the space to "go green," while still leaving plenty of room for entertaining.
The deck is 8×24, made of cedar, by a reputable contractor. It sits on the third floor on a nearly flat section of roof, above the enclosed living space on the 2nd floor and an open porch on the 1st floor. We have several lightweight pots we use for tomatoes, other vegetables and flowers outside. When filled with potting soil and plant material they weigh 25-30 pounds each. At about 15" in diameter we could put a row of about 15 of these on the deck with still ample space for sitting/entertaining — or up to 3 such rows, if in the future we wanted to grow more of our own vegetables.
As what point would the weight of the plants potentially become a problem for the structural integrity of the deck and/or roof?
Best Answer
While I realize that it's disappointing not to have every question easily answered by the internet for free, there is no way to correctly and reliably answer this question than to consult with (yes, pay money $$$ to) a civil/structural engineer, preferably one licensed to practice in your local jurisdiction (State, since you are in the USA.)
For 5 different houses, built differently, there will be 5 different answers. There is no "General" answer, and the stakes are at least your house, if not the lives of your family if you get it wrong and collapse the place while you are all asleep, etc. It is NOT a good place to "guess."
Joining a community garden near your house might make more sense as a way to get garden space.