Above the Clouds - First Steps Designing a Rooftop Garden
The options for what rooftops can be used for has skyrocketed in the past 20 years. More and more this is becoming a place where designers can provide additional amenities for the public or the building occupants. From restaurants and lounge areas to green roofs and solar panel fields. What are the basics you need to know if you are planning to convert your existing rooftop or build ground up?
The first aspect to consider is the structure. Typical unoccupied utility rooftops are designed to take minimal live loads for snow and a few service personnel. Occupied rooftop decks must be designed to handle much higher live loads, typically 100 psf or more. To put this into perspective the occupied rooftop deck live load required may be over three times the live load your rooftop was originally designed to accommodate. If you are looking at installing an occupied rooftop deck on your existing building, we would recommend consulting with an Architect and Structural engineer first to evaluate the building’s existing capacity and to see if reinforcing your rooftop deck is a feasible option.
Heights, Areas, and Number of Stories are another important consideration for an occupied rooftop deck. A significant item to consider is that most items on the rooftop are limited to a maximum of 48 inches in height to not be considered an additional story (section 503.1.4.1). Items such as spires, cupulas, towers, domes, and mechanical penthouses are exempt from this and can exceed 48 inches in height per (section 1510). If any non-exempt items exceed 48 inches in height the rooftop deck may be considered an additional story which may exceed your building’s allowable number of stories or heights per the IBC or your local zoning codes.
Another key aspect to consider is whether the building is sprinkled or non-sprinkled. An assembly occupancy space (restaurant or large lounge area for instance) on the rooftop would likely require fire sprinklers and occupant notification throughout the building since the fire area is not located on a means of egress discharge floor per (Section 903). However, if the occupied rooftop occupant load is less than 49 occupants, it may be considered a business occupancy without requiring fire sprinklers and occupant notification.
Fire Sprinklers and occupant notification also help warrant the installation of an occupied rooftop deck where previously the use would not be permitted. Fire sprinklers do not need to be installed on the actual open deck area but throughout the building and intervening floors. (Section 503.1.4) allows the occupancy located on an occupied roof to not be limited to the occupancies allowed on the story immediately below the roof if the building is equipped with a fire sprinkler system and occupant notification throughout.
The last key item to discuss is accessibility and egress. Most rooftop decks will require at least two exits off the roof per (Table 1006.3.1.). Vertical accessibility, i.e. elevators, would be required for most assembly spaces that come to mind. If the occupied rooftop deck has an aggregate area of not more than 3,000 SF a vertical accessible route may not be required per (Section 1104.4 exceptions). Once on the occupied rooftop deck all items such as walks, stairs, ramps, handrails must be accessible.
As occupied rooftops continue to grow in popularity, they are becoming more regulated. To plan a successful occupied rooftop project the design team selected needs to be familiar with the evolving rooftop code requirements and local zoning codes.
Have a rooftop project that you want to explore possibilities on? Contact us today to discuss your vision and explore the possibilities!