typically be considered a “common area” and would need to be formally added to the condominium documents through a survey and legal process.
Occupancy: Due to their sometimes-heavy use, common area rooftop decks are considered an Assembly occupancy from a code standpoint with an occupant load factor of one person per every ten square feet of area. In other words, a 400sf (relatively small) rooftop deck would be designed to hold up to 40 people at any one time. While it would be rare to have that many occupants on a roof deck, it must be designed for this “worst case” scenario. This high occupancy factor impacts the structural design as discussed above; and also impacts the requirements for access and egress as outlined below.
Access: Any common area roof deck must allow access for all building occupants and guests. By Federal Law, this includes people with disabilities as outlined in the Americans with Disabilities Act (ADA). This means that roof decks must be served by code conforming stairs and an elevator or other means of legitimate access such as a ramp or wheelchair lift. In almost all cases these elements must be added at significant expense to meet code.
Egress: Due to the anticipated high occupancy load of the roof deck, code requires two means of egress for any common area roof deck greater than 100sf in size. Since very few roof decks will be less than 100sf, this means that a minimum of two code conforming stairs must be in place and accessible from the roof deck. The stairs must also be remotely located from one-another in the vent of fire. Often, existing stairs can be extended up to the roof, but this can be another significant expense.
Fall Safety: All areas of the roof deck must be provided with guardrails at the perimeter of the deck to prevent risk of falling. Since most roof decks do not cover the entire roof, guardrails are also a good idea to keep occupants within the defined area of the roof deck and off roof surfaces. As noted above, guardrails for common area decks require engineering and often need to be attached to the structure within the roof for stability. Pre-finished aluminum rail systems are by far the most common type of guardrail used for roof decks. They come in various styles including glass and cable infill for maximum view and are very low maintenance.
Drainage: Most roof decks are installed atop a low-slope roofing system. These are often called “flat roofs” but Code and good practice dictate that all areas of a roof be sloped for proper drainage. This is even more critical under a roof deck which will tend to restrict drainage and be much more difficult to access for repair than an open roof area. Generally, slope should be a minimum of 1/4”/foot to the drain points.
Often re-sloping and/or adding new drain points is included in a roof deck conversion.
Roofing and Roof Deck Surfacing: Occasionally a roof deck surface is the actual roofing, however this is rare as there are few roofing systems designed for the heavy use a roof deck gets. Most roof decks therefore are a separate structure set atop a warrantable roofing system. The most common roof deck system is a pedestal and paver system wherein approximately 24” square pressed concrete pavers are installed over adjustable plastic pedestals. The pedestals allow nearly free drainage beneath the pavers and can be adjusted for the roof slope beneath so that the deck surface is flat. Other systems include wood framed decks or palletized systems. In all cases there should be protection in the form of an approved drainage mat between the roofing and the deck above.
No matter the type of roof deck chosen, the roofing system beneath the roof deck should be very high quality and warrantable by the manufacturer for use under the proposed roof deck system. A fully adhered single-ply membrane with welded seams and a minimum 20-year NDL (No Damage Limit) warrantee is a good choice. Design, detailing, specifying, and overseeing the installation of the roofing system should be done by a professional with significant experience as warrantees are easily voided by a relatively small lapse in design or execution.
Hardscaping and Landscaping: In nearly all cases, a roof deck includes amenities such as benches, screen walls, planters and landscaping. These elements contribute to the usefulness of the roof deck and its appeal and are often designed for wind screening or to create more private areas within the whole of the deck area. The environment of a roof deck is very harsh for most of the year; so the design of these elements needs to be carefully considered in conjunction with weight, drainage, maintenance and other factors. Again, a professional with significant experience in choosing the correct materials and plantings will be critical to the long- term success of the project.
Conclusion
There are several factors for the association to consider in addition to hiring both a licensed structural engineer and architect to evaluate the proposed project. Strategically locating the rooftop deck and evaluating its size will maintain proposed loads, exiting, and occupancy within project goal thresholds. Rooftop decks can lead to an opportunity to fix inadequate drainage and provide a desirable amenity for the development. With careful planning, thoughtful and thorough detailing, and with the HOA’s goals in mind, this rooftop amenity space can provide long-term enjoyment and increased property value for the homeowners.
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