Spotlight on: Roof Deck Options and How to Properly Install Them

Wooden Decks. A wooden roof deck is usually made up of interlocking 3x3 or 4x4 sections, raised up off the membrane on protective pads or steel supports to allow drainage and prevent damage. Sections should be removable so that the underlying roof can be accessed for repairs; if that's not possible, there should be enough crawl space below the deck for repair access.

The major limitation of wood decks is that because wood is a combustible material, the city building code states that the deck cannot cover more than 20 percent of the roof. A wooden deck system therefore is probably not the best choice if you're looking for a structure that will enable you to use as much of the roof area as possible.

Pavers. Pavers are thick, durable tiles designed for outdoor use and are commonly made of either concrete or rubber. Roof pavers must be raised up off the surface on pedestals or have built-in legs to allow drainage. Because concrete pavers are heavier than rubber, the additional load should be factored in when designing the support structure for the deck.

The advantage of pavers is that they can be easily removed for repair access to the roof surface, and they can be replaced individually when damaged. They come in a wide variety of colors, styles, and finishes, and unlike wood decks, they are not limited to 20 percent of the surface. They can cover the entire roof area.

Mineral-Embedded Layer. A third and usually less expensive option for creating a recreational roofing surface is to apply a mineral-embedded layer. This involves topping off the roof with a liquid solution, a felt membrane, and a coating of gravel, ceramic, or acrylic that becomes embedded in the solution. The raised, gritty finish acts as a protective surface and can be customized to the desired color and texture.

Mineral-embedded surfaces are best applied as a top layer of a new roof, rather than added to an existing one. The topmost roofing membrane has to be in good condition and compatible with the liquid solution used to create the new layer, which can make retrofitting problematic. It's best to check with the roofing manufacturer before proceeding with any such application.

Installation Advice.

For both wood decks and paver systems, all the sections should be secure and stable, and surfaces should be flush to avoid tripping hazards. Sections above drains should be marked for easier access. Some lightweight rubberized pavers, especially those on high-rise roofs, may be dislodged by high winds, so they are sometimes secured to each other by caulking or interlocking grooves.

 Regardless of what recreational roof system is installed, in the end the finished surface of the roof may be raised by some amount. Keep in mind that the city Building Code requires the parapet walls around the roof to rise at least 42 inches above the roof surface. If the resulting height of your roof deck is in violation of this code, you can install railings on the parapet to make up the difference rather than building it up with new masonry.

 Finally, don't forget that adding a recreational roofing system requires a permit from the Department of Buildings. If your building is a landmark property or located in a historic landmark district, a permit from the Landmarks Preservation Commission is also needed.

Be sure your new roof deck doesn't run afoul of your roof's warranty. The typical "no dollar limit" warranty can be voided by alterations or additions made without the manufacturer's authorization — even if they don't cause the leak.

Boards planning to replace their roofs and install a deck on top can secure an "overburden clause" from the roofing manufacturer, which will factor additional structural and waterproofing work into the warranty. But it's always best to get the manufacturer's blessing for your plans before going ahead. 

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