Building a Deck on a Flat Roof Building a Deck on a Flat Roof

What You'll Need
Circular Saw
Heavy Drop Cloth
Tape Measure

Building a deck on a flat roof is neither difficult nor time consuming. Two people can install a brand new deck in a weekend, with little or no previous construction experience. Before beginning, however, it is important to do two things: inspect the roof to make sure it is in good condition, and acquire any permits that may be required by the local zoning board.

Step 1: Simplify the Project

The joists of the deck, as with most flooring, will be set out on 16 inch centers. To simplify a construction project of this type, adjust the size of the project to be divisible by 16. For this project, the deck will be relatively small, but will be sized to use factory cut lumber, saving a tremendous amount of construction time. This deck will measure 16 feet by 12 feet. To build it, you will need 4 16 foot 2 x 6, and 44 12 foot 2 x 6. Order 1 box of 16d nails.

Step 2: Material Delivery

If you order the lumber from a major hardware store and let them know that you are building a deck on a flat roof, the material can be delivered on a truck with a lift. Make sure that someone will be home when the material is delivered, and you have it set directly on the roof in a convenient work area. It is a very good idea to lay down a canvas or heavy drop cloth. If you have two 4 x 4 posts or landscape timers available, lay them crosswise to the direction of the lumber, laying across the rafters, not parallel to them. This will lift your material up from the roof, and the drop cloth allows trimming the material in place rather than transporting it.

Step 3: Material Preparation

Set 2 of the 16 foot boards on each side of the spot where you want to build the deck. These are your end caps. Cut 12 of the shorter 2 x 6 to measure exactly 11 feet 9 inches. These are the joists for the deck. Place one flush with each end of the deck, and nail the end caps to them. Start at either end, and mark the end caps every 16 inches all the way to other end. Cut the two remaining 16 foot board into pieces that are 14 1/2 inches long.

Step 4: Deck Assembly

Place one joist every 16 inches, lining the center of the board's edge up with the marks on the end caps. If the fit seems too tight, check the length to make sure that it is 11 feet 9 inches. If it is, use a hammer to tap the joist into the correct position and nail in place. Place the deck planks every 6 inches, which will leave a small gap between each plank. Nail the planks in place. Install the 14 1/2 inch pieces as braces throughout the joists, with a staggered row extending across the center of the deck.

Step 5: A Note About Hand Rails

A roof deck is almost certainly going to be required by law to have hand rails. The specific requirements will vary from one location to another. When you know the requirements, use 2 x 2 lumber for the rail posts, and connect a 2 x 6 to their tops edgewise for the handrail.

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