People with flat roofs love rooftop decks, and why not? Oftentimes, it’s an otherwise wasted space. A rooftop deck can provide a whole new perspective for you. You can have a commanding view of your whole area. What a great viewpoint. Before you get started, though, there are many important things to consider. It’s best to do your homework first.
First Step: Is a Rooftop Deck Allowed in Your Area?
Before getting started, find out if a rooftop deck is allowed in your area. Do you have local zoning prohibiting a rooftop deck? Are there homeowner association restrictions in your area? Find out. If not, a great place to start is to check with your local building department. Building code officials are a wealth of information. They know the local building codes and can save you money in the long run.
Step 2: Can I Build a Deck on My Rooftop?
Can your roof structure support the additional weight? A building code official may be able to help you here. Or not. At a minimum, they will likely know what the loading requirements are in your area. You may also need a master builder or structural engineer to determine the loading capacity of your roof. They can determine whether your existing roof can support the extra weight of a deck. Never build a rooftop deck without checking this first.
Step 3: Choose your Deck Team Wisely
Architects, landscape architects, engineers, green roof professionals, master builders all have their specialties. You may want to interview several of them before deciding on your rooftop deck team. Green roof professionals often have many (or all) these resources in house. If not, they will likely consult with an architect or engineer first anyway. Ask them about their process. Find out how experienced they are. It’s well worth it.
Step 4: Plan Your Rooftop Deck Design
You may already have some ideas on how to utilize your rooftop deck space. Are you going to have plantings? An overhead element like a pergola? Seating areas? Do you need access to drains or utilities? Professional designers can help you plan wisely for your unique space. Enlisting experienced professionals can save you years of grief and add many years of enjoyment. Your call.
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Step 5: Select Your Rooftop Deck Framing
The basic options are sleepers, wood framing or adjustable pedestal systems.
- Sleepers. Sleepers are less costly up-front, but they have pros and cons. Check out this article on installing sleepers for a better understanding.
- Wood Framing. Traditional wood deck framing is an option, too. The benefits are also a low-cost option, up front. The downside is they may potentially be too heavy for your roof to support the extra weight. Because a low-clearance rooftop deck is a harsh environment, wood joists may warp, twist or rot.
- Aluminum Joists. A high-performance adjustable pedestal system with aluminum joists is more expensive up front. However, they will not rot, warp or twist and they are non-combustible.
Step 6: Select the Right Decking for your Rooftop Deck
Rooftop decks are possibly the most punishing area to build a deck. They’re low clearance (moisture can get trapped below), low ventilation and high exposure. They often see the sun all day long. Choosing the right decking to survive - and thrive - in this environment is an important decision.
What about Composite decking?
Synthetic decking options range from wood composites, to plastic capped wood composites, to cellular PVC. Most are available in a variety of colors. Some may perform well in this harsh area. Most do not. Most of the synthetics heat up and expand and contract making them uncomfortable to walk on. If you are considering this option, please do your homework first.
Softwood decking is not a very good idea on a rooftop deck. Pressure treated decking is very likely to split, crack, warp and twist in this harsh environment. Even higher-quality softwood decking, like cedar, will require a lot of refinishing up at this height and exposure. If it's not refinished regularly, expect lots of splitting and checking.
How About Hardwood Decking?
High density hardwood decking species such as Ipe, Garapa and Machiche hardwoods are an excellent consideration in this environment. There are many high-performance hardwood decking species to choose from. They will work as well as the deck layout allows. For example, the more clearance you have below the deck (height from top of roof to bottom of deck boards), the better. The spacing between the deck boards is also critical. This is very likely the only place your deck will ventilate.
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Decking Size Matters:
- Thicker deck boards perform better than thinner ones. Thicker boards are stronger and can take more punishment. (Either '5/4 x' nominal thickness or 21 mm thick decking are better than '1 x' nominal thickness decking)
- Narrower deck boards will perform significantly better than wider boards. For example, a 4” nominal deck board will ventilate roughly 40% better than 6” nominal decking. This is because there is a lot more ventilation between the deck boards. Trapped moisture can escape more easily.
- Thicker, narrower deck boards work best of all.
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