Most sundecks beyond the simple BBQ deck included with many homes will be custom additions to an existing structure. And like most custom building projects, the more thought you put in, the better the result. This means your new sundeck doesn’t begin with the first nail, but instead, with the first pencil line made in your sketchbook.

Whether building yourself or hiring out, initial planning should be done by those who will be using the deck. A good designer can help with this, but most homeowners have a pretty good idea what will work at this earliest design stage. A great place to start is by determining the deck’s shape using a bird’s eye or "plan view" sketch. Simply draw a line representing your house wall, adding to it the shape you envision for your deck. Take a few stabs at it. You may find yourself doing arcs and unusual angles, but it’s all in pencil so play with it. When you consider that most decks are about playtime, it makes sense somehow that the sticking to right angles at the design stage may not make for the best sun deck design. Some of the finest sundecks are whimsical.

While you are outside walking the shape or "footprint" of your favourite sketches, think about levels, or "elevations." Raising or lowering a deck level in places by even a single step can add greatly to a deck’s look and feel. Once an approximate idea of the deck’s footprint seems to work, consider points of access to the deck if any, and whether stairs are needed.

Thinking about elevations in decks is important for a couple of other reasons, the first being that most deck surfaces have joists supporting them. The bottom of these should be about eight inches (20 cm) above the ground in wetter areas to protect woodwork. An even more pressing consideration is railings. In general, if a deck surface is more than two feet above ground, a railing is required. If over six feet, a higher railing is needed. In my view, any elevation change on a deck should be obvious. Some mark elevation changes with planters or other obstructions for safety.

Once you’ve cobbled together an approximate shape and height, then considered access and rail questions, think about whether a roofed area suits the plan. Roofed areas increase the amount of time a deck can be used in a year in many regions. Where I come from, we call that, "More bang for the buck." Naturally, any deck roof should not conflict with the existing building, but this is true of your deck on the whole. Harmony of design will enhance your deck’s character.

Probably the biggest question in deck design is how it will be surfaced. For simplicity this choice can be narrowed to two options: wood slat or membrane. Wood lovers opt for slats. A common deck board will be cedar, typically a six inch (15 cm) wide board about one and a quarter inches (3 cm) thick as a minimum. There are other types of wood finishes available ranging from treated boards to tropical hardwoods. Whichever is chosen, an important feature of any deck board will be rot resistance. Most people will stain their slatted deck surface, which will help to decrease the threat of wood rot and keep wood looking fresh. If using treated wood, be sure you treat the engrain of cuts.

The main alternative to wood is a vinyl membrane. This membrane style comes in many colours and textures, and unlike a slat surface, will not require re-staining, but only a good cleaning from time to time. Another advantage with a membrane surface is that it will help to keep areas underneath dry. As these finishes are getting better all the time, some building authorities will accept a vinyl membrane over an enclosed living area.

Whether using wood or vinyl to surface a deck, if the area underneath is open to the elements, it is a good idea to take measures that will inhibit weed growth. If the deck is only slightly above ground level or "grade," this should be done as soon as the deck’s footing supports are in place, as it will be difficult to do once other support framing is installed. Taking steps to inhibit weed growth is particularly important with slatted surfaces as any water is intended to pass through the gaps in slats as opposed to draining off as with a membrane. We use a high quality landscape fabric held in place by gravel, and a little time spent here will save a lot of weeding time later.

With these main elements of deck design considered, now is a good time to consider other details. I haven’t advocated running off to the Internet for ideas, because I’ve found the building site usually determines most of the characteristics already discussed. As well, looking at a lot of photos may inhibit the creativity of some. Of course others may start with this approach, finding that looking at other decks and their details spurs on their creativity. Either way, seeing how others have met the many challenges of deck design can be useful, particularly when it comes to railing options. These are many. The wood lovers will likely gravitate to wood railings, but as is the case with wood deck surfaces, these will likely need to be stained, too. Aluminium rails are the usual alternative to wood. The advantage to these is low maintenance, as they require only a wipe to keep them looking good over the years. Thinking about minimising time spent maintaining a deck is a good idea, this because sundecks are all about leisure, and spending leisure time working on a deck doesn’t make a lot of sense.

With most of the nuts and bolts of your deck design considered, now is the time to take your thinking to the next level: building. If you’re confident about your carpentry skills, you’re ready to get going. If not, review the work of carpenters and deck builders in your area. Chances are they’ve built a few decks and their know-how should prove a valuable resource. Also at this stage, determine if your deck will need to be permitted by your local building authority. Though not all inspectors will offer advice, they may tell you how they would attend to certain challenges themselves, and will, at the very least, prevent you from making great mistakes if you’re just starting out.

If there is one main structural consideration in deck building, it is the question of whether or not to attach your deck directly to existing work. This is largely a waterproofing issue. If the a main building and deck are constructed simultaneously and a membrane surface has been chosen, it is usually easier to "hang" the deck frame from the main building, and the membrane will be run up the main building’s wall. This will help ensure water will not penetrate a building envelope. If slats are used, however, it is much more difficult to keep rain and cleaning water out of the building. In this event, we run a row of footings beside the house wall, making sure there is only about a one inch (2.5 cm) gap between the deck surface and the building’s cladding. This way, the deck will only look like it’s attached to the main building, and the untouched cladding will resist penetration as it would whether a deck is there or not. Yes, an extra row of support footings is an additional expense, but so is the effort of removing cladding to attach deck framing. As well, when a deck and building are not attached, there is almost no chance at all of the deck rotting out the building, a classic problem necessitating expensive repairs down the road.

Like all building projects, deck design is underwritten by a philosophy. It should match existing work as closely as possible, resist the elements well, and some would say most importantly, be a pleasure to use. And like all building projects, rushing at any stage of design and construction will be to the project’s detriment. So take your time, determine and collect your materials as soon as possible, and be sure to keep in mind at all times the main reason for a sundeck: making the most of leisure time.