Additions, large or small, are an extension of your home. They should reflect you and your needs while benefiting the rest of your home in terms of connection, size, flexibility, efficiency, and green and natural elements. Connection: Think about how your addition connects to the rest of your home. Try to select a design that disturbs the existing site as little as possible. Think about other effects your addition will have on the rest of your home, including things such as solar orientation and roof planes. Your addition could potentially add passive heating and cooling to your home, and optimize rain water collection.
Size: Make sure that the size of your addition fits its function. You should tailor the space to your needs, so as not to waste material or increase costs with excess or over-sized space.
Flexibility: As you design your addition to suit your needs, also try to plan for the future. With a little forethought, future changes can be easy to make. For example, make exterior walls load bearing so that interior walls can be easily shifted, allowing for the rearranging of spaces.
Efficiency: Create a well sealed and thermally efficient building envelope for your addition. This will decrease the heating and cooling loads that will be added to your home with more conditioned space. Remember that the building envelope is the entire enclosure of the addition, and is affected by the method of framing you choose, as well as the insulation, siding, windows, etc. that are used.
Green Elements: Research and incorporate green features into your addition. This may be through construction material (like certified or reclaimed lumber), or finishing material (like recycled glass countertops).
Natural Elements: Nature should be a part of the design of your addition. Incorporate natural views, or perhaps create new outdoor spaces. You can even plant some new trees. Not only will they add shade to your yard, but they will also help to shade and passively cool your home. Bring some landscaping into your addition design. This will add beauty and will help control water run-off displaced by the added footprint of your home.