Ensure your general contractor is licensed to perform home additions. Many states require general contractors to have a "general" license to perform basic construction tasks. However, any work done on your home that can impact its habitability often requires further licensing. Your contractor should be able to provide you with a list of his or her licenses and proof that he or she has them.

Find a contractor with experience adding to pre-existing homes. When you are putting in an addition, you can't simply assume that experience creating new structures will translate to additions. In fact, additions often require a greater level of skill. This is because the addition will need to work around the pre-existing structure in a way that does not destabilize it.

If you are concerned with building in a more sustainable way, there are a number of qualifications you should look for in a contractor. For example, a LEED-certified contractor will be able to make your addition environmentally sustainable and energy efficient. You should ask your contractor about his or her commitment to sustainability and what green building options they offer.