Some housing developments are a part of a Home Owners Associations (HOA) that requires you to receive permission from them before building a deck. Most people know if their house is under the authority of an Association. If there is any question, the Building Inspections Department will let you know before you submit your permit. There are over 23 million homes across America that are managed under HOAs. If you are planning on building a deck onto a townhouse, chances are you will need to contact a HOA. 

Each Association works in its own way, imposing different levels of restrictions in an attempt to maintain consistency throughout the development. For instance, some Associations may only allow certain types of materials for decks or require a certain style of guardrails to match neighboring decks. If your deck meets the requirements, they will usually draft a short letter granting permission to build the project. You should include this letter with your application to the building department.