A basement can be converted into an apartment for growing children, for parents who want to move in or even leased out for extra income. One of the first things to do before you proceed with a basement apartment design is to check whether your local laws allow you to make such changes in your home.
A proper design for an apartment will have to include a kitchen and bathrooms and this is often the main expense and can place restrictions on any design, as you are required to join your plumbing to existing stacks and this pre-decides the location of certain rooms. A major concern can also be the approach to the apartment, and this gets slightly complicated if you are meaning to rent the apartment and need to give your tenant free and unhindered access.
Lighting and ventilation can be a major problem that requires a solution, as getting it naturally are not easy due to the nature of basements, and artificial lighting and ventilation can lead to higher costs.