Regulations regarding basement apartment requirements vary between jurisdictions, but it is very common that a separate entrance is required. This ensures ease of access but also serves as a method of emergency egress in case of a fire. If your basement already has a door to the outside, this requirement is likely fulfilled.;
, Many building codes require separate dwellings to have a certain amount of natural light. Whether or not your unit has adequate sunlight can be tested by a local building inspector using special equipment. If you can't pass this requirement, you will have to have additional windows installed along an exterior wall in order to create a legal basement apartment.
 Another major requirement concerns the amount of insulation between your main dwelling and the basement unit. You will almost certainly have to replace the door to the stairway separating the units with a fire door; these doors are usually made from steel and can withstand a burn for 2 hours or more before giving way. Additional insulation for soundproofing and fire resistance may also be required in the floor between the units. If your basement is currently unfinished, adding this insulation will be easy.
Make sure that the basement apartment has a dedicated exit.
Ensure that the basement has enough light.
Improve the sound and fire insulation between dwellings.
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