Not required to post anything, doesn't likely require neighborhood review unless it's a zoning variance or CHAP district, and may not be required to have plans per se but they need a building permit. You can check the existing permits site and see if they have a permit; if they don't you can file a 311 for unpermitted work and get an inspection on the property. This ensures work is done to code, safely for neighboring propeties, and that it's reflected in the tax assessments.