Officially/Legally for the UK here http://www.rics.org/uk/ Although you will find codes of practice and property standards on many council websites under the housing department, the UK Gov website https://www.gov.uk/private-renting/your-... and housing charities like Shelter

Try your local Health Department.

if it is unfit, it will not pass an occupancy inspection and you will not be allowed to rent it out

If you are in the US, google your state's Landlord/tenant laws and read them.