I've heard this from homeowners multiple times and about any number of bedrooms. The house might have two bedrooms and then this little bonus/office room that they want to count as a bedroom so that it sounds better in the listing.
As defined by tax assessors and building codes, the definition of a bedroom typically means a room large enough to hold a bed as well as a closet. Different counties may require different stipulations when it comes to the definition of a bedroom. Septic systems also play a factor in how many bedrooms a home can legally have.
The number of bedrooms and septic systems coincide. In most states, you cannot have more bedrooms than what your septic system is designed to care for. If you have a three bedroom septic system and you add an additional bedroom without increasing the system, you cannot market your home as a four bedroom. However, it could have four bedrooms but you cannot legally state that that is the definition of your home if the septic system does not have the capacity for four bedrooms.
You also have to be very careful when it comes to counting how many bedrooms you actually have. There are many lawsuits out there were real estate agents and sellers can be sued over the bedroom count misrepresentation. As a buyer, you also want to make sure that the home you are purchasing has a number of bedrooms you need. You don't want to be looking at four bedroom homes only to find out there really three bedroom homes with an additional bonus room, loft or even something as small as a walk-in closet. This is just for septic systems; regulations change when we are talking about city sewer. Having more bedrooms obviously makes a home more desirable and most homeowners would want to represent their home in its best possible light. But, you don't want to be breaking any laws when you go to advertise or sell your home.
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Generally speaking, homes need to meet certain criteria when it comes to classifying a room as a bedroom or not.
The home needs to have at least 70 to 80 ft.². This means it should be at least 70 ft.² in a horizontal direction.
Home also needs an escape route. If there is no additional way out like through a window, it cannot be classified as a bedroom. There needs to be an additional outlet.
A bedroom must maintain typically 7 feet in height or greater. In some instances, like an attic, the room may have a slope but at least half of the ceiling should meet the minimum requirements.
A bedroom will need to have temperature control. It cannot be separated from the heat or cooling system from the rest of the house.
The home must have a closet. Now, this is where things get a little bit fuzzy. Older homes may have a lot of bedrooms without closets because there are built-in cabinets, drawers, and shelves. As long as the home can have a bed and an armoire or someplace to be used as a closet, it should be able to be marketed as such.
If the home cannot meet these requirements you can call the room a "bonus" room, "den", or "office". If the home has three legal bedrooms and has an additional room, you can market it as such and buyers will typically turn it into a bedroom if needed. So, bottom line; be honest about what the home is and isn't. Buyers will come to their own conclusions and then you can let them be the judge of your home.