Septic is rated based on number of bedrooms.

Septic systems are sized to number of bedrooms. The closet doesn't matter, there are specific requirements for a bedroom (ventilation, exits, minimum size...) . There is bedroom count rule in Mass Title V that says if there are more than 8 rooms in the house, you have to divide the total rooms by 2 to get the bedroom count. So an 8 room house could have 3 bedrooms for septic purposes, but a 9 room house will 4, a 10 room house will have 5... Rather than denying a construction permit because an additional room will push the house over the size of the septic system, a town will often add a deed restriction stating the number of bedrooms and allow the construction.

Your town's health department should be able to help you figure out how it will work in your specific situation.

House could have 20 baths and as long as the bedroom count matches the Septic design, that’s what will be the primary concern.

Just want to note that a closet isn't necessary for a room to be considered a bedroom in Mass (although they may be required by specific municipal codes).

Thanks. This is helpful. Excluding bathrooms, we have 8 rooms, 4 of which are bedrooms. Our septic definitely covers 4 bedrooms, but may possibly be big enough for 5. I need to call our septic company and find out. In the end, it doesn't really matter because this extra room we're putting in in the basement doesn't necessarily have to be a bedroom, but for resale, if our septic covers 5 bedrooms, and bedrooms don't necessarily have to have a closet, we'll probably call it a bedroom.

The 4th bedroom we do "officially" have is small as hell. It meets all the requirements to be considered a bedroom, but unless you're only putting a twin bed in there and a super small dresser, it doesn't really work.

Thanks. This would only really matter for resale whether our septic covers 4 or 5 bedrooms or not. We would only ever try to call the room in the basement a bedroom we were selling, but obviously if our septic only covers 4 bedrooms, it would just be a "bonus room."

But, like they said, if you go over 8 total rooms you divide by 2 and round down to the lower whole number to get the bedroom count for Title 5 purposes, or you put a 4 bedroom deed restriction on the property. Now, if the town catches the room count is another story, some would and others wouldn't. I'd guess that your system is sized for 4 bedrooms, my experience with new construction is 4 is pretty standard, you only see 5 or more if you are in a wealthy area where the extra bedroom has a bigger return.

You will need a building permit and a septic approval (varies by town). Most septic systems are not sized for more bedrooms than the initial build due to cost. So, you may need to upgrade/increase your septic system.

Most are not, however when a home changes hand an inspection is required and in many cases a new system is installed. We requested a larger system from our seller knowing we wanted to convert a bedroom. You never know, always good to check.

Lol you’re the one who mentioned the lack of closet.

Not sure of the downvote but I know I mentioned the closet and was thanking you for that info. No sarcasm.

That bedroom thing is nonsense it changed years ago. It would be the subgrade that would effect the “listing”. Of your septic is not designed for 4 water closets you’re not going to be able to do it.

I can just speak from the builder side. They are not spending money to add septic capacity over what they are building. So, certain lots may pay more to have that, but its not the standard I see.

Yeah, at least in my area, a 4 bedroom seems to be more desirable than a 3, but a 5 bedroom doesn't get much more than a 4 and they even seem to linger on the market longer.

If you are replacing a septic you should ALWAYS design for one extra bedroom. Typically, the additional cost is very minor.

I recently added a fifth bedroom to my septic and my town's regulations have changed in the 10 years since we put it in, so we are able to do it with no issue. It was something like 250 gallons per bedroom, so we had 1000, but now it's 200 per bedroom and 1000 is enough for 5 (this is just an example). Your town's health department can tell you, and they may have it online if you don't want to alert them. Hopefully you have information about the size of your system.

Building code wise, you will need an egress window in a basement bedroom.

Source? Because my reading of the current Title 5 law still talks about numbers of bedrooms because that dictates approximately how many people could be living in the house full time. Doesn't matter if those, for example, 4 people are using 2 bathrooms or 8 bathrooms, the amount of water and waste is going to be 4 people's worth.