Is there no city sewer anywhere close? From your past posts, it seems that you are in a spread apart suburb rather than a rural area? Even if there is no sewer, there are newer septic systems that you can investigate that do not require as much real estate to operate as the old ones. I absolutely would NOT go the composting toilet route or any of those other methods unless you live in an extremely green community. They would be the kiss of death for resale, even if you didn't have any problems with them during your own home tenure. And unless you live in an extremely green community, getting permits for alternative plumbing is problematic. Most areas of the country won't even allow greywater recycling, despite having drought restrictions that went on for months at a time.

lol, the nearest sewer is six miles away, we don't even have cable here! we have zoning but not like most of the world.

i'm thinking a grey water system for the showers and alt toilets.
thanks for your thoughts--i'm lucky to live where i do!

Can you not add another septic?

i hope i can, am thinking outside the box in case the engineer says it can't be done. i have the space in my barnyard, may have to subdivide first though. currently i am wading through my options, and my number one goal is to get another legal 3 bdrms at least.
6 would be even better!

"thinking outside the box in"

Often a real issue with septic.

The hazards are very large if the system does not work as designed, thus the slow change in systems and the rules they must follow.

Do you intend to flush all these toilets at the same time? I presume the main tank has a clean out plug so your local honey-dipper can perodicaly pump out the tank.

Just adding the bedrooms and not dealing with the septic is as bad or worse than the composting toilet idea. The compost has to be dealt with---and most places in the US have health laws covering human waste disposal.

Septic systems are designed by the number of people normally occupying the house. That is done by bedrooms. The frequency of use is not usually included in calculations.

Adding one or more bedrooms with out increasing the septic capacity means selling later would be impacted. How? you ask?

Simply by the house description between the previous sale and the latest one. Occupant bought a three bedroom and ten years later is selling a five bedroom. Somewhere, there will need to be a record of an upgraded septic. Even without building codes, folks knowing about septic systems will ask. No upgrade---red flag.

Grey water systems---like a french drain---are dependent on soil conditions. Adding a separate septic would probably be more expensive than replacing the old one with a larger one.

Getting a permit for an addition of bedrooms will be dependent upon getting a permit from your Health Department (or whomever controls septic permits) for an enlarged or replaced septic. You cannot use non traditional means to get around this requirement. Unless you have unlimited funding and do renovations for a hobby, your needs would be much better met by buying a larger home and moving. Your potential renovation plans are likely to cost you far more and yield you far less than would selling and putting the renovation money into a larger home.

That logic was germane some time ago, not necessarily now. With the difficulties found in trying to sell, it could be many months or years before the house would sell. If the current house could sell easily, I agree it would be better to move. If it takes more than two or three years---and there is only comparables in the area by which to estimate that-----then adding is the more sensible option.

"help? i have no clue where to even begin looking for information."

Ask your township's septic officer/sanitary engineer. It may be nothing more involved than adding another 1K tank in series which is sometimes done here. Or a nightmare of sand, grinders and winged dollars.
All depends on site conditions and his/her say anyway.

engineer is going to get here next week, and understands the scope of the issue. at this point it look like subdividing the barn from the house will get us where we need to be.
otherwise we'll have to build an entirely new house on the rest of our land, which has it's good and bad points.
the cost of that will be much higher, as i'll also have to add a well and power. in the end all i may be able to afford in that case would be a used mobile, which won't add as much value to the land as i'd like.
the best case scenario is if the engineer agrees to allow a new septic in the barnyard so i can add the new bdrms to the existing house.
i have no problem sacrificing the barnyard, as i already have another barn area ready to go.
thanks for your input, it helps!

"Adding a separate septic would probably be more expensive than replacing the old one with a larger one."

The tank size is the least of the issues.

The drain field size is the real driver, and that is directly impacted by the perc rate of the soil.