To install a composting toilet in a new home or as part of a renovation of an existing system, you might need a permit from local or state agencies. (Strictly speaking, you should get a permit for any installation.)

What your state and local agent will allow might limit your options and might rule out site-built systems. Some states have approved systems based on their own research, some do it on a case-by-case basis, and some require NSF listing. Check with your board of health agent first before you buy.