If I split 20 units into four clusters, do I need an ADA unit in every cluster?

Yes. Once you split the toilets into four separate clusters, the 2010 ADA Standards apply the portable toilet rule at each cluster, not across the whole festival site.

Under the 2010 ADA Standards (section 213.2, Exception 3), when multiple single-user portable toilets are clustered at a single location, no more than 5 percent of the units at each cluster are required to be accessible. That calculation runs per cluster. Five units in one bank still needs at least one ADA accessible unit, because you cannot round the requirement down to zero.

Keep all 20 in one bank and 5 percent of 20 is one accessible unit for that location. Break them into four banks of five and each bank is its own location, so you are looking at one accessible unit per bank. The city inspector is reading the clustering the same way most special event permits do.

Also plan an accessible route to each of those units on the grass. Level ground helps, but the path still has to work from the main circulation areas. Confirm the layout with the permit office before you lock delivery spots so vacuum truck reach and the ADA path do not fight each other.

We tried to save ADA rentals on a park festival by spreading clusters far apart. Inspector made us add the missing accessible units. Worth settling early.

The city inspector's interpretation is standard for special events because each cluster functions as a separate amenity location. Jake covered the ADA rule correctly. Your festival layout with food, beer and 1,200 people over eight hours needs more than 20 units; the guideline of one unit per 50 to 75 people is for a four-hour event without alcohol. For an eight-hour day with alcohol, you should add units. The permit office required 20, but consider requesting more to prevent long lines, especially since women typically wait longer. Place each ADA unit at the end of a cluster for easier turning space and ensure the path from paved areas is firm and stable.