Interior stairs had a switch at the bottom of the flight that controlled a high ceiling fan light in the vaulted ceiling of the adjacent great room. The switch at the top of the stairs controlled the upstairs hall light.
I usually see both switches controlling the same light. Do you see this as a problem?
That is what Robert is saying, there should be a switch at the bottom and one at the top of stairway that control the One light in stairway, a three way switch. It sounds like the ceiling fan may have been installed later and they replaced the switches and used the available circuit to operate the ceiling fan.
The stairway lighting, which must be capable of lighting the entire stairway, including all landings (top ,bottom and center), must be operable from the top and bottom landings. The switches must be located and accessible without descending or ascending any step.
There are numerous older homes with basements in this area that only have a switch at the top & no 3 way operation.
Do you know when this was made a code?
Lets say a 1966 ranch with a basement has no 3 way basement lighting.
The picture is from a 8 year old colonial that had the basement 3 way mounted in the sub floor drop ceiling. The only reason I was able to locate is the owner & his son were home and overheard me talking about having 3 way lighting and then said it was in the subfloor.:shock:
When stairs have 6 or more risers, a 3-way switch is needed at top and bottom. IRC 3803.3
I would read this that the switches needed to control the lights for the stair illumination, not the adjacent room.