i have been asked if i am willing to allow builders toilet access

We are having building work done to our property. We have finally got the go ahead to have an extention built. But they have asked if we would agree to them having access to toilet facilites and i said yes but my wife is worried. my wife has a low imune system and she is concerned at people using the toilet facilities. has anyone had building work done and said no to access to the toilet access and if so how did the builders solve this problem