Hi Emma,
Sounds like the kitchen satisfies sec 556 in that is it being used for the purpose of the charity, but if you are not certain that the rest of the house is being used for the purpose of the charity, I would ask them to advise who is living in and using the house for residential accommodation.
There is always the option of part of the property being exempt under 556 and the other part being rateable. Ask the VG for separate valuations for the two parts.
Cheers
Jane
