English to Italian Art/Literary Architecture

Hello everybody,

I'm translating a text describing a house, and it begins like this:

This small house consisted of an intervention within a heritage percent. The brief required a home with varying and multiple spaces within a limited allowable building area.

Does anybody know if 'percent' or 'heritage percent' have some specific meaning in the architecture field? Couldn't find anything in the dictionaries, and on the Internet I couldn't find any suitable context.

Thanks,
alessandro