Yours is an interesting question, with its underlying belief that whose can only properly be applied to people, not to things. This has in the past been the firm rule of grammarians and generations of children have been taught it.
Modern authorities deny that any such rule exists.
For example, in the first edition of Modern English Usage back in 1926, H W Fowler argued that the rule was no more than a folk belief and he was vehement about the rigidity it imposed. All the other writers on usage that I have consulted say the same thing, with roughly equivalent degrees of exasperation. They all point to authors of impeccable credentials over the past 400 years who have used whose to refer to inanimate objects, including Shakespeare, Milton, Dryden, Addison, Pope, and Wordsworth. The basis for the rule is that whose is the possessive form of who , so strictly ought only to be used when persons are referred to. The problem is that English doesn't have an equivalent possessive form for which or that , so we must either not use one at all, or borrow whose .