You have an interesting question. While the friend lives in the barn and helps take care of the property, it is not a true rental situation. If the friend moved out, it does not sound like the insured would look for a replacement tenant. However, there is an exchange of services, which could be seen as a rental. The policy view of other structures is geared to property used for storage of other property, since rental for private use as a garage is OK, as is the storage of business property as long as no fuel is stored. Ambiguities always are seen to benefit the insured, and this is ambiguous. Check with underwriting and add the HO 04 40, Structures Rented to Others, just to be sure the insured is covered.