The law says that a tenant must allow the landlord to inspect the rented property if it is necessary for maintenance, if it is sold or if it is necessary for re-letting.

Regarding inspection for maintenance it is not mandatory that the landlord must have knowledge of a defect or damage in order to be able to inspect a rental property. Thus, it is theoretically always possible for the landlord to visit his property. 

If the property is for sale, the lease has been terminated or the fixed-term lease is about to end, the landlord must be granted access to the property. 

The landlord's effort should be to minimize the disruption to the tenant. Accordingly, visits should be announced in good time, especially if they are to be carried out with prospective buyers or tenants. In the Zurich lease agreement, this early notification is regulated as at least 48 hours. The visiting hours are for business premises their usual business hours, for private premises between 8 a.m. and 5 p.m. and on Saturday mornings. Without good cause, the tenant must allow access to all premises and they should be tidy and cleaned to the extent that an assessment of the condition is possible. If this is not the case and a rental property cannot be sold or re-rented for reasons of tidiness or cleanliness, the landlord may consider suing for damages. 

If the tenant refuses to do so, it is necessary either to take legal action by going to the single judge in summary proceedings and requesting that the tenant be ordered to grant the landlord access for the purpose of inspection, on pain of punishment if he fails to do so. Alternatively, the tenancy may be terminated by ordinary notice or by extraordinary notice after the first written warning. If the landlord suffers damage as a result of a refusal to allow inspection, the tenant is liable for compensation. 

If the tenant refuses the inspection, the landlord may under no circumstances gain access to the property on his own authority or by force, as he would risk being charged with trespassing.