For example, is a landlord occasionally showing an apartment to prospective future renters or buyers? That is allowed, at least if the landlord does it at reasonable times and with reasonable notice. (“Reasonable” notice is usually construed as being at least 24 hours notice, for this and for other necessary intrusions.) However, trooping 8 or 10 prospective tenants through each week, without notice, would not be. Similarly, if the landlord has to perform construction to improve or maintain the building, that would generally be permissible, even if it disturbs tenants, so long as the construction is during normal working hours (e.g. 9 – 5, Monday – Friday). However, if construction or maintenance is performed at night or on weekends and it’s not emergency repairs,it would generally be considered a violation of the right to quiet enjoyment. For a third example, a landlord may come into the tenant’s leased premises if that’s the only way to access some area or infrastructure that needs repair—but again, only at reasonable times and on reasonable notice, and only if there are not other acceptable alternatives, such as access through a a common area. Landlords may protect their investments in their property; but they must do so without unduly depriving the tenant of the value of his or her lease.
In short, the question of when something is or is not a violation of the right to quiet enjoyment is a context-dependent one, and answering it depends upon performing essentially a common-sense balancing of the rights of the landlord, as property owner, versus the rights of the tenant, as renter. Therefore, if you believe that you may be being deprived of your right to quiet enjoyment, you should consult with a landlord-tenant attorney who can evaluate the full situation for you.