As you probably know, the co-op's principal document is the proprietary lease, under which your co-op is the landlord (or lessor) and each shareholder a tenant (or lessee). If your co-op's lease form is typical, the co-op must keep the building's structure and common areas in good repair and "maintain and manage the building as a first-class apartment building."

In accomplishing that, your co-op's board is protected by the Business Judgment Rule, which insulates its decisions from court review provided those decisions are consistent with the co-op's contractual arrangements and do not involve bad faith, self-dealing or discriminatory or otherwise unlawful conduct. So, if your co-op installed and maintains the ventilation unit consistent with these responsibilities and standards, then one might conclude that your co-op is acting properly and will readily prevail in litigating against you.

You have ample weapons, however, to use in defending your position. The typical proprietary lease provides that shareholders shall "quietly have, hold, and enjoy the apartment without any trouble … from" the co-op. This is a version of what is known as the "covenant of quiet enjoyment." This covenant is deemed implied in all New York State residential leases, including co-op proprietary leases, even if not formally stated.

To successfully assert the covenant of quiet enjoyment, you must establish that the landlord's conduct "substantially and materially deprived the tenant of the beneficial use and enjoyment of the premises…" (Jackson vs. Westminister House Owners Inc.) Shareholders commonly will assert this covenant if they claim that their co-op deprived them of the right to use all or a portion of their apartment. In recent court cases, shareholders have sued claiming that their co-op deprived them of use of the "terrace area, due to exterior renovations" (Jackson vs. Westminister), and of a "rooftop terrace" for certain gardening purposes (Murphy vs. Vivian Realty Corp.).

A shareholder might also suffer what is called "constructive eviction," meaning you've been compelled to abandon the apartment because of some condition affecting it.

For example, in Jacobs vs. 200 East 36th Owners Corp., a shareholder pursued litigation asserting her co-op's violation of, among other things, the covenant of quiet enjoyment in connection with "noise, low water pressure and other unpleasant living conditions." The court, however, dismissed this claim because "there was neither an actual or constructive eviction."

Consequently, the covenant of quiet enjoyment might apply to the noise from the ventilation unit if you could establish that it prevented you from using all or a portion of your apartment. In this event, you'd be entitled to compensation to reflect this.

Warrant and Peace

In the 1970s, the New York State legislature perceived that the covenant of quiet enjoyment did not provide tenants with adequate recourse in the event of the substandard conditions in their apartments. It was considered unfair that tenants had to abandon their apartments to justify not paying rent.

In 1975, the legislature enacted Real Property Law (RPL) Section 235-b, which codified what is commonly known as the "implied warranty of habitability." That meant that tenant could assert claims against substandard conditions, and withhold rent while staying put. Co-op shareholders likewise felt free to withhold maintenance — although savvy ones realized it's always better to continue paying maintenance and to sue their co-ops for affirmative relief. That way, if you lose, you're not responsible for the co-op's legal fees.