Mistaken Identity — Variance vs. Nonconforming Use
A variance is an exception to the existing zoning, whereas a nonconforming use (also known as a grandfather clause) arises when there is a change to the zoning but an existing use is still permitted to continue.

Variance — Permission obtained from governmental zoning authorities to build a structure or conduct a use that is expressly prohibited by the current zoning laws; an exception from the zoning laws. A variance gives some measure of elasticity to the zoning game.

To eliminate land speculation, many variances are granted conditioned upon the commencement of construction within a certain time period (for example, 12 months). There are use variances such as for apartment use in a single-family residential area. There is also an area or building variance where the owner attempts to get permission to build a structure larger than permitted.

The applicant usually must describe how the applicant would be deprived of the reasonable use of the land or building if it were used only for the purpose allowed in that zone; how the request is due to unique circumstances and not the general conditions in the neighborhood; and how the use sought will not alter the essential character of the locality or be contrary to the intent and purpose of the zoning code.

Nonconforming Use — A permitted use of real property that was lawfully established and maintained at the time of its original construction but that no longer conforms to the current zoning law. The nonconforming use might be the structure itself, the lot size, use of the land or use of the structure. The use will eventually be eliminated, although the nonconforming use status does not necessarily have to be discontinued upon the sale or lease of the property. By allowing the use to continue for a reasonable time, the government can assure itself that the use will not continue indefinitely and, at the same time, avoid having to pay just compensation for taking the property through condemnation.

When purchasing a nonconforming structure, a buyer should be made aware that in case of substantial destruction by fire or otherwise, the zoning statutes may prohibit reconstruction of the structure. In such a case, a buyer should discuss the possibilities of purchasing demolition insurance from an insurance agent. A nonconforming use can also terminate upon abandonment of the property.
Source: www.LanguageOfRealEstate.com