A non-conforming use shall not be enlarged or extended without variance approval. A permitted single-family dwelling on a lot that is non-conforming with respect to lot area, lot width or lot depth may be constructed, altered or enlarged and an accessory structure on a lot that is nonconforming with respect to lot area, lot width or lot depth may be constructed, altered or enlarged without an appeal for variance relief, provided that all other provisions of this Chapter are complied with.