In this subtitle the following words have the meanings indicated. “Affordable” means that housing costs do not exceed 30% of a household’s income. “Affordable dwelling unit” means a dwelling unit that is affordable to households earning 60% or less of the area median income. “Area median income” means the median household income for the area adjusted for household size as published and annually updated by the U.S. Department of Housing and Urban Development. “Board of appeals” means a board of appeals established under Title 4, Subtitle 3 of this article. “Cottage cluster” means a grouping of not fewer than four detached housing units per acre that: have a footprint of less than 900 square feet each; and include a common courtyard. “Historic district commission” or “historic preservation commission” means a commission established under Title 8, Subtitle 2 of this article. “Middle housing” means: duplexes; triplexes; quadplexes; cottage clusters; or town houses. “Mixed–use” means any combination of a residential use with a recreational, office, dining, or retail use. “Mixed–use” does not mean any combination of a residential use with an industrial or hazardous use. “Permit” means a building permit or other permit issued in writing, as required by a local jurisdiction, to authorize the start of predevelopment or construction activities to construct, alter, demolish, or relocate an existing or new structure. “Planning commission” includes a planning commission or board established under: Title 2 of this article; Division II of this article; or Title 10 of the Local Government Article. “Town house” means a complex of dwelling units constructed in a row of three or more attached units, where each dwelling unit is located on an individual lot or parcel and shares at least one common wall with an adjacent dwelling unit. “Unreasonable limitation or requirement” includes any limitation or requirement that amounts to a de facto denial by having a substantial adverse impact on: the viability of an affordable housing development in a qualified project; the degree of affordability of affordable dwelling units in a qualified project; or the allowable density or number of units of the qualified project.