Understanding Your Property's Allowed Floor Area and Impervious Surface Areas

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What is floor area?  Floor area is the total area, as measured from exterior walls, for all buildings on a parcel - this includes second stories as well.  An area of a building that has a ceiling height of 7' or greater will count as floor area.  Buildings include, but are not limited to, residences, garages, carports, guest houses, cabanas, greenhouses, sheds, etc.

Impervious SurfaceWhat is impervious surface?  Impervious surfaces are those surfaces that will not allow or will greatly reduce the penetration of water into the ground.  These surfaces include concrete, asphalt, bricks, paving stones, swimming pools, "turf stone," plastic sheeting, compacted gravel and rock areas, any gravel or decomposed granite areas/paths wider than 4', corrals, and similar surfaces.  Buildings and roofs are exempt from being counted as impervious surface unless the roof overhangs exceed (6) feet in width.  Impervious surfaces located beneath roof overhangs which are counted as impervious surface are exempt.  Additionally, if the property has an exceptionally long driveway, that portion of the driveway which is further than one hundred (100) feet from the residence shall be exempt.  For guest parking areas, the Planning Commission has approved a specific paving cell product called GeoBlock, that when used, will only count for 50% of its area as impervious surface, hence providing some relief for properties that are close to reaching their maximum allowed impervious surface area.

What are floor area limitations?  The Town regulates allowed floor area (and allowed impervious surface area) based on parcel area (acreage), average slope of the parcel, classification of geology or flood areas, and the Zoning District that the parcel is in.  This data is used in a computation located in the Town's Zoning Ordinance (18.48.010) to determine the Adjusted Maximum Floor Area for the lot.  "Adjusted" refers to the inclusion of this data in the computation that produces an "adjusted lot size" and the "adjusted" maximum floor area.  For any lot in town, the main residence and required covered parking (2-car garage or carport, attached or detached to the main residence) may not exceed 85% of the allowed Adjusted Maximum Floor Area for that lot.  The additional 15% of the allowed floor area for the lot allows for accessory structures (i.e., cabana, pool house, shed, guest house, etc.).

Why the 85% floor area limitation?  The 85% calculation for floor area regulates the mass of the residence including first floor/second floor and required off-street covered parking (2-car attached/detached garage or carport).  Again, the remaining 15% of the allowed maximum floor area allows for construction of desired accessory structures.

How many and what kind of buildings can I have on my lot?  Any structures on a lot must be subordinate to a main residence, e.g., a lot cannot have only a garage or only a barn located on it.  The total floor area of all buildings on a lot cannot exceed that lot's adjusted maximum floor area (AMFA).  The Zoning Ordinance also requires a property to have at least two (2) covered parking places (400sf minimum) in the form of either a garage or carport.  The Zoning Ordinance does allow for second units on parcels of one acre or larger. 

Framed BuildingWhat is the maximum permitted floor area for any single building on a lot?  The Town's Zoning Ordinance (18.48.010) requires that the floor area of the main residence combined with the required covered parking not exceed 85% of the property's adjusted maximum floor area (AMFA).  If the residence has an attached garage or carport, the floor area of that entire structure may not exceed 85% of the AMFA.  If the property's required covered parking is a detached structure, then the sum of the residence's floor area plus 400sf (of the detached covered parking structure) may not exceed 85% of the AMFA.