Property owners contemplating adding or creating an accessory dwelling unit (ADU) on their single-family residential property within the City of Tigard need to be aware of various code requirements. The details provided below serve as an overview of common issues related to the proposed ADU. City staff are available to meet informally or through a pre-application meeting prior to design/construction to provide feedback, etc. regarding a proposed ADU.
Land Use and Zoning: Property owners need to verify their proposed ADU is compatible with the development standards. Contact the Planning Division at 503-718-2421 for more information.
City Development Code: Chapter 220 of the Community Development Code provides standards for ADUs.
Building Plan Review and Permits: For information on building permit applications, plan review requirements and fees, etc., please call 503 718-2439.
State Building Code: The current State Building Code (SBC) includes: The 2017 edition of the Oregon Residential Specialty Code (ORSC); the 2017 Oregon Plumbing Specialty Code (OPSC); the 2014 Oregon Electrical Specialty Code (OESC). You can review these codes on-line
BUILDING CODE INFORMATION
The information listed below are specific SBC and some City Development Code References. For more information about how these requirements apply to an ADU please contact the Building Division, 503-718-2439 or TigardBuildingPermits@tigard-or.gov.
Accessory Dwelling Unit Definition
An ADU is a second or third dwelling unit on the same lot with a primary dwelling unit. ADUs provide complete and permanent provisions for living, sleeping, eating, cooking and sanitation. An ADU can be created by converting existing living area, attic, basement or garage; or adding floor area, subject to the limitations of the zoning district in which it is located; or constructing a new structure, attached structure, or manufactured home with an internal or detached accessory dwelling unit. An ADU must be separated from the primary dwelling unit with a 1-hour fire resistant rated assembly. A living area is not considered an ADU if it lacks any one of the items that define a dwelling unit, or if the living area is not fully separated from the primary dwelling (i.e., there is a doorway or opening to where the two spaces intercommunicate), or does not have a separate exterior entrance or a common internal area accessible to the outside. If so, it is considered additional living area of the primary residence and is not approved for rent, lease or hire.
Maximum ADU Size
An ADU created by an addition or within the interior of an existing primary dwelling area cannot exceed the size of the primary unit. The maximum size of a detached ADU is 800 square feet.
Building Permit Required
A building permit is required for creating an ADU and mechanical, plumbing and electrical permits may also be required. Scaled drawings are required that include (not all may be applicable): Site Plan showing the location of ADU on the property, including distances from property lines and other buildings or structures; Floor Plan showing dimensions, identify all rooms, include existing/new door and window types and sizes, locations of carbon monoxide and smoke detectors, include existing/new walls; Foundation Plan showing foundation dimensions, anchor bolts, any hold-downs and reinforcing, pads, connection details, and vent size(s) and location(s); Cross section(s) and details showing all framing-member sizes and spacing such as floor beams, headers, joists, sub-floor, wall construction, and roof construction. More than one cross section may be required to portray construction clearly. Details of all wall and roof sheathing, roofing, roof slope, ceiling height, siding material, footings and foundation, stairs, thermal insulation, wall covering, etc.); elevation views showing elevations for new construction (minimum of two elevations for additions and remodels; floor/roof framing showing all floor/roof assemblies indicating member sizing, spacing, and bearing locations; beam calculations using current code design values for all beams and joists or any beam/joist carrying a nonuniform load. Engineer’s calculations when required or provided, (i.e., shear wall, roof truss) shall be stamped by an engineer or architect licensed in Oregon and shall be shown to be applicable to the project under review. For additional information and requirements please see the Building Permit Application – Residential.
New Construction and Additions
When an ADU is constructed as an addition or separate detached accessory structure, the construction shall comply with the requirements of the Oregon Residential Specialty Code as a two-family dwelling and the City Development Code.
Alterations to the Existing Dwelling
When an ADU is created by converting existing space within the primary dwelling, the construction shall comply with the requirements of the ORSC and City Development Code.
Dwelling Unit Separation:
Dwelling units must be separated by a 1-hour fire resistant rated assembly (vertical or horizontal). Horizontal assemblies must be supported by 1-hour fire resistant rated construction. No openings are allowed in the fire resistant assembly. Exceptions may be considered based on an alternate design submitted with a minimum 1-hour fire resistant rated door assembly with a self-closing device. The ADU shall have a separate exterior entrance or a common internal area accessible to the outside. Mechanical, electrical and plumbing membrane penetrations and through penetrations in a 1-hour rated assembly have special requirements per the Oregon Residential Specialty Code. Demising wall and floor separations must meet STC rating of 45 or better.
Room Sizes:
Habitable rooms shall have a floor area of not less than 70 square feet, except kitchens. Habitable rooms shall not be less than 7 feet in any horizontal dimension.
Ceiling Heights:
All habitable rooms require a minimum ceiling height of seven feet. Rooms with sloped ceilings require at least 50 percent of the required floor area to have a ceiling height of seven feet and no portion of the required floor area may have a ceiling height of less than five feet. Conversion of existing space may have a minimum ceiling height of not less than 6 feet 8 inches.
Light and Ventilation:
All habitable rooms shall have glazed openings of not less than eight percent of the room’s floor area, and a minimum openable area to the exterior of four percent of the room’s floor area.
Emergency Egress:
Sleeping rooms in the ADU are required to have an emergency egress door or window that opens directly to the exterior. The egress openings shall have a minimum net clear opening of 5.7 square feet (5 square feet for windows opens directly at grade level). The minimum clear opening dimensions shall be 24 inches height and 20 inches wide. Emergency egress doors or windows shall be openable without any special knowledge, tool or key.
Doors:
Not less than one egress door shall be provided for each dwelling unit. The egress door shall beside-hinged and shall provide a clear width of not less than 32 inches where measured between the face of the door and the stop, with the door open 90 degrees. The clear height of the door opening shall not be less than 78 inches in height measured from the top of the threshold to the bottom of the stop.
Smoke and Carbon Monoxide Alarms:
The ADU and primary dwelling unit shall be equipped with smoke alarms. Where any fuel burning appliance is present, the ADU and primary dwelling unit shall be equipped with carbon monoxide alarms.
Energy Conservation:
New construction, additions and spaces not previously heated or cooled are required to meet the SBC energy efficiency requirements. All new doors and windows are required to meet the SBC energy efficiency requirements.
Electrical Systems:
The ADU must have readily accessible access to the electrical service panel. The NEC’s definition of readily accessible states: “capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to actions such as to use tools, to climb over or remove obstacles, or to resort to portable ladders and so forth.” Any electrical work must be performed by a licensed electrical contractor.
Heating/Cooling Systems:
The ADU must have a separate heating system (and cooling if provided). A ducted heating/ cooling system serving the ADU must be separate from the ducted system serving the primary dwelling. Other non-ducted systems must have separate climate controls for the ADU and the primary dwelling.
Plumbing Systems:
The ADU and primary dwelling unit may be served by a common potable water and sanitary sewer system. The ADU must have access to the plumbing shut off. A 3-inch sanitary building drain and building sewer cannot serve more than three water closets. Plumbing work must be performed by a licensed plumbing contractor. Additional plumbing fixtures may require upsizing of water meter. Contact the City Utility Billing Division at 503-718-2460 for water meter information.
Addresses:
Approved ADUs require a separate address from the primary dwelling prior to building permit submittal.
Fees:
Aside from the various permit fees that will be required, new ADUs must pay system impact fees or System Development Charges (SDC) Fees. Contact the Permit Coordinator at 503-718-2426 for an estimate. The information provided is not all inclusive.
For more information, please contact the appropriate entity noted above.
