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Development Services

From Concept to Construction

Phone: 503-823-7300

TTY : 503-823-6868

1900 SW 4th Ave, Portland, OR 97201

Dormer or Second Floor Additions

Information on adding onto your house or duplex, when the scope includes expanding the upper story or attic outside of the existing roof or envelope.

Applying For My Permit

The following information must be submitted when applying for a permit to add a dormer or second floor to an existing one or two family dwelling. Since every project is unique, there may be some situations where you will be asked to provide additional information.

Site Plan (Scale site plans to most appropriate scale, e.g. 1”=10’ or 1/4”=1’)
  • Property lines, with dimensions
  • Total area (in square feet) of the lot
  • Adjacent streets and any easements
  • Property address and R number
  • North arrow
  • Distance between buildings and between buildings and property lines
  • Dimensions and area (in square feet) of any proposed paving. (If your project will add more than 500 square feet of impervious area you will need to provide a mitigation form and/or a stormwater plan).
Architectural Plans (Scale of plans to be ¼”=1’ and details scaled to ½”=1’. Single line drawings are not acceptable – plans must be drawn to show wall thickness)
  • Fully dimensioned floor plans (including locations) for each floor affected
  • Use of each room
  • Plumbing fixture layout
  • All exterior building elevations affected by the addition
  • Building sections showing typical wall, floor, ceiling, roof and foundation
  • Stair details with dimensions for risers, treads and handrails
  • Insulation R value for ceiling, walls and floors
  • Gas/oil furnace and water heater location
  • Electrical light fixtures, smoke detectors and fans
  • Details of all non-typical construction
Structural Plans (Scale of plans to be ¼”=1’, details to be ½”=1’)
  • Foundation detail showing existing foundation wall thickness and footing size
  • Cross sections showing framing members, insulation, blocking, materials and floor to floor dimensions
  • Floor framing including member size, spacing and span
  • Roof framing including member size, spacing and span
  • Prescriptive wall bracing floor plans (not required if structure is engineered)
  • Any engineering calculations may be attached to the plans and engineering details incorporated into the plans or cross-referenced on the plans
  • Prescriptive wall bracing worksheets (not required if structure is engineered)
  • Connections to existing construction
To submit for a permit, bring the completed building permit application and four (4) copies of site, architectural and structural plans (for the area of proposed work and areas affected by such work) along with intake fees to the Development Services Center.
 
If you are hiring sub-contractors to do work on your project, and know who they are when applying, they will be listed on your permit at that time. If you don't know when you apply for your permit, they can be added after issuance. Sub-contractors you hire must be registered with the State of Oregon and will carry a current CCB license.
 
Things to consider:
Note: To make conversions easier, the Bureau of Development Services has set up the following special standards for existing situations:
  • Ceiling height in basements, attics and bathrooms
  • Stairs
  • Emergency Egress Windows
  • Insulation and Ventilation
(1) Evaluating Existing Space
In unfinished areas, existing features such as ceiling heights, windows, stairs and insulation may not meet current building code requirements for finished space. These conditions could make it expensive, difficult or even impossible for you to change your attic into living space. It is best to complete your research on the existing conditions before submitting plans for review.
 
(2) Attic Conversions
You must determine if the existing attic floor structure is strong enough to carry the weight of people and furniture.
 
If converting attic space to living space would mean raising the roof, the zoning code height regulations may affect your project. 
 
(3) Residential Engineering
Your project must be designed to meet all the requirements of the building code. This usually means that a full foundation with footings to the frost depth, and a complete lateral force resisting system are required.

The building code has two options for showing the building will resist lateral loads. More Information on Residential Engineering 
 

Note that plans and calculations will not be required to show that a structure will resist wind and earthquake loads if it can be considered a "minor" addition. See Lateral Bracing for Minor Additions and Dormers.

When the scope of work will change the structural load in the house, it is important that you submit engineering calculations that show the continuity of the load path from floors or other affected members all the way to the foundation of the house. It is very common that when tracing floor loads from the converted attic, it is the beam in the basement that will be overstressed. Situations like this are required to be resolved as part of the permit application. 
 
(4) Floodplains

If your house is located in a floodplain, the ability to do these types of improvements may be severely limited. Please contact Site Development staff at (503) 823-6892 to discuss your project.