How to calculate street-facing windows for your home

When does the 15% rule apply?

This rule applies to houses, attached houses, and most structures that contain residential uses.

Project descriptions that apply:

• Building a new single-family residence (NSFR)
• Alterations or additions that involve the street-facing sides of your home

When the rule does not apply

• Development on flag lots
• Development on lots that slope up or down from the street with an average slope of 20% or more. For how to measure the average slope see 33.930.060.
• Subdivisions or PUDs that received preliminary approval between 09/09/1990 and 09/09/1995

What counts toward meeting this rule?

• Windows used to meet this standard must allow views from the building to the street.
• Windows in garage walls do count toward meeting this standard.
• A main entrance door facing a street lot line.
• On corner lots or lots abutting more than one street, the standard must be met on all street-facing façades (the face of the building).
• For an alteration or addition to an existing development, you may choose to apply the standards of this section only to the portion being altered or added.

What does not count toward meeting this rule?

• Glass block windows and vents
• Windows on garage doors

Sample calculation

First, find what counts toward the total façade area

Look at the front elevation of the house.

In this example, the following will be included in the total façade area:

• Windows
• Doors
• Area behind the front steps above the grade
• Foundation about the grade
• Garage door
• Area of the gable ends

What will not be included:

• Roof area
• Facia board
• Area behind eave
• Minor projections from the side of the house like the bay window and fireplace
• Side walls of dormers

For this example home, the total façade area is 732 square feet.

Next, find what counts towards the windows and front door area

In this example, the following will be included in the total windows and front door area:

• Window openings
• Front door
• Sidelight windows

What will not be included:

• Windows on the garage door

Finally, calculate the minimum area of windows and front door required

1. Multiply the total façade area by 15%.
   
   For this example, the total façade area is 732 square feet.
   
   732.00 sq. ft. x 15% = 109.80 sq. ft.
   
   You will need a minimum area of windows and a front door to total 109.80 sq. ft.
   
    

2. Find out if your design's total proposed windows and front door meet the minimum area we calculated in the first step.
   
   For this example, let's look at the floor plan of the lower floor and the upper floor.
   
   Calculate the area of each street-facing window and door. 
   
   On the lower floor, we have a window, door, and sidelight window. On the upper floor, we have two bedroom windows. Let's calculate the area of each:
    

   Windows and doors that count towards the requirement	Value in feet from the floor plan example below	Calulated area
   Lower floor window:	7 ft. x 5 ft. =	35.00 sq. ft.
   Lower floor entrance door:	3 ft. x 6.67* ft. =	20.01 sq. ft.
   Lower floor sidelight:	1 ft. and 6 inches or 1.5 feet x 5 ft. =	7.50 sq. ft.
   Upper floor bedroom 3 window	6 ft. x 4.5 ft. =	27.00 sq. ft.
   Upper floor bedroom 4 window	6 ft. x 4.5 ft. =	27.00 sq. ft.

   *Standard door height is 6.67 ft. 

1. Then add the areas together to find the total area of the windows and front door we're proposing to build.
    

   Windows and doors that count toward the requirement	Calculated area
   Lower floor window:	35.00 sq. ft.
   Lower floor entrance door:	20.01 sq. ft.
   Lower floor sidelight:	7.50 sq. ft.
   Upper floor bedroom 3 window	27.00 sq. ft.
   Upper floor bedroom 4 window	27.00 sq. ft.
   Total area of proposed windows and door	116.51 sq. ft.

2. Compare the total area of proposed windows and door to the minimum area required that was calculated in the first step.
   
   The total area of proposed windows and door, 116.51 sq. ft. is greater than the minimum area required, 109.80 sq. ft..
   
   Congratulations! Our proposed design meets the minimum requirements for windows and door on the street-facing façade of the house.

Portland Zoning Code

For single-dwelling zones, visit the Portland Zoning Code on Single-Dwelling Zone: 33.110.235 Street-Facing Facades.

For multi-dwelling zones, visit the Portland Zoning Code on Multi-Dwelling Zone: 33.120.232 Street-Facing Facades.

For commercial or mixed-use zones, visit the Portland Zoning Code on Commercial/Mixed Use Zones: 33.130.230.A, Windows in street‐facing facades.

For employment and industrial zones, visit the Portland Zoning Code on Employment and Industrial Zones: 33.140.265.E Residential Development Street-facing facades.

Need help?

If you have questions about requirements for windows and doors on street-facing façades, please schedule a free 15-Minute appointment with a City Planner or call 503-823-7300 to leave a message for a City Planner.