In our previous blog post, we highlighted some of the requirements of the city of San Francisco regarding the replacement of windows on residential property. While the info is absolutely crucial to residents looking to upgrade their home, it’s important to note that these specific requirements vary from city to city. Today we will take a trip further south down the Peninsula and look at the guidelines for San Mateo window permits.

If the exact same size window, with no other alterations, is replacing an older window a permit will not be required to move forward with the install. A building permit will be required if you are:

  • Altering an existing window frame
  • Altering the existing window flashing (i.e. the exterior finish is changed)
  • Installing a retrofit window (i.e. replacing normal glass with Low-E glass)

Applying for the Permit: What You Need

The city requires you to submit plans for the project in order to be approved. This includes documentation that clearly and accurately depicts the size of the project (for example, floor plans and elevations). Keep in mind that the details need to be drawn to scale and clearly outline both the existing and new construction being performed. The city also requires the contact information for both the owner of the property as well as the designer.

Requirements for San Mateo Window Permits

When it comes to the new windows, San Mateo stresses the importance of safety. That’s why all new windows must have new safety glazing if they are located within 24 inches of a door and 60 inches of a walking surface. In addition to that, all new windows cannot have a U-factor (the measurement that gauges heat loss) that exceeds 0.32

In looking at the windows in terms of the room in full, they all have to have some sort of exterior window and/or skylight, and they have to total at least 8% of the total floor area. This means drastic decreases in window size might cause some red flags. Of that 8%, at least 4% of those windows have to be operable (meaning it can be opened or closed).

San Mateo also has several requirements in order to keep all new windows a viable escape option in the event of an emergency. Every sleeping room below the fourth story needs to have at least one window that opens to an alley, yard or public street. These windows also need to have an opening area of at least 5.7 sq. feet, so that a average sized person can get through it easily. If you are installing security bars or grills, there needs to a release mechanism to facilitate a quick escape.

Of course this is just a general overview and any specific questions or concerns with an upcoming project needing San Mateo window permits should contact the Building Division of San Mateo. They can be reached at (650) 522-7172 or via email at

[Image Credit: Flickr / Joe Parks]
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