Building Location, Fire-Rated Construction, and You

Everyone wants to make the most out of their property. Maximizing your open space is the most common approach, and locating your buildings (including accessory structures) as close as possible to your property line is one way to increase the open space between – and thus maximize the usable square footage of – those buildings. However this can come at one fairly big price: fire resistant requirements. This post will explain what has to be fireproofed, what that means, and what that means to you.

What Has to be Fire Resistant (aka Fireproofed)?
Any part of a building that comes within 5 feet of a property line must be fire resistant. This includes buildings on your own property like an ADU, workshop, or garage. The easiest way to imagine this is to draw imaginary property lines between your own buildings and apply the exact same logic to them as you would to your property’s boundary lines.

This means eaves, roofs, and walls that are within 5 feet of a property line must be fire resistant. One big aspect of this pertains to openings in walls and eaves. Opportunities for window, door, vent, or mechanical openings become limited if that wall is within the 5 foot zone. Existing buildings require this same level of fireproofing if they are going to be modified.

What Are the Ramifications?
This means that you must pay close attention to building locations and adjacencies and identify any assemblies for walls, roofs, or eaves, that must be fire resistant. Then the design and detailing of these assemblies must satisfy the specific requirements in California Residential Code (CRC), meeting minimum fire-resistance rating of 1 hour.

In general this means that you must have a layer of Type X Gypsum board wrapping the fire resistant areas of the building on the outside and the inside. By creating a fire resistant layer on both sides, heat transfer is slowed into the assembly giving occupants and the fire department time to extinguish the source before temperatures get high enough to initiate combustion on the other side. Fire blocking is also required to stop the spread of flames and hot gasses inside the assemblies.

One of the more complex aspects of this rule is in vented roof systems, which are required by Code. A properly vented roof will have ventilation ports both at eave level and at the ridge. In the case of buildings requiring fire-resistive construction both eave and ridge venting assemblies must be specially constructed and detailed, thus adding to construction costs.

What Does this Mean to You?
This means that if you want to maximize your property by building close to the property lines, you will have to fireproof your plans and make sure you are either outside of the 5 foot zone or plan on following these very stringent requirements. This can add costs and technical difficulties but may be the trade-off you are looking for.

For Further Reading:
• Builder Magazine features an extensive article at:
• An article on fire-resistant homes can be found at SF Gate:
• Fire-resistant construction is an important aspect in the CA Wildland-Urban Interface (WUI) zone and is described in detail at wikipedia. The link is:

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