Adding a deck to your home may sound like a few weeks’ worth of work. Planned correctly it can be, and planning starts with knowledge.
To ensure the safety of decks and their users, State and local statutes regulate most aspects of deck design. Understand these regulations, and you will streamline permitting, avoid construction surprises, and build a safe, long-lasting deck.
The guide below aims to be your crash course of the codes that govern deck design here in California.
1. Consider Setbacks
Most planning departments want to approve your deck before you can apply for a building permit. Although deck zoning requirements may vary between jurisdictions, typically, they are:
- Decks attached to a home must have the same setbacks as the home itself
- Freestanding decks must conform to accessory structure setbacks
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Take the time and research zoning constraints for your location and take them into account as you design your deck.
2. Deck Foundation
Decks are supported by foundations, which transfer loads to the soil. The system comprises concrete footings, deck posts, anchors and post caps.
Footings are concrete pads that typically rest at least 12 inches below the ground. In some areas, they extend deeper based on frost lines or when working on a steep grade. Before digging, it is important to have a structural engineer design the size and placement of these foundations, and to ensure that they do not conflict with utilities. Footing sizes correlate with your deck’s joist and beam spans, and larger decks require bigger footings.
Deck posts connect the footing to the structure. The size of these posts depends on the height of the deck and the size and span of the area above, but often 6x6 or larger wood posts are used. To ensure lateral bracing from earthquake and wind loads on tall decks, posts may be embedded into the soil or concrete footings, or anchored to the footing with mechanical connectors.
Beams are then attached using post cap connectors, and these can also be supplemented with diagonal wood braces for additional bracing.
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You may be able to build small decks that are low to the ground and on a flat grade by yourself. But for larger decks or challenging site conditions, a general contractor will be required to ensure that work is completed safely and properly. And remember: no matter the size, a permit complete with engineering plans is usually required before you start work.
3. Frame
The frame of a deck is like that of a floor. Its primary components include deck boards, joists, rim joists, and beams.
Joists, in turn, support the deck boards. The depth of the joists depends on their spans and spacing - longer spans and wider spacing require deeper boards. Joists may sit on top of beams or hang from their sides. Their ends either attach to the house, fasten to rim joists for lateral support, or are capped off by guardrail connections.
Beams transfer the loads from the joists to the foundation. The configuration of your joists determines the size and span of your beams. Longer joists typically need beams that are deeper, wider, and shorter, or more columns and foundation below will need to be added for support.
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4. Connection to Home - Know Your Options
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5. Guardrail Requirements
Decks higher than 30 inches off the ground must be fitted with a guardrail system along their open sides and at the stairs. Typically, guardrails consist of guard posts, balusters, bottom, and top railings. The system should meet the following requirements:
- The top rail should be positioned at least 42 inches above the surface of the deck, or 34 inches above the stairs’ treads
- The bottom rail should not be more than 4 inches above the surface of the deck
- The guard posts that support it should be a minimum 4 x 4, spaced not over 6 feet
- Guard posts which run parallel to the joists may be fastened to the outside of the joist; those that run perpendicular may be fastened to the rim joist
- The balusters, which are typically 2 x 2, should be spaced less than 4 inches apart
- Guardrails must be able to withstand a single concentrated load of 200 pounds in any direction, applied at any point along the top rail
If you are not sure whether your guardrail system conforms to the above requirements, seek advice from an engineer before you commit to a purchase.
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Safety should be the overriding factor when you design your deck railing, particularly if you have children. The requirements outlined above are the minimum code criteria. Be sure to strengthen your guardrails beyond code requirements when possible.
Treads are the horizontal members onto which you step when you ascend or descend the stairs. They should be at least 10 inches deep and 36 inches long, meaning that the width of the staircase will be at least 3 feet.
Risers are the vertical elements positioned between each tread. The maximum height of a riser is 7 3/4 inches, and it can vary up to 3/8 of an inch if using identically sized risers isn’t possible. If you opt for open space between treads instead of using risers, the tread-to-tread distance must be less than 4 inches.
Stringers are the sloped boards that support the treads, risers and railing, as well as the weight people using the stairs. If your stairs lead down to the yard, the stringers will transfer loads to a concrete footing at the bottom of the stairs. Stringers can be either cut or solid; the former have notches that match the profile of the stairs, whereas the latter don’t. Solid stringers are stronger, and can span a longer distance.
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7. Hardware and Lumber - Corrosion and Moisture Prevention
To prevent moisture-related problems, all of your deck’s framing members should be pressure-treated. Pressure treatment infuses wood’s pores with chemical preservatives, making it resistant to fungus, bacteria and insects. Typically, local building codes require structural members within 12-18 inches of exposed soil to be pressure-treated, but it’s best to check with your local building department.
Protecting deck hardware from corrosion is just as vital as safeguarding wood from rot and fungus. To this end, the CRC calls for galvanized or stainless steel hardware and fasteners to be used in deck construction. In addition, dissimilar metals should not come into contact with each other, as this may corrosion. Similarly, aluminum flashing should not be used with pressure-treated lumber, which contains copper-based preservatives.
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Make sure to consider waterproofing and drainage where the deck boards abut your home.
8. Seismic Requirements
If you are attaching the deck to your house, you must ensure that it's reinforced against lateral loads with at least two hold downs, or other approved tension devices. Standalone decks also need bracing to keep them upright in the event of an earthquake.
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- plot plan
- foundation plan
- framing plan
- cross-sections
- details
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10. Getting a Permit for a Previously Unpermitted Deck
Should a zoning violation emerge, you will have to apply for a variance. Building code infractions will entail remediation and re-inspection of the work before you can apply for a permit. If the deck does not meet structural requirements, more work and design may be required, and this could affect the feasibility of the project. To avoid further code issues, it’s wise to hire a professional engineer to guide you through the repairs.
If your variance application is declined, or the code upgrades are beyond your means, you will have to return the unpermitted work to its “previous state” - i.e., demolish the deck altogether.
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How We Can Help
- https://archive.org/details/gov.ca.bsc.2013.02.5/page/n133
- https://archive.org/details/gov.ca.bsc.title24.2016.02.2/page/600
- https://codes.iccsafe.org/content/IRC2018/chapter-5-floors
*Note: The content published above was made in collaboration with members of Design Everest.
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