10 Things to Know Before You Build a Deck

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

Tip

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.

Tip

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.

Deck boards make up the useable surface of the patio. They are the most visible part of the structure, and one that’s most exposed to the elements. The boards are supported by perpendicular joists which run beneath them, and carry the weight of people and things between the joists..

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.

Tip

Strengthen your deck frame with blocking between joists. This is often required at edges, but is beneficial throughout. Use the lumber left over from joist installation to make the blocking members. Blocking is typically spaced at 48 inches on center or less.

4. Connection to Home - Know Your Options

Decks can be freestanding or attached to the home. Opting for a freestanding deck will spare your home’s structure from the added loads, and will keep the envelope intact. The tradeoff is the cost of adding footings and framing to the structure.

Should you settle on attaching the deck to your home, the deck and home structures will have to connect. To do this, you will need to locate the home’s rim joist, strip the adjacent exterior finish, and attach a ledger board. Make sure to cover the ledger with corrosion resistant flashing to prevent water from contacting the rim joist. Deck joists can then be fastened to the ledger with joist hangers.

Tip

Despite additional foundation costs, freestanding decks have several advantages. They don’t penetrate the envelope, sparing you from potential leaks, and don’t add loads to the frame of your home. As an additional perk, freestanding decks that are less than 30 inches off the ground do not require a permit in most jurisdictions of the State.

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.

Tip

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.

6. Stairs

Stairs provide a transition from your home to the deck, and from the deck to the yard. Deck stairs are a system made up of treads, risers, stringers, footings, connectors, and guardrails.

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.

Tip

To make you stairs comfortable, consider the rise-run configuration. As a rule of thumb, the sum of the tread’s width and the riser’s height should equal approximately 18 inches. Make sure whatever you decide still conforms with code requirements.

7. Hardware and Lumber - Corrosion and Moisture Prevention

Moisture is the enemy of buildings. It causes wood to rot, and metal to rust. Because of decks’ exposure to elements, they are particularly vulnerable to impact of moisture.

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.

Tip

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.

All decks over 2 feet above ground must have diagonal knee bracing between posts and beams or posts and joists. Alternatively, connectors that provide resistance to swaying may be used. For higher decks, cross bracing between posts may also be required.

Tip

Attaching a deck adds gravity and seismic loads to the structure of the house. If you live in an older home, you may want an engineer to check whether the foundation and framing can support these added loads. If they don’t, opt for a freestanding deck.

9. Permits

In most jurisdictions across California, all decks attached to a home and those standing 30 inches or higher require a building permit. If your deck falls within these categories, treat it as you would any other construction project, and put together a permit application.

Some authorities having jurisdiction offer standard, pre-approved deck designs. These will expedite your permit process. If you want to deviate from a standard design, you will need at least the documents below to support your deck permit application:

plot plan
foundation plan
framing plan
cross-sections
details

Tip

To avoid multiple revision cycles with your building department, get a professional engineer to design your deck‘s structure.

10. Getting a Permit for a Previously Unpermitted Deck

The process for legalizing unpermitted work may be unique in your authority having jurisdiction, but typically, it follows the stages described below.

Your first step will be to engage with an architect and structural engineer to determine if the deck complies with local and international code standards, including setback requirements, structural stability, and layout. If everything checks out, you should be able to apply for a permit just as you would for a new project and move through without much issue.

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.

Tip

Never mind the reason behind your urge to legalize an unpermitted deck. Your building department will appreciate your voluntary admission and will guide you through all the steps. Our engineers can assist with any code upgrades your deck may need, and will help you get your deck legalized as soon as possible.

How We Can Help

Quality design will leave you with a safe, durable deck to be enjoyed for decades to come. It will also minimize and shorten your visits to the building department before construction starts. Our engineers will provide you with a deck design that’s compliant, elegant and economical. Let us put our expertise to work. Call Design Everest at (877) 892-0292 for a FREE consultation and quote. We can also connect you with a professional engineer or designer right away for a virtual consultation or virtual on-site!