Can You Use 2X4 For Deck Joists?

Are you building a low, ground-level deck? Small decks with a small step to reach the ground are easy to make using standard building materials. But even low decks need joists for support. With 2x4s as the thinnest joist option, the question becomes, can you use 2×4 for deck joists safely?

You can use 2×4 for deck joists, but only if the span is under 5’5”. A low deck like this is ideal for small, ground-level decking without stairs or guardrails. The wood type and your local building codes also determine your guidelines for safe construction.

In this article, we’ll discuss the limitations and specifications for building a deck with 2×4 deck joists.

Can You Use 2X4 For Deck Joists

Can You Use 2×4 for Deck Joists Safely?

The short answer is yes. 2x4s can work for deck joists. However, they aren’t ideal for spanning long distances without bending or breaking, so you have some limitations. Choosing 2x4s for a low-sitting deck is perfect for keeping your feet out of the mud. Or select 2x4s if you only want to use a single wood size. Either way, 2x4s as deck joists are safe as long as your design doesn’t span too far or include guard rails or stairs.

The other main limitation is the size of your deck. 2x4s are the smallest dimensional option, making them great for low, ground-level decking if they’re spaced no further than 12” on center. “On center” is the term to measure from one joist to the next, starting from one center to the center of another.

However, the smallest joist size you can use in deck construction depends on the number of beams and footings you install. Different wood types come with support and span specifications as well. These elements contribute to the structural integrity of the deck frame.

For a larger deck using 2×4 joists, you need added support. A support beam, post, pad or post buried in the ground at each end and at the mid-span would better support the joists. The goal is to provide enough stability for the decking to stay strong. You don’t want the wood to flex as you step on it.

To ensure your deck is structurally sound, check with local building codes. Building codes regulate the design and construction of structures in your area. They may include minimum requirements or otherwise affect your construction project.

Check with Local Building Codes

You want the deck you build to be aesthetically pleasing, but the most crucial part is to ensure that the deck is structurally sound. You should check with your local building codes by contacting the building inspection department, office of zoning and planning, or the department of permits.

You may need a license to build a deck in some locations. Ground-level decks rarely require you to get a permit or seek out a building inspector. You can use any material you want without permit guidelines. Adhering to your local building codes as much as possible ensures the deck will safely last for years to come.

Using 2x4s as deck joists also may not meet the minimum building codes in some locations. Areas where hurricanes or tornadoes are prevalent, like Virginia, Florida, or tornado alley have some of the country’s strictest building codes – light decks can become flying hazards in strong winds.

How Far Can You Span with a 2×4?

2×4 deck joist span

The larger your deck, the larger the deck joists must be. 2×4 joists spaced 12” on center can span no more than 5’5” between supports. This guideline limits a deck built entirely from 2x4s to a small size, or you would need to add a mid-span support beam.

Most deck joists are 16” on center, which allows you to span 1.5 times the depth in feet. It’s more common to see decks made using 2×6 to 2×12 dimensional joists. Some builders reduce the joist spacing to 12” on center to increase the maximum joist spans allowed or to strengthen the frame.

If you want to build a deck entirely with 2x4s spaced at no more than 12” on center, expect to only span around 5 feet on average.

The type of wood you use also affects the amount of span. Composite decking, for example, comes with different installation requirements when it comes to joist spacing. Many composite decking materials require a maximum of 16” on center joist spacing. Consider the species of your materials using the span table below.

Species Size Spacing Span
Aspen 2×4 12” 4’2”
Beech-Birch-Hickory 2×4 12” 5’6”
Eastern Softwoods 2×4 12” 4’2”
Eastern White Pine 2×4 12” 4’2”
Southern Pine 2×4 12” 5’5”
Douglas Fir-Larch 2×4 12” 5’2”
Hem-Fir 2×4 12” 5’1”
Spruce-Pine-Fir 2×4 12” 5’1”
Mixed Southern Pine 2×4 12” 5’1”
Alaskan Cedar 2×4 12” 4’10”
Mixed Oak 2×4 12” 5’
Redwood 2×4 12” 4’7”
Western Cedars 2×4 12” 4’7”
Mixed Maple 2×4 12” 4’7”
Northern Species 2×4 12” 4’4”
White Oak 2×4 12” 5’
Yellow Cedar 2×4 12” 5’
Yellow Poplar 2×4 12” 4’7”

Don’t see your wood type listed in the table? The American Wood Council offers a span calculator that’s extremely helpful in determining the maximum horizontal span depending on specifications like wood type, grade, and size.

How Much Weight Can a 2×4 Joist Support?

Small, low-level decks tend to have a lower weight maximum. The amount of weight a 2×4 joist can support would depend on multiple factors, like the spacing and shape of your deck, the wood grade and form, the load duration, and the actual weight of the 2x4s. If you know the weight capacity you hope to achieve, you can select the best materials for your project.

An 8-foot square deck with 12” spacing between joists could support 1,000 pounds vertically if you use top-quality wood species and no wind force present. Try using a wood column capacity calculator to find the exact amount of weight a 4 or 5-foot deck could support.

Keep in mind that you should never try to push any material to its limit. Use braces to secure the 2x4s and consult a professional if needed.

Building a Ground-Level Deck with 2×4

Building a ground-level deck without stairs or guardrails is the best option if you’re only using 2x4s. Ground-level decks rarely require a permit, so you can choose the wood species you prefer. These decks are small, and joists typically span around 5’.

With ground-level decks, you also want to treat the material for ground contact. Any lumber within 6” of the ground requires protection. You can use ground contact treated lumber or insert a cover under the deck to keep the material safe. This layer prevents weeds and plants from growing through the decking and keeps the wood from rotting.

Placing a layer of gravel around the outside border of your deck also helps to prevent rot. You want to have sufficient drainage to keep the decking in good shape. Ventilation is achieved in other ways with a low deck as well.

To build a more significant or higher above-ground deck, you would need to either move up to 2x6s or add more support to the joists. Another option is to create two 2×4 deck sections and nail or screw the two pieces together for a full-size deck with deck blocks for support.

Most builders stick to using a minimum of 2x6s for deck floor joists. If you want to add guardrails and stairs, you need at least 2x10s. 2×4 and 2×6 joists are ideal for ground-level decks without guards. However, these guidelines vary by location. The Canadian Wood Council, for example, requires a deck with guard rails to have at least 2×8 joists.

If you use 2x4s for deck joists, it may cost more money and work in the long run. The material costs more than if you purchase 2x6s because the 2x4s can’t span as far, and you must create more beams and footings for support. You also can’t include guardrails and stairs with 2x4s as your support.

The best board type to use for decking is pressure-treated lumber. It has a nice appearance and holds up well if you’re building near the ground. Another option is incised wood for ground contact or seal cuts with preservatives. These boards aren’t as prevalent because they’re more expensive and less aesthetically pleasing, but they work well for building on the ground.

Check the stamping on the lumber to identify the perfect type for your deck. The stamp indicates characteristics like ground-treated. Most wood types show Stand or BTR stamps, which means they meet the standard requirements for light framing.

What Size Boards Should You Use for Decking?

Decking over 2×4 joists is much the same as decks with larger dimension joists. The 12”o.c. spacing is ideal for most natural or manufactured boards. Pressure treated, composite, or PVC boards in 5/4”x6” are common and would work well for decking, as do 2×4 and 2×6 planks. The choice comes down to cost, maintenance, and aesthetics.


Building a deck entirely from 2x4s is only possible with a small, ground-level deck. The type of wood determines how far you can space and span the joists, and thus, how large a deck you can build.

Make sure the decking is ready for ground contact and always check with local building codes before building. The boards should be pressure-treated lumber and the deck ventilated to prevent moisture damage.

Are you planning to use 2x4s for deck joists? Let us know what you think in the comments and share this article with your friends.

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