Proper Deck Board Spacing: Last Guide You’ll Ever Need

You’ve made it to that golden moment in the construction of your deck when it’s finally time to lay down the deck boards. But as you install that first and second boards, you suddenly find yourself in a quandary. What is the proper deck board spacing? Should they butt up against each other, or do you need a gap? And if so, how big should the gap be?

Proper deck board spacing should have a 1/8-inch gap after the decking has dried out. If you install your decking using wet boards, pressure-treated decking that has not yet dried out, then you should install them with no gap as a gap will be created as they dry and shrink.

Deck spacing isn’t anything to take lightly. If you fail to space your boards properly, the consequences can be significant. Poorly spaced boards can lead to damage to deck boards and even your deck framing, or it may leave gaps that may make your deck unsafe for walking.

Factors That Influence Deck Spacing

When considering deck spacing, it’s important to remember that wood is made up of fibers that are capable of retaining moisture. The more moisture present in those fibers, the more they will expand, making the wood bigger. The less moisture, the more the wood will contract.

Because decks are outside, they are continuously exposed to changing humidity. During more humid seasons, like summer, decking will soak up more moisture, causing the boards to expand.

During the winter, when the humidity is significantly lower, the wood will dry out and reduce in size. You might have noticed this quality if you live in an older home that has solid wood doors. A door that might work just fine in the winter may in the summer swell and not close properly in its door frame.

With this in mind, if you’re installing decking in the summer, you could install it with a minimal gap, knowing that in the winter, the wood will shrink, creating a larger gap. Likewise, if installing in the winter, you might need that quarter-inch gap to account for the wood swelling come summertime.

These seasonal effects on your deck are dependent on where you live. If you live in an area that sees wide changes in humidity, you’ll need to pay attention to these factors. However, if you make your home in say Denver, Colorado, where humidity stays consistently dry throughout the year, you don’t need to worry about how humidity will affect your boards.

Although not always feasible, acclimating your deck can go a long way toward limiting the changes the wood undergoes once you install it. Most of us will purchase our wood from a big box hardware store where it has been stored in a climate-controlled area.

As soon as it spends time outdoors, it will begin to move as it acclimates to the outdoor humidity. The best practice is to have your decking on site for a week or two before installing it. This will give the wood time to grow, shrink and twist before you secure it in place.

If you can acclimate your wood, cover it and make sure it is not sitting directly on the ground, so it doesn’t soak up rain or groundwater.

The types of fasteners you choose can also affect deck spacing. While your standards nails or deck screws won’t affect spacing, fasteners for hidden screw systems like Camo or Kreg Jig will have set spacing with their installation tools that may not be able to be adjusted.

If you are planning on using one of these systems, check to make sure the one you choose offers the spacing you want before committing to it.

You’ll also want to take into account the type and intervals of your fasteners. Fasteners are what hold boards in place, resisting their efforts to bend and move as the humidity changes.

Make sure you are using enough fasteners to make your decking stay put. With this in mind, consider using screws over nails. Screws have threads that bite into the wood, making them much more likely to hold boards in place when they begin to expand and contract than nails, which can pull out more easily.

The initial moisture level is also important to consider. Treated decking, for example, can have a high moisture content when purchased, especially if it was recently treated.

You can usually tell how “wet” treated wood is by its green color. Wet wood takes time to season. Over months, treated wood will dry out and contract. You need to take this into account when determining your spacing.

Finally, wood species can also impact spacing. Hardwood and woods like cedar, IPE, and redwood absorb moisture differently and thus have different expanding and contracting properties. Make sure to consider the properties of the wood you are using when considering what size gap to use.

Why the Proper Deck Board Spacing Is Important

While the gap in your deck boards may seem like a small step in a deck project, the gap size you choose serves a significant purpose. Decking board spacing provides airflow through your deck, allowing evaporating air to escape. This helps to keep your deck’s framework dry and rot free.

Spacing is also important for drainage. The gaps allow rain and snow to drain through rather than a puddle on your deck, resulting in an unsafe walking surface, and the growth of mold and mildew.

Depending on where your deck is, you may also have a fair amount of debris raining down on it. Gaps in your deck allow this debris to fall through to the ground. Gaps that are too small will trap debris, creating an environment for rot.

Gaps between your deck boards also allow for expanding and contracting. Without gaps, the boards have nowhere to go when they expand, causing them to buckle and crack.

This can even cause damage to the joists they are attached to. Gaps that are too large are unsightly, cause tripping hazards and make your deck more susceptible to fire.

What Is the Proper Spacing Between Deck Boards?

Before deciding on how much space to leave between deck boards, check with your local building code to see if it covers deck board spacing. Many jurisdictions following the International Building Code, which requires a minimum 1/8-inch spacing between boards.

Generally, an acceptable gap between deck boards is between 1/8 inch and 1/4 inch. Both sizes have their pros and cons.

The eighth-inch spacing provides for a safer surface for walking. Smaller gaps mean fewer trip hazards or opportunities for high heels or a child’s fingers to get caught in the cracks. Smaller gaps also mean less airflow, reducing fire hazard.

But this also means there will be less ventilation under your deck. Smaller gaps also mean your deck won’t drain quite as well as a deck with larger gaps. It is also more likely to trap debris. Smaller gaps mean more boards, which means more weight on your deck.

Quarter-inch spacing does allow for better ventilation, drainage and debris removal. It also means fewer boards, which means less weight on the joists. However, wider gaps create more opportunities for trip hazards. The increased airflow created by larger gaps also makes your deck more of a fire hazard.

With these pros and cons in mind, many builders choose to split the difference and go with 3/16” spacing between deck boards.

The size of the gap you should use is also contingent on the type of decking material. Spacing with composite deck boards is just as important as it is with conventional wood. Like real wood, composite boards will also expand and contract as the humidity changes. Leave at least a 1/8″ gap between composite boards.

Determining the gap with pressure-treated decking can be a bit more complicated. Remember, pressure-treated wood is often sold wet, meaning it has not yet tried out from the chemical treatment it received.

Once installed, treated wood will dry out for a few months, which will cause it to shrink. With this in mind, wet wood should be installed butted together as a gap will be created as the wood dries and shrinks.

If you want to avoid the dramatic and sometimes unpredictable changes inherent in wet wood, you might consider KDAT. KDAT decking has been dried in a large oven or kiln to remove excess moisture from the wood.

This makes the wood less susceptible to cupping, warping, expanding and contracting that wet wood typically undergoes. This means KDAT can be installed with a 1/8-inch gap. It should be noted that KDAT does need to be immediately stained and sealed after installation to protect it from the sun.

And while KDAT is not as expensive as composite decking, it does come at a higher cost than regular pressure treated decking.

Cedar, a popular choice for decking, can also be spaced with a gap between 1/8″ and 1/4″. If the wood is not seasoned, expect the boards to eventually shrink as the sap and moisture dissipate from the board, making the gap larger. If this is the case, go with 1/8″ spacing to ensure you don’t end up with gaps that are too large and potentially unsafe.

Conversely, dry cedar boards should be spaced 1/4″ apart to avoid damage when the material absorbs moisture and expands, narrowing that gap. Leave a 1/8″ space between butted ends as cedar will also expand lengthwise.

Redwood can be spaced similarly to cedar. Again, consider how dry the wood is and the season before deciding on going with the wider 1/4” gap or a 1/8” gap.

How to Space Deck Boards

Whether you choose 1/8” or 1/4” spacing, there are a variety of ways to achieve uniform spacing between your deck boards.

A 1/8” gap can easily be accomplished through the use of an 8d nail. Lay the boards in place, using several 8d nails as spacers. While pushing the board flush against the spacers, secure the board into place with your choice of fastener.

While nails are good spacer options, they can also be difficult to work with. Nails can easily slip out of your fingers or between the boards and onto the earth below.

If nails aren’t working for you, you might try these other options:

For 1/8” gaps, try a speed square, which happens to be about 1/8-inch thick. Simply slide the square into place between the boards. Push the board firmly against the square and attach the board to the framing.

If you’re trying to create a 1/4” gap, try 1/4-inch thick plywood. Cut a narrow strip of plywood, then slide the strip between your deck boards to create an even gap.

Not sold on these DIY options for creating a perfect gap between your deck boards? Then consider investing in a professional spacing tool.

Best Deck Board Spacing Tool Reviews

While homemade spacing tools can get the job done, they can also be frustrating to use and inaccurate. Nails fall through cracks as you’re working the boards into place. And wooden spacers can get stuck in gaps after you’ve finished securing the boards, forcing you to spend time and energy prying them free.

Deck board spacing tools are designed to make the decking installation process faster by eliminating those problems.

The Camo Marksman Pro

If you’re using the Camo Edge Fastening system to attach your decking, then you don’t need to worry about spacing. Camo’s patented tool, the Camo Marksman Pro , will handle this for you.

The tool automatically creates 3/16-inch spacing. The cool thing about this tool is that it allows you to get exact spacing while at the same time installing your fasteners, saving you a significant amount of time.

Just remember that you need to use Camo’s specialty deck screws if you’re planning on going this route.

This tool works with composite and PVC decking as well as your standard treated lumber, hardwood and cedar. The downside is, if you want a gap smaller or larger than 3/16 of an inch, you’re out of luck.

This tool only creates one gap size.

 

Kreg KJDECKSYS Deck Jig

Kreg is famous among woodworkers for its collection of innovative tools that help DIYers join wood while hiding unsightly screw heads. KJDECKSYS hidden fastener deck kit from Kreg helps you space your deck boards evenly while affixing them to the frame.

The kit includes two different sizes of spacer rings that easily slide into the spaces between your decking without falling through. Each ring has a large handle that makes it easy to grip between your fingers.

The spacers included with this system, however, are large at 5/16″ and 1/4″ widths, so if you’re after a 1/8-inch gap, the KJDECKSYS won’t work for you.

Also, keep in mind that this is an entire hidden fastener system, so the price point will be higher.

 

Johnson 60-275 DeckMate Spacing Gauge

If you’re looking for a solid deck spacer that won’t cost you much, then look no further than Deck Plank and Fastener Spacing Gauge offering from Johnson Level & Tool. This little tool, which slides easily into the space between your boards, provides 1/8-inch or 3/16-inch spacing.

As an added benefit, the frame of this deck spacer doubles as a nail/screw layout guide for 2×6- inch or 2×4-inch decking. The Johnson 60-275 Deckmate is made out of hard plastic that will hold up even when being pried from tight-fitting boards.

And the best part is, this tool won’t cost you much more than lunch at your favorite fast food joint.

Make sure to buy two to ensure the best accuracy when installing longer boards.

 

Myard DJS3.2 1/8 Inches Deck Board Spacer Rings

Myard offers maybe the broadest set of size options with their deck spacers. Deck Board Spacer Rings come in five different sizes ranging from 1/8″ to 5/16″, allowing you to customize the gap between your boards.

This is especially useful when having to tweak your spacing to square your boards. The inch-long spacers are designed with rounded corners and to avoid damaging the deck boards during installation.

It also includes a handle for your fingers that makes it easier to free the spacers from fastened boards.

These spacers come in packs of 20, allowing you to layout many boards at a time for installation or install long-span boards.

 

JIG-A-DECK Deck Spacer & Fastener Alignment Guide

This tool spaces your deck boards and gives you a guide for a perfectly straight line of screws. What’s not to like about JIG-A-DECK’s spacer and alignment guide for decks.

This spacer also includes a guide for both 4″ and 6″ wide deck boards. And unlike other spacers that only provide you a tab large enough to fit a finger or two, this spacer includes a full-sized handle. This makes it easy to yank the spacer free after your deck boards are secured.

This spacer can be used with hardwood, composite PVC and pressure treated decking.

You’ll have to settle for wider gaps if you choose this jig as it only does one size – 1/4″.

 

Speed Square

Tired of cluttering your workspace with specialty tools that serve only one purpose? Looking for an old school solution to your deck spacing problem?

Try a speed square. This heavy-duty aluminum-alloy speed square makes for a nice 1/8″ spacer between your deck board. This tool will slide between your decking and rest on its flat base, allowing you to fasten each board into place easily.

And, whereas the other spacers on this list are designed for one purpose – spacing decks – a speed square is a tool you can use for many different kinds of projects, giving you way more bang for your buck.

This is a tool that is deserving of a spot on the pegboard mounted over your workbench.

 

Cepco Tool BW-2 BoWrench Decking Tool

If you’ve ever worked with wood, you know that some boards need a little persuasion to get them to line up with all of the straight ones. Even the pickiest pickers at the lumber yard (you know, the ones that leave a stack of warped boards after they’ve dug through the pile in search of the straightest ones) will end up with a few duds.

The deceptively small CEPCO Tool BW-2 BoWrench decking tool will give you all the persuasion you need to straighten those bowed deck boards. Simply attach the tool to a perpendicular joist and give it a pull close gaps up to two inches big.

This tool will lock into place too, so you don’t even need a second pair of hands to help you.

 

Decking Spacing Tips

One of the tougher tasks to accomplish, especially if you are by yourself, is getting a tight fit against your spacer as you install each board. If you’re looking for a quick fix, try using a chisel to give you leverage.

Start a nail or screw in the board. Then put the edge of the chisel into the joist pressed against the edge of the deck board.

With your spacer in place, pull the handle of the chisel to you to bring the board tight against the spacer. Then use your other hand to drive in the screw or nail.

Having trouble getting your boards to square up with the house? Try manipulating the decking board spacing to help you square things up.

When installing the decking, make sure to start on the outside edge of the board and work toward the house. When you get about five feet from the wall, measure the remaining width at both the ends and the center.

Then vary the gaps between the boards as you move to the wall to square the deck to the house. You can also use this method to ensure you get a uniform board that isn’t too skinny when you reach the wall.

What if Space Between Decking Boards is Too Wide?

Despite your best efforts to get the right gap between each deck board, you’ve ended up with gaps that are too wide. What do you do? Is ripping up the boards and doing a full reinstall your only option?

How Do You Widen Space Between Deck Boards?

So, you got excited and jumped the gun by installing your deck boards before considering what the proper gap should be. Now you’ve ended up with a gap that is too small. You’re kicking yourself and rightly so.

Don’t despair! There is a solution here. You’re not the first one to make this mistake and you certainly won’t be the last. The folks at Lounsbury Products LLC know this, and they’ve designed The Saw Guide to help you.

The Saw Guide is an attachment for your circular saw specifically designed to widen the gaps in decks. The guide is designed with grooves that slide into the gaps in your deck, allowing you to make an even cut along each board and widen the gap.

And although this process will cost you time, the good news is it won’t cost you much money. The Saw Guide is $16.95 at the Lounsbury site.

 

Conclusion

Proper spacing of your deck boards is a critical step that shouldn’t be overlooked. The wrong spacing can turn the deck project you’ve spent so much time and money on into a disaster.

Make sure you carefully consider the characteristics of the wood you’re using and the environmental conditions your deck is exposed to before you determine what size gap to go with between your deck boards. With careful consideration and a little planning, you can ensure the boards on your deck are spaced perfectly.