How to Easily Space Deck Boards

Why is it Important to Leave a Gap Between Deck Boards?

Whether you’re installing wood, metal, PVC, or composite deck boards, you need to leave space between the boards, and here’s why:

• Avoid buckling: Adding gaps between boards will prevent them from buckling, which could cause unsightly ripples, and, in severe cases, trip hazards or fastener failure.
• Prevent water infiltration: Heavy rain could force water back toward the house if there isn't space between the deck boards for water to drain through.
• Prevent mold: Gaps allow dust, plant seeds, and other airborne debris to be washed away between the gaps. Any organic matter that accumulates on top of deck boards or gets jammed between them will serve as food for molds and mildew. This could make decking look dirty.
• Keep water management systems clean: Trex® RainEscape® Under-Deck Drainage System requires that the decking above have gaps large enough to allow rainwater to wash away any debris that might accumulate on top of the membrane.

Five Factors that Impact Deck Board Spacing

The weather, the location of your deck, the type of material you’re working with, and your personal preference will all influence what the best spacing is for your deck boards. Find out more details below:

1. Temperature at the Time of Installation

Most deck boards expand when outside temperatures heat up, and contract when they cool down. If you installed composite deck boards with no gaps at all on a very cold day in January, when that June sun heats up those boards, they will expand and likely press into one another, causing buckles and distortions. Alternatively, if you leave excessive gaps when installing deck boards in the summer, they could become excessively large in the winter months. (see below for specific gap size recommendations).

2. Moisture Content

While moisture has no significant effect on composite decking, wood deck boards will expand and contract based on moisture content. Moisture plays a substantial role in installing chemically treated wood, which can have extremely high moisture content from the treatment process, which uses pressure to drive liquid chemicals deep into the wood. The gap between recently treated boards will grow as the boards shrink. The most effective way to make sure the gap between your wood deck boards stays as consistent as possible is to use a moisture meter to confirm that the boards have a moisture content of less than 15% before installing them, and to keep them protected with regular coats of moisture-resistant sealant. 

3. Deck Board Size

Longer composite deck boards expand and contract more than shorter boards. 

4. Leaves and Debris from Trees

If your deck is located under a canopy of trees, it will be more susceptible to organic debris like falling leaves, twigs, and seeds that can plug up gaps, which could cause premature deterioration, especially on wood decking. Increasing the size of width-to-width gaps from 3/16 in. to 3/8 in. will allow more of that debris to pass through, and what debris does get trapped will be easier to clean out with a garden hose or pressure washer.  

5. Personal Preference

Trex composite deck boards can be spaced anywhere between 3/16 in. and 3/8 in. While that does not seem like a big difference, it is noticeable, and you may prefer one size gap over another. One simple way to check before you commit is to lay down (without fastening) several boards with spacers of one size between them next to several more boards using spacers of a different size. Then choose the spacing you like better. If you are adding to a deck, you will want to match the existing spacing for continuity. You should always check the Installation Guide of the manufacturer for the product you are installing.

The Problem with Excessively Large Deck Board Gaps

We have already discussed several reasons why deck board spacing is important, and how having no gaps or gaps too narrow can be problematic. But gaps too wide will cause their own difficulties. Deck boards spaced too far apart don’t feel comfortable on bare feet and can be a real hazard for those wearing tall and narrow-heeled shoes. And you don’t want gaps so large that every time a fork or set of keys is dropped, a trip down below the deck is necessary to retrieve them.

Deck Board Spacing Tips

If you don't use self-gapping fastener clips, you will have to find a way to keep the deck boards a consistent distance apart. Here are some practical deck board spacing tips to help you accomplish that:

• House walls and the ends of decks do not always make a perfectly straight starting guide, so snap a chalk line to use as a guide for the first board.
• Deck board spacers can be store-bought tools or simple homemade shims made out of pieces of wood.
• Place the spacers near each joist location as you install the fasteners.
• Apply firm pressure on the board (into the spacer) as you install the fasteners.
• Spacers with wide horizontal wings are less likely to fall between two boards.
• Use bright color spacers to increase visibility and reduce the chance of tripping on one.
• The more spacers you have the faster the job will go. Some pros clamp several boards in place at once (with spacers near every joist) before installing the fasteners.
• Use a clamp or deck board straightening tool to pull crooked boards into place.
• Periodically measure to the wall or the end of the deck from both ends of the most recent board you’ve installed to confirm that the very last board will be the same width down its length. If necessary, make tiny adjustments to the size of the gap to ensure the last board will have a consistent width. 

Hidden Fasteners are Self-Gapping

Maybe the fastest and easiest way to create consistent spacing is to install grooved-edged deck boards with Trex Hideaway® Universal Hidden Fastener Clips if you are building with a composite material. These clips can take the place of Trex® Decking Color Match Screws and Trex® Decking Plugs in the field of your composite deck and are designed to create a gap of 1/4 in. These clips have a tongue on each side that allows one row of clips to secure the grooved edges of two adjacent deck boards. 

Trex Hideaway® Universal Hidden Fastener Clips are Fast and Easy to Use

To install deck boards with Trex Hideaway® Universal Hidden Fastener Clips, simply slide the clips into the grooved edge of a board; hold them in place with a scrap piece of another board, and partially drive in the screws. Then slide the next board into place onto the clips, and finish driving the screws. Install a clip at every joist location. Unlike face-driven fasteners, which require two screws per board at every joist location, only one clip is required between each board. When fewer fasteners are needed to finish the job, the installation process takes less time. 

Trex Hideaway® Universal Hidden Fastener Clips for a Beautiful and Long-Lasting Deck

Trex Hideaway® Universal Hidden Fastener Clips eliminate the need for nearly all face-driven fasteners in the field of your deck. The surface of the decking remains completely unblemished, and their black color makes them barely noticeable between the deck boards.

The screws that are incorporated into the clips are made of stainless steel, so they are guaranteed to last the life of your decking, even in areas prone to the corrosive effects of saltwater spray. Also, using the clips requires fewer penetrations into the joists, which reduces the chances of water infiltration into wooden joists. 

Trex® Universal Fastener Installation Tool

Installing Trex Clips with the Trex® Universal Fastener Installation Tool makes a fast and easy job even more efficient, reducing installation time by up to 50%. The tool eliminates the need to use a scrap piece of decking to hold the clips in place. Instead, each clip snaps into the tool which reduces the chance of dropping them. The nose cone is designed to help quickly guide the tip of the bit into the screw head, and there’s a handy bit holder in the bottom of the tool. The sturdy handle allows you to exert more force on the clip to make sure it’s fitting snugly inside the groove, and using this installation tool also allows you to drive the clip screw into place without having to install the boards on both sides before fulling seating the clip. 

How Far Apart Should Deck Boards be Placed?

The recommended width-to-width gapping for Trex composite deck boards is 3/16 in. in all weather (see heavily wooded exception above). However, composite deck boards expand and contract more along their length than their width. This is why the recommended end-to-end gap is 1/8 in. when deck boards are being installed on days warmer than 40 deg. F, and 3/16 in. on days colder than 40 deg. F. Also, when abutting the ends of deck boards into solid objects like a house, you should leave a gap of 1/4 in. when installing on a day warmer than 40 deg. F. and 1/2 in. on days below 40 deg. F.