Do You Need A Gap Between Decking Boards?

Do you need a gap between decking boards, or is this not essential?

A gap is needed between your decking boards. These gaps are designed to improve the durability and longevity of your decking and should be roughly 3mm to 6mm (1/8 inch to 1/4 inch). Without a gap between the boards, you can expect to face an assortment of issues down the road.

Benefits of Leaving a Gap Between Decking Boards

The gap that is left between decking boards is for a reason. Here are a few benefits of these gaps.

Enhanced Airflow

To help prevent your deck from rotting, sufficient airflow is important. The circulation of air will help keep the decking boards dry. The amount of airflow that exists will depend heavily on the gap size.

It can also prevent mould and allow rain and snow to drain properly through the deck.

It can also help the decking boards to expand and contract as the humidity levels and temperatures change throughout the year. Without that gap, the boards will swell and rub against each other, causing damage.

Decking Preservation

Again, the gaps between the boards will help with drainage purposes, which helps to preserve the deck in the long run.

While all decking boards are going to shrink and/or expand as a result of the humidity and temperature, it is possible to reduce the amount of moisture that is absorbed into the boards.

When water pools on the surface of the deck, the boards will soak up that moisture and expand. This can lead to the boards placing pressure on each other and deck damage.

Safety Reasons

When the gaps between the boards are too large, the deck can become a safety hazard. If there are no gaps at all or gaps of very small distance, the boards may end up warping and potentially cracking as the weather turns more humid.

This can be due to improper drainage from the smaller gaps. In other words, a small gap distance between the boards will allow water puddles to form on the deck, leading to not only damage but also the increased risk of slipping.

At the same time, though, if the gaps are too large, it can create both a fire hazard and a safety hazard. Larger gaps make the deck harder to walk on easily and make it easier for people to trip.

Factors to Consider When Determining Gap Size

The addition of a deck can be a large job, which means it is important to prepare ahead of time. When it comes to sizing the gap between the boards, there are a few things you must take into consideration to ensure you distance the boards appropriately for your situation.


When constructing a wood deck, you must consider the fact that wood can sometimes hold moisture. Depending on this moisture, the wood will expand, contract, and twist. Lower humidity levels keep the wood from changing considerably.

Therefore, you need to do some research into the average humidity levels and temperatures that occur throughout the year in your area.

For instance, if you live in an area where the humidity changes dramatically from one season to the next, the gap size will need to be chosen accordingly. If there are no drastic changes in the humidity, then you don’t need to concern yourself as much with the climate and how it affects the gap distance.


The time of year you are installing the deck will play a role in how much or how little the boards swell. So, if you are installing your deck throughout the summer months, you will want to leave a smaller gap between the boards so there is room available for expansion.

If the installation of the deck is occurring during the winter months, then a larger gap will be necessary since the boards will shrink, leaving a larger gap in the long run.

Wood Type

The type of wood being used to construct the deck is also essential, as all species don’t absorb moisture the same way. If you get a wood that tends to expand, a larger gap distance will be needed.

The same is true vice versa. Some of the most popular types of wood to use for your deck include cedar, redwood, pressure-treated wood, tropical hardwoods like ipe and mahogany, and composite wood.

How Much of a Gap Is Necessary Between Boards?

As a general rule, a gap size between 3mm and 6mm is recommended.

Opting for a 3mm gap between your decking boards will provide a more secure decking surface. When the gaps are small, there is less of a risk of things getting stuck between the gaps or someone tripping and falling.

However, at the same time, smaller gaps reduce the amount of airflow and drainage, as debris, rain, and snow are unable to fall through.

Choosing to install a 6mm gap between the boards will improve the drainage and allow more airflow. Fewer boards will also be necessary, which can result in money savings in larger projects.

Ideally, you may want to consider going in between these two measurements. If you want any advice on this topic, get in touch with us today.

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