Garden Advice

What Is the Recommended Gap Size Between Decking Boards?

If you’re wondering how to improve the curb appeal of your property, adding a deck should definitely be on the top of your list. There are many benefits to this addition – to improve your garden, create a cosy outdoor area to enjoy with family or friends, or add something interesting to an unused space. An added bonus is the fact that maintenance is not too demanding and it fits almost every design. 

However, if you are planning on building one, you must have asked yourself this question: Just how much of a gap should I leave between the boards? Don’t worry because we have the answer! 

So, if you:

  • Are wondering what gap size will work best for your needs
  • Want to know what effect the spacing between the boards will have in the long run
  • Are looking to find out the recommended gap size between boards

Continue reading to find out!

Things you should take into account when choosing the gap size

Preparation is extremely important when you’re starting such a big project. So to make things easier, we’ve summarised the most important factors for choosing the gap size between deck boards. 

The climate in your area

The first important thing to note is that wood can hold moisture. It expands and twists depending on the amount of water it retains. When there is less humidity, the wood doesn’t change its shape as much, meaning you’d have to take a closer look at the average temperatures and humidity levels in the area you live. 

It’s essential to consider the climate throughout the year. If you live in a place where the humidity differs through the seasons, you will need to choose the gap size accordingly. In areas where you don’t experience drastic changes in humidity, there’s no need to be as cautious.

The season when you’re installing the deck

Decking will absorb more moisture the more it’s exposed to the elements, resulting in the swelling of the boards. If you’re constructing the deck during the summer, leave a smaller gap to leave room for expansion. In winter, the boards will shrink, and gaps will become more prominent. If you’re building the deck during the winter, the contrary applies. You will need to leave a more significant gap (about 1/4″) as it will get narrower during the more humid seasons.

The type of wood

Different wood species will absorb moisture differently. If you get a type of timber that expands a lot, you would need to leave more space in between the boards and vice versa. 

Here are the most popular options:

  • Cedar (cedar is one of the most popular options as it is very durable and moisture-resistant)
  • Redwood (redwood is similar to cedar, and it is often used in decking)
  • Pressure Treated Wood (pressure-treated wood needs to be let dry for a few months before installation. It shrinks once it’s done drying)·
  • Tropical Hardwoods (Mahogany and Ipe are common tropical woods but come at a much higher price)
  • Composite Wood (composite wood is an eco-friendlier option, and there is a wider variety of colours. It also requires less maintenance.)

The space underneath the boards

If the deck has enough space above and below the boards, they will be less affected by the moisture. You’ve seen this often – small, dark, cramped up places gather a lot more moisture than the ones that are ventilated often and are exposed to the sun. Obviously, you can’t offer sunlight to the area under your boards, but you can make sure there is enough space there for proper ventilation and air circulation.

The type of fasteners

Fasteners are the things that prevent the boards from bending in harsh weather conditions and generally keep them in place. With standard deck screws and nails, the spacing will not be affected, but if you’re going with a custom screw system, you must keep in mind that they have a default spacing that cannot be changed. Take the measurements beforehand and you will be alright!

Why is the gap between decking so important? 

The gap size between the decking boards can be more impactful than you think. The airflow is crucial to the prevention of rotting, as it can keep the wood dry, and the gaps are the ones regulating that air circulation. The gap distance is critical because it prevents moulding by allowing snow and rain that might fall on your deck to drain through the spaces between the decks. It can also prevent debris from accumulating on your deck, which is another cause for the rotting of boards.

If the gaps are too big, the deck can become unsafe. If it is too small (or none at all), it can cause the boards to warp and crack once the humid seasons roll around and they start expanding.

The tool to properly check how much humidity your boards retain is a moisture meter. The amount of moisture locked in the wood will give you the correct indication of how much spacing to leave. To do accurate measurements, check multiple parts of the deck and take an average moisture count. The average moisture levels are anything between 11% and 14%; if it shows higher than 15%, you live in a high moisture area, and the boards will continue to shrink. 

What is the most recommended gap size between deck boards?

A distance of 1/8 inch to 1/4 inch between the boards is generally considered the most suitable. There are both advantages and disadvantages to each length.

Using a distance of 1/8 makes the decking surface more secure. If the gaps are small, there’s only a slight possibility of tripping or things getting caught in the gaps. However, as previously mentioned, smaller spacing also means that there will be significantly less airflow, not allowing for snow, rain, and debris to fall through.

(A 1/8 gap can be achieved with the help of an 8d nail or a speed square)

Using a distance of 1/4 inches means more airflow and better drainage. You will need fewer boards, but stay aware of fire safety with such well-aired construction. (Measure 1/4 gap  with plywood)

A safe option is to go between the two measurements. If you don’t want to use any of the recommended ways of sizing the gaps, you should look into spacing tools.

Hire professionals

Still, aren’t sure what gap size you should use, or perhaps you haven’t got the time or tools needed to construct your deck? You should consider hiring a professional who would choose the perfect gap size and type for the best result. The experts we work with specialise in decking installation, repair, and oiling services! They can help you build your deck using durable and weather-resistant materials and repair old or unkept decking. Oiling, repairing, even garden steps and level construction, you name it!

Need a professional landscaper?

Get in touch with a decking specialist today!

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  • Consider the climate before choosing a gap size
  • Gaps can have a long-lasting impact on the deck
  • Work to prevent rotting boards
  • The recommended gap sizes are from 1/8 inch to 1/4 
  • Familiarise yourself with the pros and cons of the gap sizes


Did you find the information helpful? Share your experience in the comment section below!

Image source: Shutterstock / Christine Bird

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