Published: 14/07/25 By: Mike Bekin
Leaving a gap between decking boards is standard practice when laying timber decking. But why? Whether you are taking on a DIY decking project or have just started out in the timber construction industry, it pays to know the right decking spacing and why you need it. Find out everything you need to know in this guide.
Why Do You Need Gaps in Timber Decking?
Decking board spacing is crucial when installing timber decking. By leaving small gaps, you allow your timber to move (a little) without pushing up against each other, making it far less likely you will see splinters or broken boards.
Your timber can appear to move when there are changes in humidity levels. Because wood is porous, meaning it allows water to move through it, the moisture content of your boards can increase and decrease as the weather changes. The TDCA specifies that outdoor timber can undergo a shift in moisture from just 12% in the summer months to 19% during winter.
As these moisture levels change, your timber boards will physically swell or contract. By leaving adequate decking board spacing, this will not be a problem.
A gap between decking boards also helps with water drainage and improves airflow, keeping your timber decking free from rot.
Recommended Gap Between Decking Boards
Generally speaking, your decking board spacing should be around 5mm. This could vary slightly depending on a few factors, including:
- The timber species you are using
- If you are using composite decking, which will require narrower gaps
- The moisture content of your timber when you are installing
For example, a more dimensionally unstable timber, such as Ekki or Opepe, is more susceptible to movement, so you may want slightly more than a 5mm gap. A timber which moves less, such as Thermowood, may not require the full 5mm gap.
In terms of moisture content, the lower the percentage on the day of installation, the larger the gap you will need. For context, we recommend installing timber decking boards at a moisture content of around 16%. If your timber boards are at 14%, this is not a huge problem, but you might need to leave a 6-7mm gap depending on your timber species.
Tips for Decking Board Spacing
When leaving a gap between decking boards, there are some tips to make installation easier. To help you, here is our advice for accurate decking spacing:
- Use Spacers or a Deck Board Jig: To maintain consistent gaps between boards, use plastic spacers or a deck board jig. These tools help create uniform spacing and reduce guesswork as you go.
- Mind the Fasteners: Hidden fastener systems can maintain even spacing and a clean look, but are not suitable for a lot of the species we supply, so if you are using screws or nails, pre-drill and align carefully to avoid shifting boards or uneven gaps.
- Work with the Weather: Install decking during stable weather conditions. Extremely hot or cold days can affect the material’s dimensions, leading to inaccurate spacing when the weather returns to normal.
Why Does Your Decking Show Uneven Gaps After Time?
Timber naturally expands and contracts when humidity changes, causing decking boards to “move”. Even tough species, such as Cedar and Ekki, are not exempt from occasional movement.
If you do not install your boards with proper fixings and the right spacing between them to allow for this swelling and shrinking, you often end up with odd gaps which look uneven. This can also happen if your fixings have come loose with a lot of wear and tear, allowing your timber boards to shift a little and thus changing the look of your decking.
How to Prevent Uneven Timber Decking Gaps
The best way to stop uneven gaps from appearing is to plan ahead. At the time of installation, ensure you have taken steps to account for movement, with long-term use in mind. We recommend:
- Use spacers during installation: Use decking spacers to leave a consistent gap between boards. The TDCA recommends between 5-8cm, and you can find spacers with this exact sizing so that there is no need to measure each gap. Simple!
- Choose stainless steel fixings: These are far better for timber and will not rust or loosen as easily, keeping boards secure for longer.
- Regular maintenance checks: A quick inspection every few months helps you spot small shifts in your decking boards before they become noticeable.
- Keep your deck clean: Debris (such as stones or leaves) which becomes wedged between boards can, in some cases, begin to push them apart. Regular sweeping of your decking will help keep it clear of items that could get lodged between the boards.
How to Fix Uneven Timber Decking Gaps
If you are dealing with uneven gaps, you can usually fix the issue without replacing the entirety of your decking. To do this, you have a few different options:
- Look for loose fittings, and tighten any which you find (you might need to replace broken screws or nails with new ones for a more secure fit), moving the boards back into place as you do
- Replace timber boards which have warped or shrunk too much, using decking spacers to ensure they are correctly placed and installed
- For wide gaps caused by poor installation, insert a slim infill strip cut from matching timber to avoid needing to move multiple decking boards
Once boards are realigned, lightly sand any rough edges, then apply decking oil or stain so the repaired area blends seamlessly with the rest of your deck.
Find Stable Timber at EcoChoice
Want to worry less about gaps between decking boards? Choose a dimensionally stable timber with our help and reduce movement in your boards. Get in touch to find a sturdy timber species and start your timber decking order.
