Best Decking Spacers for Perfect Gaps: 2025 Expert Review
DR Joinery
Expert Joiner & Timber Specialist
One of the most common mistakes I see with DIY decking projects is incorrect spacing. If the boards are too tight, they buckle when it rains; too wide, and it becomes a trip hazard. Many people try to improvise using nails or screws as spacers, but these often fall through the joists or damage the timber grain.
In York, where we battle damp conditions for much of the year, ensuring adequate drainage and airflow is critical. The gap between your boards isn't just aesthetic; it allows water to run off and air to circulate, preventing the dreaded rot that plagues so many garden structures.
In this review, I've selected three decking spacer tools that ensure consistent, professional results. I've chosen a budget-friendly multi-tool, a high-visibility quality option for site work, and a specific single-size spacer for speed.
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Specs vs. The Real World
The Spec: "Usage of Nails/Screws as Spacers"
"It's free and easy to just use a 6-inch nail to space boards."
Nails are cylindrical and often get stuck when the timber is pinched tight, or they drop through the gaps into the mud below. They can also bruise the edge of softwoods like pine. Purpose-made plastic spacers are flat, easily retrieved, and non-damaging.
The Spec: "Standard 5mm Gap"
"A 5mm gap is standard for all decking."
Not always. Timber is a natural material that moves. If you are laying wet, pressure-treated softwood in winter, it will shrink in summer, so a smaller gap might be needed. If laying kiln-dried hardwood in summer, it will expand in winter, requiring a larger gap. Having a spacer with multiple options is essential.
My Top 3 Recommendations
Three options to cover different needs and budgets
3Dimensional Studio Decking Spacer 4 Pack Multiple Gap Widths
3Dimensional Studio
This pack represents excellent value for money. It's a classic multi-sided tool offering 4mm, 5mm, 6mm, and 8mm gaps on a single unit. This versatility is brilliant for adapting to different timber conditions without needing to buy multiple tools.
The Good
- Cheap and cheerful - excellent value
- Multiple sizes on one tool allows for adjustment if timber varies
- Made from recycled materials
The Bad
- Green colour can blend in with grass if dropped
- Can be slightly fiddly to find the right side if working fast
Installer Tip:
Use the 8mm setting if you are laying very dry softwood in the summer heat. Once the Yorkshire winter hits, that timber will swell significantly, and you'll be glad for the extra room.
Priced at £5.49 at the time of writing
Check Price on AmazonDecoralin Decking Spacers 4-Pack – Multi-Size Board Gap Tool (Yellow)
Decoralin
Whilst slightly more expensive, these spacers serve a robust purpose on a busy site. They include a 10mm option which is ideal for scaffold boards or chunkier sleepers, and the high-visibility yellow ensures they don't get lost in the sawdust.
The Good
- Bright yellow colour prevents loss on site
- Includes larger 10mm gap (great for sleeper beds)
- Durable PLA+ material handles rough handling
The Bad
- Slightly higher price point
- Does not include a 4mm option (starts at 5mm)
Installer Tip:
The 10mm gap is particularly useful if you are building raised beds using scaffold boards rather than standard decking. It provides a chunky, deliberate shadow line that looks fantastic on rustic garden projects.
Priced at £6.99 at the time of writing
Check Price on Amazon5mm Decking Spacers 4 Pack (Single Size)
3Dimensional Studio
Sometimes, having too many options slows you down. If you know you need a standard 5mm gap—common for composite decking—these single-purpose spacers are faster to use. There's no rotating to find the right side; you just slot them in and drill.
The Good
- Fastest workflow - no checking sizes
- Wide sides prevent the spacer twisting
- Standard 5mm fits most composite decking systems
The Bad
- Only offers one size
- Not adaptable if your timber varies in moisture content
Installer Tip:
These are perfect for composite decking where expansion and contraction are more predictable than timber. The wide flat edge helps keep the boards perfectly parallel over long runs.
Priced at £5.49 at the time of writing
Check Price on AmazonFrequently Asked Questions
What is the best gap size for timber decking?
Why shouldn't I just use nails/screws for spacing?
Do I need to space the ends of the boards too?
Can DR Joinery repair my existing rotten deck?
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