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Width between decking boards

I am planning on building an outdoor deck using Merbau decking boards 140 x 19mm. I used the specrite calculator to determine how many linear metres I need but I don't know what size gap between decking boards has been used by the calculator.

I was thinking of a 5mm gap. I am not in a high risk bushfire area but it is a bushfire zone.

Any advice on what size gap the calculator uses or what size gap people recommend would be appreciated.

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Comments

EricL

Hello @Whiteagle

Welcome to the Bunnings workshop community. Thank you for joining us and sharing your question about decking panel gaps.

The most common gap size used is 3mm. However, please make sure to follow local council ordinances especially when it concerns bushfire safety rules when constructing a deck. I suggest using Icon Plastics Deck Spacer - 4 Pack to keep a uniform gap between panels. I'll have to get back to you concerning the gap the Specrite calculator uses. I agree with you that it would be handy if the gap could be adjusted. As soon as I have more information, I'll post it here.

Please keep us updated with your progress, we look forward to seeing the start of your decking project.

If you need more advice or information, please let us know.

Eric

MitchellMc

Hi @Whiteagle,

I'm sure @EricL and I can find out the exact spacing gap used for you after the weekend. I just wanted to point out, though, whether the gap used is three or five millimetres the amount of boards needed is likely very similar. Say you have a deck that is 10 metres long by 5 metres wide the decking calculator will say you need 380 linear metres or 67 x 5.7-metre boards. If the decking is laid along the 10 metres length, there will be space for 35 boards laid side by side over the 5-metre width with no gap. Add your standard three-millimetre gap, and that's 105mm of total gap between all boards, and 35 boards will still be needed as the gap is not over the 140mm width of one board. Increase the three-millimetre gap to a five-millimetre gap, and that's 175mm of total gap between all boards, and it's only removed the need for a single board.

That's a bit convoluted, but basically, it means whether the calculator is using 3mm or 5mm spacing, it's only going to affect your overall board count by possibly one or two boards. If it's a small deck, it might not change your board count at all. You'd typically order a few extra decking boards in case any can't be used.

I'm building a three-metre by three-metre deck at the moment. I haven't decided what spacing I'll use, but I've already ordered the exact number of boards. Whether I use a three or a five-millimetre spacing, it doesn't change the number of boards I need.

Please let me know if you have any questions.

Mitchell

Whiteagle

https://www.workshop.bunnings.com.au/discussion/comment/16886#Comment_16886

Thanks Mitchell and Eric.

Yes I can see the spacing won't make a big difference to the amount of boards needed. I used a calculator on the web and it came up with different results to the specrite calculator so I was trying to find out more about what assumptions (e.g gap between boards) were used in the calculation. The specrite calculator also allows for 10% wastage and I expect I will have a lot less than that.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/71025#Comment_71025

@Whiteagle,

The 10% wastage is likely for unusable lengths of timber and to adjust cut lengths to suit joist locations on a staggered board deck. If you are using 5.7-metre boards on a 5.7-metre long deck, there will be no wastage. However, if you are using 5.7-metre boards on a 3-metre deck, then you'll have a 2.7-metre offcut. The next length, you'll use the 2.7-metre offcut, but if there is no joist to support the end of the board at 2.7 metres, you'll need to trim it down to the last joist and might lose 10% of it. This will continue along the deck, and you might also end up with the last 30cm of a board that's unusable.

It all comes down to what boards you can get and how well they suit the size of your deck.

Mitchell

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