Gap between decking boards: how much is right?
Why an 8 mm gap?
Hardwood swells slightly when it is wet and shrinks back in a dry summer. Boards laid too tight push against each other and can lift. A gap that is too wide catches heels, toys and leaves. For Ipe decking boards of 21 x 140 mm, an 8 mm gap avoids both problems. Rain drains straight through, and the underside of the deck dries out faster.
Keeping the gap even with clips
Our decking boards have a groove along each long edge. A black coated stainless steel clip slides into that groove and is screwed to the joist. The clip sets the 8 mm gap for you, so there is no need for spacers or a tape measure, and no screw heads show on the surface.
The board ends have a tongue and groove, so the boards click together lengthways and you do not have to land every end joint on a joist. Each end has a bevelled edge, which gives a neat double V at every join. It looks smart and saves a lot of time when laying.
How far apart should the joists be?
Space the joists 40 to 45 cm apart, centre to centre. Any wider and the deck will bounce slightly underfoot. We recommend Ipe joists as well, so two different timbers never work against each other and the frame lasts as long as the boards: 25+ years.
Do not skip the weed membrane
Lay weed membrane under the joists. It stops weeds growing up through the gaps but still lets rainwater drain away.
The short version
- Gap between boards: 8 mm.
- Joists: 40 to 45 cm apart, ideally Ipe.
- Fixing: black coated stainless steel clips and screws, invisible from above.
- Under the deck: weed membrane.
To work out how many boards, joists and clips you need, use the decking calculator, or see our deck framing and Ipe decking.
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