Why inconsistent gap between boards on new deck

by Dan
(London, Canada)

I have just had a deck installed using the Fiberon system. On one side of the deck, the boards are close together (1/8" maybe). It looks good.

Part way across the deck, the gap is suddenly 1/4" or more. The installer said he doesn't know why this is so. And that the wider gaps are the usual case. The "hidden" fasteners are quite visible. Looks bad. What can be done?

Editor's Comments

Fiberon boards are according to the manufacturer's own documentation supposed to be 5.35" (136mm) wide. The recommended spacing between boards is 3/16" and 1/8" from the end of one board to the next.

Composite decking is known to shrink and expand along its length, not its width. Or at least very minimally across the width.

Experienced carpenters will know that this is the opposite from what natural wood does. Wood expands very little along its length - as little 2% whereas it can expand 6-8% across its width.

The boards should all be a consistent width and it sounds like you are describing a situation where they have shrunk across their width in an irregular manner.

What Can Be Done?

Sadly, very little can be done other than remove the boards and reinstall them tighter to the recommended 3/16" gap, which by the way is not much compared to the existing 1/4" gap.

The real mystery here is have the boards actually shrunk or were they simply installed with different spacing? Measure the boards to determine if they have shrunk differently or at all. Then contact Fiberon and ask with the acceptable width shrinkage movement is.

Has Anyone Else Experienced Boards Shrinking Across Their Width?

If you have some personal experience in this area please help Dan out and add your comments.

Comments for Why inconsistent gap between boards on new deck

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Aug 30, 2020
Watch the thermomer NEW
by: Les Ismmore

Butt gaps vary with temperature. For our recent project it was over 90°F. the gap utilized was a tight 1/16". We actually notice the expansion and contraction as the temperature changes.

Jun 09, 2020
thanks NEW
by: Jason

Great suggestion. Thanks!

May 14, 2020
No easy fix
by: Richard

There is not simple fix to this because you have to raise the deck to tilt it away from the house.

But your support posts are set into the ground. The soil around the posts is low and so the water is collecting around the post. This will shorten their life span significantly.

You really should build new footings and this time make sure the posts are elevated and dry. Here is a good article to read

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