Does composite decking expand and contract?

Cast your mind back to your days in school and you may recall your science teacher going through the basic laws of physics on how changes in temperature impacts different substances. Or the likelihood is that much like myself you paid very little attention and were way too occupied engraving something into the school desk trying to impact generations to come with the knowledge of your existence. Luckily though, because we see it in our daily lives, it doesn’t take a physics 101 class to know that a shift in temperature or moisture has an impact on our windows, doors, decks etc.

Composite Decking is made of both recycled wood and plastic. Plastic, when heated, like most materials, will expand to varying degrees. This is best explained by (my science teacher would be so proud) something called the Coefficient of thermal expansion. Which basically describes how the size of an object will change as temperature changes. So, when the temperature gets hotter, plastic expands and returns back to its normal size when temperature drops. Likewise, wood, although in a different manner, expands more due to moisture than it does to heat, although heat does plays its part. Wood fibers, when in contact with water, will absorb the moisture and tend to expand when heated. They will later shrink as it returns to normal levels of moisture.

Decking boards made from composite do not swell as much as a traditional timber deck would. This is because composite decking is water resistant and amongst many of its other benefits, anti-slip. But with the composite boards being a mixture of plastic and wood they will still expand and contract due to heat. When you’re planning to lay your deck, this need to be a consideration. Most composite decks are installed using either 6mm or 3mm fastener clips. This allows enough space for the boards to expand and contract into. Additionally, unless your decking area is enclosed all the way around then the composite boards will have additional space to expand into. This would also allow you to butt boards together where you have a long run. If however, you do have an enclosed area (ie there is a wall or a fence all the way around) then extra caution should be used, especially when butting boards together. The correct procedure here would be to use a fastener clip between the composite boards. Correct installation will ensure the screws and fasteners stay in place, secure the boards and give plenty of space for any expansion and contraction of your composite decking boards.   Deckorum Composite Decking only uses the Grade A materials in its composite decking boards. Unlike most composite decking manufacturers that use high levels of plastic in their boards as a cost cutting exercise, Deckorum uses high density poly ethylene which makes up no more than 35% of the board’s composition. This ensures the boards don’t expand any more than they need to in the elements. With the option of a 3mm or 6mm board securing fastener clip, you can also decide on the aesthetic finish of your deck.