There has been a long standing debate on whether decking grooves should face upward or downward. Many experts and amateurs have weighed in on this debate and but the fact of the matter is that the decking boards should always be installed with the grooves facing downward. Many people may disagree with this notion claiming that the grooves are meant to act as an anti-slip feature but this is not the case. The grooves are also not meant to act as a decorative feature. The decking grooves are meant to prevent moisture and build-up of mould underneath the deck by allowing sufficient air-flow. Many manufacturers of decking boards only maintain their warranties if the boards have been installed with the grooves facing down. This means that if they are installed with the grooves facing upward the warranty becomes void.
Another reason why the grooves should not face upward is because the crevices will eventually lead to a build-up of grime. This is definitely an unpleasant situation and it could lead to subsequent discoloration of the deck. It could also make the deck quite slippery.
The only exception is when laying a decking boards for a wheelchair ramp. In this case the upward facing grooves would help in increasing traction for the wheelchair’s rubber tires.