installed face down to allow water to dry out and ventilate the area where the decking board meets the joist. Many people (including tradespeople) install grooved or routed decking face up which will allow water to stand in the grooves and accelerate rot and slip factors which could be a problem. Other matters to consider are the ease of cleaning and the feel under (bare) foot. Our advice is to install grooved decking with the grooves face down.