I'm planning a deck build in the UK. The 3 biggest DIY retailers here all seem to sell decking boards which are grooved on both sides. There's a lot of mixed advice from the videos/instructions I've been checking out. Some say it's a matter of preference and others say you must absolutely put the grooved side down: http://www.build.com.au/should-decking-grooves-face-or-down
So, should I be looking elsewhere for boards or does it really matter?