I thought that myself, but I heard a few people say that it doesn't really much difference. Probably best to stick with grooves up. Cheers mate.
Well there's a thing. That's from an Antipodean website though. Their water goes down the plug ole the wrong way.
All decking I've seen and done has been grooves up Chippie. Perhaps I've just been led to believe that's norm...interested in other opinions and also begs the question 'why have the grooves' ? Can't be just a drip rail surely?!
Don't start this grooves up/down debate again it'll go on forever, decking manufacture put the grooves in for drainage to aid grip, so work it out for yourself as to which way up they should be.
I know jack about decking or which way it's supposed to be installed to be honest. But I know that if you want to reduce friction you reduce the area of contact. That's why ice skates are skinny blades and not 3 inch blocks. Dunno if this principle applies to dead trees though.