Flooring – Tongue and groove floorboards – which way up

flooring

I bought some tongue and groove floorboards. I noticed the tongues and grooves were not centered in the edge but were offset. 

   ┌───────────────────────────────────────────┐ 
 ┌─┘                                         ┌─┘                      
 └─┐                                         └─┐
   │                                           │  ← thick side
   └───────────────────────────────────────────┘

I guess there must be some reason for it. There must be some benefit.

Which way up should I lay these, as shown in diagram or the other way up?

P.S. To make sense of comments & parts of answers that relate to the specific boards I was using – see prior revision.

Best Answer

Taken from my books, dated 2002 and 1948. Nothing has changed. Thicker side up. carpentry book 2002 carpentry book from 1948 Part sentence below the second image relates to cutting the tongue "slightly nearer the bottom surface than the top":

Incidentally the gap on the underside mentioned on the first image is the clincher. It's not always there but if it is then it confirms that that edge is to face away from sight.

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