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Installers typically like to install the strip flooring perpendicular to the framing below. This makes the floor a little stronger. It can be layed in the other direction, but it just wont be as strong as it could be and could lead to a bouncier floor.
In addition, keep in mind that the direction can also trick the eye into making the room feel long and narrow (laying the strips parallel to the longest walls). Or it can help a narrow room feel wider (laying the strips parallel to the shortest walls).
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Best of Luck, Brian
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The floor is concrete slab... So that's not an issue... But I think - from the front door looking down the lenght of the great room is best... And she thinks it should be width way to make the room look wider...
But I think the room looks plenty wide... So realy the question would be; is their a rule?
There is no rule. If I was laying it, I would lay the strips parallel to the shortest walls; that is just my preference, visually it helps a rectangular room feel more square.