I have spent the last several days reading all of the pertinent posts from Jan, 2007 forward. What a great wealth of information. I have had many of my questions answered but still have a few.

I already have purchased the Kahrs American Traditionals woodloc product. But am not sure what direction to install it. All of the posts say it should be perpendicular to the floor joists. However, we have installed radiant heat on TOP of the 3/4" OSB which lays perpendicular to the floor joists. The radiant heat consists of 8" OSB sleepers spaced one inch apart. The sleepers are glued and nailed down. The aluminum plates lay in the space and the tubing connect to the aluminum plate. So - should the floor still lay perpendicular to the joists (I-joists on 16" centers) or be laid perpendicular to the radiant heat sleepers?

Here is a basic layout of the room (not even close to scale). The footprint of the house is 32 deep x 40 wide. I am planning on putting the wood down in the family room, living room and library.


--------------------------------door---------------------------------
-------------------------------------------------------|
--------------------------------------------------------| tiled kitchen
----------family room--------------------------------|
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
xxxxxxxxxxxxxdoorxxxxxxx|-stairs---| ---------------------------------
xxxxxxxxxxxxxxxxxxxxxxxx|down---|-----------------------------------
xxxxxxLaundry roomxxxxxx|----------|------------living-----------------
xxxxxxxxxxxxxxxxxxxxxxxx|---------|-------------room----------------
xxxxxxxxxxxxxxxxxxxxxxxx|---------|-----------------------------------
------------------------xxx1/2x|---------|-----------------------------------
------------------------xxbathx|---------|-----------------------------------
------------------------xxxxxxx|---------|----------------------------------
------library----------------------------------------------------------------
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
--------------------------------------door----------------------------------

My second question is should I put a transition going from the tiled kitchen to the corner of the stairs going down. This would break the flow of the floor but I am reaching the max of 40' wide if I have to lay the wood, what would be up and down in this diagram. The 40' width also means I should have a 3/4" gap all the way around. That causes problems with the baseboard not being quite wide enough.

Kris

The recommendation for flooring to be installed perpendicular to the floor joists applies to floors that are fastened down by nails or adhesives. Since the floor you are installing is a floater, you should be able to install it in any direction you wish. My inclination would be to install it perpendicular to the OSB sleepers. Most install floaters in the direction that is most appealing or the long way of a room.

I don't quite understand your second question. Are you concerned about expansion? A 3/4" expansion around the perimeter is overkill, IMO, even for a floater. I would say 1/2" would be adequate. What does Karhrs recommend?

It seems that they have modified their requirements. It used to be something like for dimensions over 36' add 1/8" for every 6'. I did a living room that was 40' by 40' over radiant heat. We left a 5/8" gap.

I would under cut the drywall. this gives you a 1/2" expansion space behind the baseboads. Then your base boards can cover the 1/4" left to make your 3/4" gap.