Expert: Ted Barnhill (Principal, Design45 LLC) - 1/30/2008

Question
Hello,
I reside in Denver, and am remodeling my basement.  By best practices I am implementing a floating wall.  It floats on the bottom plate.  I would like to add a fireplace along with this, but am curious to know how to have a floating wall with mantle connect to and a 'floor' mounted fireplace?  I hope that makes sense.  Would you recommend a floating wall floating on the top plate?  I have never seen that before.  Also, my top plate runs parallel to the joists.
Thanks for your help.

Answer
Jeff,

I would suggest that you let the top plate float instead.  Such floor-mounted detached partition walls are commonly installed to address the issue of truss uplift, in which trusses in a cold attic deform due to irregular moisture/temperature, raising the ceiling up to 1" above the homes central partitions.  

Leave a 1" gap between the top plate of your wall (which is attached to the floor as normal) and the cross-blocking that you will install between your joists.  Leave a gap above your wallboard and hold back the ceiling drywall from the edge.  To hide the gap, you will need to install cove or crown trim attached to the ceiling only.

Be sure to install your chimney and other mechanicals (gas supply line?) to allow for vertical movement of the fireplace.  This probably means a long horizontal run such as for a direct vent fireplace.  (I've never seen a vertical sliding joint for a chimney.)

Good luck, and feel free to follow up with additional questions.  -Ted