How to stiffen the subfloor of an upstairs bathroom

bathroomsubfloor

I have been doing polished concrete throughout my house. My wife loves it more than I thought she would and now wants me to do it upstairs. I am afraid that the subfloor flexes too much, which wasn't a problem on the slab.

I don't want to put down anything too thick over it or the profile will be too much against the adjacent carpet. What is the thinnest way to stiffen the floor? I am going to use lathe so I don't really care about the cement board. I just want to get the flex out.

Best Answer

There are two choices to stiffen a floor system

  1. Halve joist span with a beam.
    The beam-in-joist method has the advantage of minimal final impact on the room below. It does mean spanning the beam to a load bearing walls.
  2. Double up joists in area. This requires removing floor or ceiling to sister existing joists. The joists also have to span as far as the existing joists.

The beam-in-joist solution should be confirmed with a building plan review for point load considerations under the transferred supports.

Update: I did come across a very thorough article from Fine Homebuilding "6 Ways to Stiffen a Bouncy Floor". (its a .pdf file)

Could I suggest a roll or 2 of Ditra (Schluter) under some nice tile?

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