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Floor thickness and radiant heat…

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jimcorliss
jimcorliss Member Posts: 1
in Radiant Heating
I’m planning on building a floor of 3/4” advantec underpayment with 1/2” cement board and 7ml thin Florida ceramic tile . Is this too much thickness if I was to have runs of 1/2” pex tubing under the underlayment in hopes to have radiant floor later when I’m ready to hook it up ? 

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  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,985
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    No, but why would you use cement board?   Get a real Tile pro in there and do a Mud Job.  A solid,  monolithic slab is better structurally and creates a stronger thermal mass.  Cement board, for an application like this, if I am reading correctly, is for guys that can't do a mud job.  Mad Dog 🐕 
    Consulting by Mad Dog & Matt Jr.
  • hot_rod
    hot_rod Member Posts: 22,158
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    That is a very common way to install tile these days, in bathrooms also, floors and walls. Not so easy to find someone that does mud sets anymore and it would add additional thickness to the floor. So transition strips may be needed between the bath and other room.
    Make sure there is no bounce to the floor, over-spanned joists for example, that tends to be more of an issue than the type of set, as for tile problems.

    It is always a good idea to do a room by room heatload to assure you can get adequate heat from the floor. typically two aluminum plates per joist bay is the way to go, able to provide 25- 27 BTU/hr./ sq ft.T
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PC7060
    PC7060 Member Posts: 1,160
    edited July 2023
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    Concrete board underlayment is old school as well; membranes such as Schulter Ditra are much easier.  I recently used DitraXL on a ceramic tile install for two bathroom; 3/4” total stack up.  Although for certain applications nothing beats a mud bed!

    For heat transfer, the CBU is a good option although no need to use 1/2” thick material, 1/4” material is fine.  CBU doesn’t increase the strength of the floor, it simply provides a decoupling layer between the wood floor and tile to prevent vibration induced cracking of tile and grout.   
    Bed the board in thinset and follow screw schedule per the manufacturer technical data sheet.  You wouldn’t believe how many people fail to bed the backer board in thinset although all manufacturers require it, “I’ve been doing it this way for 30 years“.   :neutral:

    Verify the floor meets a minimum of L/360 defection rating for ceramic tile and L/720 for natural stone. 

    Johnbridge.com has a nice tool to calculate flor deflection. 







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