DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Flooring (
-   -   Questions for the tile pros (

Maintenance 6 06-19-2008 01:05 PM

Questions for the tile pros
I've done practically all kinds of building construction and maintenance, but I'm not well versed in the latest ceramic/porcelain tile installation processes. I have a laundry room that currently has 3/4" advantec sub-flooring on top of 2x8 joists, 12" centers, maximum span is 8'6". I plan to install 12x12 tiles as a floor finish. I have 1-3/8" from the top of the advantec to the surface of an adjacent finished floor. I want to match the surface height of the two floors. This floor will also have radiant underfloor PEX heat. I'm looking for information on what materials to use to create a lasting, servicable floor. I also plan to do a bathroom that has the same sub floor/joist layout, but height will be an issue as I am not matching anything there. Any suggestions will be greatly appreciated!!

angus242 06-19-2008 01:51 PM

Have you chosen the radiant subfloor yet? What is the thickness of the tile to be used?

Here's what I can recommend:

subfloor (your existing 3/4")
infloorboard subfloor
1/4" hardi

This combo, assuming your ceramic will be 3/8", will put you right in the ballpark. Infloorboard is 5/8" and uses 3/8" pex. Make sure you never run the pex under cabinets or other permanent structures. Use regular 5/8" ply in those locations.

As always, follow manufacturers installation recommendations.

Good luck!

ps, there is no 1 right way. I'm sure other suggestions will follow. Also, if you follow my suggestions and cover any Ditra seams with Kerdi strips and follow Schluter's recommendations, you could have a waterproof floor.....which in a laundry room isn't such a bad idea. However, a floor drain is a completely different issue!

Steven62 06-19-2008 02:11 PM

Angus has some good advice, and I always suggest familiarizing yourself with TCNA (Tile Council of North America) guidelines.
Copies are available online here:

Bud Cline 06-19-2008 05:12 PM

...on 2X8 floor joists???:)

angus242 06-19-2008 05:48 PM

Am I wrong?
7.25" tall, 1.5" wide, 12" on center, and 8.5' unsupported span, the deflection is .108". Doesn't that fit what ceramic can be installed at?

Bud Cline 06-19-2008 07:54 PM

Don't know never checked it. Two by eights are usually a scarny thing but the twelve inch centers may be the saving-grace.:)

JazMan 06-19-2008 11:27 PM

Two by 8" at 12 o.c. spanning under 9 ft. is a very stiff floor, stiffer than most 2x10" and 2x12" 16" o.c. at normal span. Does the radiant system have a name or is it generic?

What I don't understand is Angus's suggestion of installing Hardi over Infloorboard. How you gonna install Hardi without puncturing the Pex?


angus242 06-19-2008 11:42 PM

1 Attachment(s)

Originally Posted by JazMan (Post 132001)
How you gonna install Hardi without puncturing the Pex?

Same way you'd install hardwood over careful!

Actually, infloor specs call for it:

warmsmeallup 06-22-2008 06:59 AM

You could always use low voltage Zmesh radiant, depending on room dimensions, and not worry at all about where the nails go!

Maintenance 6 06-24-2008 06:45 AM

Thanks!! That is just the info and advice I was looking for. For what it's worth, my chart says that #2 SPF 2x8s on 12" centers can run out to 13'6" and still be within L360 for deflection.

JazMan 06-24-2008 08:13 PM


You're right, my chart says the same thing as long as it's not southern SPF. BUT, that is not a good spec for ceramic tile. What I mean is that span is calculated with the standard 40/10 live load/dead load which is bare minimum for regular flooring. When I figure ceramic tile I recommend going to at least 50/15, or 50/20.

With this higher requirement the max span is 12'7" and 12' 4". Use Southern variety and both max spans drop to 11'7". Remember, this is to meet bare minimum of L360 for ceramic and porcelain. I know this doesn't effect your case, but there may be others reading this.:thumbsup:


All times are GMT -5. The time now is 03:19 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1