Pressure-treated lumber to build a bench or curb

QUESTION

I’m looking for the spot in the TCNA Handbook that states that you are not allowed to use pressure-treated lumber to build a bench or curbs. Is there any way you can send that to me or tell me what page in the book it is?

ANSWER

In the TCNA Handbook’s shower methods section, under the requirements for wood studs, it states they must be dry and well braced. The general requirements for wall bracing are found in ANSI A108.11 in section 4.1 Wood Framing requirements. It states all framing lumber should have a moisture content not in excess of 19%. Most pressure-treated lumber has moisture content ranges of 30% to 70%. In a tile assembly, pressure-treated wood has a tendency to twist and contort as it starts to dry out. The rigidity of the tile assembly cannot generally handle that type of movement, and can fail from it. Also view page 30, Chapter 2 of the 2018/2019 NTCA Reference Manual for information about questionable and unsuitable substrates. 

Robb Roderick

Robb Roderick has been in the tile industry for nearly 25 years. He has worked with homeowners, builders, architects, and interior design professionals on projects in both residential and commercial settings. Prior to coming onboard with NTCA, Roderick was a member of the association for several years and is a CTEF Certified Tile Installer. He graduated from Missouri State university in 2000 and has also served in the United States Army as a medic. Roderick tours the country bringing NTCA Workshops and CTEF Educational Programs to local audiences nationwide.