TCNA tightens steam shower requirements
In 2013, the Tile Council of North America (TCNA), the organization that sets the guidelines for tile installations, is rumored to have made a modification to their specifications for constructing tile steam showers. It’s all about perm ratings- and Schluter Kerdi fabric no longer cuts it.
(edit: this is now in place and no longer a rumor)
Perm ratings are used to measure vapor permanence- basically how well steam passes through the wall. Kerdi is rated at 0.75 perms. It used to be that anything under 1.0 perms was OK to be used in a steam shower. But this year the rules committee lowered the perm rating to 0.50 perms (test E-96 procedure E). While Kerdi board (0.48) squeaks through, the Kerdi membrane does not.
Thankfully Schluter already manufactures a product that can be used under the new steamer requirements: Kerdi DS. Manufactured for steam showers in Europe, DS has a perm rating of an impressive 0.18. The tradeoff is that the DS material, at 20 mils thick, is quite a bit thicker than normal Kerdi at 8 mils.
Additionally, there are other products available for use in commercial steam showers such as Nobleseal TS. New products and with new technology are coming out all the time so be sure to check the manufacturer’s data sheets for use in steam showers.
Keep in mind that these new specifications are for commercial steam showers only. A steam shower is a type of shower that has a steam generator inside of it. Schluter’s Kerdi is still a great product for a normal everyday shower and is a product I would highly recommend for that purpose.
Admin note: As mentioned in the comments, this new rule will only apply to commercial (high use) steam showers. Thanks to John Whipple for this update.