#MAPEITechTip: Perm Rating-why it is important to consider in a steam room/shower?


MAPEI Product Support

 October 26, 2016. 4:03 PM

While steam rooms are found mostly in commercial health spas, fitness clubs, hotels and cruise ships-many homeowners are installing combination steam showers in their homes to a create spa-like bathroom en suite. While this new trend can add value to a home-poorly designed steam showers can turn into costly installation nightmares. Steam showers are not ‘modified’ showers- these systems require special design considerations and installers who understand these requirements.  One of the key elements of a well-designed steam shower is understanding ‘perm rating’-what is it? why is it important to consider?

Steam Showers Are Not the Same as Traditional Showers
Steam rooms/showers have their own micro-climates (moisture, heat, steam) that can tax all of the system components every time they're turned on.  In a matter of a few minutes, the environment inside a steam shower will go from being relatively dry and cool (typically 74º F at 50% RH) to where the air is completely saturated with super heated water vapor (approximately 115º F at 100% RH).  When this super heated moist air comes in contact with the walls and ceilings (which are lower in temperature than the super heated air) it causes the moisture in the air to condense into water droplets, producing a “rain forest” effect inside the steam shower.  These extreme conditions require that the entire installation assembly not only be able to perform at elevated temperatures and high moisture content, but also be able to deform and flex with the effects of thermal growth and shrinkage-every time the steam room/shower is turned on.

If improperly designed a steam room/shower can lead to costly repair issues such as mold growth, failure of the wall, floor and ceiling assemblies.  Improperly pitched ceilings and seats can cause water to drip on occupants. Or in extreme cases, water intrusion can cause the tile or stone to lose bond, pop off, possibly causing injury and costly damage.  And while steam showers can add value to a home or business, poorly designed or installed steam room/shower can cause your investment to quickly go down the drain!

Steam room/shower-consider ‘perm rating’
Why is ‘perm rating’ important when selecting the components and designing the steam room/shower?  The perm rating is the amount of moisture vapor that a membrane allows to pass through in a given time under a given pressure-limiting the amount of moisture vapor allowed to escape steam showers through the walls.  Always refer to industry standards for acceptable building practices, such as outlined in the most current TCNA (Tile Council of North America) Handbook, in addition to all local, state and city codes pertaining to steam room/shower.
The TCNA detail methods SR613 and SR614 for steam shower installations requires the use of a bonded waterproof membrane, between tile and substrate, with a “perm rating,” of 0.5 perms or less. Or, if the perm rating is higher, a secondary membrane is now required behind the tile substrate. This permeance rating of 0.5 perms or less, is tested using ASTM E96 “Standard Test Methods for Water Vapor Transmission of Materials” to try and simulate the moisture (vapor) conditions that the components will be exposed to in a steam room/shower.  Selecting a waterproofing that meets ASTM E96 (Procedure E—Desiccant Method at 100°F and 90% relative humidity) requirements, provides the added protection needed in conjunction with the other system components for optimum design parameter.  MAPEI’s Mapelastic AquaDefense is the perfect installation product for steam showers since it meets the requirements of ASTM E96-Procedure E.

Remember while a steam room or steam shower can add value, improperly designed steam room or steam showers can be costly reminders of the damage that moisture, heat and steam can do to a tile or stone installation.  Taking the time to do it right the first time using the right installation materials and design will ensure a steam room or steam shower that will last for the life of the home or business.


MAPEI Product Support

MAPEI Product Support


Load more comments

Log in or register to add a comment.

Keep in touch

Subscribe to our newsletter to get Mapei news