This is a legacy version of the WELL Building Standard. Please check the latest version here.

Humidity control

Extremely low humidity can lead to dryness and irritation of the skin, eyes, throat and mucous membranes. Conversely, high humidity may promote the accumulation and growth of microbial pathogens, including bacteria, dust mites and mold, which can lead to odors and cause respiratory irritation and allergies in sensitive individuals. Additionally, higher humidity levels can lead to increased off-gassing: an increase in relative humidity of 35% can increase the emissions of formaldehyde by a factor of 1.8–2.6.

Part 1: Relative Humidity

At least one of the following is required:

a.8 A ventilation system with the capability to maintain relative humidity between 30% to 50% at all times by adding or removing moisture from the air.
b. Modeled humidity levels in the space are within 30% to 50% for at least 95% of all business hours of the year. Buildings in climates with narrow humidity ranges are encouraged to pursue this option.
Part 2: Shower Moisture Barrier

The following is required between showers and locker rooms, if present:

a.132 An airlock or ventilation barrier.

Applicability Matrix

Core & Shell New & Existing Buildings New & Existing Interiors
Part 1: Relative Humidity - O O
Commercial Kitchen Education Multifamily Residential Restaurant Retail
Part 1: Relative Humidity O O O O O
Part 2: Shower Moisture Barrier - O - - -

Verification Methods Matrix

Letters of Assurance Annotated Documents On-Site Checks
Part 1: Relative Humidity MEP Spot Measurement
Part 2: Shower Moisture Barrier MEP Spot Check

U.S. Environmental Protection Agency. A Brief Guide to Mold, Moisture, and Your Home. . Published 2010. Accessed September 15, 2014 .


The EPA's A Brief Guide to Mold, Moisture, and Your Home recommends maintaining relative humidity between 30% and 50%.


Wenger Corporation. Planning your athletic facility. Published 2011. Accessed March 25, 2015.


The guide states to consider an airlock or ventilation barrier between showers and locker rooms.