Doctrines For Moisture Control

Moisture ManagementProblems associated with water-induced failures became more prevalent in the 1980’s as a result of changing paradigms in design and construction practices.   These failures are often attributed to air-tight, energy-efficient designs initiated during the global energy crisis of the 1970’s.  Although applicable, this over-simplification ignores the fact that many energy-efficient buildings of this era have remained free of water problems.  A more complete understanding for the causes of moisture-related failures is derived from a combination of factors pertaining to inadequate design, inappropriate design for intended climates, use of more complex architectural features, poor construction practices, inadequate quality control, and the use of building materials having moisture storage and drying capabilities differing from earlier assemblies.

When considering design criteria for moisture control, design professionals and contractors would do well to heed this elegant doctrine first outlined by ASTM MNL 18 in 1994.

  1. The building will not leak.
  2. The building will not allow the accumulation of water where the building may be adversely affected.
  3. The building will not be unduly affected by predictable influx of moisture in the physical construction.
  4. The building will expel water which enters into the construction predictably.
  5. The building will not utilize materials which tend to entrap excessive amounts of water under predictable circumstances.

ASTM E241 later refined these principles as a three-point strategy.  Though not so keenly written, the intent remained the same:

  1. limit moisture sources;
  2. minimize moisture entry into the building or building envelope;
  3. remove moisture from the building or building envelope.

Everything old is new again.  Today’s designers and builders are offered even greater guidance with ASHRAE 160: Criteria for Moisture-Control Design Analysis in Buildings.  Interesting, the most restrictive criteria contained in ASHRAE 160, those that prevent corrosion and mold, were first published two decades earlier by the International Energy Agency, which issued Annex 14 to address condensation problems resulting from changing practices in building energy conservation.  Now we are in a new era of ultra-efficient buildings involving LEED, net-zero energy, and passive house – all noble in intent but rife with designs that often ignore the basic and enduring principles of moisture management.