Building science: how water moves through a house

In plain English

Drying works with physics, not against it. Heat moves toward cold, wet moves toward dry, high pressure moves toward low, and everything heads for equilibrium. A restorer's job is to tip those flows in the right direction.

Many "sudden" water losses turn out to sit on top of a slow, chronic problem — a hidden construction defect or a long-running leak — and drying fails until that is found. Because a building's structure, systems and contents are all connected, a small change in one can have outsized effects elsewhere, including on occupants' health.

The S500 asks restorers to understand how the building was designed and built — materials, and how they relate to strength, sound and fire ratings — before deciding how to dry and restore it.

The S520 mold standard makes the same point for mold work. Every building has unplanned openings, and with a driving force behind them (wind, the stack effect of rising warm air, fans or ducts) they pull air in from garages, crawlspaces and attics. Remediators should understand the four ways moisture moves (liquid flow, air transport, vapor diffusion and capillary action) and how materials respond to it, from porosity and absorption to drying rate and how readily they grow mold, before writing a work plan.

Key points

• Heat → cold, wet → dry, high → low pressure.
• Look for chronic causes behind "sudden" losses.
• Everything in a building is connected.
• Understand the construction before drying it.

Official text

This topic is covered in our own words because the standard behind it is copyrighted; we cite it below rather than reproduce it.

Citations

• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Sec. 4, Building and Material Science, p. 27. Best practice
• IICRC S520, ANSI/IICRC S520 Standard for Professional Mold Remediation — Secs. 3.2–3.4, unplanned openings, mechanisms of moisture flow, effects of moisture on materials, p. 30. Best practice

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