Forensic water intrusion diagnosis · Lesson 1 of 4

Forensic water intrusion diagnosis: principles and terminology

Why diagnosis is a method; the four components of a leak; the forces that move rain; why a stain is not the entry point; when the water is condensation; the three D's of rain control; and the safety limits before anyone looks.

You will be able to: Name the four components of a leak and the three conditions and four forces behind rain penetration, separate the place water shows from the place it enters, and say what AFS contributes to an investigation and what it does not.

11 min · 12 slides · 7 questions

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Slide 1 of 12

Diagnosis is a method, not a guess

Building Science Corporation says failure to control rain is likely the oldest and most common serious building enclosure performance problem.

The Department of Defense roofing criteria (UFC 3-110-03) say to pay special attention to flashings because most leaks originate at these areas.

A diagnosis in this course means a cause shown by evidence, with the alternatives tested and the limits stated.

Sources

Building Science Digest 013, Rain Control in Buildings (John Straube, 2007, updated 2011) - Building Science Corporation
UFC 3-110-03 Roofing (1 May 2012, Change 5, 12 June 2020), sections 7-3 and 7-6 to 7-7 - U.S. Department of Defense, published by the Whole Building Design Guide

Videos for this lesson

What this video shows: Christine Williamson of Building Science Fight Club explains how to identify the four components of a leak and why each matters in a typical framed wall.

Video: Christine Williamson: The Four Elements of a Leak | BSFC | AIA by Acelab, on YouTube. Chosen from the video's published description.

Glossary

Leak (four components): Building Science Fight Club's description: a source of water, a pathway for it to travel, a driving force that pushes it along, and something that can be damaged. There is no leak without all four.
Entry point: The place where water crosses the enclosure. It can be far from the symptom, so it is located by measuring from a reference point and inspecting the neighboring elements.
Symptom: The place inside a building where water shows, such as a ceiling stain. UFC 3-110-03 notes that moisture reported as a roof leak can come from adjacent walls, windows or mechanical units.
Capillary suction: In NRC Canada's list of forces behind rain penetration, the force that draws or holds water in a space bounded by wettable surfaces.
Condensation: Water that deposits inside a wall from moist air rather than from rain. In NRC Canada's 1976 worked example, air leakage through a crack carries far more water than diffusion does.
Three D's of rain control: Building Science Corporation's frame for rain control: deflection, drainage (with storage and exclusion), and drying.