Water intrusion
Why water gets into a building, and why finding it usually means cutting into the wall.
Water intrusion means water getting past a building's exterior walls or roof. Investigators report that most leaks originate not in the flat wall material but at joints, seams, and terminations, the places where two components meet. Finding the true source often requires cutting into the wall, a planned, evidence-based part of the investigation.
Where the water is actually coming from
A board that assumes a leak means the siding or stucco itself failed is usually looking in the wrong place. Water rarely gets through the field material of a wall. It gets in where two different materials or components meet: a window flashing, a control joint, a roof-to-wall transition, a penetration for a pipe or vent.
"Ninety percent of all water intrusion problems occur within 1 percent of the total building exterior surface area."
Source: IIBEC Interface article, Michael T. Kubal, IIBEC
This is a widely repeated industry estimate, not a measured statistic from a standards body, but it shapes how a competent investigation is scoped: check the joints and terminations first, not the whole wall evenly. The same concentration pattern is the leading explanation for why building envelope failures and roofing problems so often trace to transitions rather than flat surfaces.
Finding the source often means opening the wall
Water travels sideways and downward inside a wall assembly before it shows up as a stain on drywall. That means the visible damage and the actual entry point are often in different places. ASTM's standard guide for evaluating water leakage treats the whole wall as one system and covers the range of methods used to trace a leak back to its source.
"Investigative techniques discussed may be intrusive, disruptive, or destructive. It is the responsibility of the investigator to establish the limitations of use, to anticipate and advise of the destructive nature of some procedures, and to plan for patching and selective reconstruction as necessary."
Source: Overview of ASTM E2128, Colin Murphy and Lonnie Haughton, IIBEC Interface, IIBEC
In practice this means the investigator, not the board, decides where and how to cut in, and plans the repair of that opening as part of the job. If litigation is a possibility, opening a wall before giving the responsible party notice can raise its own problems. See destructive testing and preserving evidence before authorizing anything.
What this means for how a board scopes the work
Two practical consequences follow from the 90 percent in 1 percent pattern. First, an investigation budget spent evenly across every square foot of wall is spent badly, the money is better aimed at joints, terminations, and penetrations. Second, a single stain inside a unit does not tell you where the water entered. That is a job for a forensic investigator, not a guess by the board or a general handyman.
Whether your governing documents or state law require notifying a builder or contractor before any destructive opening varies, so confirm this before work begins rather than after.
Check yourself
Answer before you read the explanation, recalling it is what makes it stick.
A board is scoping a water intrusion investigation and wants to know where to focus first. Based on industry experience, where should the investigator concentrate?
An investigator concludes the only way to trace a leak is to remove a section of the wall. Under ASTM's guide for evaluating water leakage, whose job is it to plan for the resulting damage and repair beforehand?
A director hears the '90 percent of leaks in 1 percent of the surface area' rule of thumb and asks what it means for the upcoming investigation. What is the right takeaway?
Sources
- ASTM E2128, Standard Guide for Evaluating Water Leakage of Building Walls (scope), ASTM International
- Overview of ASTM E2128 (Standard Guide for Evaluating Water Leakage of Building Walls), IIBEC
- IIBEC Interface article by Michael T. Kubal, January 2001, IIBEC
- Building Envelope Water Intrusion Expert Witness, Adam J. French
Construction Defects
Next, see how these same joints and terminations show up when a building's envelope fails more broadly.
Whether you need the builder's or contractor's consent before cutting into a wall, and whether your insurance covers the cost of the investigation itself, vary by your governing documents, your policy, and your state's notice statutes.