A Builder’s Guide to Water Lessons From the Field – Bill Lanni

The Roof’s Real Job

The purpose of a roof is simple: get the water off the building efficiently. Everything else—architecture, appearance, symmetry—comes second. If a roof moves water efficiently, it will protect the structure. If it doesn’t, the building will eventually reveal that mistake, no matter how beautiful the design looks on paper. Many modern designs reverse the priority. They start with appearance and assume the roofing materials will solve the water problem later. That is a dangerous assumption. Materials eventually fail. Gravity never does. A roof that relies on proper slope and clear drainage will always outperform a roof that relies only on waterproofing materials.

Where Roofs Actually Fail

Roofs rarely leak in the middle of a large roof field. They fail where things change:

• where a roof meets a wall

• where slopes collide

• where a penetration interrupts the surface

• where the roof geometry becomes complicated

These transitions require flashing, and flashing requires craftsmanship. In practice, poor flashing at roof transitions is one of the most

common causes of roof leaks.

Dead Valleys and Crickets

One of the most dangerous roof conditions is a dead valley, where two roof slopes collide and water has nowhere clear to escape. Water slows down in these pockets, debris accumulates, and hydrostatic pressure begins to work against the roof system. This is where a properly designed cricket becomes essential. The cricket divides the water flow and restores gravity’s natural drainage path. When a cricket is missing or undersized, water simply waits until it finds a weakness.

Dutch Gables and Complex Roof Geometry

Dutch gables are a beautiful architectural feature, but they introduce complicated drainage transitions.

These areas often include:

• short valleys

• wall intersections

• sudden slope changes

If flashing and sequencing are not correct, water will eventually exploit these transitions. Architecture may create beauty, but water only cares about gravity and pathways.

Chimneys and Large Roof Penetrations

Large penetrations such as chimneys interrupt the natural flow of water down the roof. Without a properly sized cricket behind the chimney, water accumulates on the upslope side and begins searching for entry points around the flashing. Sealants eventually fail. Proper geometry is the true defense.

Gutters: The Forgotten Hydraulic System

Many contractors treat gutters as decorative trim. They are not. A gutter system is stormwater plumbing attached to a house. Unfortunately, most contractors never calculate gutter capacity. They simply install whatever size gutter is common in the area.

This leads to several common failures:

• undersized gutters

• too few downspouts

• poor downspout placement

• long gutter runs feeding a single outlet

When heavy rain arrives, the gutter becomes overwhelmed and water backs up behind the fascia.

When Gutters Fail

Once gutters overflow, water begins to travel places it was never meant to go.

Depending on the building design, this can lead to:

• rotten fascia boards

• attic moisture and mold through perforated soffits

• stucco saturation

• foundation moisture problems

Homeowners often think the roof is leaking, when in reality the drainage system failed.

The First Clue Inside a Building

Before opening a wall or pulling out a moisture meter, experienced inspectors often feel something first. Humidity imbalance inside a building has a physical sensation. Years of walking into homes teaches the body what normal indoor air should feel like. From there the investigation begins: Is the humidity caused by water intrusion overwhelming the HVAC system? Or is it a mechanical failure preventing the HVAC system from removing moisture? In humid climates, the first cause is often the culprit.

The Builder’s Responsibility

Water never stops searching for a path. A builder’s responsibility is to make sure every possible path leads safely away from the structure. When roofs and drainage systems are designed with gravity in mind, buildings protect themselves for decades. When gravity is ignored, water eventually reminds everyone who is in charge.

“Water never stops looking for a path. A good builder makes sure every path leads away from the building.”