Waterproofing Exterior Walls

It might take years to see the effects of moisture infiltration to the house, but the results can be structurally devastating and expensive to repair. Preventing water from entering through the exterior wall is one of the most challenging parts of construction.

Waterproofing Methods

A barrier system is commonly used to prevent moisture infiltration in a frame construction, with the application of waterproof material designed to keep the moisture out. Barrier systems can be effective, but they’re prone to small joints, cracks or other pathways that allow water to enter. Once the water enters, the barrier may even keep it there.

The preferred alternative is a water-resistive barrier system – also called the drainage plane system – which anticipates that water will get behind exterior cladding. With this method, water-repellent materials are installed in a manner that drains any water passing through the cladding.

For masonry construction, which is a concrete frame with concrete CBS or concrete block infill, openings for windows and doors are subject to water infiltration. The openings are addressed before the stucco or windows are installed, with the application of a waterproof substrate – usually a fluid-applied material. Windows and doors are installed with a gap between the frame and the wall to keep incompatible materials separate; for example, aluminum can corrode due to contact with cement-based materials, such as stucco. The gap is filled with a high-quality silicone sealant. A second sealant joint, the “beauty bead,” is installed to finish the installation.

Waterproofing Materials

Fiberglass face gypsum sheathing is becoming the standard in the construction industry, since it is resistant to incidental water that breaks down plywood sheathing products.

A water-resistant barrier (WRB) is installed over the sheathing, often a wrap-type weather barrier, such as Tyvek. Each successive layer is lapped over lower layers – similar to roof shingles – so that water flows down to a flashing location and out.

Flaws in installation may result in water getting behind the wrap, leading to damage. Fluid-applied barriers, which can be sprayed or rolled directly on the sheathing, are gaining in popularity because they’re less difficult to install properly. If water does manage to penetrate one location, the rest of the sheathing is still protected by the barrier. Adding color to the fluid helps ensure adequate coverage.
Flashing is installed around openings in the exterior wall system to provide a continuous plane that ties into the weather barrier. A flexible adhered membrane, often called peel-and-stick flashing, is used around windows, dryer vents, hose bibs, fixtures and other penetrations.

Communicating with the Crew

Drawings aren’t always sufficient for communicating the detail work that’s required to ensure that waterproofing elements will be installed correctly – sometimes the crew doesn’t even see the drawings.

Instead, mock-ups are constructed and left on site for reference. They show how conditions will be addressed at critical points, such as window and door openings, balconies and penetrations. Several mock-ups might be required for complex projects; sometimes they might be put together in the back of a pick-up. Ideally, a mock-up can be built in-place for reference during construction, and then completed.

Field Testing

Water infiltration tests during construction catch problems with the installation – often the only time they can be addressed. Testing is conducted on mock-ups and also throughout the project as it proceeds, picking locations randomly.

Failures during testing aren’t unusual, especially during the initial testing. They could be due to inconsistencies in installation, deviations from the plan, or conditions that weren’t foreseen. Resolving them is a matter of conducting repairs and testing again until the failure is remedied. The objective is that any part of the building will pass on the first test by the end of construction.

For more on waterproofing exterior walls, listen to Paul Beers and Chris Matthews of GCI Consultants, LLC on the Everything Building Envelope podcast, and check out other waterproofing articles on the GCI Consultants website.