Why Weather Barriers Are a Must With Exterior Foam Sheathing

While exterior foam sheathing acts as a good insulator and can help meet new codes and standards for energy efficiency, it has important weaknesses as a water resistive and air barrier.

DuPont™ Tyvek® weather barriers protect wall systems from water damage and air intrusion that can occur if foam sheathing is used without an additional weather barrier.

Testing Identifies Problems

Even though foam sheathing is sometimes used as a water resistive barrier and air barrier, problems with this installation method have been observed during laboratory testing, and confirmed with issues observed in the field.

Problem 1: Dimensional Instability

Over time, foam sheathing boards change size, expanding and contracting with temperature fluctuations. This phenomenon is known as dimensional instability. It can cause taped butt joints to become taxed and ultimately fail, allowing water and air into the wall cavity, which can significantly impact R-value.

Problem 2: Poor Water Management

Another issue with foam sheathing is reverse shingling. This occurs along taped foam joints, because foam sheathing cannot be lapped to allow for proper water shedding. Water can enter through the top of the taped seam and continue into the wall system, creating significant moisture intrusion issues.

DuPont™ Tyvek® WRB Helps Solve the Problems

By creating an air and- water resistant barrier, Tyvek® weather barriers can protect foam sheathing from water damage that can compromise its insulating properties, if dimensional instability or reverse shingling occur.

Application Specific Solutions

From Tyvek® building wraps to Tyvek® Fluid Applied weather barriers, DuPont Building Envelope Systems offer a range of innovative application options for establishing a weather resistant barrier when using exterior foam sheathing insulation.

Learn more about foam sheathing problems – and optimal installation to enhance durability and energy efficiency. Get the facts.