How should vertical seams be installed for water resistive barriers?

For water resistive barriers, vertical seams should indeed be lapped at least 6 inches. This practice is essential for maintaining the integrity of the barrier, as overlapping the seams significantly reduces the chance of water infiltration. A sufficient overlap helps ensure that any water hitting the wall will run down the barrier and not be able to penetrate through the seams.

Using a minimum of 6 inches also considers possible variations in installation conditions and helps create multiple layers of protection against moisture. This overlap is a crucial aspect of effective water management in building envelopes, particularly in climates prone to precipitation.

Other installation methods, such as sealing seams with adhesive tape, may provide some level of water resistance but typically are not as reliable over time without a substantial overlap. Overlapping by just 3 inches would not provide an adequate barrier against water penetration and could lead to vulnerabilities. Installing seams flush with each other would eliminate any overlapping, significantly increasing the risk of water intrusion at those seams. Thus, lapping the seams by a minimum of 6 inches is the most effective method for ensuring a robust water resistive barrier.