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3 Best Practices for Sealing Wall Penetrations — and Preventing Mold Ignoring these crucial details can lead to a water intrusion nightmare

Many builders know they need to take care to prevent moisture intrusion, which can cause structural failure, shorten the life of exterior claddings and paints, foster mold, rot and insect infestation — and lead to costly litigation.

But while these same builders may take pains to use the latest in water management techniques and products, they often forget to use the same caution around a common source of moisture intrusion: wall penetrations.

Whether it’s holes for electrical, plumbing or HVAC, these penetrations are the crucial details that often get forgotten when it comes to moisture prevention. Many builders simply tape around wall penetrations and cover them with a makeshift treated piece of lumber. But that slipshod method often creates a weak spot for moisture to enter the structure.

It’s that kind of small detail that can matter most when it comes to the difference between solid moisture management and a water intrusion nightmare. In fact, one third to one half of all structures have damp conditions that may encourage development of pollutants such as molds, which can cause allergic reactions — including asthma, according to the Environmental Protection Agency.

Here are three best practices for properly sealing wall penetrations — and preventing mold:

1. For circular penetrations: Circular holes for HVAC and other hose or pipe penetrations require a different approach to wrapping and flashing because of their shape. There’s a good, better, best approach for these penetrations. The good approach is to use a flexible flashing tape. When using this method, first cut a flap in the housewrap above the pipe and fold it up out of the way. Next, install flexible flashing tape in a half moon below the pipe, overlapping the housewrap. Install a second half-moon of flexible tape above the pipe, lapping the ends over the half-moon below and tape the seams. A better way is to use a flexible flashing that can stretch around the pipe for a tighter seal. But the best practice is to use a liquid-applied sealant that comes in either a tube or brush-on application that will seal out water and air in one application.

2. For square or rectangular holes: These holes should be wrapped and flashed the same way windows are handled for optimal moisture prevention. That means following ASTM E2112, which offers a guide for how to wrap window openings and install flashing. Using drainable wraps in combination with flashing adds even more insurance against water damage.

3. For all openings: Housewrap should only be slit so the opening can be flashed and the housewrap folded down over the flashing to avoid reverse shingling. For best results, flash all penetrations first, and then install specially designed mounting blocks, such as Tamlyn XtremeBlock. These molded plastic mounting blocks come in a variety of configurations with built in flanges, flashing and slope to protect against moisture and encourage proper water runoff. While more expensive than wood blocks, the slight additional cost of XtremeBlock easily offsets the labor required to create a water-sealed, airtight penetration and provide a finished, professional look In addition, the installation of specialty mounting block can be done after mechanicals are installed, which solves trade sequencing problems.

For more on moisture intrusion prevention and install videos, go to our TamlynWrap® Installation Videos.