Housewrap Errors

Green building and remodeling programs, the U.S. Environmental Protection Agency’s IAQ Plus program and Energy Star now are paying well-deserved attention to managing moisture in construction. These programs are recognizing that a home’s durability and indoor air quality can be affected by easily correctable mistakes when installing housewraps.

Millions of homes each year are re-sided, reroofed and have windows replaced. This is an excellent time for contractors to take a serious look at the building enclosure and make sure it’s watertight. Thoughtful attention to proper construction details, installation and integration of flashings, building wraps and papers are critical to the longevity of homes. The following are the most common mistakes contractors make when
working with housewrap.

1: Roof-wall Intersections
A 1-inch rainfall will deposit 1,250 gallons of water on a 2,000-square-foot roof.

During a wind-driven rain, a wall does not know it is not a roof. Therefore, it is important to ensure crews understand how to flash penetrations and install housewraps and kick-out diverter flashings at roof-wall intersections so water runs away from a structure. Water trapped beneath claddings can lead to deterioration and defects.

Because water flow is heavily influenced by gravity, roof-wall intersections are very leak prone. In addition, lots of materials are coming together at one location, and different trades are involved in putting the pieces together. Diligent remodeling contractors need to ensure these areas are flashed properly before roofing and siding is finished. To protect against leaks, contractors must understand proper moisture management means employing a system to reject water; it does not mean installing products haphazardly.

To protect against leaks, contractors must understand proper moisture management means employing a system to reject water; it does not mean installing products haphazardly.

Notice the moisture concentration at the roofwall intersection and over the window in Image 1. This intersection needs kick-out diverter flashings, which redirect water away from these troublesome details.

Image 2 shows what happens when kickout diverter flashings are not used at roof-wall intersections. Water has penetrated behind the water-resistive barriers, or WRBs, and the area did not dry before it got wet again, leading to rapid deterioration. Premolded, seamless, kick-out diverter flashings, such as the one shown in Image 3, are an excellent solution for reducing leaks at roof-wall intersections. The polypropylene product works well in cold and warm climates, can be used with any roof slope and costs about $12.

Metal kick-out diverter flashings often are poorly field-fabricated (as shown in Image 4), which can lead to leaks.

2: Reverse Shingling
Another mistake made when working with housewraps is poor flashing design, which can lead to common errors, like reverse shingling. For example, Image 5 shows a horizontal valley where the roof meets the wall. The metal flashing is reverse-shingled over the brick. Proper inspection is required to avoid flashing-related leaks.

There is a gap between the step flashing and WRB in Image 6 because the WRB was improperly installed behind the step flashing. Any water that gets behind the siding will run down the housewrap and penetrate between the step flashing and housewrap, leading to a ceiling leak.

A solution to this is to treat your walls like roofs. Few contractors would install roof shingles without an underlayment or flashings and would never lap the bottom shingles over the shingle courses above. In the same way, walls always should be covered by a WRB. Then, the WRB should be installed “shingle fashion,” so the upper layers overlap lower layers and step flashings. In Image 7, a peel-and-stick flashing seals over the metal step flashing onto the sheathing. If any water gets behind the housewrap, it will run onto the peel-and-stick flashing to daylight. Image 8 illustrates a real-world, properly integrated kick-out diverter flashing with peel-and-stick flashing and housewrap.