Water Management

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Most builders understand the importance of managing water around their houses. When putting a water management strategy in place, it takes more than getting the idea across to your teams that wet is bad and dry is good. Problems occur because of two reasons: a breakdown in the process or a process that ensures follow-through with a water management strategy was never established.

February 01, 2005

 

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Up on the roof

Most builders understand the importance of managing water around their houses. When putting a water management strategy in place, it takes more than getting the idea across to your teams that wet is bad and dry is good. Problems occur because of two reasons: a breakdown in the process or a process that ensures follow-through with a water management strategy was never established.

 

 

Sloping exterior surfaces and the surrounding grade provides positive drainage.

On the left, the drainage plane is layered shingle fashion.  On the right, reverse layering guides water into the wall cavity.

A strategy for water management needs to include waterproof materials such as house wrap and flashing. The term "waterproof," however, can be misleading. If you walk with a waterproof raincoat and umbrella in a downpour, you may still get wet. Puddles will dampen your pant leg, and wind will push the rain under your collar and through the opening of your coat if you're not buttoned up. In the same sense, a good strategy for the home not only requires the right materials, but also needs to outline the process of installing the materials so water runs away from the home. In particular, design and construction teams must understand and implement the specific technique of shingling into that process.

Any water management strategy needs to reinforce the principle of shingling — a critical concept that doesn't just apply to the roof. Foundation processes may vary per climate; however, above grade your water management strategy is made up of three components: the drainage plane, roofing materials and flashing. Preparing your teams in the careful installation of the three components and underscoring the shingling concept will reduce many problems in the long run.

The Drainage Plane

The drainage plane is generally a waterproof material made up of house wrap or building paper. Similar to an ill-fitting raincoat, the drainage plane that is improperly installed doesn't offer complete coverage, so after the clouds roll in, a customer callback is sure to follow. If your teams haven't incorporated a shingling technique, the water could go behind the drainage plane material and lead to water damage, mildew or mold within the home.

Shingling involves applying the house wrap or building paper from the bottom of the wall to the top, making sure the upper layer overlaps the lower layer of each course. Shingling ensures that water stays on the exterior without the opportunity to flow behind the drainage plane. Reverse layering, where the lower layer overlaps the upper layer, can actually lead water into the home. Another point to include in your drainage plane process is to double it at the inside and outside corners to provide protection from wind-driven rain. Wrap the drainage plane around the corners, taking it past the corner for at least six inches. Apply a double layer at the corner by applying a strip of house wrap or building paper running vertically at the corner. With these installation details, the drainage plane provides a continuous surface that keeps moisture out of the little nooks and crannies, where big damage can occur. Only a continuous drainage plane that provides thorough coverage can prevent callbacks and ensure satisfied customers.

Roofing

To ensure continuous control of water above grade, the roof needs to work as the home's umbrella — allowing water to cascade freely along the exterior surface and away from the home. Teams need to adhere to the shingling principle with the roofing and roofing paper. To minimize the chance of water seeping into gaps at the top of each shingle or course of roofing paper, teams should start at the eaves and install upwards to the ridge, with each top layer overlapping the bottom.

It's important to plan for additional protection for valleys, hips and ridges by overlapping the roofing paper on each side of these areas. In valleys, the roofing paper should be layered and cut in a way that directs water into the valley. If one side of a valley is steeper than the other, or if one side has a much larger surface area than the other, as in the case of a dormer, keep in mind that water will flow more quickly down that side of the valley. If you're installing a closed-cut valley, cut the shingles at the steeper, or larger, roof to direct water into the valley. At the ridge, tiles and shingles should be layered in shingle fashion, moving along the ridge in the opposite direction of prevailing winds, so winds will blow water over the ridge shingles or ridge tiles instead of under them. At the eave, a drip edge will ensure continuity of the flow of water away from the home.



Flashing is only as good as its smallest piece.  If the flashing is too small for the application, water can drive behind it.

 

Flashing

Flashing is the next component of your water management strategy. Like the clasps of a raincoat, flashing works to reinforce a continuous drainage plane around the home. The intersections, penetrations and openings around a home are all potential places for drainage disaster. Wherever the drainage plane needs to change direction, flashing is critical to keeping the water moving along the exterior. Think of a customer's once-beautiful bay window that now has rotted wood because water seeped through the lintel. Reinforce the idea that flashing should be used throughout the home. Common applications include along windows, roof valleys, chimneys, dormers, door sills and plumbing vents. Weep screeds in stucco and through-wall flashing in brick veneer are other forms of flashing that expel water that has sneaked past the exterior finish.

Layers of flashing material, such as folded sheet metal and asphalt-impregnated paper, will direct water away from the home. Self-adhesive flashing membranes can be used to seal gaps and form a seal between two surfaces, such as around a window sill.

As with the roof and drainage plane, your teams need to understand the importance of layering flashing in a shingle fashion. Flashing must have ample height and width that ensures complete coverage of vulnerable areas. Wind or the momentum of the water can easily defeat inadequate flashing by pushing moisture up and behind it. When using metal flashing, use fasteners made of a similar metal in order to prevent corrosion that would keep the flashing from doing its job.

Don't forget about the foundation

Just as processes need to be established above grade to ensure water management, below grade components need to be planned for, followed up on and implemented. Depending on your location and climate, your water management strategy will need to address the type of construction below grade through aspects such as a foundation drainage system, vapor barrier and waterproofing. Water management strategies and proper grading are important to put in place below grade because water can seep into the home through hydrostatic pressure, the wicking of capillary action and vapor diffusion.

A thorough strategy will prevent both the obvious leaks and the subtle seeps from enraging customers and draining profits—but only if there's a process that ensures your design and construction teams understand the principles and implement the strategy properly. Only a complete water management system, which includes a comprehensive strategy and process, can prevent damage to the home and the builder's reputation.

 

 

 

 

 

 

 

 

 

Up on the roof

The following steps illustrate a good process for installing roofing paper by as explained in one of BuildIQ's online courses on water management.

  1. The drip edge: Either have the drip edge installed at the eave before the roofing paper or make sure that the drip edge is tucked under the roofing paper. Typically, the drip edge has a leg that carries three inches up the roof's surface. The roofing paper should overlap this leg at least one and a half inches.
  2. Overlapping and fastening: Each course should be lapped at least two inches over the underlying course. When two or more pieces of roofing paper are required to continue a course, the ends should be lapped at least four inches. End laps in a succeeding course should be located at least six feet from end laps in the preceding course. Each course should be fastened to the sheathing with only enough nails to hold it in place. Use only approved fasteners. Make sure that the roofing crew repairs all tears and gaps.

    Hips and ridges: The roofing paper should overlap at least four inches on both sides of all hips and ridges. Overlapping the paper at least four inches in these areas keeps wind-driven rain from getting behind the paper as it moves up and across the roof.
  3. At the rake: The drip edge should overlap the roofing paper so that the drip edges overlap one another properly at the corners.
  4. Valleys: Valleys must drain relatively large amounts of runoff, so they require additional weather protection. Typically, a 36-inch wide strip of asphalt-saturated felt paper should be centered in the valley. The strip should overlap the upper leg of the drip edge one and a half inches.
  5. Valleys: All courses of roofing paper should overlap the valley flashing at least two inches on both sides.
  6. Example of the drainage plane installed with the correct amount of overlap.
  7. Example of proper overlapping in a roof valley. Alternating courses are interwoven.
  8. Example of proper overlapping at a roof hip.

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