An Open or Closed Case for Roofing Valleys? – Family Roofing

Posted on by David Reid

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An Open or Closed Case for Roofing Valleys?

 

A roof valley is a spot where two roof surfaces meet.  Each roof plane has a layer of shingles that need to smoothly intersect at the valley, even though they are laid at slightly different angles.  Over the years, roofers and manufacturers have come up with a few different ways to install the valley and merge those two roof planes together.

The roof valley is a challenging part of the roof to install.  The water from both roof planes is channeled into the valley, so it carries the most water.  Therefore, the roof valley will see the most wear and is the second most likely spot on a roof to develop a leak.  Manufacturers may require you to have a certain roof valley type in order to be covered by their limited warranty. So, your choice of roof valley installation method is critical to maintain your warranty and get the best longevity from your roof.

The valley area of a roof—the straight lines formed when two different planes of the roof meet—is a critical area that handles a tremendous amount of water run-off.  Valleys are typically found where gable dormer roofs meet the main roof, or when a house has angled wings or additions where two roof sections in different planes meet.  A house with an L-shaped or T-shaped footprint, for example, always will have roof valleys where the two sections of the house meet.  The opposing surfaces of the roof planes drain the water towards the valley area, where it is then channeled towards the edge of the roof.

One of the details that varies between homes is the method of flashing the valley areas of the roof.  There are two common methods for completing the flashing of a valley in a shingle roof system: closed valleys or open valleys.  To understand what makes a valley either closed or open, it is important to understand how a valley is constructed.

If you are looking to invest in a new roofing system, you’ll have to decide what method of flashing to consider for this crucial roof component.

Steps Taken During Installation

To better understand the two methods, it is worth discussing how roofers prepare the would-be valleys of the roofing system.  Before they assemble the roof covering, they first install an underlayment over the entire roof decking or sheathing.  Then, they apply either a self-adhering ice and water shield or another underlayment with a heavier gauge that will serve as the valley lining.

About Closed Roof Valleys

A closed roof valley is a flashing method in which the installation of the roof covering is extended to where the two opposing roof planes meet.  This “closes” the entire valley area, with the self-adhering underlayment layer completely hidden from view.  Easier and faster to install, it is a cost-effective method because it doesn’t require additional materials.  Since the area is covered by shingles, the closed valley makes the roofing system more appealing when seen from the ground.

About Open Roof Valleys

An open roof valley, meanwhile, is a flashing method in which a sheet of pre-bent metal is installed after the valley lining is placed.  The roofers apply the shingles, cutting and sealing the ones that overlap the metal. An open valley can easily and quickly shed ice and water.  It also minimizes shingle granule loss, leading to a long-lasting look. It can have as stunning an appearance as the closed valley if done properly.

What Is a Closed Valley Roof?

Before the installation of a shingle roof assembly, the roofing contractor installs an underlayment over the entire roof deck.  Incorporated into the underlayment may be a self-adhering ice and water shield or another type of underlayment that is a heavier gauge than the underlayment that covers the remainder of the roof system.  This self-adhering underlayment acts as the valley lining.

For a closed valley, the roofer will install the shingles onto the roof deck and extend the asphalt shingles through the area where opposing roof planes meet, so that the shingles cover, or “close,” the valley area.  When finished, the valley will be covered with shingles so that the self-adhering underlayment is completely covered with the asphalt shingles.  The asphalt shingles serve both as the valley lining and as the wear surface to protect against water.

What Is an Open Valley Roof?

In comparison to a closed valley, an open valley adds another layer of lining into the valley.  After the self-adhering underlayment is installed across the valley, a pre-bent metal valley lining is installed.  This valley flashing material can be manufactured from any metal that will resist the effects of weather, acid rain, and other contaminants.  Galvanized steel, aluminum, and copper can all be used.

As the asphalt shingles are installed over the roof deck, the shingles are extended into the valley.  However, these shingles are not run entirely through the valley area, but rather the center of the metal valley is left exposed.  In addition, it is important to avoid nailing the shingles through the valley metal.  A chalk line is then used to strike a line from the top of the valley to the bottom of the valley.  The shingles are then cut out of the valley area, “opening” the surface of the valley lining to water run-off and the environment.  With an open valley, a strip of metal will be visible on the roof wherever two opposing roof planes meet.

When to Choose a Closed Valley Over an Open Valley

There are several reasons why contractors and homeowners might choose to install an open valley or closed valley:

  • Aesthetics:  Contractors, designers, and owners have preferences as to the appearance of one type of valley over the other.  It is important to remember that a closed valley conceals the valley lining and allows the planes of the roof to blend together.  Open valleys, on the other hand, leave the metal exposed, which may be more pleasing to the eye, especially if copper is used as the valley lining.

  • Cost:  Contractors may be able to reduce the cost of materials on roofing projects by eliminating the metal being installed in the valleys.  This will reduce the installed cost of the project, especially if there is a significant number of valleys in the roof system being installed.

  • Functionality: Installer’s and designer’s opinions differ as to the functionality of closed valleys versus open valleys.  Closed valleys may have a tendency, if not constructed properly, to channel water under the shingles laid over the bottom layer of shingles.  However, open valleys may be susceptible to water back-up along the top of the cut-off shingles in the valley if not properly trimmed, potentially causing roof leaks.

In short, both options should be considered when replacing the roof system on your home or building.  If you are choosing to complete your roof replacement yourself, make sure that you consider these various factors before beginning your installation.  If you have decided to have a professional roofing contractor complete your roof replacement, be sure to discuss with them how they will address the valley detail.  Addressing the valley detail before work begins will allow you to consider the possibilities and ultimately get the appearance and functionality you want in your roof system.