Where two sloping roof areas intersect and create an internal channel on the roof which drains runoff water from higher roof sections is known as roof valley. You can say that a valley on the roof is the most critical detail on the roof because it collects and drains a lot of water during rain. An improper installation of this valley would be the cause of roof leaks.
Initially, we can install a roof valley in three ways: woven, closed cut, and open. There are many techniques that you need to learn for each type of installation, which will be explained in this post. If you are going to install a valley then you should decide before how to shingle a roof valley, you have to consider your materials, desired look, and the climate of your area.
The three methods
In the roof valley installation, the most critical part is the preparation of the valley with an underlayment. The underlayment is the most essential and important part of every valley and provides to the valley with a waterproof base. All valley installation methods it is necessary to underlay these layers. You should use quality underlays which would be durable polyester membranes on bitumen base. Underlayment sheets for the valley should be centered in the valley and fully secured with only enough fasteners to keep them in place until the primary valley installation is complete. Some underlayment may not require enough fastening. The underlayment layers from the two adjacent roof planes must overlap the valley base sheet at least 15 cm. All fasteners also should be kept a minimum of 15 cm from the centerline of the valley.
- Closed-Cut Shingle Valley Roof
The roofing contractor installs an underlayment over the entire roof deck before the installation of a shingle roof assembly. Incorporated into the underlayment can be a self-adhering ice and water or any other type of underlayment which is heavier gauge than the underlayment is covering the remainder of the roof system. This self-adhering underlayment would act as the valley lining.
For a close cut shingle valley, the roofer crew install the shingles onto the roof deck and extend the shingles of asphalt through the area where joining opposite roof planes, so that the shingles close the valley area. When it will finish, the valley will be covered with the shingles so that the self-adhering underlayment is completely covered with asphalt shingles of the roof. In this type, the asphalt shingles serve both as the valley lining and as the wear surface for protection against water.
These valleys can be installed quickly and have a sharper and cleaner look than woven valleys. Form the ground, it looks as the shingles are meeting in a clean line in the center of the valley. Actually one layer of shingles crosses the valley beneath the other layer of shingles.
You are recommended to start the installation with the shingles on the valley side with the minimum slope or smaller distance to the ridge.t In that way larger amounts of water from the steeper rood section of the larger roof accumulate in the valley and would not flow under the shingles.
- Open Valley Roof
If you make a comparison between a closed and open valley roof, you will find that an open valley adds another layer of lining in the valley area. After self-adhering underlayment installation across the valley, a pre-bent metal valley lining is valley will be installed. This valley flashing material you can get from any metal manufacturer that will resist the effects of weather, contaminants and acid rains. Aluminum, galvanized steel, and copper can be used.
Because the asphalt shingles are installed over the roof deck, these shingles are extended into the valley. However, these asphalt shingles are not running entirely through the valley, but rather the center of the valley which has lines with metal lining is left exposed. In addition, this is very important to avoid nailing the shingles through the valley metal. A chalk line is then used to strike a line from the top to the bottom of the valley. The shingles are then cut out the area of the valley, opening” the surface of the valley lining to water run-off and the surrounding environment. In an open roof valley, a strip of metal lining would be visible on the roof where two opposing planes of the roof will meet.
A quick guide on how to install an open valley:
- Snap to chalk lines from ridge to eaves 8CM apart increasing in width by 1CM per meter to the eaves.
- Trim your shingles to these lines and cut the 5CM triangle of the top corner to direct the rainwater into the valley.
- Nail these shingles 5CM back from the existing chalk line.
- Do not use an asphalt shingle trimmed to less than 25CM in the length to finish a course towards the valley.
- You can trim a part of the adjacent shingle in the course to allow a lengthy portion to be used if necessary.
- Every end of the each shingle should glue with bituminous mastic.
- There would not be exposed nails along any part of the valley.
When to Choose a Closed Valley or an Open Valley
There are many reasons why contractors and homeowners might choose to install a closed valley or an open valley.
Cost: contractors are reducing the cost of materials on roofing projects by eliminating the metal being installed the roof valleys.it will reduce the installation cost of the project, especially if there is a number of valleys in the roof system being installed.
Functionality: sometimes installers and designers’ opinions differ as to the functionality of the open valley versus closed valley. Closed valley may have a tendency, if closed valley not constructed properly, to channel water under the shingles laid over the bottom layer of the asphalt shingles. However, open valleys can be susceptible to water back along the of cut shingles in the open valley if not properly trimmed, potentially causing roof leaks.
Aesthetics: designers, contractors, and owners have preferences as to the appearance of one type of valley over the other type of valley.it is very important that a closed conceals the valley lining and allows the opposite planes of the roof to blend together. On the other hand, open valleys leave the metal exposed, that may be more pleasing to the eye, especially if valley lining is made by copper.
In fact, both options can be considered when replacing the roof system on your building or home. If you are going to replace the roof by yourself, make sure that you have considered these all factors before beginning your installation.
You have decided to have a professional contractor for this purpose, be sure to discuss with them how they would address the roof valley details. Dressing the valley details before starting the work will allow you to consider the possibilities and ultimately you would get the appearance and functionality you want in your new roof system.
3. Woven Valley Shingle Installation
In a woven valley installation, roofing professionals lay shingles in the valley and weaves them together. Some of the homeowners prefer the look which woven valley provides. In case, if shingles are not laid properly in the valley, a woven valley will not flat, detracting and creating bumps from the overall look of the roof. With this method, there is no need to use bituminous mastic in the valley. However, it is very important to push the asphalt shingles snugly into the woven valley, while not nailing within 15CM of the valley center if it is not done properly Hollow space may develop beneath the shingles. The empty space makes shingles vulnerable to penetration, either by footstep, hail, or another type of debris.
Woven valleys can be suitable for 3-tab shingles or low-profile shingles as the single-layer construction allows them to be woven together and be overlapped by easy ways. When you are going to make a roof and considering how to shingle a woven valley with architectural shingles (”Cambridge Xpress” and “Cambridge Xtreme”). You should take into account their reduced flexibility and thickness.
4. Fourth Method/ Bonus method
The fourth method is easiest, money, and time effective!
One variant of the open valley named “Californian valley”. In some communities, it is called Cambridge valley” because it is only possible to do with Cambridge or laminated shingles. For this method, the last shingles on shingles on both cut side of an open valley install sideways, so that they run up and down the valley parallel with chalk lines. In this way it saves the time of cutting shingles and the fastest way to shingle roof valley too.
You should note that any valley which has properly installed is a critical component of any roof, ensuring the long-term protection of this critical area. You are recommended to install laminated shingles, or architectural shingles, using the open valley method, for better roof performance. Always consult your local roofing contractor to help you in your roofing decision with right selection of materiel.