As we a saw in "Why does my roof leak"? the #1 reason of roofing problems is improper installation. Since proper roof installation is so important we are going to begin to examine the asphalt shingle roof installation process in this post. We are going to assume that the roof sheathing is solid, bare, clean, in good condition and ready for the roofing process to begin.
The first step is applying the underlayment. There are 2 roofing materials used as an underlayment. As the word suggests these roofing materials lay under the roof shingles and provide additional protection in deterring water penetration.
Ice and Water Shield or Water Barrier
Ice and Water Shield is important for helping to combat ice dams and is very necessary in the "snow belt" regions. Shingle roofs are designed to allow water to flow from the highest part of the roof to the lower sections where it will exit the roof. The shingle roof is not designed to hold water or prevent water from being forced up and behind the shingles. If the ice and water shield is installed properly any water that may back up and under the shingles because of wind or an ice dam will not soak into the roof sheathing and leak into the house.
The waterproof water barrier is placed directly on the sheathing of the roof. It is self-adhesive and comes in 3 foot rolls. In most cases one course of the water barrier applied at the bottom edge of the roof is not sufficient protection. It is best to apply a second course by slightly overlapping the first course so the protection is extended further up the roof. If there are any walls adjoining the roof such as upper level walls, dormer walls or chimney walls a course of the water barrier should be applied along the wall and roof junction and should extend up the wall a minimum of 4 inches.
It is vital that the first course extends down over the edge of the roof and behind the gutter (if there is no gutter extend it down to the point that the edge metal will cover it). This will seal the junction of the roof sheathing and the fascia board. Please note that any edge metal such as the drip edge or gutter edge is then secured over top of the ice and water shield. If it is placed under the water barrier it will be possible for an ice dam to force water behind the fascia board and into the soffit or up and under the edge metal where it can soak into the roof sheathing and cause leaks.
If there are valleys on the roof one course of the water barrier is applied the entire length of the valley before the metal valley is installed. If the slope of the roof is low an additional course on each side of the valley that overlaps the middle course will extend the protection.
Roofing Felt or "Tar Paper"
After the water barrier is applied to the roof the rest of the roof is covered with roofing felt that is also applied in courses from the bottom of the roof to the top. Each course will overlap the previous one and is installed over any metal valley.
The combination of the ice and water shield and the roofing felt plays an important role in deterring water penetration on asphalt shingle roofs. If installed properly the shingle roof will have added protection and successfully divert water off the roof and on to the ground even during periods of wind, snow and ice dams.
Sunday, November 22, 2009
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