Roof flashing is also needed along the edges of a roof at the gable wall. Drip edge flashing is used along the edges of a roof to prevent water from wicking back under the shingles. Special flashing is needed in climates where ice dams occur. The most common type of roof flashing is roll flashing. This is available in aluminum, copper, and galvanized steel. It's is available in widths from 6 inches to 20 inches, and in lengths of between 10 feet and 50 feet. Other types of flashing include corner flashing, which can be continuously bent around the corner of a roof, and pre-bent flashing. There are also multi-part pre-engineered flat roof flashing systems in which the parts clip together.
Slope Roof Chimney Flashing
Chimney flashing consists of several parts as shown in the illustration. Chimney flashing prevents water from entering at the point where the chimney and the roof meet. Typically, step flashing is used along the edges of the chimney stack. Leaks often occur at the chimney when flashing fails. Damaged flashing can be cemented or patched; however, it is also a sign that the roof may need to be replaced sooner than later. Every chimney is different, so installing chimney flashing is often a custom project. In most cases, chimneys are not attached to the frame of the house. As a result, when the house settles or shifts, the chimney becomes the perfect place for leaks. Other times that the chimney flashing will need to be replaced include when it is missing, when it is rusted through, when it is totally covered with roofing tar, or when the shingles are going to be replaced.
If the roof is comprised of asphalt or wood shingles, the chimney flashing can be replaced or installed by an experienced do-it-yourselfer. In the alternative, if the roof is made of slate or tile, the flashing techniques are much more complicated and should usually be left to a professional. Before beginning this advanced project, it is important to consider whether working on top of a roof is a comfortable scenario. In addition, metal pieces must be measured, cut, bent, and layered so that they fit tightly around the chimney and will shed water; so, do a self-check of your skills to make sure the project can be adequately completed.Hiring someone to replace chimney flashing may cost quite a bit; however, it guarantees that the job will be done correctly and safely. Just make sure to hire a reputable contractor and someone who is insured.
This is the best option for a less experienced craftsperson or someone with a fear of heights, vertigo, or other health issue. For those who want to go out on their own and install chimney flashing, there are at least two options. A metal work shop should be able to custom cut new chimney flashing by following the pattern of the old flashing or by following specific dimensions. The other option is to cut the metal at home with special metal cutting equipment. Cutting the metal at home is the cheapest; however, it also is quite a bit of work and leaves plenty of room for error for an inexperienced metal cutter. After the metal is cut, installing the chimney flashing will take a full day for even an expert.
Slope Roof Valley Flashing
Valleys require particularly sturdy flashing because they carry more water than any individual roof plane. On most roofs, metal valley flashing is installed after the roofing felt liner and before the primary underlayment and finish roofing.On some asphalt-shingle roofs, shingles are woven across the valleys, eliminating the need for metal flashing. This is generally the best way to handle valleys between roof planes of different pitches. Another fairly common technique for asphalt-shingle roofs is to flash valleys with roll roofing that's the same color as the shingles. To do this, first nail an 18" wide strip along the valley, with the finished surface down; set nails 1" from the edges and 12" apart. Then roll out a 36" wide strip, finished side up. Center it over the first strip and nail it down.Toinstall metal valley flashing for an asphalt-shingle roof, first roll out a length of 15-pound roofing felt cut to the length of the valley. Push it snugly into the valley, then nail it every 2-4' along the outside edges. If you need more than one length of flashing to cover the valley, start at the bottom and overlap the first piece with the second one by at least 6".
Slope Roof Drip Edge Flashing
Drip edge flashing helps keep water from wicking back under the shingles. Drip edges are corner-shaped metal strips that nail along the edges of the roof. They allow water from the roof to run cleanly off the edge. Without a drip edge, water may run down the side of the fascia and siding - causing stains and eventual damage. The drip edge also supports the part of the shingle that extends past the decking.
Along the eave, drip edge is nailed under the builder's felt and over the fascia. As an extra precaution, you may want to cover the nailheads with roofing cement then stick the felt down. At the rake, drip edge is installed over the felt and fascia. This protects the felt from high winds and blowing rain. In climates where ice dams occur, flash the eaves with a special rubber ice-shield membrane or roll roofing.
Industrial Flat Roof Sheet Metall Flashing
Building owners across the Canada are realizing that no part of the country is completely safe from devastating high winds. Few aspects of a building's construction are more important in reducing the damaging effects of those winds than the roof system. The pressures created by high wind speeds put an exorbitant amount of stress on the perimeter flashing of low-sloped roof systems, which often hold the roofing system in place. If the edging on these buildings does not properly secure the roof, the damage can be devastating. Not only could the roof system blow off, but the insulation could also become saturated and the deck damaged. All of these outcomes would lead to extensive water infiltration and costly damages to the building's interior, not to mention the potential safety hazards for the building occupants.
The integrity of the perimeter flashing is a critical first line of defense against roof failure, because membrane attachment to the deck cannot resist the loads created when the perimeter secure element fails, and this leads to progressive loss of membrane coverage (peeling of the membrane from the deck). The ANSI/SPRI ES-1 Wind Design Standard for Low-Sloped Roof Systems is a comprehensive guide to designing and installing a quality, wind-proof roof-edge system. It outlines specific tests and measures to determine what materials and installation techniques are required of roof-edge products based on a building's type and location. In addition, there are other aspects of prefabricated, perimeter-edge systems that make them beneficial in protecting a building owner's roofing investment.
The consistency of pre-manufactured, roof-edge products creates a system that is aesthetically appealing, easy to work with, and helps increase a roof's overall performance. On the other hand, field-fabricated products often vary from one project to the next. This can lead to a number of problems, including inadequate engagement between the clip and the fascia or coping, varying appearances, improper gauges, and sub-par coverage over the entire roof edge.
Another benefit of pre-manufactured, roof-edge products is the potential for comprehensive long-term warranties. Few roofing contractors will cover their sheet-metal work for more than a few years, while edge-metal manufacturers are currently offering warranties for as long as 25 years. Many of these warranties cover problems that arise from wind damage. Of course none of these benefits matter if the products are not properly installed. It can be the greatest product, the best warranty, and the most attractive roof edge in the world, but it is only scrap metal if it is not installed properly. Pre-manufactured materials are typically pre-punched at the factory, which allows contractors to easily install the products with the proper number and spacing of fasteners. This eliminates the possibility that a contractor will install the material incorrectly. It is also important that contractors use the proper fasteners when installing edge-metal systems. Regardless of what roof-edge system a building owner chooses, it is imperative that it provides adequate protection during the most demanding situations.
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