By Frank Ross
The most common places for damaging water leaks in residential construction occur where roof flashing is installed, and poor installation is most often the cause of failure.
Flashings are the critical material that forms the barrier between the primary roofing material (asphalt shingles, ceramic tiles, etc.) and objects that don’t get covered by that material. Regardless of the roofing material, the critical areas with the highest potential for leaks are these transitional areas.
Pliable metal flashing is used to direct water away from valleys or dormers created by changes in the roofline, plumbing or fan vents, a chimney, or a skylight installation. Copper is the preferred material, though there are other cheaper materials being used today and is practically leak proof when installed properly. Poor installation of non-copper metals that depend on caulks or roofing cement to seal out moisture are certain to leak over time as constant exposure to the elements slowly destroys the adhesive and elastic qualities of these chemical sealants.
Depending on the material used, the lifespan of a roof can range dramatically, and this means that the flashing in these critical areas of exposure must meet or exceed the life span of the roofing material. When flashing metals are used it is critical that they must be easily shaped and soldered, brazed or welded readily. And while some installations can be done using crimps, a permanent seal is the most secure option.
Soldered joints will stand the extreme temperature swings and the resulting expansion and contraction that a roof is exposed to. The most troublesome areas are where flashing must be formed around a corner such as a chimney or dormer, or where two pieces must be spliced together. Traditional flashing metals include copper, tin coated steel, lead and galvanized steel.
Copper flashing is the preferred metal because it performs far better than other metals in all areas of concern. It is malleable and easily formed, easily soldered and is very durable. Copper sheeting used for roof flashing is also known as 16-ounce copper because the .0216” thickness required for this application weighs about 16 ounces per 12” x 12” sheet. Tin coated steel and galvanized steel will eventually rust and corrode. While it is possible to paint tin and galvanized metals, it is very difficult to get paint to adhere properly due to oils on the surface from the manufacturing process. Cleaning the surface is required, special primers and several coats of the finish paint are best but seldom used, so peeling or flaking paint will eventually give way to rust and flashing failure. Aluminum cannot be soldered, and if it is used to flash around a chimney or a brick wall, it will corrode rapidly. The chemical composition of the mortar will attack and destroy the aluminum!
Valley flashings are generally divided into two categorize, open and closed. As implied by the name, open valleys are visible when completed and closed valleys are not. When open valleys are installed, long sheets of 16 oz. (minimum) copper are cleated to the sheathing and underlayment before any shingles are applied. Adjacent sheets of copper are overlapped a minimum of 8″. The sheets are nailed only at the top and copper or bronze nails are used.
Closed valleys are constructed as the shingles are installed by inserting copper flashing squares between successive layers of shingles. These flashing squares are folded on the diagonal.
When slate or tile is used for the primary roofing material, 20 oz. plain or lead coated copper is recommended for use in valley flashing. But keep in mind that building codes vary widely across the U.S., so you should check with your local codes before beginning any project.
Once you’re ready to start, remember that QuickShipMetals.com has an extensive stock of copper sheeting in all sizes and thicknesses that are appropriate for roofing flashing. Give our friendly customer service staff a call for a price quote that won’t send you through the roof!
Call toll-free: 1-888-334-2177
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