Courtesy of gravity, one immutable law of nature is water will always flow relentless down a slope. As it runs downward, your roof flashing allows it to pass harmlessly over any cracks, crevices and gaps in your building’s exterior. While caulking is fine for weather proofing small gaps, such as around doors, windows and eves, caulk should not be confused, or substituted, for flashing. If your roof flashings are damaged contact Jim Brown & Sons Roofing for a free estimate today.
What is Flashing?
Roof flashing is a layer of waterproof material, typically a metal such as aluminum, that prevents water from finding its way into places it does not belong. Flashing is typically used in roof valleys and around edges of roofs where it is difficult, or sometimes impossible, to cover properly with other roofing material.
Flashing is designed to shed water in the same manner as shingles or metal roofing. For it to work correctly, flashing must be installed with all seams facing downhill. Flashing is usually layered with other building materials, such as felt paper, where the top edge of flashing is protected.
To determine if flashing has been installed correctly, follow rain water as it rolls down the side of your roof. The water should move across all surfaces on its journey downward, without encountering any open seams or raised lips to blocks its progress.
Preventing Water Damage to Areas Where the House Meets a Deck
Here the flashing should extend up the wall at least four inches to form an efficient water barrier. If the flashing does not extend far enough up the wall, over time moisture will cause wood to rot and the metal fasteners, holding the deck together, to fail. This will always result in a time-consuming and expensive repair.
When installed on a deck, the flashing should be brought down the building’s outside wall and over the top of the piece of lumber attached to the house at the edge of the deck, called the “ledger” board; this board holds the deck framing in place against the house.
Many homeowners have removed an aging outdoor deck only to discover the home’s siding and framing has turned into something resembling the consistency of paste that is occupied by a prospering colony of insects. This is typically the result of damaged or missing flashing, as without proper flashing there is nothing to prevent running water from infiltrating into the wall behind the ledger board.
Types of Flashing
Flashing can be made from virtually any type of material, provided it is impermeable to water and won’t degrade from being in contact with an incompatible substance. As an example, during 18th-century construction many roofs were flashed with birch bark to prevent water from getting into roof valleys. Two-hundred years later many of these roofs still don’t have trace of water damage.
Today, builders usually use one of these more modern materials to flash roofs:
● Aluminum is durable, easy to shape and relatively inexpensive. However, aluminum does have a tendency to corrode if it comes into contact with materials that have a high alkaline content, such a concrete or cement siding. Aluminum will also deteriorate from being in contact with the new copper-rich-preservatives, used to replace the older arsenic compound in pressure-treated lumber. This lumber is often used in outdoor applications, such as decking.
● Copper flashing is more expensive and more difficult to shape than aluminum, but is extremely durable and compatible with the newer wood preservatives.
● Polyvinyl chloride, commonly known as PVC, is chemically inert, very easy to shape and is not affected by chemically-treated wood.
● Lead is extremely soft and pliable and is a favorite flashing choice of masons for flashing around chimneys. However, lead does carry some potential health risks.
● Galvanized steel is quite inexpensive, but it is not as durable as other materials.
● More recently, a bituminous tar-like material with an extremely sticky backing has become popular for flashing applications. It is an exceedingly tough and very pliable material that self-seals around fasteners. However, the bituminous material will decompose with prolonged exposed to sunlight, so it must be covered with another material, such as aluminum, but should keep the roof protected for many years.
All of these materials are supplied in rolls of various widths that can be trimmed and formed as needed, right on the job site.