The Evolution Wall Flashings
The same can be said about construction in general, and especially exterior wall assemblies. In those instances, the selection of a thru-wall flashing product that can be brought flush to the outside face of the veneer is critical.
and even more important is the concern of melting of the asphaltic products under high heat. Masonry wall flashing should serve as a moisture collection location and also offers a barrier to infiltrating moisture which diverts it away from the inside of the wall cavity.
Good chimney flashings are two-part. Each of these ideally would have a base (step if it’s on the sides) flashing and a cap (counter) flashing; however, bottom flashings and top flashings (where there is no saddle) often are one piece.
This flashing wraps a few inches around the sides of the chimney. Flashing is a waterproof material used by masons to direct water out of a wall. Not all flashings are created equal!
Some architects and engineers prefer to use a copper flashing coated with flexible asphalt. Do not be afraid to ask your mason what flashings are going into your walls and why. The next code requirement—flashing at perimeters of exterior openings or locations where water could enter the wall—is sometimes misinterpreted or confused with air/moisture/vapor barrier requirements.
This definition applies to metal exposed copings and exposed flashings over wood or other exterior trim elements. Salt spray in coastal areas may accelerate corrosion. I can’t say for sure without seeing your roof, but most flashing problems can be patched or repaired fairly easily. Modified asphalt offers the waterproofing effectiveness of traditional modified bitumen products with low temperature adhesion. They are a far less expensive alternative to the old multi-wythe brick structures and, of course, much faster to build. Older architecture often incorporated corbels and recesses around its openings to keep moisture away from problematic areas. Nothing is more damaging to masonry than moisture. Over time, water will work to break down masonry joints and, if unprotected for long periods, it will degrade the anchoring systems within the wall as well.
The masonry industry understands that water penetration through the outer wythe of veneers will occur. For this type of wall to function properly, the drainage cavities have to be kept clear of mortar droppings and other blockage.
Through Wall and Other Masonry Flashings – Masonry Flashings
Today, we talk about air barriers, vapor barriers, and weather-resistive barriers as part of almost every wall assembly conversation. Once at the job, the stainless pieces would then be joined together like a big jigsaw puzzle and either soldered or “glued” together to create a watertight system.
It can break down joints, degrade anchoring systems, and cause mold to generate. Where should the flashings be installed in a masonry wall? Some chimneys are clad in wood, stucco or aluminum siding. The overlap between these two flashings allows movement without disturbing the water-tightness. On a chimney, flashing is required at the bottom, the sides and the top. Let’s look at how chimney flashings are installed. These base flashings are nailed to the deck. The cricket usually is made of the same material as the roof sheathing (plywood or waferboard in modern construction). All of the base flashings are fitted against, but not attached to the masonry. In good quality work, the top is bent and set 1 to 11⁄2 inches into a mortar joint (reglet). Just as the bottom base flashing did, the bottom cap flashing wraps around the sides of the chimney. The top edge of the cap flashings is bent and set into mortar joints. For example, sealants and flashing technology have improved over the last few years. When making a flashing lap or sealing around dowels, butyl can be an ideal choice. The material can also be installed in a range of weather conditions. Quality flashing products ensure longer lasting masonry projects. Here’s a photo of the same wall taken a few days later after the new limestone capstones were installed. It provides normal soft soldering capabilities and delivers easy folding. Stainless steel penetration flashings have proven to be the longest lasting and most reliable roof flashing type. Through-wall flashing is used at all points where moisture may enter the wall, and in selected places particularly susceptible to water damage. On nailable sheathing, the flashing should be fastened with wide head nails or cleats. The flashing is then installed along the horizontal plane where water exits through weep vents. This assists at preventing moisture from reentering the wall system and flashings that extend to the face of masonry have performed successfully for years.
The hemmed-edge flashing must be sealed and adhered to concrete or the surface below to prevent water from entering under the flashing system. Installing the horizontal flashing leg, drip edge, or flush edge at a slight bevel to the exterior assists in directing moisture to the outside of the wall assembly.
Heat resistant: will not degrade in high heat applications (like spray polyurethane foam applications). Load-bearing walls performed well as long as it stopped raining before water was absorbed all the way through the mass of the wall. Sometimes, masonry ledges or projecting elements (often referred to as water tables) deflected water off the façade as it flowed down the face of the building.
Water must be resisted at the outside face of these walls. Flashings are provided at the same locations as in veneer construction. When flashings are specified to be terminated within the face of the masonry veneer and not “daylighted” to the exterior, water may flow off of the edge of the flashing and be retained within the wall.
As moisture migrates toward the inner wythes, it softens and weakens the mortar joints in the old construction, often leaving them to later crumble away.
Unfortunately, as many good products as bad are lost in this process. A flashing material in cavity wall construction needs to act as a means to moisture collection, and then more importantly to the diversion of it.
Simply checking the manufacturer’s warranty should give you a good idea of how long to expect the material to last. Copper flashings exceed synthetics in puncture and tear resistance as well, assuring a stout collection area for any moisture pooling within the wall cavity.
The simplest details make all the difference. The written material is also incredible. As noted earlier, attention to full mortar joints and correctly proportioned cement, sand and water in the mix also are major contributors to the longevity of the structure.
Good joint tooling reduces the permeability of the wall, period. Every flashing detail helps to maintain its continuity and, when overlooked, will undoubtedly lead to a failure in the collection system. The first consideration of the flashing system is continuity, or having the least amount of laps and seams. Everywhere a joint or seam exists, so too does the opportunity for a failure in the wall. The laps themselves are extremely important, and inevitable on just about any wall. The corners of a wall or end dams at windows often are problem spots where moisture gets behind the flashing, either for lack of a good lap seam, or lack of one at all.
Flashing installations differ from type of material and backup wall condition. The flashing height should be consistent with the anticipated height of excess mortar collecting on top of it. Shown is metal flashing secured in the mortar joint prevents any moisture from pooling under or behind it. One of the most important details of the flashing installation is located on the outside of the wall. This most certainly will lead to a moisture-related problem over time. With all flashing types, the better option is to use a premade drip edge, which has a greater uniformity and more options in its visual appeal.
So where do flashings need to go?
Parapets finished with coping stones require maintenance, as mortar joints or sealants eventually will degrade in this orientation. In this condition, the metal sections should be soldered in lieu of using a mastic, assuring a strong bond between sections. and what’s discouraging is that these are simple details, things we’ve read about or seen in practice for years. All surfaces to receive the membrane shall be free of water, dew, frost, snow and ice. Sealant should not be applied past the outside of the window frame. The sill flashing detail requires that a backer rod and sealant be applied below the flashing. The lower edge of the flashing should extend about 1/2″ beyond the face of the brick, and have a downward bend to provide a drip.
With hollow brick, the flashing must fully cover the internal holes. If this flashing material is used at a shelf angle, a proper seal below it may not be possible. The last two details show typical shelf angle flashing. The detail on the left shows the copper flashing resting on the shelf angle. This can be achieved by the application of a bituminous coating on the shelf angle or the insertion of a strip of asphalt saturated felt.
It should project out about 1/2″ beyond the face of the brick below and be bent to form a drip. The ends of both head and sill flashings should be dammed to prevent moisture penetration. A wood trim piece covers the copper flashing. The cavity below the flashing is filled with mortar. Galvanized steel can be a cost-effective alternative to copper and stainless steel. There are also different types of galvanizing with different longevity rates. The paint will protect the metal until the mortar cures. Therefore, avoid aluminum in masonry construction wherever possible. Limitations of sheet metal include the cost of the material and labor costs required to form the flashing and to construct watertight joints. Fishmouths often occur at top vertical edges of the metal if the substrate is not perfectly straight. Copper fabric is also flexible enough to conform to irregular substrates. The bituminous versions cannot be exposed to direct sunlight, so the material cannot extend past the face of the masonry and form a drip.
These membranes are flexible and can be formed around many penetrations. The variety of dimensions allows the material to be unrolled along the length of shelf angles and other long flashings, avoiding laps and joints in the flashing materials.
Another product is a vinyl ethylene film bonded to fiberglass reinforcement. Special tapes and mastics are used to seal terminations and penetrations. A manufactured, mortar-control device is used to catch droppings at the base of the drainage cavity so that they cannot block the weeps. This action helps prevent the bottom piece of flashing from deflecting downward as the lap seam is created. However, the flashing must form around the toe of the angle. However, the lintels are not continuous. The intent of this practice is to prevent water from flowing off the end of the lintel, discharging water at the jamb of the window or door.
Flashings at these locations should have an upturned back leg to prevent water from flowing off the back of the flashing. If the window or door is near the base of the wall, the flashing should form a continuous envelope and be connected to the adjacent wall flashing.
Masonry Wall Construction
Parapets are subject to increased vulnerability from freeze-thaw distress because they are exposed to the elements on three sides. The mortar can harden and block the flow of water out of the weeps. This has created an emphasis on the effective management of the water penetration.
Flashing At The Base & Weep Holes
Flashing at the Base & Weep Holes Featuring master mason Bryan Light, the “Brick Masonry Techniques for Builders” DVD …