Thru-Wall Flashing: Then and Now

Copper still is king

By Keith A. Lolley

A wise man once said, “change is good;” an even wiser man added, “... if change is necessary.” Over the last 10 years, the thru-wall flashing industry certainly has seen its attempt at change. Words such as “innovative” and “green” are being used in numerous print ads to attract architects and contractors.

Longevity is the most important consideration when choosing a flashing product. When installing thru-wall flashing, there are very few opportunities for a “do over.” If installed incorrectly, or with inferior materials, the cost of replacing the flashing will be extremely expensive. Replacing flashing is not like replacing a window. Since the backup wall will still be in place, the new flashing will need to be secured with either a reglet or termination bar. All these additional labor and material costs can be avoided. Knowing the pro’s and con’s of the various types of flashing materials in today’s market is more important than ever because along with the terms “innovative” and “green,” we are also hearing the terms “mold” and “litigation.”

There are many different types of materials being offered as thru-wall flashings in today’s market, consisting of both metallic and non-metallic membranes. All can be marketed effectively, but can all perform effectively? When choosing the right thru-wall flashing, it is important to consider longevity.

Copper

For moisture protection, one material stands out – copper. Copper has been the preferred flashing material within the architecteral and mason contractor communities for more than 100 years. Copper flashing is offered in a sheet, pre-bent, or composite form. Composite copper, also known as laminated copper, is the most widely specified of all copper flashings because of its pliability. It can be adjusted easily in the field to fit various applications. Available in copper weights from 2 oz. to 7 oz., laminated copper also is cost-effective comparison to heavy gauged flashings, which gives architects and owners piece of mind without the additional costs.

All copper flashings are UV-resistant and compatible with the acids and alkali found in fresh mortar. Copper, unlike other non-metallic flashings, can be left extended from the wall to form a drip edge. Other types of flashings, such as rubberized asphalt and PVC membranes, are not UV-resistant and need to have a drip edge to allow the thru-wall flashing to actually run through the wall.

Composite copper flashings come with various laminate options. Each laminate serves a particular purpose. For instance, the widely specified copper fabric flashing consists of a full sheet of copper with an impregnated fiberglass scrim within an asphalt coating. The fiberglass scrim gives the copper superior tensile strength and shear resistance, while the asphalt coating allows for proper bonding in the mortar joint. Copper fabric also is available in a non-asphaltic form. Still providing the same tensile strength and shear resistance of the asphalt-coated copper fabric, non-asphaltic copper composite flashings are compatible with any latex sealant on the market. The absence of asphalt makes the flashing lighter, which allows manufacturers to more than double the amount of lineal footage put on each core.

A fairly new invention in copper laminated flashings are pre-formed Cop-R-Corners. These corners and end dams are manufactured from a 5 oz. copper weight, which allows for minor adjustments in the field. These watertight corners provide permanent protection when flashing inside and outside corners.

Composite copper has the ability to be installed in a mortar joint, reglet, or termination bar like most of the other flashing membranes, but this is where the comparison ends. Copper is rigid enough to span cavity walls effectively, which is very important when considering which thru-wall flashing to use.

Masonry flashing should be placed at the following locations:

• The base of the wall
• Over doors
• Window headers
• Window sills
• At every support angle
• At the roof and wall intersect
• Parapets
• Chimney’s
• Any other obstructions.

Rubberized Asphalt

Rubberized asphalt, otherwise known as peel and stick flashing, has a questionable ability to span the cavity-in-cavity wall construction. This type of flashing could need additional in-wall supports to receive the flashing. Rubberized flashings also are subjected to the drool effect. The interior of a masonry wall can gain enough heat to melt the rubberized flashing, causing it to leach through the weeps and stain the adjacent masonry.

The installation of a metal drip edge is required when working with rubberized asphalt flashing because of UV incompatibility. The rubberized asphalt should be adhered to the top of a metal drip edge to eliminate the chance moisture could get back into the wall. The metal drip edge is exposed to the sun. Once it heats up, the possibility of asphalt drool takes place.

Because rubberized asphalt is so susceptible to climate conditions, architects now are specifying the use of a termination bar to guarantee the self-adhered flashing stays adhered. Without the support of a termination bar, how long will the flashing stay adhered? Will the manufacturer give a guarantee in writing?

PVC Membranes

In the past, architects specified PVC membranes for use in thru-wall flashing applications. PVC membranes still are used because of their low cost. However, most flashing manufacturers do not endorse the use of PVC as a thru-wall flashing because the failure rate is extremely high. Over numerous freeze/thaw cycles, the plasticizers in PVC begin to migrate, which causes the membrane to become brittle and crack. Cracked flashing equals big problems. Here is a picture of why not to consider PVC as a thru-wall flashing.

Some of the new flashing products on the market today come with built-in drainage devices. Laminating a wicking mat to a flashing material is not innovative technology. It has been done before with negative results. These flashings not only draw moisture out of the wall, they draw moisture into the wall, creating a thru-wall flashing that holds moisture in the bed joint. The acids, salts and alkali found in fresh mortar also could clog these drainage mats, making them useless in a matter of years.

When constructing a building to last 50 to 100 years, it is important that the flashing last as long. To date, copper is the only flashing material with a proven track record to last the life of the wall.

Keith A. Lolley is vice-president of Advanced Building Products, Inc., of Springvale, Maine.

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