This article focuses on flashings for shelf angles and at lintels. These two areas are similar in that, whether or not drips are required, water must not be allowed to re-enter the wall below the flashing.
Most masonry experts have recommended use of a drip edge at the outlet end of the flashing system to route water draining from the wall out and away from the wall's face. Although stainless-steel drip edges are effective, they may not always be the best detail.
There are a number of recommendations, however most do not entirely solve the problem. Although cutting the flashing off flush with the wall is better than cutting it off over the brick cores, it does not prevent water on the flashing from re-entering the wall. And wind-driven rain can still be forced into the wall between the flashing and the masonry below when this joint is not sealed.
In the article, "Selecting Through-Wall Flashing," Carolyn Schierhorn reviews the various flashing materials and points out that cost should not drive the decision-making process for flashing selection.
All of the sources reviewed discussed the options for material selection. You have to look at the whole picture and try to find the best flashing you can for your particular situation. Some questions that may help to identify the quality you need in a flashing system are:
What is the building's projected life?
- Will the building be torn down or rehabilitated in 25 years?
- What is the quality of the labor force that will install the flashing?
- Will there be onsite inspection during construction?
The answers to these questions will help you to answer the more general question of whether the life-cycle costs of the materials and details are compatible with each other and with the intended use of the building.
In developing a detail that would lead to a successful flashing, even without drips, the following parameters should be considered:
The flashing must extend to the face of the wall. If the flashing is terminated within the wall, some of the water collected on the flashing will inevitably flow back under the flashing and into the wall, creating water-related problems, efflorescence, migration to the interior of building, and corrosion of the shelf angle.
From an aesthetic consideration, eliminating the drips is desirable, yet water must not be allowed to re-enter the wall.
Without drips the sealant under the metal edge is easier to install and monitor so it is less important that water be directed away from this joint.
Based on these objectives, the following materials will result in a functional and durable flashing:
Self-adhering, rubberized asphalt flashing is ideal because of its flexibility, self healing property, and ease of bonding to adjacent surfaces.
- A stainless-steel metal edge should be used because it eliminates possible galvanic action that can occur with copper while retaining long-term durability. This material eliminates the staining common with copper flashing and is more durable than galvanized flashing. It also allows the rubberized flashing to be installed in accordance with the manufacturer's recommendations and the joint below the flashing to be sealed. The metal edge also means that any future repairs to the sealant joint will be more easily made and won't affect the flashing system. Resealing a flexible flashing edge or even a drip edge is difficult and can result in damage to the flexible flashing, bending of the drip edge, or sealant adhesion failure.
- Silicone sealant has a longer life than other sealants and so is preferred. Proper preparation of the bond surfaces is important to reduce the likelihood of premature adhesion failure.
- A cavity drainage material and weep system can ensure positive drainage of moisture on the flashing. Pea gravel is often used, but it can be plugged by mortar droppings that form a solid cap over the gravel and prevent the moisture from reaching the weeps. Pea gravel can also cause soiling of the face of wall from dust that rinses out and drains from the weeps.
In designing a flashing system, you will need to understand the intent of the overall project's design recommendations, review the project requirements, and address any discrepancies that might exist between the various recommendations. Once the design is finalized, it should include recommendations on materials that are compatible with each other and with the design intent, and details that clearly define the flashing requirements. Ultimately, whether or not drips are used must be decided based on the specific conditions of each project.