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Selected Northwest Details: Flashing and Copings
1) Copings
2) Flashings
3) Details
1. Copings
1. The coping, or covering at the top of a wall, is a crucial element in achieving watertight masonry construction. Three essential items comprise good coping details:
1. impermeability
2. continuity
3. drainage
1.1. Impermeability. The traditional stone coping is an impermeable material that has an excellent track record, however, as a result of todays changing architectural styles and cost awareness, stone copings are used on relatively few projects. Impermeable copings of aluminum or steel have replaced all but a few stone copings.
Metal copings are light in weight, easy to install, impermeable and available in many colors. They are the recommended first choice to achieve watertightness. Where metal is architecturally unacceptable, the second choice is precast concrete. The precast concrete units can be produced in a variety of colors and shapes to compliment the masonry materials.
Brick is often desired by designers for copings, because of aesthetic reasons, however, it must be emphasized that brick is a permeable material that can be penetrated by water. The impermeable flashing below these brick copings becomes essential. Water leakage and efflorescence problems are most frequently associated with permeable copings. Where permeable copings are used, careful attention must be paid to detailing and workmanship.
Prefabricated copings using prelaid masonry with reinforced concrete inside the cut out units can be used to reduce the permeability of an all masonry coping.
1.2. Continuity. A coping is seldom achieved by a single unit and thus joints are an important factor for weathertightness. Metal copings must be properly crimped at joints. Joints that are not crimped, but lapped, may be a source of water entry. Provisions must also be provided for thermal movement of metal copings. Continuity in stone or precast concrete copings is typically achieved by caulking at the joints. Continuity in brick or block copings is achieved at the flashing layer below, because the number of mortar joints between the units makes continuity on the top surface difficult to achieve.
Building code provisions require that copings be designed to resist forces due to an earthquake. Masonry copings are frequently anchored by steel dowels that penetrate the flashing membrane and present difficulties for continuity. Careful workmanship must be provided at all times to insure continuity in laps at these flashings and anchor penetrations. To eliminate the use of dowels, the designer should consider details where the coping overhangs the wall and a lip is extended down the face of the wall.
Recommended Minimun Gauges for Copings
| Width of coping top (in.) | Galvanized Steel (Gauge) | Stainless Steel (gauge) | Aluminum (in.) | Copper (oz.) |
| through 12 | 24 | 26 | 0.023 | 16 |
| 13 to 18 | 22 | 24 | 0.036 | 20 |
1.3. Drainage. Suitable drainage paths from copings are important, both for watertightness and appearance. Overhangs, drips and slopes are essential parts of good design to prevent staining the wall surfaces from pollutants collected on the upper surface.
With impermeable copings, drainage occurs at the top surface which should be sloped away from the face of the wall at a recommended minimum of 1/8" in 12".
On the other hand, permeable copings require two drainage paths: a first path at the top for surface runoff, and a second path at the flashing for water that may penetrate the coping. Water penetrating masonry copings may dissolve any soluble salts in the mortar or units. The flashing should be sloped away from the face of the wall to prevent efflorescence from these salts appearing at the copings.
2. Flashing
Masonry requires flashing and coping for its protection from water, moisture and vapors. Flashing material therefore must be:
- impervious to moisture penetration
- durable in the environment: resistant to corrosion caused by exposure to the atmosphere and/or to the caustic alkalies present in mortar
- the soluble constituents of the flashing should be low enough to prevent discoloration of the masonry surface
- sufficiently tough to resist puncture, tearing, or other damage during construction
- easily formed to the desired shape, and cap able of retaining this shape throughout the life of the structure.
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
