Tempo:
Flashing should also be used over windows and doors (drip flashing in this location is also called “head flashing”), unless they are protected by an overhang. This flashing is required where the vertical distance between the window or door and the underside of the overhang is more than one-quarter the horizontal projection of the overhang. For example, flashing is required if the top of a window is more than 300 mm (12 in.) below an eave that projects 1.2 m (4 ft.). Head flashing should extend from the top of the window or door to up and under the sheathing paper or membrane. Where the sills of windows and doors in exterior walls are not self-flashing, flashing must be installed between the underside of the window or door and the wall below.
FLASHING PERFORMANCE REQUIREMENTS The following performance requirements should be considered when materials to be used as flashing are selected:
Water Barrier The flashing assembly that includes materials and joints must shed water without allowing leakage. The ability of the flashing to seal and be detailed to avoid leakage is fundamental. Creating an effective and durable joint seal is often difficult. It is good practice to provide a secondary, continuous flexible membrane flashing under jointed materials such as brick, stone or sheet metal.
Movement Capability The flashing must be able to accommodate differential thermal and structural movements. As a result, it must either be made of a flexible material or have joints designed to accommodate movement such as thermal expansion and
contraction of all building components including the flashing itself, normal deflections under service loads, shrinkage and creep of concrete and wood; and expansion of brick after construction.
Terminations Terminations should be formed into sharp breaks and to be sufficiently rigid at points of discharge to adequately project water away from materials below.
Durability The flashing must be tough enough to resist physical damage during construction, as well as normal wear, which may be related to the environment and building maintenance activities. Other factors to be considered include deterioration from corrosion, metal incompatibility and galvanic action, deterioration due to exposure to ultraviolet (UV) light, extreme (hot and cold) temperatures, freezing water and fatigue due to movement. For more information on durability, consult the CSA Standard S478-95: Guidelines on Durability in Buildings. In general, the service life of flashings must be equal to or more than that of the wall system or roof system at locations where maintenance or replacement of flashings would be uneconomical.
Compatibility Flashings along with their primers and sealants must all be chemically compatible with adjacent materials. Avoid contact between dissimilar metals, as this can lead to galvanic corrosion when the metals are moist. Water acts as the electrolyte, and dissimilar metals as electrodes. Alkaline concrete and mortar aggressively attack materials such as aluminum and copper. These materials should be protected from contact with concrete or mortar by the
FLASHING PERFORMANCE REQUIREMENTS The following performance requirements should be considered when materials to be used as flashing are selected:
Water Barrier The flashing assembly that includes materials and joints must shed water without allowing leakage. The ability of the flashing to seal and be detailed to avoid leakage is fundamental. Creating an effective and durable joint seal is often difficult. It is good practice to provide a secondary, continuous flexible membrane flashing under jointed materials such as brick, stone or sheet metal.
Movement Capability The flashing must be able to accommodate differential thermal and structural movements. As a result, it must either be made of a flexible material or have joints designed to accommodate movement such as thermal expansion and
contraction of all building components including the flashing itself, normal deflections under service loads, shrinkage and creep of concrete and wood; and expansion of brick after construction.
Terminations Terminations should be formed into sharp breaks and to be sufficiently rigid at points of discharge to adequately project water away from materials below.
Durability The flashing must be tough enough to resist physical damage during construction, as well as normal wear, which may be related to the environment and building maintenance activities. Other factors to be considered include deterioration from corrosion, metal incompatibility and galvanic action, deterioration due to exposure to ultraviolet (UV) light, extreme (hot and cold) temperatures, freezing water and fatigue due to movement. For more information on durability, consult the CSA Standard S478-95: Guidelines on Durability in Buildings. In general, the service life of flashings must be equal to or more than that of the wall system or roof system at locations where maintenance or replacement of flashings would be uneconomical.
Compatibility Flashings along with their primers and sealants must all be chemically compatible with adjacent materials. Avoid contact between dissimilar metals, as this can lead to galvanic corrosion when the metals are moist. Water acts as the electrolyte, and dissimilar metals as electrodes. Alkaline concrete and mortar aggressively attack materials such as aluminum and copper. These materials should be protected from contact with concrete or mortar by the
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