Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Through-Wall Flashing and Masonry Moisture Control
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## Inspection Hold Points
−## Because flashing is concealed course by course, inspection must occur while each flashing run is still exposed. {note}
+## Because flashing is concealed course by course, inspection must occur while each flashing run is still exposed.
### Installation of masonry above a flashing course shall not proceed until the flashing, its laps, end dams, weeps, and cavity drainage medium at that course have been inspected and accepted.
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## Flashing material selection follows from the severity of wetting and thermal exposure at each location. {note}
−### The flashing material at each location shall be selected for the wind-driven-rain exposure, freeze-thaw exposure, and ultraviolet exposure of that location, with base-of-wall and parapet conditions treated as the most severe. {note}
+### The flashing material at each location shall be selected for the wind-driven-rain exposure, freeze-thaw exposure, and ultraviolet exposure of that location, with base-of-wall and parapet conditions treated as the most severe.
−### Base-of-wall flashing collects the entire column of water draining down the cavity and sits in the zone of splash, snow, and de-icing salt. Parapet flashing is exposed on two faces and undergoes the widest thermal swing of any wall location. {note}
−
```datasheet
label: Exposure severity (governs material and thickness selection)
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```
+### Base-of-wall flashing collects the entire column of water draining down the cavity and sits in the zone of splash, snow, and de-icing salt. Parapet flashing is exposed on two faces and undergoes the widest thermal swing of any wall location. {note}
+
## Cavity Width
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## The four material families each carry a different cost, durability, and compatibility profile; the choice drives nearly every downstream detail. {note}
−### Through-wall flashing material shall be one of: sheet metal (copper, stainless steel, or galvanized steel); EPDM membrane; rubberized-asphalt (SBS) self-adhered membrane; or composite metal-laminate membrane. {note}
+### Through-wall flashing material shall be one of: sheet metal (copper, stainless steel, or galvanized steel); EPDM membrane; rubberized-asphalt (SBS) self-adhered membrane; or composite metal-laminate membrane.
−### Metal flashing is the most durable and is preferred where it terminates at an exposed drip; membrane flashings are more forgiving of complex geometry and laps but require a metal drip edge at the face. Composite laminates pair a thin metal foil with a self-adhered membrane to combine the two. {note}
−
−### Aluminum shall not be used as masonry flashing in contact with mortar. {note}
−
−### Portland-cement mortar is strongly alkaline; it corrodes aluminum rapidly. This is the single most common material-selection error in masonry flashing and is non-negotiable. {note}
−
```datasheet
label: Flashing material family
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```
+### Metal flashing is the most durable and is preferred where it terminates at an exposed drip; membrane flashings are more forgiving of complex geometry and laps but require a metal drip edge at the face. Composite laminates pair a thin metal foil with a self-adhered membrane to combine the two. {note}
+
+### Aluminum shall not be used as masonry flashing in contact with mortar.
+
+### Portland-cement mortar is strongly alkaline; it corrodes aluminum rapidly. This is the single most common material-selection error in masonry flashing and is non-negotiable. {note}
+
## Sheet-Metal Flashing
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### Rubberized-asphalt flashing shall be a self-adhered SBS-modified membrane of 40 to 60 mil thickness, with low-temperature flexibility and lap-seal adhesion consistent with ASTM D1970.
−### Rubberized-asphalt flashing shall not be exposed at the face of masonry. {note}
+### Rubberized-asphalt flashing shall not be exposed at the face of masonry.
−### Ultraviolet exposure and thermal cycling delaminate exposed SBS membrane and bleed a dark stain onto the masonry face. SBS flashing shall always terminate behind a metal drip edge. {note}
+### Ultraviolet exposure and thermal cycling delaminate exposed SBS membrane and bleed a dark stain onto the masonry face. SBS flashing shall always terminate behind a metal drip edge.
### Rubberized-asphalt flashing shall be held back a minimum of 1/2 in. (13 mm) from the face of masonry, and 3/4 to 1 in. (19 to 25 mm) is preferred, to prevent staining.
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### Solvent-based and coal-tar sealants shall not be used against rubberized-asphalt membrane, and bitumen-based products shall not be used against EPDM. {note}
−### Solvent and coal-tar chemistries attack SBS membrane, and bitumen plasticizers migrate into and degrade EPDM. The compatible sealant family shall be specified explicitly rather than left to the field. {note}
+### Solvent and coal-tar chemistries attack SBS membrane, and bitumen plasticizers migrate into and degrade EPDM. The compatible sealant family shall be specified explicitly rather than left to the field.
−### Dissimilar metals in contact shall be isolated with bituminous paint or polyethylene tape to prevent galvanic corrosion. {note}
+### Dissimilar metals in contact shall be isolated with bituminous paint or polyethylene tape to prevent galvanic corrosion.
### Copper flashing against galvanized-steel shelf angles or aluminum window frames forms a galvanic couple that corrodes the less-noble metal. Copper mortar contact can also bleed a green stain; mortar at copper flashing shall comply with ASTM C1329 composition limits. {note}
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## Weeps are the only exit for water that the flashing collects; their type and spacing determine whether the wall actually drains. {note}
−### Weep openings shall be provided in the head joints of the first masonry course immediately above every horizontal flashing location, including base of wall, lintels, shelf angles, and sills. {note}
+### Weep openings shall be provided in the head joints of the first masonry course immediately above every horizontal flashing location, including base of wall, lintels, shelf angles, and sills.
### Omitting weeps above a lintel or shelf angle is a common error that traps water on the flashing and produces efflorescence and freeze-thaw spalling at that course. {note}
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## The weep type trades off drainage capacity, insect resistance, and appearance. {note}
−### The weep type shall be open head joints, plastic or wire weep-tube inserts, or manufactured weep vents, selected for the required drainage capacity and the project's insect and appearance requirements. {note}
+### The weep type shall be open head joints, plastic or wire weep-tube inserts, or manufactured weep vents, selected for the required drainage capacity and the project's insect and appearance requirements.
−### Open head joints drain fastest but admit insects unless screened or vented with an insert; tube inserts and manufactured vents restrict insects at some cost to drainage rate. {note}
−
```datasheet
label: Weep type
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```
+### Open head joints drain fastest but admit insects unless screened or vented with an insert; tube inserts and manufactured vents restrict insects at some cost to drainage rate. {note}
+
## Weep Spacing
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## Mortar that falls into the cavity and piles on the flashing bridges the cavity and dams the weeps; controlling it is as important as the flashing itself. {note}
−### A cavity drainage medium shall be installed in the cavity directly above the flashing to keep mortar droppings off the flashing and maintain the weep drainage path. {note}
+### A cavity drainage medium shall be installed in the cavity directly above the flashing to keep mortar droppings off the flashing and maintain the weep drainage path.
### A mortar net, cavity drainage mat, or drainage mesh of polyamide or polypropylene holds mortar droppings above the flashing so water still reaches the weeps. Omitting this medium from the specification while showing it only on a detail is a frequent source of RFIs and field disputes. {note}
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## Continuity of the Drainage Plane
−## The through-wall flashing and the backup WRB must form one continuous drainage plane; a gap or a reversed lap between them feeds water into the wall. {note}
+## The through-wall flashing and the backup WRB must form one continuous drainage plane; a gap or a reversed lap between them feeds water into the wall.
−### The flashing turned-up leg and the WRB shall terminate on the same plane of the backup wall and shall be lapped so that water is directed outward, with the flashing lapped over the WRB leg in shingle fashion unless the WRB manufacturer's tested detail directs otherwise. {note}
+### The flashing turned-up leg and the WRB shall terminate on the same plane of the backup wall and shall be lapped so that water is directed outward, with the flashing lapped over the WRB leg in shingle fashion unless the WRB manufacturer's tested detail directs otherwise.
### The default shingle order is flashing over WRB so that water on the flashing cannot run behind the membrane below. Some tested WRB systems reverse this at specific transitions; where they do, the manufacturer's tested detail governs. Coordinate the membrane specification itself with [[sync/air-barriers]]. {note}
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## The base-of-wall flashing is the most heavily loaded run in the wall and the one most often compromised by mortar fill. {note}
−### Base-of-wall flashing shall be installed continuously at the bottom of the drained cavity, turned up against the backup per the turned-up-leg requirement, with weeps and cavity drainage medium at the first course above. {note}
+### Base-of-wall flashing shall be installed continuously at the bottom of the drained cavity, turned up against the backup per the turned-up-leg requirement, with weeps and cavity drainage medium at the first course above.
### The base-of-wall flashing receives the cumulative drainage of the entire wall above it, so its end dams, slope, and weep continuity are the highest-consequence details in the assembly. {note}
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## Every horizontal structural interruption of the veneer is a new collection point that needs its own flashing, weeps, and end dams. {note}
−### Flashing shall be installed over every lintel and shelf angle, turned up against the backup a minimum of 6 in. (150 mm), with end dams at each end and weeps in the course above. {note}
+### Flashing shall be installed over every lintel and shelf angle, turned up against the backup a minimum of 6 in. (150 mm), with end dams at each end and weeps in the course above.
−### A shelf angle interrupts the continuous cavity and supports the veneer above it; water draining down the cavity reaches the shelf angle and must be intercepted and expelled there rather than continuing past it. {note}
+### A shelf angle interrupts the continuous cavity and supports the veneer above it; water draining down the cavity reaches the shelf angle and must be intercepted and expelled there rather than continuing past it.
### Flashing at shelf angles shall not bridge the horizontal expansion joint below the angle in a way that prevents the joint from functioning.
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## Parapets are exposed on two faces and are the wall condition most prone to flashing failure from thermal movement and freeze-thaw. {note}
−### Parapet through-wall flashing shall be installed below the coping bed and coordinated with the coping counterflashing, which is specified under [[sync/sheet-metal-flashing-and-trim]]. {note}
+### Parapet through-wall flashing shall be installed below the coping bed and coordinated with the coping counterflashing, which is specified under [[sync/sheet-metal-flashing-and-trim]].
### The through-wall flashing under the coping is owned by this standard because its function is to drain the cavity; the coping cap and its counterflashing are roofing-edge metal owned by the sheet-metal standard. The two must be detailed as a coordinated pair so water shed by the coping lands on, not behind, the through-wall flashing. {note}
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## Sequence
−## The flashing must be installed in the correct sequence relative to the backup, WRB, and cavity media, because each layer is concealed by the next. {note}
+## The flashing must be installed in the correct sequence relative to the backup, WRB, and cavity media, because each layer is concealed by the next.
### The Contractor shall install the WRB and flashing in the sequence shown on the accepted details so that every lap is shingled to direct water outward and no flashing edge is left exposed behind the cladding.
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### In rehabilitation work where existing flashing has failed or is absent, the replacement flashing extent, the saw-cut or rebuild method, and the weep and drainage provisions shall be detailed for the specific existing assembly [[drawing: rehabilitation flashing extent and method]]. {note}
−### Cut-and-insert reglet flashing, full course rebuild, and surface-mounted termination are all valid retrofit strategies; the choice depends on what the existing wall allows and shall be detailed rather than left to the field. {note}
+### Cut-and-insert reglet flashing, full course rebuild, and surface-mounted termination are all valid retrofit strategies; the choice depends on what the existing wall allows and shall be detailed rather than left to the field.
```datasheet
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- Lap sealant or splice tape
```