How to Specify Counter Flashing (Complete Waterproofing Guide)
Counter flashing must overlap base flashing correctly.
Complete Roof-to-Wall Waterproofing Guide
Counter flashing is installed:
- ✔ Over apron flashing
- ✔ Into masonry reglets
- ✔ Along parapet walls
- ✔ Around chimneys
- ✔ At roof-to-wall transitions
Its purpose is to:
- ✔ Protect base flashing
- ✔ Seal vertical transitions
- ✔ Shed water over lower flashing
- ✔ Prevent capillary water entry
Counter flashing must overlap base flashing correctly.
1️⃣ What Defines Counter Flashing?
Counter flashing is defined by:
- ✔ Reglet insertion depth
- ✔ Vertical wall leg height
- ✔ Drip return detail
- ✔ Overlap over base flashing
- ✔ Thickness
- ✔ Material
- ✔ Masonry or cladding type
Without wall type and base flashing geometry, it cannot be designed properly.
2️⃣ Reglet Detail (Critical)
Counter flashing often inserts into:
- ✔ Masonry cut groove (reglet)
- ✔ Brick mortar joint
- ✔ Concrete saw cut
Common insertion depth:
- 20 mm
- 25 mm
- 30 mm
Reglet must be:
Mechanically secured
Properly sealed
Incorrect depth causes water intrusion.
3️⃣ Vertical Wall Leg Height
Wall leg must extend high enough to:
✔ Prevent water bypass
✔ Cover base flashing top edge
Common heights:
- 100 mm
- 150 mm
- 200 mm
- 300 mm
Height depends on:
- Rainfall intensity
- Wall height
- Code requirements
4️⃣ Overlap Over Base Flashing
Counter flashing must overlap base flashing.
Typical overlap:
50–100 mm
Overlap must allow:
Water to shed outward
Incorrect overlap causes water tracking behind flashing.
5️⃣ Drip Edge / Kick-Out Detail
Lower edge may include:
- ✔ Drip return
- ✔ Safety hem
- ✔ Stiffening fold
Drip edge prevents:
Capillary backflow
Water running behind base flashing
Must be specified.
6️⃣ Masonry vs Cladding Application
Counter flashing differs depending on:
- ✔ Brick wall
- ✔ Concrete wall
- ✔ Metal cladding
- ✔ EIFS system
Masonry requires reglet insertion.
Cladding may require screw-fixed return.
Wall type must be defined.
7️⃣ Thickness Range
Common thickness:
- 0.45 mm
- 0.50 mm
- 0.60 mm
- 0.75 mm
Heavy-duty commercial projects may require thicker flashing.
Thickness improves:
- Dent resistance
- Wind stability
- Long-term durability
8️⃣ Material Type
Common materials:
- Galvanized steel
- Galvalume
- Prepainted steel
- Aluminum
- Stainless steel
Material should match base flashing and roof system.
In coastal zones:
Aluminum or stainless may be required.
9️⃣ Corrosion Exposure
Counter flashing is often vertical and exposed.
Specify corrosion class:
- C2 – rural
- C3 – urban
- C4 – coastal
- C5 – marine
Higher exposure requires stronger coating.
🔟 Thermal Movement
Long flashing runs require:
- ✔ Expansion allowance
- ✔ Slip joints
- ✔ Sealant flexibility
Aluminum expands more than steel.
Thermal movement must be considered.
1️⃣1️⃣ Installation Method
Counter flashing may be:
- ✔ Inserted into reglet
- ✔ Surface mounted
- ✔ Embedded into mortar joint
Fastener spacing must be defined.
Sealant type must be specified.
1️⃣2️⃣ Typical Coil Width
Coil width =
Wall leg + overlap flange + reglet return + drip return + bend allowance.
Example:
- 150 mm wall leg
- 75 mm overlap
- 25 mm reglet insertion
250 mm + bend allowance → approx. 280–320 mm
If hem included, add additional allowance.
Exact developed width must include:
- ✔ Bend radii
- ✔ Thickness compensation
- ✔ Springback correction
Never approximate coil width.
1️⃣3️⃣ Machine Engineering Requirements
Counter flashing can be produced on:
- ✔ Trim roll forming machine
- ✔ Press brake
- ✔ Dedicated flashing line
Typical roll former:
-
6–14 forming stations
-
40–70 mm shafts
-
5–15 kW motor
-
Hydraulic cut
Reglet return requires accurate bend control.
1️⃣4️⃣ Production Speed
Typical speeds:
10–25 m/min
Simple geometry allows efficient production.
1️⃣5️⃣ Tolerance Requirements
Typical tolerances:
- Angle ±1°
- Insertion depth ±1 mm
- Overlap ±2 mm
- Length ±2–3 mm
Angle precision critical for reglet fit.
1️⃣6️⃣ Common Specification Mistakes
- ❌ Not defining reglet depth
- ❌ Insufficient overlap over base flashing
- ❌ Ignoring wall type
- ❌ Using too thin material
- ❌ Not including drip return
- ❌ Guessing coil width
Counter flashing failure often leads to long-term hidden leaks.
1️⃣7️⃣ Developed Width Reminder
Developed width must include:
- ✔ Wall leg
- ✔ Overlap flange
- ✔ Reglet return
- ✔ Drip return
- ✔ Hem allowance
- ✔ Bend allowance
- ✔ Thickness compensation
- ✔ Springback correction
Accurate flat pattern calculation is essential.
1️⃣8️⃣ Final Counter Flashing Specification Checklist
Before tooling or machine approval:
- ✔ Confirm wall type
- ✔ Confirm reglet depth
- ✔ Confirm wall leg height
- ✔ Confirm overlap over base flashing
- ✔ Confirm drip return detail
- ✔ Confirm thickness range
- ✔ Confirm material type
- ✔ Confirm corrosion class
- ✔ Confirm thermal movement detail
- ✔ Calculate developed width
- ✔ Confirm coil availability
- ✔ Confirm production speed target
Only then proceed.
FAQ Section
Is counter flashing required?
Yes in most roof-to-wall systems.
What is a reglet?
A groove cut into masonry to insert flashing.
Does overlap matter?
Critical — water must shed over base flashing.
Should thickness match base flashing?
Typically yes.
Can it be press-braked?
Yes for small production runs.
Is coil width moderate?
Yes — typically 250–350 mm range.