How to Specify Counter Flashing (Complete Waterproofing Guide)

Learn how to specify counter flashing including reglet detail, leg size, thickness, material and roll forming requirements.

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.