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Base flashing, counterflashing and reglets · Lesson 1 of 4

Base flashing, counterflashing and reglets: principles and terminology

Why a roof-to-wall joint has two layers, the trade terms an installer meets on details and specifications, the families of counterflashing termination, one-piece versus two-piece, the code duty to flash, and where AFS work ends.

You will be able to: Explain the two-layer logic of a roof-to-wall joint, define base flashing, termination, counterflashing, cap flashing, reglet and receiver, name the ways the counterflashing top edge is held, and state the fall-protection boundary for the crew.

9 min · 10 slides · 6 questions

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Slide 1 of 10

Two layers at one joint

Where a roof meets a wall, base flashing turns up the wall from the roof and counterflashing comes down from the wall above and laps over it.

Hodgin describes counterflashing as a second (upper) layer of protection that keeps water from getting behind the lower layer.

Roof-to-wall termination, in sectionA masonry wall on the left meets a low-slope roof on the right. From the bottom: roof deck, insulation and cover board, field membrane. The membrane base flashing turns up the wall face and is held at its top by a termination bar. Higher up, a reglet is cut into a mortar joint; a lead wedge sits at its back and a fill closes its front. The red counterflashing comes out of the reglet, runs down the wall face over the top of the base flashing, and ends in a rounded hem kept clear of the roof. Water running down the wall lands on the counterflashing, then on the base flashing, then on the roof.8 in minabove roofABCDEHGFJKLNot to scale

Section through a low-slope roof meeting a masonry wall: the membrane base flashing runs up the wall to a termination bar, and a counterflashing set in a reglet in a mortar joint comes down over it with its hemmed lower edge kept clear of the roof. Water running down the wall lands on the counterflashing and then on the base flashing.

A
Roof deck
B
Insulation and cover board
C
Field membrane
D
Membrane base flashing up the wall
E
Termination bar and fastener
F
Reglet cut in a mortar joint
G
Lead wedge at the back of the reglet
H
Mortar or sealant fill, per specification
J
Counterflashing (AFS metal) with a rounded hem at the lower edge
K
Lap of counterflashing over base flashing
L
Clearance between the bottom edge and the roof
The two layers. Heights are measured from the finished roof surface. Values come from the governing document: the 8 in height is IKO's minimum, laps run 2 to 4 in by source. Not to scale.

Sources

Videos for this lesson

What this video shows: GAF's installation overview of its parapet wall flashing with counterflashing detail for EverGuard TPO and PVC single-ply systems (manufacturer system).

Video: Parapet Wall Flashing with Counterflashing Detail | TPO Commercial Roofing | GAF Drawing 301 by GAF Roofing, on YouTube. AFS checked its description against this lesson.

What this video shows: GAF's installation overview of a membrane termination with counterflashing at a rooftop unit, for EverGuard TPO and PVC systems: the same two layers on a curb.

Video: Termination at R.T.U. with Counterflashing Detail | TPO Commercial Roofing | GAF Drawing 503B by GAF Roofing, on YouTube. AFS checked its description against this lesson.

Glossary

Base flashing
The flashing that turns up a wall from the roof at a roof-to-wall joint. To NRCA it is membrane (plies or strips of roof membrane); UFGS 07 60 00 also specifies metal base flashing.
Counterflashing
NRCA: formed metal or elastomeric sheeting secured on or into a wall, curb, pipe or rooftop unit to cover the upper edge of a base flashing and its fasteners.
Cap flashing
NRCA's first meaning: flashing that covers the upper edges of the membrane base flashing, the same job as counterflashing.
Termination
NRCA: the treatment or method of anchoring and/or sealing the free edges of a membrane in a roof or waterproofing system.
Reglet
A groove cut into a mortar joint of a wall that receives the top edge of a counterflashing, where it is held with lead wedges (Levine; UFGS 07 60 00), or a manufactured receiver set in or on the wall for the same purpose (Fry Reglet).
Two-piece counterflashing
A receiver fixed in or on the wall plus a separate counterflashing that snaps into it (Fry Springlok), so the counterflashing can be removed for roof work (a UFGS 07 60 00 option).