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378 The NRCA Roofing Manual: Steep-slope Roof Systems—2013 Slate Roof Systems | Chapter 3—Slate

For all metal crickets, NRCA suggests wood framing and decking be installed beneath crickets to support them.

Figures 3-27 and 3-28 illustrate examples of crickets used behind chimneys.

Counterflashing: Apron, step, cricket and backer flash-ings require some form of counterflashing to cover and protect their top edges from water intrusion. In many instances, the wall covering or cladding material performs the counterflashing function. When this does not occur, a metal counterflashing mounted to a vertical wall should be installed along the top edge of the flashing metal. See Figure 3-29.

The counterflashing material should be compatible with the cladding or substrate (e.g., aluminum and masonry should not be in contact).

Where wall cladding counterflashes wall flashing metal (e.g., step flashing), NRCA recommends that cladding material and water-resistive barrier extend past and cover the top edge of the flashing metal a minimum of 2 inches.

For additional information regarding counterflashing, refer to the Architectural Metal Flashing section of The NRCA Manual: Architectural Metal Flashing, Condensa-tion Control and Reroofing.

Skylight Flashings: Skylights, in terms of roof flashing, are much the same as other vertical surface flashings, particularly chimney flashings. Skylight flashings gener-ally consist of an apron flashing, step flashing and backer flashing. In most instances, the skylight unit itself func-tions as the counterflashing. Refer to Appendix—Roof Accessories for detailed information regarding skylights.

Steep- to Low-slope Transitions: Sometimes, slate roof systems terminate and drain onto adjacent membrane roof systems. In these situations, a slate roof system also serves as the counterflashing for the membrane roof system.

For steep- to low-slope transitions, NRCA recommends the slate be held back a minimum 10 inches above the transition. See Figure 3-30.

Figure 3-27: Wood cricket built on the upslope side of a chimney

Figure 3-28: Metal cricket flashing for the upslope side of a masonry chimney

APPROX. 1”

SEALANT

INSERT COUNTERFLASHING WITH

UNDERBROKEN TOP HEM FOR

FRICTION FIT

OPTIONAL: SOFT-METAL WEDGE

Figure 3-29: Metal counterflashing inset in masonry mortar joint

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376 The NRCA Roofing Manual: Steep-slope Roof Systems—2013 around a penetration. The flange can be set into asphalt roof cement or elastomeric flashing sealant for additional protection. These flashing components are often supplied by other trades but may be installed by a roofing contrac-tor. See Figure 3-21.

Vertical Surface Flashings: Flashings at a vertical surface-to-roof plane intersection should have a relatively smooth substrate on the roof plane and vertical plane, up to a sufficient height, to receive the metal flashing. Rough or contoured vertical surfaces, such as cut stone and rough timber, should be provided with a flush substrate above the roof line configured to accept the vertical flashing and/or counterflashing, or it may be possible to use soft-metal flashings formed to follow the substrate’s contours.

Four types of metal flashings are commonly used at loca-tions where a slate roof system intersects a vertical surface (e.g., chimney, wall, curb): apron flashing, step flashing, cricket or backer flashing, and counterflashing. See Figure 3-22.

Generally, before flashings are applied, a layer of self-adhering polymer-modified bitumen sheet or other ap-propriate underlayment should be applied to a roof deck around roof penetrations. Self-adhering membrane under-layment may be installed to a roof deck at the base of walls and around chimneys or curbs. A self-adhering water and ice-dam protection membrane can assist in keeping water from migrating into a roof system at these roof-to-wall intersections during times of severe freeze-thaw cycling.

Apron Flashings: Apron flashings provide a weatherproof-ing transition material where a roof area intersects a head wall. Common locations for apron flashings are the front or downslope side of a dormer, chimney or curbed roof penetration and other horizontal-to-vertical transitions.

See Figure 3-23.

Step Flashings: Where a roof area intersects a side wall, individual pieces of metal flashing are installed at the end of each slate course. This is referred to as step flashing.

NRCA recommends using metal step flashing pieces sized so they match the slate in length to achieve a minimum step flashing head lap. The step flashing width should be a minimum of 8 inches to obtain a 4-inch extension onto each underlying shingle and about a 4-inch vertical height over the exposed face of each overlying shingle.

See Figure 3-24.

STEP FLASHING

COUNTERFLASHING

APRON FLASHING

CRICKET OR BACKER FLASHING

Figure 3-22: Sheet-metal flashing components used at a chimney

Figure 3-23: Apron flashing at a masonry chimney

METAL FLASHING SLEEVE METAL FLASHING SLEEVE

WITH RAIN COLLAR

Figure 3-21: Various types of penetration flashings

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377The NRCA Roofing Manual: Steep-slope Roof Systems—2013

NRCA suggests that step flashing used with slate thicker than 1/4 of an inch has its vertical leg increased propor-tionately to obtain a 4-inch horizontal leg and 4-inch ver-tical height over the exposed face of each overlying slate.

Special attention needs to be paid to the bottommost step flashing where an eave intersects a continuous wall to en-sure water is diverted to the outside of the wall covering.

NRCA recommends a kick-out at this intersection. See Figure 3-25 for examples.

Cricket or Backer Flashing: When a roof area intersects an upslope side of a chimney or curbed roof penetration, either a cricket or backer flashing should be installed at this location. A cricket diverts water around a penetra-tion, and a backer flashing provides a weatherproofing transition material where a sloped roof intersects the back side of a penetration.

Backer flashing is generally limited to penetrations that are 24 inches wide or less. See Figure 3-26.

NRCA recommends designers specify crickets at the upslope side of chimneys or curbed roof penetrations when the chimney or curb is more than 24 inches wide.

A backer flashing or deck flange of a cricket flashing should have hemmed edges and should extend upslope under slate a minimum distance equal to three times the slate exposure. Underlayment should overlap the upslope edge of the flashing.

Figure 3-24: Step flashing at a vertical wall (refer to Figure 3-21 for kick-out flashing options)

Figure 3-25: Examples of kick-out flashings

Figure 3-26: Sheet-metal backer flashing at a chimney

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CHIMNEY WITH CRICKET FLASHING

SHEET-METAL

COUNTERFLASHING

SHEET-METAL

APRON FLASHING

WITH HEMMED EDGE

SLATE

SOLDER OR

SEAL CORNERS

SHEET-METAL

STEP FLASHING

UNDERLAYMENT

TURNED UP WALL

SHEET-METAL COUNTERFLASHING

SHEET-METAL CRICKET

FLASHING WITH HEMMED

EDGESOLDER OR

SEAL CORNERS

STEP FLASHINGBOTH

SIDES OF CHIMNEY

CRICKET FLASHING AT MASONRY CHIMNEY

APRON FLASHING AT MASONRY CHIMNEY

3" MIN.

SLATE-16

REFER TO THE INTRODUCTION OF THE CONSTRUCTION DETAILS CHAPTER FOR ADDITIONAL INFORMATION.

FOR SECUREMENT AND JOINERY OPTIONS FOR SHEET METAL AND COUNTERFLASHING OPTIONS, REFER TO THE NRCA ROOFING MANUAL:

ARCHITECTURAL METAL FLASHING, CONDENSATION CONTROL AND REROOFING.

THIS DETAIL APPLIES TO CHIMNEYS THAT ARE WIDER THAN 24 INCHES.

LAP UNDERLAYMENT

OVER FLASHING

419The NRCA Roofing Manual: Steep-slope Roof Systems—2013 Slate Roof Systems | Chapter 6—Construction Details

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421The NRCA Roofing Manual: Steep-slope Roof Systems—2013 Slate Roof Systems | Chapter 6—Construction Details

CURB-MOUNTED SKYLIGHT

BACKER FLASHING

SLATE

SKYLIGHT

APRON FLASHING

TURN UP UNDERLAYMENT

AT CURB

SKYLIGHT FLANGE

OVERLAP STEP

FLASHING APPROX. 2"

OR INSTALL

COUNTERFLASHING

SEALANT

STEP FLASHING

INSTALL CRICKET AT SKYLIGHTS THAT ARE WIDER THAN 24 INCHES.

REFER TO THE INTRODUCTION OF THE CONSTRUCTION DETAILS CHAPTER FOR ADDITIONAL INFORMATION.

WHERE DEEMED NECESSARY, HOLD SLATE UP ONE COURSE DEPENDING ON ANTICIPATED DEBRIS AND/OR SNOW ACCUMULATION.

SLATE-18

LAP UNDERLAYMENT

OVER FLASHING

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