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Indoor airPLUS

Technical Guidance to the Indoor airPLUS Construction Specifications

1. Moisture Control

Sections 1.7 - 1.10: Water-Managed Roof Assemblies

1.8 Fully Flash Roof-Wall Intersections

Fully flash roof/wall intersections and all roof penetrations. Install step flashing at all roof/wall intersections, except metal and rubber membrane roofs, where continuous flashing should be installed. “Kick-out” flashing shall be installed at the low end of roof/wall intersections to direct water away from walls, windows, and doors below. In all cases, flashing shall extend at least 4 in. on the wall surface above the roof deck and shall be integrated with the drainage plane above (shingle style) to direct water onto and not behind flashing. In addition, intersecting wall siding should terminate a minimum of 1 in. above the roof, or higher according to the manufacturer’s recommendations.

Detailed Illustrations

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Step 1 of 3 - Kickout flashing - beginning run of step flashing

Step 1 of 3 - Kickout flashing - beginning run of step flashing

Step 2 of 3 - Successive sections of step flashing integrated with courses of shingles

Step 2 of 3 - Successive sections of step flashing integrated with courses of shingles

Step 3 of 3 - Drainage plane material covers step flashing

Step 3 of 3 - Drainage plane material covers step flashing

Why

Step flashing integrates the water-shedding functions of the wall cladding with those of the shingles or other roof deck surfacing material. Flashing protects the vulnerable area where a wall and roof deck meet (e.g., where a roof intersects the wall of a dormer or the gable-end of a garage roof connects to the larger wall of the main house). Without this protection heavy rains and wind can push water against this junction and drive water behind the wall cladding and under the shingles. The result is rotting walls, roof decking, and mold.

Significant amounts of water can flow along these layers of flashing. Unless there is a "kick-out" flashing at the bottom, water rapidly flowing near the intersecting wall can reach the eave of the roof and over-shoot the gutter. This water will flow down the wall adjacent to the end of the gutter, sometimes leak behind the siding and the house wrap, and elements such as window and door units, (often with inferior flashing in their original installation into the wall) are commonly damaged by rot. “Kick-out” flashing will divert the water away from the wall and angle it into the gutter.

How

Kick-out flashing can be constructed from roofing coil stock or purchased pre-made from roofing suppliers. Install the vertical leg of the kick-out flashing between the wall sheathing and the house wrap (or building paper), then install the first section of step flashing to overlap the kick-out flashing. Tuck the vertical leg of this first section of step flashing under the house wrap, then apply the first course of shingles. Tuck the next section of step flashing under the house wrap and lap the horizontal leg over the previous one before applying the next course of shingles. The sequence continues until the roof is completely flashed to the wall. A gap should be left between the roofing and the siding so rain water will not wick up behind the siding.

One of the challenges is ensuring that various trades work together to ensure that the wall's drainage-plane is integrated properly with the step flashing. For example, scheduling may not allow the roofing system to be installed immediately after the roof decking is completed. In that case, if the framing crew is to install the house wrap, they should avoid fastening the material at its extreme bottom edge where the wall meets the roof decks; providing a 6- to 8-inch "skirt" will allow the roofer to later cleanly tuck the step flashing under the house wrap without damaging this sheeting material.

References/Additional Information

  • Builder's Guide to Mixed Humid Climates, Lstiburek, Joseph, 2004, Building Science Press. See www.buildingscience.com/ exiting epa.
  • Durability By Design, A Guide for Residential Builders and Designers, U.S. Department of Housing and Urban Development, Office of Policy Development and Research, Partnership for Advancing Technology in Housing, PATH, May, 2002. See www.hud.gov/ exiting epa.

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Best Practice: "Cricket" Roof - Protecting the Vulnerable Chimney-Roof Connection

When a roof deck slopes down to intersect a chimney, protruding from the main roof line, roof leaks at this point are very common. The collection of leaves and other debris or the build-up of snow at this juncture often creates leaks. Regular flashing techniques are often inadequate to handle the large quantities of water that rapidly flows against the chimney's wall where it protrudes through the roof. However, a small cricket roof, running perpendicular to the main roof, effectively deflects and channels the heavy flow to either side of the chimney.

Click on the image for a full-page version

Asphalt shingled "Cricket" roof

Cricket roof with shingles

Chimney (at point where it exits roof) is exposed to significant water flow from roof above, and standard flashing approach is prone to failure.

Chimney (at point where it exists roof) exposed to water draining from the roof area above

"Cricket" directs water to either side of chimney structure, avoiding extensive flashing of the vertical stone surface (prone to failure) eliminates collection point for leaves and other debris

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References/Additional Information

  • International Residential Code, R801.3, Roof Drainage. Get a copy of the Codes at www.iccsafe.org/ exiting epa.
  • BSP-040, READ THIS: Before You Design, Build or Renovate. Building Science Corporation, 2006. Get a copy at http://www.buildingscience.com/ exiting epa
  • Architectural Sheet Metal Manual, Sheet Metal and Air Conditioning Contractors' National Association, Inc., (SMACNA) Sixth Edition - Sept., 2003. See www.smacna.org/ exiting epa.

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