Technical Guidance to the Indoor airPLUS Construction Specifications
1. Moisture Control
Please see "How to Use This Guidance".
Sections 1.1 - 1.4
Water-Managed Site and Foundation
Sections 1.5 - 1.6
Water-Managed Wall Assemblies
Sections 1.7 - 1.10
Water-Managed Roof Assemblies
- 1.7 Direct Roof Water Away from House
- 1.8 Fully Flash Roof-Wall Intersections
- 1.9 Install Self-Sealing Bituminous Membrane
- 1.10 Install Self-Sealing Bituminous Membrane in Cold Climates
- BEST PRACTICE: Roofing Underlayment Upgrade
- BEST PRACTICE: Roof Drip-edge
- BEST PRACTICE: Wind Baffles - Attic Insulation
Sections 1.11 - 1.13
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.
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Please refer to the Construction Specifications 1.8 Fully flash roof/wall intersections..."
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.
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.
- Builder's Guide to Mixed Humid Climates, Lstiburek, Joseph, 2004, Building Science Press. See www.buildingscience.com/ .
- 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/ .
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.
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- International Residential Code, R801.3, Roof Drainage. Get a copy of the Codes at www.iccsafe.org/ .
- BSP-040, READ THIS: Before You Design, Build or Renovate. Building Science Corporation, 2006. Get a copy at http://www.buildingscience.com/
- Architectural Sheet Metal Manual, Sheet Metal and Air Conditioning Contractors' National Association, Inc., (SMACNA) Sixth Edition - Sept., 2003. See www.smacna.org/ .