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Understanding Drainage Planes, BSD-105

Reference

Guide providing information about controlling rainwater through use of drainage planes.

Proper installation of flashing for drainage

Proper installation of flashing for drainage

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Taped Insulating Sheathing Drainage Planes

Guide

Guide describing techniques for installing insulating sheathing as a continuous drainage plane on walls.

Proper shingling of drainage plane materials

Proper shingling of drainage plane materials

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Window flashing is overlapped to provide a continuous drainage plane.

Window flashing is overlapped to provide a continuous drainage plane.

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Measure Guideline: Guidance on Taped Insulating Sheathing Drainage Planes

Reference

Measure Guideline research report providing simple, long term, and durable solutions when using tapes and flashing membranes in conjunction with the exterior face of rigid polymeric foam sheathing to create the drainage plane of a wall system.

Wrong – There is no flashing installed at the bottom of the exterior walls to create a drainage system

Wrong – There is no flashing installed at the bottom of the exterior walls to create a drainage system

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Right – There is flashing installed at the bottom of the wall to create a satisfactory drainage system

Right – There is flashing installed at the bottom of the wall to create a satisfactory drainage system

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Wrong – There is no flashing installed at the bottom of the exterior walls to create a drainage system

Wrong – There is no flashing installed at the bottom of the exterior walls to create a drainage system

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The weep holes are spaced at the correct distance to provide a complete drainage system

The weep holes are spaced at the correct distance to provide a complete drainage system

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Wrong – The corners are not properly flashed, leaving a vulnerable area in the drainage system

Wrong – The corners are not properly flashed, leaving a vulnerable area in the drainage system

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The sheathing has rotted because there was not a sufficient drainage gap behind the stucco cladding

The sheathing has rotted because there was not a sufficient drainage gap behind the stucco cladding

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Right – The water-resistant barrier is layered over the step flashing to provide a complete drainage system

Right – The water-resistant barrier is layered over the step flashing to provide a complete drainage system

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Install all layers of the drainage plane to overlap, not underlap, to direct bulk water down and out of the wall.

Install all layers of the drainage plane to overlap, not underlap, to direct bulk water down and out of the wall.

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The water-resistant barrier, weep screed, and stucco lathe are properly layered and will create a complete drainage system

The water-resistant barrier, weep screed, and stucco lathe are properly layered and will create a complete drainage system

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Proper flashing around windows is especially important when the rigid foam serves as the drainage plane in the wall

Proper flashing around windows is especially important when the rigid foam serves as the drainage plane in the wall

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Right – The flashing is properly installed to create a complete drainage system with continuous rigid insulation sheathing/siding

Right – The flashing is properly installed to create a complete drainage system with continuous rigid insulation sheathing/siding

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Wrong - Stucco has rotted and cracked above a window because of water damage due to lack of proper flashing and drainage.

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Right – There is flashing installed along the top of the window and the water-resistant barrier is layered over to create a complete drainage system

Right – There is flashing installed along the top of the window and the water-resistant barrier is layered over to create a complete drainage system

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Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

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Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

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Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

Flashing at bottom of exterior walls with weep holes included for masonry veneer and weep screed for stucco cladding systems, or equivalent drainage system

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Furring strips provide drainage gap behind lap siding; screen is added at bottom and top to prevent entry of insects and wildfire embers

Furring strips provide drainage gap behind lap siding; screen is added at bottom and top to prevent entry of insects and wildfire embers.

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Rigid foam insulation can serve as the drainage plane when all seams are taped. Furring strips provide an air gap behind the cladding.

Rigid foam insulation can serve as the drainage plane when all seams are taped. Furring strips provide an air gap behind the cladding.

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Step and kick-out flashing at all roof-wall intersections extending ≥ 4 in. on wall surface above roof deck and integrated with drainage plane above

Step and kick-out flashing at all roof-wall intersections extending ≥ 4 in. on wall surface above roof deck and integrated with drainage plane above

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The fluid-applied asphalt coating provides a weather-resistant, moisture resistant layer around the house, serving as a continuous drainage plane and flashing for window and door openings.

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A liquid-applied water barrier covers the walls, serving as a drainage plane, air and vapor barrier, and secondary window flashing beneath the rigid foam that will be installed next.

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Flashing may tie into the porch and direct drainage under the porch, which protects the porch-wall interface from moisture; note also the washers that separate the porch and home to prevent additional wicking.

Flashing may tie into the porch and direct drainage under the porch, which protects the porch-wall interface from moisture; note also the washers that separate the porch and home to prevent additional wicking.

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This basement is insulated on the exterior with rigid foam over dampproofing, with granular backfill and footing drains to facilitate drainage away from the foundation, a termite shield to protect from pests, and cellular PVC to protect the rigid foam.

This basement is insulated on the exterior with rigid foam over dampproofing, with granular backfill and footing drains to facilitate drainage away from the foundation, a termite shield to protect from pests, and cellular PVC to protect the rigid foam.

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The “down” and “out” approach to flashing – metal flashing directs water down and out of building assemblies

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