Water Managed Existing Roof Penetrations

Scope

Provide flashing and sealing integrated with the air and water control layers for vents and other roof penetrations
Provide flashing and sealing integrated with the air and water control layers for vents and other roof penetrations

Provide a continuous water control layer across the roof assembly by sealing all roof penetrations as follows:

  • Inspect the roof framing to verify existing conditions and develop specific detailing for flashing all roof penetrations.
  • Flash and seal new roof penetrations through an existing roof.
  • If replacing the roofing, or upgrading the roof with new exterior foam insulation and new roof cladding, inspect water management details around all penetrations and replace with new flashing as needed. Install the water control materials in shingle fashion. Penetrations may include vents, flue stacks, chimneys, sky lights, mounting brackets for solar panels, etc.

Description

Vents, flue stacks, chimneys, sky lights, mounting brackets, etc., are all penetrations through a roof’s water management control layer. Any of these penetrations represents a weak spot in the roof’s armor where water could leak into the attic, with the potential to cause significant damage over time. Any time renovations are conducted that involve the roof – for example, when reroofing a home or when upgrading the attic insulation by installing rigid foam above the roof deck (and installing new roofing) or when doing some renovation that involves creating a new penetration in the roof (for example, installing a skylight or brackets for solar panels), installers should take the opportunity to inspect all of the penetrations through the roof to determine if proper flashing and other water management details are in place to prevent water leaks.

Controlling rainwater is the single most important factor in the design and construction of durable roof assemblies. The fundamental principle of water management is to shed water by layering materials in such a way that water is directed downwards and outwards out of the building or away from the building. The key to this fundamental principle is drainage.

Sloping roofs should be used to drain water away from the top of buildings - the steeper the slope, the better. It is vital that any roof penetrations are properly flashed to prevent water entry. The materials that form the water control layer should overlap each other in shingle fashion or be sealed so that water drains down and does not collect on the roof.

Membranes or formable flashings around roof penetrations should be integrated into the roof’s drainage plane. Flat roofs should never be truly flat; all flat roofs should be tilted and sloped to drains in the roof that carry rainwater out of the building.

Figures 1 through 4 show examples of water management details around four common roof penetrations – a vent pipe, a flat roof drain, a skylight curb, and a solar panel mounting bracket. The figures show the water management details integrated with rigid foam insulation that has been installed above the roof deck and beneath the cladding as part of a roof insulation upgrade. However, in most aspects, these details also apply to roofs that have not had rigid foam installed on the roof deck. Further details for sealing around a pipe are described in the how-to steps below.

Water management details are properly integrated with the roof insulation, underlayment, and cladding around a vent pipe

Figure 1. Water management details are properly integrated with the roof insulation, underlayment, and cladding around a vent pipe. Reference

Water management details for a roof drain installed along with rigid foam on a flat roof

Figure 2. Water management details for a roof drain installed along with rigid foam on a flat roof. Reference

Water management details at a mechanical curb for a skylight

Figure 3. Water management details at a mechanical curb for a skylight. Reference

Water management detail for a solar panel rack mounting block installed in rigid foam that was installed over an existing roof

Figure 4. Water management detail for a solar panel rack mounting block installed in rigid foam that was installed over an existing roof. Reference

How to install Water Management protection around a vent pipe roof penetration

1.   Inspect the integrity of the roof system (roofing membrane and/or cladding). Check for any deficiencies, water damage, active leaks, etc. Proceed with re-flashing if and only if required repairs have been performed.
 
2.   Inspect the structural integrity of the roof. Check the roof framing for any deficiencies, rot, insect damage, etc. Proceed with re-flashing if and only if required repairs have been performed. Based on the findings, review specific detailing and revise the roof assembly plans as needed. Follow the minimum requirements of the current adopted building code regarding the wood roof framing construction.
 
3.   Cut a hole through the roofing that is 0.5 inches larger than the pipe and fit in the pipe. Extend the pipe 2 feet above the roof sheathing. Install closed-cell foam backer rod and urethane sealant in the hole around the pipe as an air control layer.

Step 3

4.   Install insulating sheathing in multiple layers with joints staggered and taped. Install closed-cell foam backer rod and urethane sealant at the pipe perimeter.

Step 4

5.   Install 5/8” plywood roof sheathing over the layers of rigid foam using H-clips. Cut the plywood around the pipe penetration.

Step 5

6.   Cut two sections of peel and stick roof membrane that will each extend out from the vent pipe for 18 inches. Cut a notch out of each section so the membrane will lay flat around the pipe. Install the section of membrane on the downhill side of the pipe first, to fit around the pipe penetration and lay flat.

Step 6

7.   Install the membrane flashing collar. This collar will overlap the down-slope piece of fully adhered roof membrane.

Step 7

8.   Install the upper layer of the fully adhered roof membrane. Cut the membrane around the pipe penetration and lap over the membrane collar and over the edge of the lower layer of membrane.

Step 8

9.   Install asphalt shingles, stopping just below the pipe.

Step 9

10.   Install the metal flashing collar over the membrane flashing collar. Overlap the metal collar onto the lower layer of the asphalt shingles.

Step 10

11.   Continue installing shingles around and above the pipe. These shingles will cover the upper edge of the metal flashing collar. Cut the shingles around the pipe penetration.

Step 11

 

Ensuring Success

Inspect the existing roof framing for any deficiencies and make any corrections if necessary.

Ensure that the water control layers of the roof system overlap each other in shingle fashion.

Climate

No climate specific information applies.

Training

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Presentations

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Videos

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CAD Images

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

ENERGY STAR Certified Homes

[Guidance for Version 3.0, Rev 08 is coming soon.]

ENERGY STAR Certified Homes is a voluntary high-performance home labeling program for new homes operated by the U.S. Department of Energy and the U.S. Environmental Protection Agency. Builders and remodelers who are conducting retrofits are welcome to seek certification for existing homes through this voluntary program.

The ENERGY STAR Certified Homes (Version 3.0, Rev. 07) Water Management Checklist specifies:

Water-Managed Roof Assembly

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

3.2 For homes that don’t have a slab-on-grade foundation and do have expansive or collapsible soils, gutters & downspouts provided that empty to lateral piping that deposits water on sloping final grade ≥ 5 ft. from foundation or to underground catchment system ≥ 10 ft. from foundation.

3.3 Self-sealing bituminous membrane or equivalent at all valleys & roof deck penetrations.

3.4 In 2009 IECC Climate Zones 5 and higher, self-sealing bituminous membrane or equivalent over sheathing at eaves from the edge of the roof line to > 2 ft. up roof deck from the interior plane of the exterior wall.

2009 IRC

Section G2427.7.5 (503.7.5) Roof penetrations.

Section P2606 Waterproofing of openings.

M2301.2.7 Roof and wall penetrations.

Section R903.2 Flashing.

2012 IRC

Section G2427.7.5 (503.7.5) Roof penetrations.

Section P2606 Waterproofing of openings.

M2301.2.7 Roof and wall penetrations.

Section R903.2 Flashing.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

None Available

References and Resources*

  1. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2009

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  2. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2012

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  3. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: January, 2006
    Book presenting the best techniques for energy and resource efficient residential construction in the colder climates of North America.
  4. Author(s): Pettit, Neuhauser, Gates
    Organization(s): BSC
    Publication Date: July, 2013
    Guidebook providing useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate.
  5. Author(s): Loomis, Pettit
    Organization(s): BSC
    Publication Date: May, 2015
    This Measure Guideline provides design and construction information for a deep energy enclosure retrofit solution of a flat roof assembly.
  6. Author(s): National Roofing Contractors Association
    Organization(s): National Roofing Contractors Association
    Publication Date: December, 2006

    NRCA's premier technical publication gives you the most current and useful technical information in the roofing industry.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team

Last Updated: 05/01/2017

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