Roof Edge Protection

Scope

Design and construct or retrofit roof assemblies to resist wind pressures at roof edges during high-wind events.

  • Install fully adhered roof membrane over the entire surface area of the roof deck.
  • Install code-compliant metal drip edges at eaves and gables/rakes. 
  • Secure cladding at roof edges.
    • Install asphalt shingles at eaves over an asphalt shingle starter strip that is adhered to the fully adhered membrane underlayment or the to drip edge or both.  Set asphalt shingles that are installed at eaves and at gables and rakes in a minimum 8-inch wide strip of flashing cement.
    • Install metal roof cladding over a “slip sheet” installed between the metal roof and the fully adhered membrane. Also use a continuous cleat to mechanically attach the metal roofing.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

The greatest stress roof assemblies experience in high wind zones is at roof edges. That is where roofs experience the highest positive and negative air pressures. Roof assemblies need to be able to resist the wind pressures that can act on them during high wind events such as hurricanes. In addition to the highest wind pressure differences, roof edges can also experience the greatest rainwater loads. In sloping roofs, all of the rainwater incident on the roof area drains downward to the roof edge.

This guide provides guidance for the construction of roof edges in sloping roof assemblies for residential construction. The guidance is applicable to both new construction and the re-roofing of existing roof assemblies.

During high-wind events, high localized areas of negative pressure (“suction”) occur above roof edges due to the development of vortices (Figure 1). These pressures become more pronounced with sloping roofs typical of residential construction (Figure 2 and Figure 3). Most roof covering “blow-off” occurs at roof edges for these reasons.

During high wind events, vortices form along the edges of the roof creating areas of localized negative pressure (“suction”) above the roof.
Figure 1. During high-wind events, vortices form along the edges of the roof creating areas of localized negative pressure (“suction”) above the roof. (Source: Building Science Corporation).
During high wind events, sloped roofs and flat roofs experience higher uplift forces than flat roofs with parapets.
Figure 2. During high wind events, sloped roofs and flat roofs experience higher uplift forces than flat roofs with parapets. (Source: Building Science Corporation).
Strong wind passing over a sloped roof cause positive pressure on windward side and negative pressure on leeward side and at vortices above windward eave.
Figure 3. As wind passes over a steep sloped roof, it generally pushes on the near side and pulls on the far side of the roof but separation of flow at the eaves can cause areas of high negative pressure, or suction, at the near side above the eave. (Source: Building Science Corporation).

In high-wind zones it is recommended – as a minimum requirement - that a fully adhered roof membrane underlayment be installed at roof eaves and roof rakes. This could be a single-ply membrane such as TPO, EPDM, or PVC, or a built-up modified bitumen, or fluid-applied membrane. Improved performance and reduced risk occurs if a fully adhered roof membrane underlayment is installed over the entire surface area of the roof deck – not just at roof eaves and roof rakes. 

If a fully adhered roof membrane is not installed over the entire surface area of the roof deck, and a mechanically fastened underlayment is installed instead, alternative roof deck air sealing and water control requirements are necessary to provide acceptable performance and acceptable risk in high wind zones. Alternative roof deck air sealing and water control requirements can be found in the Insurance Institute for Building and Home Safety (IBHS) Fortified Home Hurricane Technical Summary.

In high-wind zones, it is recommended that drip edges be installed at roof eaves and roof rakes (Figure 4). The following drip edge installation requirements are recommended:

  • Code compliant metal drip edges should be installed at eaves and gables or rakes (applicable codes set the minimum gauge required).
  • Drip edges should overlap a minimum of 3 inches at joints.
  • Eave drip edges should extend a minimum of ½ inch below sheathing and overlap the top of the roof sheathing edge a minimum of 2 inches.
  • The drip edge should be mechanically fastened to the roof deck at a maximum spacing of 4 inches and the fasteners should be compatible with the flashing.
  • Drip edges at eaves can be installed over the fully adhered membrane underlayment if flashing cement is used to seal the edges.
  • Drip edges at gables or rakes should be installed over the fully adhered membrane underlayment.
Right – Install metal drip edge at roof edges in high wind and rain areas.
Figure 4. In high-wind zones, metal drip edge should be installed at roof eaves and roof rakes. (Source: Building Science Corporation).

Asphalt shingles that are installed at eaves and gables or rakes should be installed over an asphalt shingle starter strip that is set in a minimum 8-inch-wide strip of flashing cement adhered to the fully adhered membrane underlayment and/or to the drip edge (Figure 5). Asphalt shingle courses are then installed over the starter course (Figure 6).

Where drip edge flashing is installed over the fully adhered membrane at the eaves, flashing cement should be used to seal the upper drip edge of the flashing (Figure 7).

With metal roof assemblies, the approach is modified to include a “slip sheet” (typically a loose laid building paper) between the metal roof and the fully adhered membrane. The function of the “slip sheet” is to account for the significant movement that metal roof assemblies experience due to temperature changes over the course of a day, week, or season. Additionally, a continuous cleat is necessary to mechanically attach the metal roofing (Figure 8).

Right – Start asphalt shingle installation with a starter strip set in an 8-inch strip of flashing cement.
Figure 5. Start asphalt shingle installation with a starter strip set in an 8-inch strip of flashing cement. (Source: Building Science Corporation).
Right – Install asphalt shingles over a starter strip set in an 8-inch strip of flashing cement.
Figure 6. Install asphalt shingle courses over the starter course which is set in flashing cement. (Source: Building Science Corporation).
Right – If drip edge flashing is installed over fully adhered roof membrane at eaves, use flashing cement to seal the upper edge of the flashing.
Figure 7. If drip edge flashing is installed over fully adhered roof membrane at the eaves, use flashing cement to seal the upper edge of the flashing. (Source: Building Science Corporation).
Right – Under metal roofing, sheathing is protected by metal edging over a fully adhered membrane and a slip sheet of loose laid building paper.
Figure 8. Under metal roofing, sheathing is protected by metal edging over a fully adhered membrane and a slip sheet of loose laid building paper. (Source: Building Science Corporation).

 

Ensuring Success

In high wind zones it is recommended – as a minimum requirement - that a fully adhered roof membrane underlayment be installed at roof eaves and roof rakes.

Asphalt shingles that are installed at eaves should be installed over an asphalt shingle starter strip that is adhered to the fully adhered membrane underlayment, or to the drip edge, or both.

Asphalt shingles that are installed at gables/rakes should be installed set in a minimum 8-inch-wide strip of flashing cement.

Climate

IBHS Fortified Home Hurricane and High Wind Standards

Drip Edge

Drip edge must be installed (at eaves and rakes) with 3-in. laps. Drip edge shall extend ½ in. below sheathing and extend back on the roof a minimum of 2 in. Drip edge at eaves and at gable ends shall be installed over the underlayment. The drip edge shall be mechanically fastened to the roof deck at a maximum of 4 in. on center.  Note: For shingle roofs, starter strips must be adhered at the eave and rake. Either embed the starter strip in roofing cement or use self-adhered starter strips

Videos
Publication Date
Author(s)
Guertin
Organization(s)
Fine Homebuilding
Description
Video presentation explaining proper roof membrane and shingle installation, including key weak points where moisture can get in during a disaster weather event.
CAD

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, Version 3/3.1 (Rev. 09)

ENERGY STAR Certified Homes requires that builders comply with the National Water Management System Builder Requirements which specifies water management details for roofs, walls, foundations, sites, and building materials.

Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.

DOE Zero Energy Ready Home (Revision 07)

Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Exhibit 1, Item 2) Ceiling, wall, floor, and slab insulation shall meet or exceed 2015 IECC levels and achieve Grade 1 installation, per RESNET standards. See the guide 2012 or 2018 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

Exhibit 1, Item 6) Certified under EPA Indoor airPLUS. See the EPA Indoor airPLUS checklist for additional building and site water management requirements.

Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state.

2009 – 2018 International Energy Conservation Code (IECC) and International Residential Code (IRC)

2018 IRC R301.2.1 Wind design criteria. Buildings shall be constructed in accordance with the wind provisions of this code using the ultimate design wind speed in Table R301.2(1) as determined from Figure R301.2(5)A. Where not otherwise specified, the wind loads listed in Table R301.2(2) adjusted f height and exposure using Table R301.2(3) shall be used to determine design load performance requirements.

Section R402.2.2 2018 IECC notes that in parts of ceiling where the attic design does not allow space to install more than R-30 of insulation, R-30 will suffice; however, this exception is limited to no more than 500 square feet of total ceiling area.

Retrofit: 

2009, 2012, 2015, 2018, and 2021 IECC

Section R101.4.3 (Section R501.1.1 in 2015, 2018, and 2021 IECC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

IBHS Fortified Home Hurricane and High Wind Standards

Drip Edge

Drip edge must be installed (at eaves and rakes) with 3-in. laps. Drip edge shall extend ½ in. below sheathing and extend back on the roof a minimum of 2 in. Drip edge at eaves and at gable ends shall be installed over the underlayment. The drip edge shall be mechanically fastened to the roof deck at a maximum of 4 in. on center.  Note: For shingle roofs, starter strips must be adhered at the eave and rake. Either embed the starter strip in roofing cement or use self-adhered starter strips

 

 

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.

References and Resources*
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Webpage providing video links and Spanish/English handouts for installing roofs to meet the hurricane and high wind resistant guidance in the IBHS Fortified Home criteria.
*For non-dated media, such as websites, the date listed is the date accessed.
Contributors to this Guide

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

Building Science Corporation

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