T E C H N I C A L B U L L E T I N. (WSRCA) Technical Bulletin No S1 Summer To: WSRCA Members

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2 (WSRCA) Technical Bulletin No S1 Summer 2018 Western States Roofing Contractors Association WSRCA Headquarters 275 Tennant Avenue Suite 106 Morgan Hill, CA Tel: Fax: T E C H N I C A L B U L L E T I N The Voice of the Western Roofing and Waterproofing Industry To: WSRCA Members From: WSRCA s Steep-slope Committee Subject: Technical Information & Suggestions Regarding Ice-Damming on Watershedding Steep-Slope Roofs ******************************************************************* Greetings WSRCA Members: BACKGROUND INFORMATION: During the past few winters, WSRCA Member Contractors in varying areas of the western U.S. have reported an increasing number and intensity of winter-time icedam formation and resultant damage at various buildings in the western states. INTRODUCTION: This Bulletin s discussion of ice-dams, along with guidelines and suggestions for mitigation of ice dams, is focused on steep-slope roof systems in general and primarily on ventilated (i.e., theoretically vented, so cold-in winter ) watershedding steep-slope roof systems. These ventilated/cold watershedding steep-slope roofs are frequently, though not exclusively, found on single-family and multi-family residential construction. These ventilated steep-slope roofs are also found on light commercial (e.g., dental and medical clinics, etc.) and some institutional buildings (e.g., schools, community centers, etc.). This document also considers ice-damming on warm (i.e., non-vented, but compact insulated) watershedding steep-slope roofs, which are frequently found with cathedral-ceiling or vaulted-ceiling construction on multi-story townhouses, other split-level residential, smaller scale commercial, and on many churches, and some other institutional projects. THE ICE-DAM CYCLE: Ice-dams are the naturally occurring eave edge refreezing of snow-melt water, typically at or upslope from the exterior wall line of a building. The subsequent repetitive back-up and refreezing of snow-melt along downslope roof perimeters and eaves is typically the initiator of melt-water (i.e., snow and/or ice melt) intrusion through layer(s) of watershedding roofing systems. Five (5) stages of ice-dam formation are depicted and explained on the following pages. For reader clarity, the roof type sometimes used in heavy snow and ice climates have large Field-built ridge vent systems as is depicted in the following drawing excerpted from WSRCA s Cold-Weather Tile Manual, Detail No. CWT- 10. WESTERN STATES ROOFING CONTRACTORS ASSOCIATION

3 WSRCA Tech Bulletin No S1 July 2018 Page 2 of 16 WSRCA s Cold-Weather Tile Manual, Detail No. CWT Snowing: The first stage of initiating ice-dam formation is the depositing of snow on the roof. Follow-on snowfalls, interspersed with the four (4) later stages (described below), replenish the reservoir of upslope melt-water that can feed and expand ice-dam formation, which can cause leaks and other issues. 2. Please Note: On the following ice-dam cycle drawing simple cross-section views are depicted, and to keep page count at a minimum, please realize that at the ridge-to-gutter length has been minimized with a crasssection cut line so small sketches could be used to depict each stage of the ice dam cycle.

4 WSRCA Tech Bulletin No S1 Page 3 of Thawing: On-roof snow-melt is caused by heat loss from the interior of a building, as well as solar warming (i.e., from the heat of the sun through the snow). Building heat loss may be in the form of air exfiltration, heat conduction through the ceiling and roof assembly, and heat convection within the attic air. Ceiling insulation is frequently pinched at constricted cavities, such as at locations near outer walls causing potential hot spots in the winter. Thawing or melting due to the building s heat loss from the interior may not be apparent to casual observation but frequently occurs out of sight, within and below the snow cover. 4. Freezing: Snow-melt water drainage down the slope often freezes near the building s outer wall line where the roof transitions from above a heated interior space to subfreezing exterior temperatures both above and below the eave beginning the stage of ice build-up. Freezing may occur due to night time radiative cooling of the roof to the clear and colder night-time sky and temperature drop and/or distance away from the building s interior heated space. Visible symptoms may include the formation of icicles along, at or below the eave, gutter or soffit. 5. Thawing: Subsequent days snow-melt accumulates upslope of what becomes a progressively growing icedam. Water build-up or ponding upslope of the icedam is typically where lateral flow and water intrusion into watershedding roofing systems takes place, as watershedding roof systems rely on the steepness of slope for water resistance rather than being waterproof with low-slope membrane-roof characteristics.

5 WSRCA Tech Bulletin No S1 Page 4 of Refreezing: Typically, ice-dams grow in size due to repetitive (i.e., multi-day) daytime melting and nighttime refreezing. Ice-dam growth typically occurs laterally and then upslope and with progressive buildup in height above the roof deck. Water intrusion within a water-shedding roof system (e.g., migrating between shingles and underlayment) expands as it refreezes yet again. This repetitive thawing, freezing, thawing and refreezing can separate and damage the affected roofing (e.g., shingles, etc.), and can migrate through underlayment laps and into underlying components. More severe wetting and potential damage may occur due to expansion of interstitial ice at the sheathing and roof structure levels. Thus, during a sub-freezing spell, a primary key to minimizing ice-dams is the reduction of snow-melt, which in turn may be mitigated by keeping the entire roof system or assembly below freezing temperature(s). CONDITIONS AFFECTING ICE-DAM FORMATION: Several controlling elements should be deliberated when considering steep-slope roof design or reroofing and the mitigation or control of ice-dams. Among the numerous items to be considered are: The climate the project is located in; The roof slope; The type of roof assembly (e.g., cold-ventilated roof or warm-compact insulated roof); The primary roof covering (e.g., asphalt shingles, tile, metal roofing, etc.); The roof design and vented or non-vented; Component configuration; Insulation; Ventilation; The building heating system; Potential air infiltration; The roof s details and the layout of the roof including the related roof transitions (e.g., valleys, clerestory roof elevation changes where drifting can occur, etc.) and intersections (e.g., chimneys, skylights, plumbing vents, other roof penetrations, etc.).

6 WSRCA Tech Bulletin No S1 Page 5 of 16 Climate Considerations: While technical resources are available for estimating the likelihood of ice-dam formation in various geographic locations, an empirical indicator is the history of ice-dam problems in the climatic location and/or region of your project. The long-term weather and climatic data, the experience and knowledge of local contractors, experienced roof designers, workers and building departments are the start to anticipating ice-dams and the potential means and methods to mitigating icedams and their affects. Other climate-related factors include the effect of night-time clear skies, which accelerate the rapid cooling of roofs and refreezing of daytime melt-water, the orientation of the project roof, local topography and anticipated snow depths. Clear night-time sky radiative cooling often causes refreezing of snow-melt when freezing temperatures may not otherwise occur or be as severe on overcast or cloudy nights. Roof slopes oriented to the south experience greater snowmelt due to day-time solar radiation. Conversely, ice dams on roof areas oriented to the north may endure longer and prolong ice-dam issues. Local topography and wind patterns affects depth of snowdrifts, or inversely, snow scour. Counterintuitively, snow has some insulation capacity so that deep snow cover may adversely warm (i.e., 33 degrees F) the roof deck of warm/compact roof assemblies. In addition, deep snow may block individual roof vents and ridge ventilation openings of cold/ventilated roof assemblies, thus accumulating attic heat, melting the snow cover and contributing to ice-dam formation. Roof System / Roof Assembly Configuration: Roof Type As noted above, two general types of steep-slope roof assemblies may be considered concerning ice-dams: Cold/ventilated roof systems; and Warm/insulated compact roof systems. The physics of heat in these two roof types affects ice-dam formation. Cold/ventilated roof assemblies, if sufficiently ventilated, may allow less snow-melt because the sub-freezing air temperature in the ventilated roof cavity or space (e.g., the attic) keeps the roof sheathing, underlayment and primary roof covering (e.g., asphalt shingles, etc.) below freezing also. Warm/compact roof assemblies, in contrast, despite thick insulation, eventually conduct enough heat to melt snow cover. Roof Configuration Complex roof layouts or configurations can make for complex behavior of ice-dams. Interestingly, valleys, hips, overhanging eaves, closed or open soffits, headwalls,

7 WSRCA Tech Bulletin No S1 Page 6 of 16 sidewalls, skylights and other roof elements can contribute to the complex behavior of internal heat flow and air movement, the success of ventilation air pathways, heat conduction and snow depth, including the effects of wind-driven snow drifting, which all can affect ice-dam formation and severity. Interior elements, such as vaulted or cathedral ceilings, chimneys, the location of heater and heat registers, and others, can also significantly affect heat conduction and ventilation and so affect ice-dam formation and severity. Extensive overhanging eaves warrant special caution because of the increased probability of upslope melt-water refreezing over large eave areas and the consequent likelihood of widespread damage. Short eaves, such as where fascia project only an inch or two for a ventilation gap, are near to the building s heat which tends to keep melt-water in liquid state. Reaching the gutters, melt-water tends to refreeze because of freezing air on three sides: above, outboard and below. Longer eaves, projecting as much as several feet beyond the heat of the exterior wall, are that much more removed from the building s heat and enveloped in subfreezing air that causes refreezing, ice dam build-up, resulting in water intrusion and damage. Some have observed the formation of ice dams at extended eaves located above dark color south facing walls where solar heat builds-up below the eave. At compact insulated roof assemblies, some have chosen to extend the insulation through the eaves in order to minimize daytime heat transfer to the snow pack above the eave. To the contrary, some roofing contractors have reported skepticism of the function of insulated eaves for compact insulated roof assemblies as they have observed ice dam problems occurring during more severe winters. The several variables of orientation, solar radiation versus cloud cover, amount of insulation, daytime versus nighttime temperatures, mild versus severe climate patterns, and ventilated versus compact roof assembly indicate the topic of insulated eaves may be a subject for further examination. Heat and Insulation Insulation does not prevent the conduction of interior-generated heat through roof assemblies or into roof cavities and attics, but rather slows down the transfer of heat into the roofing system. Thicker insulations and higher thermal resistance (i.e., R-value) may minimize ice-dam formation during shorter duration freezes, but eventually allows snowmelt during longer periods of exterior freezes. As noted above, thick snow, which is a mild insulator, may affect the location of the melting plane within a roof s snow cover. For example: a foot of lightweight fluffy snow may add insulation value of R-10 to more than R-20, above the roof covering. As a result, on warm/compact roof assemblies, the 33-degree or higher melt temperature may occur within the snow cover rather than on the surface of the roofing. Thermal bridging through fasteners, sandwiched sheet metal flashing flanges, and other non-insulation components may also contribute to the duration and volume of snow-melt and/or refreezing affects. Air Infiltration Air mass is able to transport many times more heat than is typically conducted through insulation. Therefore, air leakage from interior spaces (e.g., through unsealed can lights, kitchen range and/or bathroom exhaust fan ducting air leaks, etc.) into attics

8 WSRCA Tech Bulletin No S1 Page 7 of 16 and roof assemblies may have a greater effect than insulation on snow-melt. Air exfiltration from building interiors into roof assemblies is more likely a concern in older roofs and older buildings, which are less airtight. Newer roofs are more likely to be tighter, some of which may include an air infiltration barrier or vapor retarder. Vapor retarders may also perform as air barriers. Vapor permeability of roofing materials plays a lesser, indirect role regarding ice-dams. A lowperm (i.e., vapor permeability unit of measure) rated ice-dam protection membrane installed above well-ventilated and properly insulated attic likely presents little, vapor/condensation issues, but achieving the well ventilated and properly insulated is difficult with some buildings. A low perm, ice-dam protection membrane above a warm/compact roof assembly, however, is sequentially misplaced as a potential vapor trap, which may cause condensation within the warm/compact roof assembly. BUILDING CODE REQUIREMENTS & RELATED DATA: The 2018 International Building Code (IBC) and International Residential Code (IRC) requirements for Ice Barrier read similarly. For water-shedding roofs, ice barrier is required in regions where there has been a history of ice forming along the eaves causing water backup. Roofing contractors, roof designers and building owners should confirm the specific requirements for ice barrier with their local building department. Ice barrier, per both the IBC and IRC, is required from a line 24-inches upslope of exterior walls to the lowest edges (e.g., to the fascia) of roof surfaces. It is prudent roofing practice to base this 24-inch upslope measurement from the interior face of the exterior wall. While WSRCA prefers the term ice-dam protection membrane, contractors, designers and owners should be aware of the I-Codes synonymous term ice barrier. Ice-barrier, as defined by I- Codes, is a minimum of two layers of asphalt saturated underlayment cemented together, or self-adhering polymer-modified bitumen sheet membranes. IRC Figure R403.3(2) Air-Freezing Index an Estimate of the 100-Year Return Period, a nationwide contour map of freezing temperatures, may help identify ice-dam prone regions. A footnote indicates, It is used as a measure of the combined magnitude and duration of air temperature below freezing. Thus, it might be used in conjunction with NRCA recommendations, below. IRC Table R403.3(2) Air-Freezing Index for U.S. Locations by County compiles similar data in tabular form. Industry Benchmark Guidelines: WSRCA recommends ice-dam protection membranes in cold climates where snow and ice are common and in areas of significant snow accumulation. WSRCA further recommends icedam protection membrane should be installed in all potential ice damming locations such as along downslope eaves in valleys, around chimneys, crickets, around roof penetrations, and up

9 WSRCA Tech Bulletin No S1 Page 8 of 16 rake edges. At downslope roof edges it is recommended to extend ice dam protection membrane upslope a minimum of 24-inches inside the interior face of the exterior wall. This means covering more than just the lowest 24-inches of eaves upslope of the fascia or gutter. Rather, cover all roof areas from the fascia/gutter line, upslope across all overhanging eave areas and exterior wall areas, then continue upslope 24-inches measuring from the interior face of the exterior wall. NRCA recommends that ice-dam protection membrane be installed in locations where the average temperature for January is 30 degrees Fahrenheit or less. NRCA provides a map of such areas. Further, NRCA recommends ice-dam protection membrane be installed a minimum of 36-inches upslope of the outer wall s interior line when the roof slope is less than 4 in 12. In all cases, conservative judgement should be exercised while conforming to, or exceeding, the most rigorous requirements or benchmarks, whether Code, WSRCA, NRCA or others. SOLUTIONS: Solutions to ice-dam problems may best be interpreted as ventilation, ice-dam control or mitigation rather than complete prevention of ice-dams. Because of the broad variety and types of the current steep-slope watershedding roofs, existing as well as those yet to be designed and constructed, in conjunction with the variety of [micro-] climate conditions, the industry should understand that there are no universal and absolute solutions to ice-dam prevention. For new roof projects, detailed design attention should be given to ventilation, insulation, icedam protection membrane, the membrane s extent (e.g., distance upslope, potential number of plies, etc.), and whether there are or are not overhanging eaves. For existing roofs and reroofing projects, ice-dam protection membrane is a practical strategy of ice-dam control or mitigation of moisture intrusion and damage. WSRCA members should encourage clients to consider several strategies in addition to ice-dam protection membrane: retrofit of ventilation, sealing and airtight taping of interior penetrations that would otherwise allow interior air and heat leakage into the roof cavity, and the need for insulation review and upgrade or retrofit, or replacement in addition to ice-dam protection membrane(s).

10 WSRCA Tech Bulletin No S1 Page 9 of 16 Ventilation Optimal ventilation, with regard to ice-dam mitigation, keeps the roof deck and roofing system below freezing, during periods of exterior freezes, by flushing air through, and thus heat out, of the attic or roof ventilation cavity. Venting of attics and cathedral ceiling roof cavities, utilizing downslope and companion upslope venting is the most common means for ventilation of steep-slope water shedding roof assemblies. Historically, attic ventilation requirements prescribed by building codes were based primarily on condensation-related concerns for example, roofs with vapor retarders are allowed less ventilation (1:300 ratio) than those without a vapor retarder (1:150 ratio). Ventilation for ice- dam control, however, is grounded on larger openings and cavities for moving larger volumes of sub-freezing exterior air into downslope eave (e.g., intake) vents, through the roof cavity or attic and out upslope roof vents (e.g., exhaust) or ridge vents. Whether for ice-dam control or condensation control, it is good basic roof design practice to balance eave ventilation intake-air openings in approximately ratio with ridge or upslope exhaust-air openings. (See WSRCA Bulletin concerning roof ventilation.) Cathedral ceiling roof assemblies, with ceilings attached directly to the underside of sloped roof rafters or trusses, are special cases of ventilated roofs. Research concerning roof ventilation for effective control of ice-dams on cathedral ceiling roof assemblies (see references) indicates that the necessary vent opening size and vent space above the insulation is related to the amount of roof insulation, roof slope and length of the slope. The research indicates that much larger openings and larger cavity height above the insulation is necessary-beyond that required by codes for effective condensation and/or ice-dam mitigation. Vented nail-base insulation panels, though conceptually similar to vented cathedral ceiling roof assemblies, typically do not provide nearly sufficient ventilation and air-flow for ice-dam mitigation and condensation control in all such roof configurations. Warm/compact steep-slope roof assemblies conduct heat through insulation over time and narrow closed cavities or spaces are susceptible to condensation, and contribute to ice-dam formation. Properly sized ventilation cavities, such as can be constructed with over-framing assemblies, located above a compact insulated roof assembly, can provide the ventilation necessary to move sufficient air under the elevated roof sheathing and thus reduce the likelihood of snow-melt and mitigate ice-dams.

11 WSRCA Tech Bulletin No S1 Page 10 of 16 Ice-Dam Protection Membrane / Ice Barriers Both the International Building Code (IBC) and the International Residential Code (IRC) indicate that a history of ice-dam formation is prudent criteria for deciding to install an ice barrier (the IBC and IRC term) or ice-dam protection membrane (WSRCA preferred term) in roof assemblies. The IRC, however, requires ice barrier if adopted or specifically specified by the local building department in Table R301.2(1) the Climatic and Geographic Design Criteria. Ice-Dam Protection Membrane Material An effective ice-dam protection membrane, relies on waterproof membrane-like qualities and watertight integrity at end laps and side lap seams as well as an ability to self-seal around potentially thousands of roofing fasteners that may penetrate the membrane. Minimum ice-dam protection membrane materials allowed by codes are two layers of asphalt-saturated underlayment felt, cemented together, or self-adhering polymer-modified bitumen sheet membranes. Higher quality and multiple layer, redundant underlayments installed in membrane configuration and in shingle-fashion are prudent and should be considered for roofs in snow and ice prone climate. During installation, attention must be given to flashing around penetrations, patching at punctures and tears caused by aggressive-soled boots, tool scuffed locations, and abraded spots of trafficked-in damage from on roof debris. Note: Many single-layer mineral-surfaced roll roofing materials, when not set in hot asphalt, torch-fused, or fully adhered in adhesive, should not be considered a waterproof membrane roof covering and should prudently receive an ice-dam protection membrane. Ice-Dam Protection Membrane Location Codes require ice-dam protection membrane extending from the lowest edges of all roof surfaces, including overhanging eaves, extending not less than 24-inches upslope of exterior walls. On steeper roofs, greater than 8 in 12, icedam protection membrane is required to extend at least 3 feet upslope of exterior walls. Lowest edges includes covering all of the overhanging eaves, fascia etc. with ice-dam protection membrane. In addition to code requirements, special consideration should be given to valleys, at roof-to-rising wall transitions, sidewalls, chimneys, skylights, and other penetrations. When low perm-rated ice-dam protection membrane covers much or all of a roof, thorough, active, and proper attic ventilation must be verified for condensation control. Special caution regarding summer-time hot spots and winter-time vapor traps should be exercised if installing a low-perm ice-dam protection membrane on a significant portion or all of a warm/compact roof assembly.

12 WSRCA Tech Bulletin No S1 Page 11 of 16 Insulation The loss of insulation s effectiveness over time should also be considered. In addition to energy loss and health considerations, the result of ineffective insulation on melting temperatures within snow cover is vital with respect to ice dam control. Insufficient or ineffective insulation in both ventilated and compact roof assemblies allows heat loss that promotes snow-melt and subsequent ice-dam formation. Likewise, wet, degraded, ineffective insulation also allows heat loss, snow-melt and ice-dam growth. All insulation types, whether fiberglass blanket, rock wool batts, cellulose fill, polyiso boards, EPS/XPS, or spray foam should be considered. Owners and roofing contractors should discuss the installation practicality and monetary feasibility of retrofitting under-designed insulation or replacing ineffective, wet damaged insulation for their multiple benefits of ice-dam control, energy conservation and health benefits. With R-values in the range of R-10 to R-20 per foot, the insulation capacity of snow should not be underestimated. For example, one roofing contractor reported ice-dam problem roofs with 5- feet of snow lying on R-50 compact roof assemblies. Assuming the snow also has insulation value of R-50 (i.e., R-10 per foot) means that the temperature of this roof covering is the thermal mid-point between the interior and exterior temperatures: When the daytime interior temperature is 70 Fahrenheit and the daytime exterior temperature is 10 F, then the roof covering is approximately 40 F. (70 10 = 60 difference. Half of 60 = is 40 also = 40.) Snow is melting a few inches above the roof covering, and then refreezing at the eave. When the nighttime thermostat is set back to 60 Fahrenheit and the nighttime exterior temperature is 0 F, then the roof covering is approximately 30 F. The roof covering is 35 F, however, if the thermostat is not set back. With a much lighter, fluffier snow (i.e., R-20 per foot) similar melting temperature profiles might occur with just 2½ feet of snow. Or, older compact roofs with only R-30 insulation might exhibit similar melting temperature profiles with as little as 1½ feet of light, fluffy snow. Deep snow may add significant insulation to a roof assembly, altering the thermal profile of the roof assembly and relocating the melting plane upward into the overlying snow.

13 WSRCA Tech Bulletin No S1 Page 12 of 16 Roof Maintenance An experienced Roofing Contractor retained for maintenance can play an important role in severe climates or in unique weather conditions for control of ice-dams and control of damage due to ice-dams. Removing snow from the roof removes the latent reservoir of soon-to-be-meltwater waiting to refreeze as an ice-dam. Unplugging snow from upslope roof vents increases airflow through the attic or roof cavity, thereby decreasing the likelihood of overly large ice-dams. However, if choosing to remove snow and ice, great caution must be exercised. Work on steep, slippery roofs is, obviously, a safety concern. Snow removal tools and equipment, ice removal tools and inexperienced workers can easily damage roofing materials, adding to problems. Where deemed appropriate, electric snowmelt cables (e.g., heat trace wires) may cover entire overhanging areas up from the gutter and fascia edges to upslope from the exterior wall line. Electrical and fire safety should be considered if choosing to install electric heat trace cables. IN SUMMARY: Control of ice-dams and the potential damage that they can cause is a significant concern of Owners, roof-designers and roofing contractors working and living in ice-dam prone areas of the western states. The ever more mobile roofing industry prompts roofing contractors based even in warmer, milder climates to be concerned with ice-dams for those projects that take them to cold regions. Ice-dam formation and ice-dam progressive growth often occurs in a somewhat predictable, cyclical pattern of snowing/thawing/freezing/thawing/refreezing. Climate and weather, affect ice dam formation and growth. Local experienced contractors, local building owners and building departments have the empirical data, historical knowledge, and/or jurisdiction of the project locale s behavior of snow, temperature, wind and geographic effects on ice-dam formation and ice-dam progressive growth. The specific roofing system, whole-roof assembly and configuration as well as building heat, insulation and air infiltration all play roles in ice dam formation and growth.

14 WSRCA Tech Bulletin No S1 Page 13 of 16 Two important mitigation strategies appear viable: ice-dam protection membrane, and ample ventilation. Ice-dam protection membranes, as required by codes and local building departments, is a practical ice-dam mitigation solution for steep-slope water-shedding reroofing projects. Cold-roof ventilation, with sufficient in net-free air flow to minimize snow-melt, is also an important strategy for ice-dam mitigation. Roofing contractors who suggest ventilation retrofit and upgrades for their reroofing clients may potentially find additional avenues of work and prudent solutions to building Owner s ice-dam leak issues. EXAMPLES OF ACTUAL ROOFS IN DIFFERENT CLIMATES: Suburban Denver, CO Sub-freezing ambient air temperature both above and below this compact-insulated roof eave overhang caused the refreezing of upslope snow-melt water drainage, and formation of intermittent ice-damming. Roof deck insulation, extending outboard of the thermal envelope (red dotted line) provides minimal control of ice-dams because subfreezing temperatures surround the eave overhang. Ice build-up and damming formed at this eave overhang despite the heat-trace cables used. Sometimes multiple rows of heat-trace cables are needed to cover and affect the entire overhang areas. Alaska Bush Example of a steep-slope compact roof assembly (SIPS panels) with overframed ventilation cavities that tend to keep the roof covering (asphalt shingles) below subfreezing ambient air temperatures. Permeable house-wrap sheeting is located on the SIPS deck to allow breathing of the insulation while impermeable ice-dam protection membrane is located on the elevated, vented, over-frame raised sheathing. A vapor trap could form if low perm ice-

15 WSRCA Tech Bulletin No S1 Page 14 of 16 dam protection membrane were to be installed directly on the SIPS deck. Deep drifting snow at the headwall indicates a greater likelihood of downslope ice-dams, while wind scoured thinner snow at the rake edge predicts lesser likelihood of downslope ice-dams. Columbia River Gorge, OR The upper-left photo depicts icicle formation through soffit vents and recessed light fixtures indicates snow-melt water intrusion upslope, and the lack of sufficient extent of ice-dam protection membrane upslope of the exterior wall. Snow-melt water working its way through overhanging soffits and refreezing has caused the pervasive icicles. The upper-right photo depicts icicle formation extending from the roof and flowing down the wall to this building s lower-story and weeping out the cladding indicates water intrusion upslope of an ice-dam, flowing behind the upper story s board & batten cladding, which has migrated down with gravity to flow out at the floor line flashing and refreeze as icicles from behind the cladding. Cascade Foothills, WA Although located in a region of less frequent snowfalls and more temperate climate where ice-dams are not typically expected, this vented nail base roof assembly illustrates: Thermal bridging pattern at roofing fasteners resulting in increased snow-melt. Downslope/upslope pattern of snow-melt at vented cavities. Vented nail base cavities are typically much smaller than some experience and research implies are necessary for thorough roof ventilation, mitigation of condensation, and control of ice-dams.

16 WSRCA Tech Bulletin No S1 Page 15 of 16 Upper roof area s down spouts contribute to drainage volume and larger ice-dams at the lower eave, where ice will form during times of freezing and sub-freezing temperatures, which all indicate the importance of the inclusion of an ice-dam protection membrane in the roof system. Roofing Contractor s Ice Dam Test Bed This roofing mock-up was constructed of very conventional roofing components: Wood panel sheathing. Self-adhering ice dam protection membrane. Asphalt shingles. Pneumatically driven roofing nails. The sharp-edged wire remnants of the coil wires remained on each shank of pneumaticallydriven roofing nails, which tore small channel(s) in the asphalt shingles and the ice dam protection membrane next to the nail shank, allowing water intrusion through the ice-dam protection membrane. Water entered around the affected nail holes in the field of the roof and at nails inadvertently driven through the roof that was overlying wood panel joints. The contractor concluded that the asphalt shingles and ice dam protection membrane could not effectively selfseal around the nail shanks affected by the protruding coil wire remnants.

17 WSRCA Tech Bulletin No S1 Page 16 of 16 REFERENCE DOCUMENTS: WSRCA/TRI Tile Roofing Manual for Cold Climates, 1998, Reprinted Air Vent Inc. Attic Ventilation: Tips and Answers from the Experts December CertainTeed Shingle Applicators Manual, January Fryer, Mark; Brown, E. Staples; Design of Ventilated Attic Spaces for Buildings in Cold Regions; State of Alaska Department of Transportation and Public Facilities Division of Planning and Programming Research Section 2301 Peger Road Fairbanks AK 99701, January State of Alaska Department of Transportation & Public Facilities; Roofing Standards Manual, February Tobaisson, Wayne; Tantillo, Thomas; Buska, James; Ventilating Cathedral Ceilings to Prevent Problematic Icings at Their Eaves; Proceedings of the North American Conference on Roofing Technology September 1999, Toronto, Ontario. Holladay, Martin; How It Works: Ice Dams; Fine Home Building, December 2015 / January Holladay, Marin; Preventing Ice Dams; Fine Home Building, May Rupar, Maciek; Ice Dam Busting: Eradicating Ice Dams Begins Below the Roof Deck; Professional Roofing, June Hoffman, Jeffrey; An Ice Dam Analyzed; Journal of Light Construction, March Ireton, Kevin; Venting the Roof; Exterior Finishing Fine Home Building, June WSRCA Steep-Slope Committee; Laminated Shingles & Water-Shedding Roof Systems for Lower Slopes, January/February ARMA Asphalt Roofing Residential Manual Pages Eave Flashing for Ice Dam Protection, LEGAL DISCLAIMER All rights reserved. All content (text, trademarks, illustrations, reports, photos, logos, graphics, files, designs, arrangements, etc.) in this Technical Opinion ( Opinion ) is the intellectual property of Western States Roofing Contractors Association (WSRCA) and is protected by the applicable protective laws governing intellectual property. The Opinion is intended for the exclusive use by its members as a feature of their membership. This document is intended to be used for educational purposes only, and no one should act or rely solely on any information contained in this Opinion as it is not a substitute for the advice of an attorney or construction engineer with specific project knowledge. Neither WSRCA nor any of its, contractors, subcontractors, or any of their employees, directors, officers, agents, or assigns make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party s use (or the results of such use) of any information or process disclosed in the Opinion. Reference herein to any general or specific commercial product, process or service does not necessarily constitute or imply its endorsement or recommendation by WSRCA. References are provided as citations and aids to help identify and locate other resources that may be of interest, and are not intended to state or imply that WSRCA sponsors, is affiliated or associated with, or is legally responsible for the content reflected in those resources. WSRCA has no control over those resources and the inclusion of any references does not necessarily imply the recommendation or endorsement of same.