3 Energy-Saving Technologies to Consider with Metal Roofs

A roof’s primary function is to keep a building weatherproof. A roof’s secondary function—and approaching nearly equal importance—is to be an energy-efficient element of the building envelope. From an energy efficiency standpoint, we’re accustomed to the inclusion of insulation. Are we as accustomed to the ideas that roof color and air leakage matter for energy efficiency? The building industry is embracing all of these technologies in an effort to save energy.  So how does an installer make it all work?


Photo Courtesy of NAIMA

Insulation requirements for roofs on metal buildings (according to the 2015 IECC) range from R-19+R-11 LS up to R-30+R-11 LS, depending on climate zone. The first layer is draped over the purlins and requires a thermal spacer block with an R-3.5. A second layer is installed at perpendicular and is required to include a liner system (LS), which is a continuous vapor barrier installed below the purlins and is uninterrupted by framing members. The crisscrossed layers help reduce convective air movement within the insulation layer, making the insulation layer more effective. And, good news!—the vapor barrier can also be an air barrier. So, on to air barriers.

Air Barriers

Even small air leaks in buildings can account for a 30 to 40% heat loss during heating season (winter), regardless of the amount of insulation. It can’t be overstated—air barriers are critical to an energy-efficient roof and overall building envelope. The LS, or vapor barrier, can be an air barrier only if the seams of the LS are sealed to prevent air passage. The junction between the air barrier in the roof and walls is critical; it must be joined to be continuous. Often, a separate material (adhered membranes or spray-applied foams) is used as the transition from wall to roof. Or, the roof and wall air barriers might end on opposite sides of a perimeter beam or purlin, connecting the two air barriers. Also, any penetrations through the roof need to be sealed to the air barrier. Being continuous/having continuity is key to constructing a properly functioning air barrier!

Roof Color

We’ve heard a lot about roof color. Where air conditioning is prevalent (e.g., the Southwest), highly reflective roofs make sense, especially if there is minimal insulation. Where heating is prevalent, roof color becomes less effective for energy efficiency for a couple reasons. One, buildings require significant amounts of insulation, and two, there is much less direct heat gain from the sun over the course of a year. Where heating and cooling are both used regularly (e.g., Nashville, Chicago), it’s not a matter of “black or white.” There are many metal roof colors that are moderately reflective, so they balance reflectivity and heat gain as the seasons change.

Contemplate the interaction of insulation, roof color and air barriers on each metal roofing project.

Fire Resistance of Metal Panel Roof Systems

Fire Resistance of Metal RoofsMetal is inherently fire resistant.  The codes acknowledge that; however, certain limits are placed on metal’s fire resistance when used as part of a metal roof system.

Metal panels transfer heat very well—they get hot quickly and give up heat quickly.  And, in many cases, there is a building component (roof deck, framing) directly under metal panels.  Metal roof systems are required to be fire classified because of the concern about the combustibility of the materials under the metal panels.

Fire Resistance Classifications

The 2012 and 2015 IBC, in Section 1505 of Chapter 15, states that fire classification of roof assemblies is based on two tests—ASTM E108 and UL 790—that are fundamentally identical.  Each requires a spread of flame test and a burning brand test.  Tested roof systems are fire classified Class A, B, or C, where the most fire-resistant roof assemblies are Class A, and Class C is least resistant.

Building Code Fire Resistance Requirements

Building codes establish fire resistance requirements for roofs based on the type of construction (e.g., concrete/steel, wood) for the building.  A common misconception about roofs’ fire ratings is that building codes require Class A.  Not true—the IBC does not require Class A roof assemblies for any type of construction!  Only roofs on buildings located in wildfires zones (e.g., Southern California) will likely be mandated to be Class A.  (It is worth mentioning here that the vast majority of low- and steep-slope roof systems sold and installed in the U.S. are Class A.)

The building code lists a number of roof types deemed to be Class A (in other words, testing is not required).  Appropriately, metal panels are included: ferrous (steel) and copper shingles or sheets, metal sheets, and shingles on noncombustible decks (e.g., steel, concrete—not wood), or on noncombustible framing where a deck is not included (e.g., directly over metal purlins).  The key is that the deck or framing is noncombustible.

If metal panels are installed over combustible decks, the assembly needs to be tested using ASTM E108 or UL 790.   An exception for combustible decks is that 16 oz./sq. ft. copper (or thicker) can be installed over combustible decks and be considered Class A without testing.

Building with Fire Safety in Mind

The code requirements for fire resistance of metal panels are logical and not overly burdensome.  Most metal panel manufacturers have tested their roof assemblies, and most, if not all, metal panels and shingles can be used in Class A fire-rated roof systems.

Codes: More than the IBC and IRC

IBC IRC CodeWe all know to look to IBC Chapter 15 and IRC Chapter 9 for information about roof systems.  These two “Roof Assemblies and Rooftop Structures” chapters include the requirements for fire, wind, impact, materials, and reroofing.  But did you know the scope of the building code (IBC Section 101.4) references additional model codes that are considered to be part of the requirements of the IBC?  From a roofing perspective, this scoping reference brings into play the International Energy Conservation Code (IECC) and the International Existing Building Code (IEBC).

The creators of the model codes are attempting to ensure that buildings (and roofs, in our case) are designed and built according to the most recent model codes even if they haven’t been specifically adopted by a state or local jurisdiction.  If a jurisdiction adopts and enforces the 2015 IBC, by reference the 2015 IECC and 2015 IEBC are in effect.

How do 2015 IECC and 2015 IEBC affect roofs?
The IECC Commercial Provisions include energy efficiency requirements for the same buildings for which IBC Chapter 15 roofing requirements are required.  The IECC includes minimum insulation, air barrier, and reflectivity requirements for building envelopes.  Prescriptive R-values and U-values are provided for roofs, and they are based on climate zone, metal buildings, and attics.  Minimum levels of solar reflectance and thermal emittance are required for low-slope roofs on buildings with air-conditioning in climate zones 1, 2 and 3.

Air barriers—used to reduce or eliminate air leakage—are required for new construction.  These are based on materials, systems, or the whole building.  Sheet steel and aluminum are listed as materials that meet the air barrier requirements.  Of course, the joints and seams are critical to the effectiveness of metal roofing panels when considered to be air barriers.  When reroofing, air barrier requirements are not triggered, which is significant.  But the insulation requirements are triggered.

Roofing and structural considerations
The 2015 IEBC includes sections about reroofing (Section 706, which is new in the 2015 IEBC) and structural considerations (Section 707).  The IEBC divides “Alterations” of buildings into three types: Levels I, II and III.  A level I alteration includes the removal and replacement of existing materials.  Reroofing is a level I alteration, which triggers the requirements of Chapter 7.  The Structural section includes a requirement to upgrade a wind-resisting roof diaphragm when more than 50 percent of the roof is removed where the design wind speed is greater than 115 mph, and in special wind zones.  While these are small portions of the United States, it’s important to understand this requirement.

Build roofs with the full scope in mind
Look beyond the roofing chapters to ensure that you design and build buildings according to the most recent building codes.

Ventilation for Steep-Slope Roofs


Ventilation can be a confusing topic.  What is the purpose of ventilation?  Is ventilation required for all types of roofs?  What do the model codes require?

What is Ventilation?

Ventilation, when done properly, removes heat and moisture from traditional attics and from rafter spaces.  The removal of heat and moisture is necessary for buildings to operate efficiently and not deteriorate prematurely.  Ideally, an attic should be the same temperature and have the same humidity level as the exterior.  Convective ventilation—natural air flow from eave to ridge—means air comes in at the eaves and is exhausted at the ridge, taking the heat and moisture with it.  Importantly, ventilation is outboard of the insulation layer for the home or building.

Ventilation Requirements

The IRC and IBC have very similar requirements, found in the 2015 IBC, Section 1203 and the 2015 IRC, Section R806.  Ventilation is not tied to the type of roof system installed, as some believe.  Because ventilation improves the overall performance of a building, regardless of roof type, ventilation is required when steep-slope metal roofs are installed.

The amount of ventilation is based on the floor area of the attic.  The ventilating area should be at least 1/150 of the floor area.  Ventilation amounts can be reduced to 1/300 if half of the ventilation is at the eave and half at the ridge.  This allows the convective flow to work efficiently, allowing the reduction in the total ventilation amount.  In climate zones 6, 7, and 8 (i.e., the northern third of the US), an air barrier is required at the ceiling level in order to use the reduced amount of ventilation (i.e., 1/300).  A vapor retarder reduces the amount of moisture that can accumulate in the attic space; therefore, less ventilation is needed and required.

Because the model codes discuss ventilation only for attics and enclosed rafter spaces, the requirements are necessary only for steep-slope roofs.  Low-slope roof systems are not installed over attics or cathedral ceilings; therefore, the requirements for ventilation aren’t triggered when a low-slope roof is installed. Not because of the low-slope roof, but because there isn’t an attic or a cathedral ceiling.

Is ventilation in your scope of work?  In nearly all situations, the metal panel installer will install the ventilation components at the ridge.  And, unless the ventilation at the eave can remain in place, the installer should take the opportunity to install the ventilation components at the eave.  Eave ventilation can easily be made of metal, and can be an “add” to your scope of work for new and replacement roofs.

Understand ventilation requirements, improve long-term performance, and expand your scope of work.

Reroofing and the Building Code

Reroofing is and always will be the predominant project type in the roofing industry.  Roughly 70-90% of all roofing projects (depending on the year) are performed on existing buildings.  Understanding the reroofing requirements in the building code is critical to proper design and construction.  And fortunately, the reroofing requirements are not all that complicated.International Building Code

The 2015 International Building Code, Section 1511, Reroofing provides the building code requirements when reroofing.  Reroofing projects are divided into two types: recovering and replacement (which includes full removal of the existing roof).

Metal panel reroofing projects must meet the same fire, wind, and impact requirements for roof systems for new construction; however, they do not need to meet the minimum slope requirements (¼:12 for standing seam; ½:12 for lapped, nonsoldered and sealed seams; 3:12 for lapped, nonsoldered, non-sealed seams) if there is positive drainage.  Also, reroofing projects do not need to meet the secondary drainage requirements (i.e., installation of emergency overflow systems is not required).

The requirements for metal panel and metal shingle roof coverings are in Section 1507.4, Metal roof panels and Section 1507.5, Metal roof shingles of the 2015 IBC.  These apply for new construction and reroofing, and include information about decks, deck slope, materials, attachment, underlayment and high wind, ice barriers, and flashing.  The 2012 IBC has the same requirements; the 2015 IBC added new language about deck slope and attachment requirements for metal roof panels.  Nothing was changed for metal roof shingles.

In general, recovering is only allowed if there is one existing roof in place, except if a recover metal panel roof system transmits loads directly to the structural system (bypassing the existing roof system).  This provides a great advantage for metal panel roofs!  The existing roofs do not need to be removed, but new supports need to be attached through the existing roof (typically a metal panel roof) directly into existing purlins.

If metal panels or metal shingles are installed over a wood shake roof, creating a combustible concealed space, a layer of gypsum, mineral fiber, glass fiber, or other approved material is required to be installed between the wood roof and the recover metal roof system.

Good roofing practice is codified in the reroofing section of the IBC; contractors who design and install a recover or replacement metal roof are legally required to follow locally adopted code requirements.  And, of course, all metal roofs must be installed according to the manufacturer’s approved instructions.

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