Energy Efficiency

10 min read Updated 26 August 2026
⋯
Views
More
    Namespaces
    Contents

    Energy Efficiency

    Energy efficiency in a building is the ratio between the comfort and services a building delivers and the energy it consumes to deliver them. The roof assembly is one of the largest single influences on that ratio. In a heating-dominated climate such as most of Canada and the northern United States, the ceiling and roof are where a large share of winter heat is lost; in cooling-dominated climates, the roof surface is the main point of summer solar heat gain. Related product-level topics are covered in Cool Roofs, Green Roofs, Roof Insulation, Insulated Roofing Materials and Roof Ventilation.

    How a roof assembly gains and loses energy

    Heat moves through a roof by three mechanisms, and an energy-efficient roof addresses each of them:

    • Conduction through the ceiling or roof deck, which is limited by insulation. Resistance to conductive heat flow is expressed as R-value (imperial, h·ft²·°F/Btu) or RSI (metric, m²·K/W); one RSI unit equals about R-5.68.
    • Air leakage through gaps at attic hatches, plumbing stacks, pot lights, top plates and chimneys. Natural Resources Canada (NRCan) treats the attic as a priority for air sealing, because escaping warm, moist house air both wastes heat and deposits moisture on the sheathing.[1]
    • Radiation absorbed at the roof surface from sunlight and re-radiated downward from a hot roof deck into the attic. Surface reflectance, emittance and radiant barriers act on this path.

    Because the mechanisms interact, insulation added over a leaky ceiling delivers less than its R-value suggests; NRCan's retrofit guidance therefore seals first and insulates second, noting that spray foam on the attic floor can serve as both air seal and first layer of insulation.[2]

    Insulation and R-value requirements

    Residential energy codes set a prescriptive minimum ceiling R-value by climate zone. In the United States the International Energy Conservation Code (IECC), duplicated in IRC Chapter 11 (Section N1102, corresponding to IECC R402), raised ceiling requirements substantially in its 2021 edition. The U.S. Department of Energy's determination analysis for that edition records the change: climate zones 2 and 3 moved from R-38 to R-49, and climate zones 4 through 8 moved from R-49 to R-60.[3] The 2021 code also added an exception for roofs where the framing does not leave room for the full R-60 depth at the eaves.[3]

    In Canada, Section 9.36 of the National Building Code (NBC) and the provincial codes derived from it express the requirement as an effective thermal resistance for the whole assembly, tabulated by heating-degree-day zone. The British Columbia Building Code 2018 table for houses with a heat-recovery ventilator or heat pump requires ceilings below attics to reach RSI 8.67 (about R-49) in climate zones 4 and 5 and RSI 10.43 (about R-59) in zones 6, 7A, 7B and 8, and permits no eave-depth reduction for attic ceilings.[4] Alberta's prescriptive-path checklist for the 2023 NBC (Alberta Edition), which applies in zone 7A cities such as Edmonton and Calgary, lists RSI 10.43 for ceilings under attics in a house without a heat-recovery ventilator, RSI 8.67 with one, and RSI 5.02 (about R-28) for cathedral ceilings and flat roofs.[5]

    Prescriptive minimum ceiling insulation, attic (vented) ceilings
    Code and climate zone Requirement Approximate equivalent
    2018 IECC / IRC N1102, climate zones 2–3 R-38 (nominal) RSI 6.7
    2021 IECC / IRC N1102, climate zones 2–3 R-49 (nominal) RSI 8.6
    2018 IECC / IRC N1102, climate zones 4–8 R-49 (nominal) RSI 8.6
    2021 IECC / IRC N1102, climate zones 4–8 R-60 (nominal) RSI 10.6
    BC Building Code 2018 Table 9.36.2.6.-C, zones 4–5 (with HRV or heat pump) RSI 8.67 (effective) R-49
    BC Building Code 2018 Table 9.36.2.6.-C, zones 6–8 (with HRV or heat pump) RSI 10.43 (effective) R-59
    NBC(AE) 2023, zone 7A, no HRV RSI 10.43 (effective) R-59
    NBC(AE) 2023, zone 7A, with HRV RSI 8.67 (effective) R-49
    NBC(AE) 2023, zone 7A, cathedral ceiling or flat roof RSI 5.02 (effective) R-28

    Sources: U.S. values from the DOE determination analysis;[3] Canadian values from the BC Building Code and Alberta checklist.[4][5] Nominal R-values count only the insulation product; effective values also account for framing, sheathing and air films, so the two columns are not directly interchangeable. Local amendments are common, and older houses were built to far lower standards, which is why attic top-ups are usually the highest-return roof-related retrofit.

    Continuous insulation and thermal bridging

    Framing conducts heat far better than the insulation between it, so insulation placed only between rafters or joists is bridged and the assembly's effective R-value falls below the product's nominal value. Continuous insulation, such as rigid foam or mineral wool boards placed above the roof deck or below the rafters, covers the framing and is the usual way to meet an effective-RSI requirement in cathedral ceilings and low-slope roofs, where there is no attic in which to pile loose-fill. Above-deck insulation on Commercial Roofing membranes such as TPO Roofing and PVC Roofing is almost always continuous for this reason; see Insulated Roofing Materials.

    Ventilation

    Attic ventilation does not add R-value, but it removes moisture and, in winter, keeps the roof deck cold enough to limit ice damming. NRCan's guidance for accessible attics under peaked roofs uses a ratio of 1 to 300 of unobstructed vent area to insulated ceiling area, with the vent area increased where screens reduce free flow, and recommends keeping insulation clear of masonry chimneys and recessed light fixtures.[2] Details on baffles, soffit and ridge venting are in Roof Ventilation.

    Reflectivity, emittance and cool roofs

    The "coolness" of a roof surface is determined by two measured properties. Solar reflectance is the fraction of sunlight the surface reflects; thermal emittance is the efficiency with which the surface releases heat it has absorbed. Both are measured on a scale from 0 to 1, and higher values mean a cooler roof.[6][7] The DOE consumer guide states that installing a cool-coloured roof on a home can shave at least 5 to 20 percent from cooling costs, with the largest savings in hot and warm climates, and lists cool membranes and coatings for low-slope roofs (pitch of 2:12 or less) and cool asphalt shingle, tile and metal products for steep roofs.[7] Reflectance degrades with soiling, so ratings distinguish initial from aged values.[6]

    In heating-dominated climates a reflective roof gives up some winter solar gain, though the effect is small over a well-insulated, vented attic; see Cool Roofs and Urban Heat Island Effect.

    ENERGY STAR and cool roofing

    For two decades ENERGY STAR maintained a certified-product category for reflective roofing. The U.S. Environmental Protection Agency sunset that specification on June 1, 2022, after which brand owners were required to stop using the ENERGY STAR name and mark on roof products.[8] Roofing still advertised with an ENERGY STAR rating relies on a discontinued program; the Cool Roof Rating Council's rated-product directory is now the reference for reflectance and emittance claims.[6]

    Radiant barriers and thermal mass

    A radiant barrier is a low-emittance foil facing an attic air space, usually stapled to the underside of rafters or laminated to the roof sheathing. It reduces the radiant heat a hot roof deck sends to the attic floor. Its value is greatest in hot, sunny climates with ducts in the attic; in Canadian climates the same money usually buys more benefit as additional ceiling insulation, and a foil layer installed on the attic floor loses effectiveness as dust settles on it.

    Thermal mass, such as concrete or clay tile, Green Roofs growing media or a ballasted membrane, slows rather than blocks heat flow; it dampens the daily temperature swing and shifts cooling load away from the afternoon peak but does not replace insulation in a cold climate.

    Solar-ready and rooftop energy generation

    The 2021 IECC includes a solar-ready appendix that jurisdictions may adopt, reserving an unobstructed, structurally adequate roof zone and a conduit path for a future photovoltaic array.[3] Planning a re-roof with solar in mind means keeping penetrations and vents off the sunniest plane, confirming the Roof Structure can carry the added load, and choosing a covering whose service life matches the panels.

    Codes and standards

    • IECC / IRC Chapter 11 (United States): prescriptive R-values and U-factors by climate zone, plus performance and energy-rating compliance paths.[3]
    • ASHRAE Standard 90.1 (Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings): the commercial-building benchmark that sets roof insulation and, in warm zones, roof reflectance requirements for buildings outside the IECC residential scope.[9]
    • NBC Section 9.36 and the provincial codes derived from it (Canada, houses and small buildings): effective thermal resistance by heating-degree-day zone, with a prescriptive, trade-off and performance path.[4][5]
    • National Energy Code of Canada for Buildings (NECB): the Canadian counterpart to ASHRAE 90.1 for larger buildings.
    • LEED and similar rating systems award points for envelope performance and heat-island reduction; see LEED Certification.

    Incentives

    Incentive programs change frequently and should be checked at the time of a project. In the United States, the Energy Efficient Home Improvement Credit (Internal Revenue Code section 25C) allowed a credit equal to 30 percent of the cost of qualifying improvements, with an annual cap of $1,200 for building-envelope items, and insulation and air-sealing materials qualified provided they met the IECC standard in effect at the start of the previous calendar year. The IRS states the credit applies to improvements made through December 31, 2025.[10] Roof coverings themselves are not listed as qualifying property under that credit.[10] Canadian federal grant programs for insulation retrofits have opened and closed in recent years, and provinces and utilities run their own rebates; current eligibility should be confirmed before a contract is signed.

    Practical priorities

    For an existing house, the sequence that generally returns the most energy savings per dollar is: seal attic bypasses; top up attic insulation to the current code level for the climate zone; correct ventilation so the added insulation does not trap moisture; and only then consider surface reflectance, radiant barriers or a Roof Repair vs Replacement decision. A Roof Inspection and Maintenance visit is a good time to check insulation depth and ventilation. When a full replacement is planned, above-deck continuous insulation and a rated cool surface can be added at modest marginal cost; the choice among Roofing Materials should weigh climate, slope and service life together rather than reflectance alone.

    Frequently Asked Questions

    How much attic insulation does a house need?

    Current model codes require R-49 in U.S. climate zones 2–3 and R-60 in zones 4–8 under the 2021 IECC, while Canadian codes require an effective RSI of about 8.67 to 10.43 (roughly R-49 to R-59) for ceilings below attics depending on the heating-degree-day zone and whether the house has a heat-recovery ventilator. Older houses commonly have far less, so a top-up is usually worthwhile.

    Does a cool roof help in Canada?

    Reflective surfaces reduce cooling loads most in hot climates; the DOE estimates savings of at least 5–20 percent of cooling costs, with the largest gains in warm regions. In heating-dominated Canadian cities, ceiling insulation, air sealing and ventilation produce larger year-round savings, and a reflective surface is a secondary benefit best suited to low-slope commercial roofs with summer cooling loads.

    Is ENERGY STAR roofing still a certification?

    No. The U.S. EPA sunset the ENERGY STAR roof products specification on June 1, 2022, and manufacturers were required to stop using the mark on roofing after that date. Reflectance and emittance claims are now verified through the Cool Roof Rating Council's rated-products directory and referenced in building codes such as ASHRAE 90.1 and California Title 24.

    Are there tax credits for roof insulation?

    In the United States the section 25C Energy Efficient Home Improvement Credit covered 30 percent of the cost of insulation and air-sealing materials, within a $1,200 annual cap, for improvements made through December 31, 2025, but roof coverings themselves did not qualify. Canadian federal and provincial rebate programs change frequently, so eligibility should be confirmed with the utility or provincial agency before work starts.

    Should insulation or air sealing come first?

    Air sealing. Natural Resources Canada's retrofit guidance seals attic bypasses such as plumbing stacks, electrical boxes, top plates and the attic hatch before adding insulation, because leaking house air carries both heat and moisture into the attic. Insulation placed over unsealed gaps performs below its rated value and can lead to condensation and mould on the underside of the sheathing.

    Sources

    1. ↑ Natural Resources Canada — Keeping The Heat In, Section 4: Comprehensive air leakage control in your home (attic bypasses and air sealing priorities).
    2. ↑ 2.0 2.1 Natural Resources Canada — Keeping The Heat In, Section 5: Roofs and attics (air-seal-then-insulate sequence, 1:300 attic ventilation ratio, clearance from chimneys and recessed lights).
    3. ↑ 3.0 3.1 3.2 3.3 3.4 U.S. Department of Energy, Building Energy Codes Program — Energy Savings Analysis: 2021 IECC for Residential Buildings (PNNL-31440) (Table D.5: ceiling R-values by climate zone for the 2018 and 2021 IECC; exception for roof assemblies with insufficient depth for R-60).
    4. ↑ 4.0 4.1 4.2 Government of British Columbia, BC Publications — British Columbia Building Code 2018, Division B, Section 9.36 Energy Efficiency (Table 9.36.2.6.-C effective thermal resistance for ceilings below attics by climate zone).
    5. ↑ 5.0 5.1 5.2 City of Edmonton — NBC(AE) 2023 9.36 Energy Efficiency Prescriptive Path Summary and Checklist (minimum effective RSI for ceilings under attics, cathedral ceilings and flat roofs, with and without HRV).
    6. ↑ 6.0 6.1 6.2 Cool Roof Rating Council — What is a Cool Roof? (definitions and 0–1 scale of solar reflectance and thermal emittance; initial versus aged ratings).
    7. ↑ 7.0 7.1 U.S. Department of Energy, Energy Saver — Consumer Guide to Cool Roofs (definitions of solar reflectance and thermal emittance; 5–20% cooling-cost savings estimate; low-slope defined as pitch of 2:12 or less).
    8. ↑ ENERGY STAR (U.S. EPA) — Roof Products Specification Version 3.0 (statement that the roof products specification was sunset on June 1, 2022, with the EPA sunset decision letter).
    9. ↑ ASHRAE — Standard 90.1 – Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings (scope of the commercial energy standard).
    10. ↑ 10.0 10.1 Internal Revenue Service — Energy Efficient Home Improvement Credit (30% credit, $1,200 annual limit, insulation and air-sealing eligibility, credit available for improvements through December 31, 2025).

    Internal Links for Further Exploration

    Retrieved from "https://roofs.wiki/index.php?title=Energy_Efficiency&oldid=897"