The Energy Star Homes Program Raises the Bar with Version 3
The Energy Star program — the first rung on the green building ladder — is scheduled to get more stringent, with new airtightness and HVAC mandates and tougher requirements for larger homes
Beginning on January 1, 2012, homes enrolled in the Energy Star HomesA U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are at least 15% more energy-efficient than homes that minimally comply with the 2004 International Residential Code. Energy Star Home requirements vary by climate. program will need to comply with a new specification — dubbed Energy Star Version 3 — that is stricter than the current Version 2 specification.
Version 3 will still offer builders two possible paths to obtaining an Energy Star label: a performance path and a prescriptive path. Since it's impossible to provide a comprehensive description of Version 3 in a short article, I’ll confine myself to commenting on some of the highlights of the new specification.
By now, Energy Star builders are familiar with the Thermal Bypass Checklist. The Version 3 specification has given the checklist a new name: the Thermal Enclosure System Rater Checklist.
Joining that checklist are three new checklists:
- The Water Management System Builder Checklist
- The HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. System Quality Installation Contractor Checklist
- The HVAC System Quality Installation Rater Checklist
Among the requirements found in the Water Management checklist:
- Builders must install pan flashing on the rough sills of all window and door openings.
- Builders are prohibited from using any materials (including framing lumber) with “visible mold.”
While it’s hard to imagine that builders won’t be tempted to slip in the occasional 2x4 with a spot of mold on it, the checklist probably won’t slow down progress on many building sites, since the entire checklist lacks teeth. The only person required to verify that the builder has complied with the checklist is — drumroll, please — the builder.
Lowering the HERS Index goal
Energy Star builders will need to achieve HERS Index targets that are lower (that is, stricter) than the Version 2 HERS targets. Actual HERS targets will depend on the climate zone — in Vermont, most Energy Star homes will need a HERS Index between 60 and 70 — and the size of the home.
That’s right — Version 3 includes a “size adjustment factor.” The bigger the home, the lower (stricter) the HERS target. The Energy Star program deserves credit for this long-overdue innovation.
To calculate the size-adjustment factor, The Energy Star program assumes that
- a 1-bedroom home should measure 1,000 square feet;
- a 2-bedroom home should measure 1,600 square feet;
- a 3-bedroom home should measure 2,200 square feet;
- a 4-bedroom home should measure 2,800 square feet; and
- a 5-bedroom home should measure 3,400 square feet.
If you plan to build a larger home — for example, a 3-bedroom home measuring 2,600 square feet — then the Energy Star program will require you to achieve a lower HERS Index than if you built a 3-bedroom home measuring 2,200 square feet.
Addressing thermal bridging
To reduce thermal bridging, the Version 3 specification requires builders to choose one of five wall-construction methods:
- A continuous layer of rigid foam insulation (at least R-3 in climate zones 1-4 and at least R-5 in climate zones 5-8);
- Structural insulated panels (SIPs);
- Insulated concrete forms (ICFs);
- Double stud wall framing; or
- Advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. (optimum value engineering).
The foam-sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. option sets a very low bar for builders — an issue I’ll get back to at the end of this blog.
New air barrier details
The Version 3 specification introduces a new, better definition of an air barrier material: “For purposes of this checklist, an air barrier is defined as any durable solid material that blocks air flow between conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. and unconditioned space, including necessary sealing to block excessive air flow at edges and seams and adequate support to resist positive and negative pressures without displacement or damage. EPA recommends, but does not require, rigid air barriers. If flexible air barriers such as housewrap are used, they shall be fully sealed at all seams and edges and supported using fasteners with caps or heads > 1 inch diameter unless otherwise indicated by the manufacturer. Flexible air barriers shall not be made of kraft paper, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness shall be > 6 mil.”
Among the air barrier details required by the Version 3 specification:
- Wind-wash protection (for example, air-sealed blocking) at the perimeter of insulation installed on an attic floor (facing the soffit);
- At least R-10 insulation and weatherstripping at all attic access hatches and panels on top of drop-down stairs;
- Maximum air leakage rates (as determined by a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas.) that vary by climate zone: 3 ach50 or better in zone 8, 4 ach50 or better in zones 5-7, 5 ach50 in zones 3-4, or 6 ach50 or better in zones 1-2.
A low bar for insulation
The Version 3 specification requires that cavity insulation be installed to meet the Grade I installation standard developed by RESNET. The requirement calls for insulation to be installed without gaps or flaws and with less than 2% of the insulated area showing signs of insulation compression. Although the Grade I installation standard is difficult to achieve with fiberglass batts, builders should have no trouble achieving it with cellulose or blown fiberglass.
In a home with exterior foam sheathing, cavity insulation can be installed to a lower installation standard (Grade II) than in a home without foam sheathing.
The Version 3 specification requires visual inspection of installed insulation — something that is impossible with some insulation methods. For example, when cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. is blown into wall cavities after drywall has been hung, visual inspection of the insulation is impossible. So far, the EPA has not come up with a solution to this inspection conundrum.
Although building codes have long required insulation to be installed according to manufacturers’ instructions — in other words, without any gaps or compression — that code provision has been widely ignored. Although the Energy Star requirement that insulation be installed to the Grade I installation standard appears to be a new provision, it is simply a restatement of an existing (unenforced) code provision.
The Version 3 specification allows Energy Star builders to use insulation levels that barely meet code. For example, the 2009 IECC International Energy Conservation Code. requires the use of R-38 ceiling insulation in Climate Zones 4 and 5. But the code allows lower insulation levels — as low as R-21 — when builders use the alternative equivalent U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. calculation path or the alternative “Total UA” compliance path. Either of these code compliance paths will satisfy the Version 3 specification, as long as the attic insulation covers the exterior wall top plates.
For years, energy experts have been urging builders to install above-code levels of insulation, so it’s discouraging to see that the Energy Star Homes program has decided to allow builders to install insulation levels that barely meet code.
According to Sam Rashkin, the EPA’s national director for the Energy Star Homes program, the Version 3 specification includes a low bar for insulation because of pressure from builders — or, as Rashkin explained in an e-mail, “We ... [wanted] to avoid some potential ‘poison pills’ for production builders.”
Venting combustion appliances
The Version 3 specification requires that in Climate Zones 4-8, all furnaces, boilers, water heaters, wood stoves, and fireplaces must be sealed-combustion units (with ducted outdoor combustion air) or must be power-vented.
In Climate Zones 1-3, atmospherically vented appliances are still permitted.
Installing and commissioning HVAC equipment
According to the new specification, installers of HVAC equipment in Energy Star homes must have passed a special course and been “credentialed.” Currently, the only organization that has such a credentialing program is the Air Conditioning Contractors of America (ACCA), which offers the training under its “Quality Assured Contractors” program.
For more information, see the ACCA Web page on “Quality Assured Contractors.”
The Version 3 specification includes many new requirements for homes with forced-air systems:
- Any supply ducts installed in unconditioned spaces need R-8 or better duct insulation.
- Any return ducts, bath exhaust ducts, or kitchen range ducts in unconditioned spaces need R-6 or better duct insulation.
- The maximum leakage rate for a forced-air duct system will be 6 cfm @ 25 pascals per 100 square feet of the home’s conditioned floor area.
- The maximum leakage rate to the outdoors for a forced-air duct system will be 4 cfm @ 25 pascals per 100 square feet of the home’s conditioned floor area.
- Every forced-air system will need a filter rated at MERV 6 or higher.
- The air flow of the whole supply duct system must be measured and must be within 15% of the design air flow.
- The air flow at each supply register must be measured and must be within 20% of the design air flow.
- The maximum pressure difference between a bedroom with a closed door and a common room of the house (measured with the forced-air system operating) will be 3 pascals.
- If the home has central air conditioning, then the installer must verify that the subcooling deviation is no greater than ±3°F and the superheat deviation is no greater than ±5°F.
- If the house is equipped with a central-fan-integrated supply ventilation system, then the furnace or air handler blower must be powered by an ECM (electronically commutated motor) and the fresh-air duct must be equipped with a motorized damper wired to a control that prevents overventilation or underventilation.
Builders who are anxious about some of these provisions should note that the new requirements don’t come with any teeth. The person responsible for verifying all of these requirements is the HVAC installer.
For the first time, Energy Star homes will now be required to include a mechanical ventilation system complying with the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. standard. It’s about time.
The specification requires ventilation air inlets for supply or balanced ventilationMechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery (see heat-recovery ventilator and energy-recovery ventilator). systems to be at least 4 feet above grade. This provision means that many homes will no longer be able to install such inlets through the basement rim joist.
What Version 3 gets wrong
The Energy Star Version 3 specification gets many things right, and the EPA should be commended for raising the bar on Energy Star home requirements.
Unfortunately, the new specification gets several things wrong:
- The specification allows builders in Climate Zones 4 through 8 to omit interior air barriers at rim joists. In other words, rim joists in those zones can be insulated with unfaced fiberglass batts. Sam Rashkin predicts that this lax provision won't be a problem, because the stringent Grade I installation spec will make the use of fiberglass batts unlikely. However, it remains to be seen whether raters will really have the backbone to fail fiberglass batt jobs with installation defects.
- An early proposal prohibiting furnaces, air handlers, and return-air ducts from being located in garages was cravenly eliminated. According to Rashkin, “That was a battle with the American Gas Association. We said, ‘What battles do we want to fight?’ The AGA is a pretty big player.”
- Rather than requiring above-code insulation levels, the specification allows builders to install insulation that barely meets minimum code requirements.
- The specification allows builders in cold climates to use very thin rigid foam wall sheathing — for example, R-5 foam on a 2x4 wall with R-13 batts in Vermont. Such thin foam can allow moisture accumulation or condensation in the wall cavity.
- The specification’s envelope air leakage goals (between 3 ach50 and 6 ach50, depending on climate zone) are too high.
I'd like to give credit to Li Ling Young, whose presentation on Energy Star Version 3 at the Better Buildings By Design conference in Burlington, Vermont, inspired this article.
Last week’s blog: “Disappointing Energy Savings for Energy Star Homes.”
- U.S. Environmental Protection Agency
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