DOE ZERH: Mountainside Architectural Beauty

This home builder had the unenviable task of building a super energy-efficient dream home on a difficult building site.

Perched high on a mountainside in southwestern Colorado, the Glacier Club Modern Home offered commanding views and incredible challenges for the home builder. Mantell-Hecathorn Builders of Durango, Colo., was up to the challenge, delivering a home that was architecturally stunning and surpassed the builder’s own goals for high performance by winning a Housing Innovation Award from the U.S. Department of Energy (DOE) Zero Energy Ready Home (ZERH) program.


Construction of Glacier Club Modern Home posed a number of challenges, including its high altitude and its location against a highly sloped rocky mountainside. Photo: Christopher Marona Photography

“This was by far the most challenging site and house design in Mantell-Hecathorn Builders’ 44 years of building custom homes,” says Hunter Mantell-Hecathorn, a principal in the custom home building company started by his parents Greg and Tara in 1975. “If ever there was a home that required constant innovation, this was the home.” 

Located on a half-acre parcel at 7,600-foot elevation, with a 40-degree rock slope, the site required blasting to nestle and anchor the foundation into the rocky mountainside. The builder also had to contend with heavy snowfalls that could accumulate on and around the house and a fractured rock substrate that allowed subsurface moisture to percolate upward through the rock fissures to the site’s surface, especially during spring thaw and heavy summer rains. 

These issues added to the complexity of site excavation; the builder installed an all-encompassing system of French drains under and around the home, as well as surface drains, radon trenches, and pipes under the lower level. 

“The extremely complicated foundation plan required consistent and precise interaction with the surveyor, blasting subcontractor, excavator, concrete subcontractor and engineers,” Mantell-Hecathorn says. “The site topography and space constraints required extensive additional effort to simply achieve construction, and provided significant challenges to successful attainment of the DOE ZERH standards.”

Key Features

Walls: 2-by-6 24-inch on center advanced framing, R-38 total: 5/8-inch drywall. In cavity 

2.5-inch closed-cell spray foam plus 3-inch loosefill fiberglass. On exterior, coated OSB sheathing, 2-inch rigid foam, rainscreen under stucco or stone, or 3/4-inch furring strips under siding.

Roof: Shed roof, 5⁄8-inch coated OSB sheathing, ice-and-water shield, metal roof.

Attic: Cathedral ceilings: 3/4-inch tongue-and-groove Douglas Fir, 5/8-inch drywall, 11- 7⁄8-inch I-joists, R-19 batt, 7-inch closed cell spray foam.

Foundation: Insulated basement, R-23 total: 55/8-inch drywall, 2-by-4 studs, 24-inch on center; 3-inch closed-cell spray foam, 8-inch poured concrete, water proofing, 2-inch rigid foam, drainage board.

Windows: Triple-pane, low-e2, aluminum clad wood fixed frames, interior motorized blinds, U=0.19, SHGC=0.50.

Air Sealing: 1.5 ACH 50.

Ventilation: HRV, continuous ventilation, boost switches in bathroom, MERV 13 filters.

HVAC: Radiant floor heat from wallhung gas boiler, 96 percent AFUE; 22 SEER AC; passive solar.

Hot Water: Wall-hung gas-fired boiler, 96 percent AFUE, 80-gallon push button recirculation pump.

Lighting: 100 percent LED, integrated lighting controls.

Appliances: Energy Star dishwasher, clothes washer and refrigerator.

Solar: 7.2-kW PV system.

Water Conservation: WaterSense fixtures; drought-resistant landscaping.

Energy Management System: Smart thermostats, lighting automation, PV tracking. 

Other: Aging-in-place, all low-to-no-VOC and formaldehyde-free products.

By all accounts, Mantell-Hecathorn Builders was successful in meeting the challenge, implementing the innovative design by renowned regional architect Jon Pomeroy in a three-level, 4,937-square-foot home plan that achieved a Home Energy Rating System (HERS) score of 46. 

A typical code-built home would score an 80 to 100 on the HERS score and a net-zero home would score a 0. When the 7.2-kW solar photovoltaic system is included on this house, the HERS score drops to 20, and projected annual energy costs are more than cut in half. That means an annual bill of about $1,000 per year, or less than $85 per month, which is far lower than most homeowners could expect to pay for heating and cooling a home one-third the size. 

Even without the PV, the annual energy costs are expected to be $2,500, a projected savings of $1,400 over a home just built to the local energy code, which is the 2009 International Energy Conservation Code (IECC).

Building Process Cost Cutters

Building to this level of energy efficiency is nothing new for Mantell-Hecathorn, a long-time ENERGY STAR builder in a state that has no licensing requirement for general contractors, in counties that don’t inspect for energy efficiency, and in jurisdictions that until recently hadn’t updated their energy code since the 2003 edition. 

La Plata County, where Durango is located, recently adopted the 2009 IECC and the City of Durango just adopted the 2015 IECC code this year, thanks in part to education by the Mantell-Hecathorns.

Mantell-Hecathorn Builders committed to building all of its homes to the DOE ZERH specification in 2013 when the program started. It has certified 14 homes so far. They are the only builder in southwest Colorado to make this 100 percent commitment. 

The DOE ZERH certified home program gives builders a road map to build homes that are more energy-efficient, comfortable and durable than current code requires, and a third-party verification process helps convey confidence to the homeowner that the home will deliver what Mantell-Hecathorn promises. 

Greg Mantell-Hecathorn stresses the value of the third-party verification required by the DOE program. It makes it known “that we are providing our clients and the community with homes that provide long-lasting value, greater comfort and performance, and which are tested to meet those high standards for superior quality and energy efficiency,” he says. “We believe that the DOE Zero Energy Ready program provides the best verifiable platform for high-performance standards, while allowing the flexibility to be adapted to the wide variety of custom homes that we build.”

Headed in the Right Direction

On this home, builders took full advantage of the exceptional southern exposure of the site for optimal solar collection and passive solar heating potential. They installed a 7.2-kW array of solar panels on the standing seam metal roof and large amounts of glazing on the south-facing side of the home. 

All windows are triple-paned, with an insulation value of U-0.19 (R-5.26). The windows have two low-emissivity coatings to help minimize radiative heat transfer through the glass. The windows are not gas filled due to the high altitude. 

All windows have aluminum-clad wood frames and most are fixed rather than openable, which provides unobstructed views, better resistance to wind pressures, and more air tightness. The windows have a high solar heat gain coefficient (SHGC) of 0.50 to allow in beneficial solar heat gain in the winter.

Mantell-7-Aerial Shot 2-web

The home’s roof is broken into multiple slanted, curved and flat planes structured over OSB sheathing and closed-cell foam insulation. Photo: Christopher Marona Photography

Motorized blinds installed on the interior side of the windows can be scheduled to operate automatically to keep out unwanted summer solar sun. Deep overhangs and covered balconies also minimize heat gain from high overhead summer sun. Lighting controls are integrated with the home automation and energy management system.

The standing seam roof cladding covers a roof that is broken into multiple slanted, curved, and flat planes on this modern home. The roof structure consists of 12-inch I joists with no attic space. All of the upper level consists of cathedral ceilings that are insulated with 7 inches of closed-cell foam against the underside of the OSB roof sheathing plus R-19 of fiberglass batt. The sheathing is completely covered with an adhered ice and water barrier underlayment.

The walls consist of 2-by-6 at 24-inch on-center stud-framed walls that are filled with 2.5 inches of closed-cell spray foam, which provides insulation, air sealing, and some structural rigidity to the walls. The remainder of the wall cavity is filled with 3 inches of loose-fill fiberglass. 

The walls are sheathed with a coated OSB product, then topped with 2 inches of rigid foam. A rainscreen was installed behind the stucco and stone cladding, and 3/4-inch furring strips were installed behind wall sections with lapped siding. The walls have a total insulation value of R-38. 

bto-toz-Mantell-info-300-webIn addition to the spray foam layer in the wall, cavities, and the underside of the roof deck, sections of the floor that were cantilevered were also insulated from underneath with spray foam. All wood-to-wood seams were sealed with caulk and tape and wood-to-concrete seams were caulked.

The below-grade walls of the basement were poured concrete that was protected on the exterior by a spray-on crystalline waterproofer, 2-inch rigid foam, and a plastic drainage board. The interior walls of the basement level were framed 2-by-4 24-inch on-center stud walls, with 3 inches of closed-cell spray foam, giving the below-grade walls a total insulation value of R-23.

The home achieved an airtightness of 1.5 air changes per hour at 50 Pascals. To provide ventilation, a heat recovery ventilator was installed to bring in fresh air through a MERV 13 filter and to exhaust stale air. The HRV was separately ducted to provide fresh air to every room in the house and to exhaust air from several locations, including the kitchen and bathrooms, which have boost switches to more quickly remove steam.

A 96 percent efficient wall-hung boiler provides domestic hot water to the home and hydronic radiant floor heating to all three floors. Passive solar gain adds to the space heating. Cooling is provided by a SEER 22 heat pump.

Energy Star appliances, LED lighting, and low-flow EPA WaterSense-labeled fixtures add to energy and water savings.

A main-floor master bedroom and elevator are among the aging-in-place features designed into the home. The home meets all of the requirements of the EPA Indoor airPLUS including the use of low and no-VOC and formaldehyde-free products. While a beautiful home and low-energy bills are the result, Mantell-Hecathorn’s attention to detail and focus on quality construction are what they are most proud of.

“We focus on high performance, not just energy efficiency and lower utility costs, but also building durability, something homeowners can pass down to future generations,” says Hunter Mantell-Hecathorn.

It’s All About Teamwork

The company lives up to its motto, “personal attention to detail, one home at a time,” limiting projects to two or three per year, so that Hunter or Greg can personally be on site daily to ensure that quality standards are being met by the subcontractors and crews. Mantell-Hecathorn Builders employs five full-time carpenters who receive training, construction documents and daily oversight. 

“We don’t experience much turnover in our employees, as we always have interesting, challenging, and fun projects to work on,” says Hunter Mantell-Hecathorn. “They can feel pride in their work, and we treat them as valued, respected members of our company.” 

The company put effort into finding subcontractors willing to meet their standards. Mantell-Hecathorn meets with subs during budget formation and plan development, provides written scopes of work for each trade detailing construction methods and materials, requests the best crews, and meets regularly with the principals and the onsite supervisors for each subcontractor trade during construction. “Quality construction is something we take a lot of pride in, and our company is known for that dedication,” he says.