Mark Kiefer grew up on a farm in Iowa and learned early on that we, as humans, are responsible for the resources we have and what we leave behind for future generations. Now the Windsor-based custom home builder has decades of experience in the construction industry and prioritizes sustainability in every one of his projects.

The family-owned and -operated business, Kiefer Built Contracting, won a 2025 SIPA Building Excellence Award for a home they built in Red Feather Lakes that far exceeds industry standards for energy efficiency. Like Kiefer’s other builds, the home is constructed with structural insulated panels (SIPs)—styrofoam sandwiched between two pieces of oriented strand board (OSB)—which make it twice as strong and twice as energy efficient as a stick-build house.

Red Feather home

“Energy codes and building codes are pushing a lot of this,” Kiefer says. “We’re just trying to go even further beyond what the energy and building codes require.”

Sustainability meets fire resistance

The Red Feather home was both a challenge and an opportunity for Kiefer to put energy-efficient building materials to the ultimate test. The modern mountain home was built on a steep hillside, and at an elevation of 9,200 feet, he knew the design had to withstand strong winds and the ever-present fire danger.

Structurally, the home required eight-inch walls (as opposed to the typical six-inch walls) and was built to withstand 169 mph winds. SIPs panels were used on the walls and roof for enhanced durability and insulation, and insulated concrete forms (ICFs, or concrete poured between pieces of styrofoam) were used in the basement. ICFs, also known as “Fox Blocks,” guard against moisture, preventing mold and rot while strengthening the foundation.

The SIPs panels are a big reason why the Red Feather home earned a score of 32 on the Home Energy Rating System, which measures a home’s air exchange per hour with a blower door test. “Anything under 100 is awesome,” Kiefer says, meaning it’s airtight and incredibly energy efficient.

Since the home is in an area prone to wildfires, they installed steel siding and a steel, monosloped roof. None of the cladding is flammable, which was important in constructing a mountain home made to last. It also has radiant floor heat and will likely be a zero-energy home as the owner had solar panels installed.

“One thing we do that’s a big deal is manage the entire project,” Kiefer says. “On that house specifically, we had to manage all the nuances of the Larimer County building department. There are a lot of things a homeowner thinks they can do on their own, but this was complicated.”

Comfortable living

Kiefer’s knack for building energy-efficient homes is also apparent in a spec home he built in Greeley’s Pine Ridge Estates community alongside Aubrie Larsen, a Realtor and interior designer. Larsen, owner of Lakeside Design and Aesthetics, says the project allowed Kiefer to demonstrate his sustainable building practices and overall style.

“It’s purely the builder’s expression, so it’s a representation of what comes naturally to them,” she says of spec homes. “It’s a good place for a client to see the type of home the builder wants to build, is good at building and is passionate about.”

Like with the Red Feather house, they integrated SIPs panels into the spec home’s design to create an airtight space that is quiet, comfortable and conserves energy. The house is 100-percent electric and has a variable-speed heat pump to keep it at the perfect temperature using “exactly the right amount of energy—no more and no less than what’s required,” Kiefer says. The result is a cozy home without drafts or a noisy furnace.

They also installed engineered floor joists, which create a more structurally sound floor system that reduces flexing and noise throughout the house. Most of the plumbing and HVAC can fit up into the floor joists, which minimizes the number of soffits in the basement.

“Mark is the only builder I’ve seen do engineered flooring to go that extra step,” Larsen says. “During a time when most builders are looking for ways to build cheaper—even if it means sacrificing quality to expand their profit margins—Mark is always looking for ways to build homes that are more sustainable, efficient and of the highest quality and longevity possible.”

The spec house was built with multigenerational living in mind, featuring a third garage that enters into a semi-private suite. The garage is perfect for storing toys such as ATVs and boats, though it also gives a mother-in-law or other family member their own place to park.

“In a lot of cultures around the world, people live together,” Kiefer says. “We’re living with our son, daughter-in-law and their two little boys. I think that interaction between grandparents and grandchildren is healthy for both the old and the young.”

Kiefer describes the spec house as “peaceful,” with its spacious floorplan, dark accents and natural finishes made of wood and stone. He and Larsen paid close attention to the air quality throughout the building process, selecting a top-notch induction range and finishes that don’t release harmful chemicals such as formaldehyde.

“One of my favorite quotes is from Winston Churchill: ‘We shape our buildings; thereafter they shape us,’” Kiefer says. “That happens inside a home, from the amount of sunlight coming in to the materials used. Obviously we can never build the perfect structure—materials aren’t perfect and neither are human beings—but we’re striving for that.”

Below: Pine Ridge Estates home in Greeley. Photos by CleanCapture Property Solution.