Nest Egg

Nest-Egg-Image

This earth-sheltered home in Ontario offers great energy efficiency and a unique design, but it’s not for the faint-hearted DIYer.

Written by: Jack Kohane
Photos by: Daniel Dutka

Scott and Mary Macpherson like the fact they spend only about $150 to heat their home all winter, and nothing to cool their 3,500-square-foot interior living space during the hottest summers. They’re comfortably burrowed inside a NestEgg Home, encased in 150 tons of concrete, enveloped by twice that volume (on three sides) in soil.

“We opted for an earth-sheltered home because of its benefits over a surface house,” says Scott, as we enter the 48-feet-long (and 18-feet wide) subterranean cement-lined tunnel leading to his front door. “The big plus is energy efficiency. There’s very little heat loss (approximately R-33 rating on the exposed walls). The south side is nearly all glass and receives more energy in heat from the sun than it loses. And because earth sheltered homes are built of high-mass materials (primarily concrete), they absorb the heat of the day and re-radiate it back into the home at night.”

Formerly referred to as underground architecture, they’re now more commonly known as earthsheltered, earth-bermed, or earth-covered homes. Other terms used to describe structures constructed  in underground spaces include semi-subterranean, and terratectural (earth-covered architecture, in which a building is constructed within an excavation, waterproofed and then backfilled and earth-covered).

At the turn of the millennium, the Macphersons purchased the 97-acre cattle farm, tucked in the rolling landscape of Rockwood, Ontario east of Guelph. Their idea was to build an earth-sheltered home on the south-facing hillside slope. “We’re secluded here, surrounded by trees and valleys,” says Mary, her arms outstretched to embrace the vista. “Our closest neighbours are deer who come to the yard to nibble on grass and apples.”

In searching out construction ideas, they surfed the Internet for companies that specialize in do-ityourself earth-sheltered home designs. “There are many of them on the web, but none located in Canada that suited our needs,” says Scott. They eventually landed on Formworks Building, Inc., based in Durango, Colorado.

An earth-sheltered home is the chameleon of houses. It can take on the look and feel of almost any style – from Victorian to ultra-modern, Gregorian, Cape Cod, and even suburban-housing development styles. The NestEgg Home system has the advantage that it can be customized to any configuration, adding connecting modules as desired to suit individual taste and purpose. At a construction cost of about $100 per square foot, it’s also competitive with most conventional housing designs.

Increasingly popular in the U.S., especially in the south, where earth-sheltered homes offer the greatest protection from natural disasters and environmental stresses like tornados, hurricanes, blizzards, earthquakes and damage from baseball-size hailstones, these residential alternatives are built to last.

“Most modern homes are in a constant state of re-building and maintenance,” says Scott. “Rot, insect infestations, water damage, and simple wear and tear mean that homeowners must frequently expend time, energy, and money caulking, painting, re-roofing, fumigating and combating decay.”

Because most of the home is covered in earth, there are few materials to maintain – no roof shingles to replace every 10-20 years, no siding to paint  every two to five years. Due to the durability of the materials used in many earth-sheltered homes, their structural lifespan is estimated at between 200 and 1,000 years.

The Macphersons say the project’s biggest challenge was getting building permit approval. After much explaining about what earth-sheltered homes are all about, and presenting the details of Scott’s plan, the permit was eventually granted and the first bucketload of soil on the site was lifted in August 2001.

“We purchased the basic Formworks NestEgg Home system for about $35,000 (US), which includes the main structural steel beams, foundation anchor plates, the forming system, rebars, all nuts and bolts, and fully illustrated construction manuals,” says Scott. “There are dozens of architectural designs and interior layouts to choose from, but they all begin with an inner concrete dome in 24-, 32- and 40-foot diameter models.”
The Macpherson’s dome home kit was delivered from Colorado on a large flatbed truck. A “free form” home made of steel and concrete, its steel frame is erected on a conventional concrete slab floor, then covered with a steel rebar grid. Concrete is then shot into the skeletal framework to form a concrete hemispherical shell. The “skeleton” becomes part of the finished shell and adds to its inherent strength.

“This home is as strong as a bomb shelter, even though there are only four inches of concrete lining the ceiling and walls,” says Mary. “We’ve had bulldozers driving across our roof, and the dome easily withstood the tremendous weight.”

Scott cautions that dome home construction isn’t for the faint-hearted DIYer. Improvising and being innovative may be needed at times. “Although we found that Formworks offers the simplest way to build an earth-sheltered home, to do it right requires much more than digging out a hole in the ground, pouring concrete and then piling the dirt back on.”

Combined with his expertise in construction and mining, Scott has patented a new form of spray-on plastic that’s used as a structural ground support in mine shafts. His company, Spray On Plastics, uses solvent-free polyurea (called RockWeb), which creates a web-like mat on surfaces, and is fire-retardant, impervious to moisture, and dries rapidly when applied.

“I opted to use my own product to waterproof my house,” says Scott, who found that the sheetstock polyethylene waterproofing system recommended by Formworks was labour intense, and would require a large amount of time. Since winter was fast approaching, and the first sprinkles of snows beginning to fall, a fast solution was needed. Scott’s RockWeb ground support system proved perfect for the application. A layer of flexible plastic approximately 125 mil thick was sprayed over the entire dome, and covered with two inches of polyurethane foam insulation. “In the end, this process provided a complete, seamless seal that will last for hundreds of years,” says Scott. Working seven days a week, the dome home was completed in May 2002. “But it remains an ongoing project today,” Mary says. A second-storey walkout balcony from the master bedroom has been added, as well as terraces for gardens along the home’s exterior walls. There are plans for adding a green house off of the upstairs deck in the future as well. A fashionable cupola at the apex of the dome, which allows natural light to funnel deep inside, has been expanded to sport more windows for greater sunshine penetration.  “It’s cool and pleasant in summer,” says Scott.

“The normal temperature of the earth five to 10 feet below grade is about 50 F all year round, so in the summer there’s a natural cooling effect from the earth in relation to the air. The house is airtight, no cold drafts, thus it’s warm and cosy all winter. We do have a wood-burning stove for added heat, but it’s probably one of the smallest models ever made. We hardly use it.”