The house at 5312 Bradley Boulevard was alive Tuesday night.

Valets scrambled to park cars. Caterers clanged in the one-car garage. Men in suit coats and women in party dresses sipped drinks in the great room, on the flagstone patio and in a small guest house. Upstairs, a woman flitted through the rooms, taking them in.

"Oh, this is a fun room," she said in the upstairs game room, before disappearing down a wide hall.

It was the official opening of Sandy Spring Classic Homes' "Bradley Green Home" – a 6,200 square-foot shingle-style model home – and the small cottage behind it, the first built by Retreats, a new company affiliated with the builders.

Both of the buildings are notable because of their construction: Most of it happened off site at Haven Custom Homes' facility in Pennsylvania. Both the green home and the cottage were built using modular construction, which cuts down on build time, cost and environmental impact, according to Sandy Spring. The Bradley Green Home was also constructed with a wide array of earth-friendly features, allowing curious residents to pick and choose features they might be interested in for their own new homes.

Traditional custom home construction can take up to a year and a half to build, said Mimi Brodsky Kress, a partner with Sandy Spring.  Modular construction streamlines the process and saves on materials used. "It's done – from start to finish – in five months," Brodsky Kress said.

Energy-saving features of the green home include high efficiency windows, Energy Star appliances, and geothermal heating and cooling. An energy management system can regulate the amount of energy being used depending on energy thresholds that the homeowner can pre-program. A solar hot-water system heats water with energy drawn from solar panels, making up for about 75 percent of the home's hot water. The lot has "living" retaining wall with plantings in order to prevent erosion. A rainwater harvest system collects rainwater in a 3,000 gallon water tank to be pumped through irrigation hoses to gardens around the house.

The home was built to the U.S. Green Building Council's LEED Bronze standard, though it still hasn't received its official certification, said Sandy Spring publicist Barbara Martin.

Construction for the model home would cost about $1.25 million – or $3.2 million for the entire lot – if it were on the market, Brodsky Kress said. Construction of similar homes would cost $950,000 to $1 million without upgrades, she said.

In the back yard of the home's 39,000 square foot lot sits the Reatreats cottage. The small building – which includes a bathroom, kitchen and great room – is the company's first.

The cottage, itself, was a testament to the speed of modular construction, said Retreats CEO Harvey Seegers.

 "We probably started the company less than three months ago and finished here 24 hours ago," Seeger said. "It's been a start up with Silicon Valley speed."

The company offers six styles of cottages starting at $175,000 and range in size from 450 to 1,000 square feet. The cottages, designed by architect Russell Versaci, all meet his ideal of a "traditional, new old house."

Versaci said the cottages, which can be shipped nearly complete on a flatbed truck, would be ideal for guest homes, starter homes for young couples, home offices, art studios or in-law suites for older family members.

"We're ready to go on any of these," Versaci said.