When Margaret and Grant Pomeroy set out to rebuild the boathouse at their weekend home on Balsam Lake, about 80 miles northeast of Toronto, Ontario, they asked that it be invisible from their cottage. "We really wanted to enjoy our views of the sunsets," says Margaret.

Their designers at Agathom Co. were thrilled at making a building disappear. "It's a marvelous puzzle," architect Adam Thom recalls. "We knew we had to throw out the ideas of the standard boathouse. But that's when we started rubbing our hands together.

Margaret was interested in a green roof, but those are tricky to engineer close to water. Adam and his partner, Katja Age Sachse Thom, found an unorthodox answer: steel culverts, made in the eastern Canadian provence of New Brunswick, typically used for mining or railway tunnels. "It's very heavy-gauge steel, a quarter-inch thick," Adam says. "It's real industrial stuff.

The idea of turning massive steel arches into a boathouse seemed a bit preposterous, even to the designers. But when they presented the concept to Margaret, who had no prior experience with modernist experimentation, she didn't blink. Agathom and the builders demolished the old boathouse, leaving a gap surrounded by steep slopes; into this space they laid steel arches 17 feet in diameter, marching almost 30 feet away from the water. Beneath, the dock was built using congenital concrete footings covered with a beautifully crafted wood floor.

All the earth works had the neighbors concerned, at least until the boathouse completed its vanishing act. "People were worried while we were digging that we were going to create a monstrosity on the lake," Adam says. "But as the project progressed, less and less could be seen.

In the end, the building fulfills the Pomeroy's request that it blend in. With its steel bones largely hidden, it touches on the rough design language of local boathouses: the doors facing the water boast nautical-style hardware and are covered with beveled siding in raw cedar, a familiar material in the area. And the little hill on top has become a perfect place to enjoy a new view of the lake.

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