Peter Cohen is 84 years old, lives in the sticks—a couple of miles outside Ellsworth, Maine—and likes to write letters. Don’t get me wrong: This self-described ancien is no Luddite. He’s a friend of email and progressive politics, and his green Prius sports an “Octogenarians for Obama” sticker. But the métier in which I’ve found him to be at his best (discounting architecture, where he’s designed a handful of smart, inexpensive, and structurally innovative houses over the last half century) involves letterhead, a return-address stamp, and that increasingly rare commodity, a typewriter ribbon.

His classy, bespoke envelopes, with “Peter M. Cohen & Associates, Architect” running vertically down the left-hand side; the typewritten perfection of his missives; and his geometric, all-caps handwriting all plainly say, “This man is an architect of the old school.” One who studied with Josep Lluís Sert at Harvard in the 1950s, who helped Louis Kahn choose the furniture for Kahn’s First Unitarian Church in Rochester, New York, and who is, by his lights anyway, “the only living American architect to shake Le Corbusier’s hand. Twice.” But beyond the graphics, textured paper, and architect’s letterhead you’ll find a man who wants to communicate.

Cohen has written me somewhat regularly since I visited his home last summer, usually with an additional detail about his house or a list of materials he used but just as often to inquire after my well-being and to comment on the state of local and national affairs.

If every architect could communicate with half the wit, warmth, and clarity typical of a Cohen dispatch, there’d be little room for the Derridean deconstructivists and half-baked Tschumiites who lard the halls of more than a few American design schools. A letter from last month opens like this: “Dear Aaron, Despite our nation shuddering at the word ‘derivatives’ I have found among the dozen houses I have designed that five are indeed derivatives of a spine-and-module system started 48 years ago. None, to the best of my knowledge, have proven toxic.”

The same goes for the home that he shares with his wife, Sally; their Abyssinian, Rosie; and their golden retriever, Daisy. The Cohens moved to Maine in 1985 after Peter retired from teaching architecture at Cornell University, first taking up residence in the filled-out bones of an antebellum barn brought along from Ithaca. Their new house, the wryly dubbed Maison Amtrak—“it has a marked resemblance to the usual newspaper photos of a typical derailment,” he quips—sits just up a wooded slope from the Union River. It’s the latest in a series of the five houses that make use of Cohen’s own spine-and-module design system. With a central corridor comprising the kitchen, service areas, hallway, main entrance, and mechanical compo-nents, Cohen is free to clip modules such as bedrooms, offices, living rooms, or decks onto the frame. He has attached them strategically to take advantage of surrounding views and topography. Originally implemented on a house he designed in 1961, the system is still a pliant and viable strategy for homes of all sizes. Cohen says that the plan “works well with irregular, sloping sites with views and woods, rather than the typical rectangular plot of a quarter acre or less.”

Little surprise, then, that a low, rectangular window best glimpsed while lying in Cohen’s own bed (he encouraged me to test it out) should have one of the best views in the house, straight through the pines to the river below. Sally’s bedroom, the same size as Cohen’s at 16 by 16 feet, is just across the hall, a concession not to a deteriorating marriage but to Cohen’s confession to being “an active sleeper.” The final two modules of the top floor consist of the garage and dining and living room, which measures 16 by 28 feet. The former is home to the aforementioned Prius and the latter to an arresting view of the Union and a lifetime’s accumulation of design know-how.

A visiting architect might marvel at the huge window looking out into the trees and the cleverly placed air duct that keeps it from fogging up in subzero winters; then at the operable window placed unobtrusively in the sidewall to allow the ventilation that the fixed-casement glass doesn’t; and finally at the custom bookshelf, aged to a rich brown and meant to house a proper design library and conceal “the maw of a television.” But chez Cohen, subtlety trumps wild flourish, which means that those weary from an hour’s tour, like my wife, will likely miss the home’s deft details as they head straight for the sun-drenched Eero Saarinen–designed Womb chair Cohen has prized for decades. “It was through Sert that we got that chair. I was just about to graduate from the Graduate School of Design, and [Walter] Gropius had just left, so Sert, then the dean, got all his students the architects’ rate,” he says. Then, the bargain still not lost, he adds, “Forty percent off!”

As we sit in the living room, Cohen describes how his house, a dream in the summer, is just as efficient in the winter: “Snow, after a sunny winter day, will slide off avalanche style from the pitched roofs, and rain is heard as a pleasant, soft patter.” Structural insulated panels (SIPs) that make up the walls and roof keep the Cohens warm, the house green, and the costs of both construction and heating down. SIPs also offer the stability and strength to cope with the average Maine snowfall. Just as I was longing for winter so I could curl up with a book, snugly ensconced in the house during a nor’easter, Cohen and I stepped out onto his deck, the most sensible place to pass a summer in Maine.

Made of pressure-treated Douglas fir two-by-fours turned on their ends and spaced with plywood blocks, the deck separates the dining room and living room module from the master bedroom module and is simply grand when the weather’s fine. “The boards have grayed out, and rain or spilled drinks fall through the slats to the ground below,” Cohen says, adding, “Spike heels are unseen in Maine.” To prevent a perilous drop off the edge of the deck, geraniums planted in steel cylinders cut lengthwise and mounted on wooden supports create a blazing barrier without obstructing the view down to the river. Though much of Maison Amtrak’s appeal is in its clever engineering, Cohen’s aesthetic sense is equally developed, and it was on those grounds that he was loath to add a railing to the deck. He made the case for his planters to a building inspector, who conceded that stringing up a tennis net in addition to the geraniums would suffice.

Downstairs, Cohen’s office, much of it below grade, is kitted out with the ephemera of his other passion: piloting small planes. The room gets wonderful light through a bank of river-facing windows, as does Sally’s office down the hall, which doubles as a guest room. The exposed concrete walls keep things cool in the summer and warm in the winter, though a botched job on the initial pour led Cohen to clad the walls in Homasote—a structural fiberboard produced in New Jersey—and cover them with an impressive collection of posters. Cohen credits a trio of local craftsmen, George Daley, Crosby Noyes, and Peter Whittlesey, with correcting some initial mistakes in the construction and bringing Maison Amtrak up to par.

It’s impressive that a then-seventy-something architect, who might otherwise have retired to the warmer climes of, say, Florida, brought off the place at all, but to do the whole project for $300,000 including the riverfront land is something of a coup. Resale value wasn’t on Cohen’s mind—“This is a house for the last part of our lives,” he says—but making the most of what he had to work with was. Along with the SIPs, the use of local wood, local builders, and a host of off-the-shelf options like storage cabinet kits from Home Depot account for a savings in both energy and materials. Cohen sought “a house built of good-quality materials without faux details and ornate fittings.”

Living pretty close to the middle of nowhere also helped keep costs in check, though one of Cohen’s smartest moves was making use of the spine-and-module system. By putting all the mechanical elements in a central core, as opposed to noodling throughout the house, he managed to save space, money, and energy and organize the home to best suit its tricky site. The system also calls to mind the work of Cohen’s mid-century idols like Buckminster Fuller and Kisho Kurokawa, who aimed for a malleable, vibrant, surprising architecture based on modules attached to a central core.

It’s the rugged Maine landscape that Cohen treasures most, though, and he has designed his home to best engage it. Beyond simply capturing the views and making the most of the pines, Cohen’s design is also essentially interested in the needs of people living in the landscape. One of his letters describes the five-by-five-foot shower that he has come to relish “after showering for 15 years in a space that approximated a London telephone stall.” He often shares the larger space with Daisy after their “mud-splattered hikes” in the woods.

Though his notes now allude to the challenges of “acting my age,” he and Sally carry on, finding no small joy in their home, their surroundings, and their new president. The letters will continue, I hope, perhaps turning from his house to other aspects of his life and career. I hope he’ll write to tell me more about his experience working with Kahn, his time building a hospital in Kabul in the 1970s, or his days flying around the Northeast. Architecture and his life as an architect are rarely far from Cohen’s mind, though. One of his most recent letters ends on an introspective, optimistic note, an apt sign-off from perhaps the state of Maine’s only remaining mid-century modernist.

“I wonder why I persevered and built another spine-and-module residence for myself,” he writes. “But we are most comfortable and satisfied with the result after nine years. There is minimal maintenance and we are managing as independent anciens.”