I grew up in a Swarthmore house, so I understand that the character of such a house reflects much more than the sum of its parts. And yet, although thoughtfully crafted components alone aren't sufficient to create a wonderful house, they do provide an essential foundation.
Morevover, the relationship of the parts to one another, whether functionally (ergonomics) or aesthetically (balance), and the relationship of the parts to the whole (architectural coherence), help determine whether or not a house works as living space and feels like home.
This is fine as far as it goes, but a house is more movie than snapshot, more a dance than a tableau: a house evolves. Designing the relationships among its constituent parts is therefore more choreography than composition.
Many Swarthmore houses were built close to a century ago, when many of the activities and conveniences comprising modern household life had yet to be imagined. These houses had back stairs and butler's pantries but no powder rooms and only the meagerest of clothes closets; coal chutes and clawfoot tubs but no showers or laundry hookups; lead drainpipes under the bathroom floors and little or no insulation in the walls. Central air, hot tubs, skylights and decks were but a gleam in the eyes of Popular Science editors. Family rooms, home offices, basement bars and breakfast bumpouts were not yet on the domestic horizon.
By and large, these houses contain more than enough space for these sorts of upgrades; the challenge lies in figuring out how to incorporate them without throwing the balance between the surrounding elements out of whack. For example, the house I grew up in had a single bathroom, the standard hall bath on the second floor. The decision to add a powder room (a clear necessity from a practical as well as a resale perspective) occasioned much anguish over where to carve into existing space. Ultimately, a modest bite was taken out of one rear corner of the dining room. Given the alternatives, it wasn't an indefensible choice, but it disrupted the lines of a series of casement windows connected by trim into a single graceful element mirroring a similar bank of casements on the opposite wall. It destroyed the symmetry of the room.
In retrospect, a better choice might have been to take a chunk out of the back half of the kitchen, an unremarkable addition already serving as a laundry area as well as a breakfast nook with a circular table of astonishingly inefficient footprint. But finding the space required for a powder room in the geometric excess of a kitchen table may require thinking uncommonly far outside the box.
In any event, in most old houses, such modifications have been made many times over, for better or worse. New purchasers of these houses find themselves needing not only to implement upgrades that previous owners never got around to, but also, sometimes, to undo multiple earlier generations of alterations as well.
As a thought experiment, we might conjure up an eighty year old house that's been scrupulously maintained yet never improved in any way. Now let's imagine this house being acquired by a charming young twenty-first century family. An architect is hired to make the house over into twenty-first century living space, up to date in every way, yet without sacrificing its essential character. Leaving aside for a moment the question of how its essential character may be ascertained without living in it, we can suppose that a satisfactory design will eventually be arrived at, and that given enough patience, enough capital, and the right complement of tradespeople, the makeover will be fully realized.
The reality, in contrast, is that every eighty year old house is in the eightieth year of an ongoing renovation project with a parade of foremen, a continuously revised set of specs, no final plans, and no completion date.