They kept the same zip code and gave up the lawn, and it is a trade they can defend in detail. He is a structural engineer who spent thirty years on bridges and has developed a professional distrust of anything that has to be maintained from a ladder. She runs clinical trials for a research institute down Rockville Pike, work that lives on strict sequence, and she likes coming home to a house that behaves the same way: entry level for arrivals, main level for everything social, private floors stacked above. Weekday mornings are efficient by design, coffee standing at the island, both cars out of the garage by seven-thirty. Their daughter takes the ground-floor suite between hospital placements, and the arrangement holds because nobody has to cross anyone else’s evening to get to bed. The best hour is the last one, up on the roof terrace with the treetops level with the railing and the office windows across Rock Spring going gold, close enough to the street to hear the neighborhood and high enough to be finished with the day.