Online commenters on Nextdoor are bemoaning our “McMansion pandemic,” described also in letters to the editor as “monsterfication” of Arlington’s suburban housing stock.

New luxury homes under construction are lambasted with such affectionate terms as “grotesque….eyesore…ridiculous….horrendous….ugly…horrid….cattle barn…eee-yuk.”

The rise of large-scale “garage-mahals” has brought “rampant demolition of smaller, older, perfectly livable homes” that are replaced by $2 million — $3 million “megamansions,” laments preservationist Tom Dickinson, who has recruited more than 90 to his virtual organization Save Historic Arlington.

The county issues 300-400 demolition permits annually, notes Dickinson (who spent decades photographing older homes), only a small percentage of which “had issues that would justify demolition. The environmental costs of building new are never calculated or factored into the approval process, nor are the impacts of loss of trees, vegetation, ground cover, and resulting water run-off/drainage problems.”

You’d have to be living under a rock not to notice that today’s low interest rates fueled a boom in homebuilding by builders working for profit. So in a two-fer, I asked Tripp DeFalco, founder of Arlington-based DeFalco Home Design who is both an architect and a builder, whether these new homes are really so ugly, and whether they’re the wave of the future.

“There are two drivers from a design perspective,” he said. “The appraisal process, which is broken” and the incentives for builders to make the most of value of scarce land.

Personally, DeFalco sees “no reason to build a big house, and most of my current clients end up with smaller houses than a developer would build.” But appraisers “give no credit for something well-designed, for aesthetics, for higher efficiency,” more insulation, higher-grade systems, longevity of materials themselves. There’s no recognition for life-cycle costing, or expensive geo-thermal HVAC, he said. The final sale price is “based on other comparable property, what somebody else did in the neighborhood in past 12 months.”

A developer looks to maximize profit, which means pumping up the house size, sometimes for a “box,” DeFalco adds. After factoring in transaction fees, brokerage fees and carrying costs, he looks for the “outsale” numbers before the “go-no-go decision based on the land.”

No one builds more than one kitchen (the most expensive room, followed by bathrooms). “So if there’s going to be five bathrooms, why not inflate the bedrooms and living spaces, which are relatively cheap to build? Why buy a lot for $1 million and make $200,000, when you can make $300,000?”

Preservation is “not part of the conversation,” DeFalco acknowledges. “Let’s face it, as a developer, my job is developing a property and selling it, so who cares what happens after that?”

The derisive term “McMansion” does not offend him. “I’ve received hundreds of calls from neighbors who didn’t like what I’m doing and are not shy.” But all is done in compliance with county zoning and by-right development, he adds.

“It’s not necessarily the developers’ fault ­— they’re responding to real economic pressure” and competition, DeFalco says. Today’s astonishing prices mean “I couldn’t afford to move into my own neighborhood.”

Arlington is “going through an evolution, and it may not all be pretty,” he says.

“As land becomes more valuable, it’s natural someone will replace [a structure] with a larger or higher-performing home.” With our good schools and transportation, everyone wants to be here. Arlington is a victim of its own success.”

Fun recent visit to the triple border between Arlington, Falls Church and Fairfax: the site of the Pope-Leighey house designed by Frank Lloyd Wright, which was disassembled in 1964 and moved to Woodlawn Plantation, to make way for I-66.

Neighborhood stalwart Anita Cerio showed me the lot off Meridian St. at Locust St. where she visited Margaret Leighey, who, with husband Robert, was the second owner of the Usonian home built in 1940 for Washington Star editor Loren Pope.

Mrs. Leighey was Cerio’s Sunday school teacher: “A gentle soul, she would invite me over for homemade cookies, proudly showing off the ferns in her garden.”