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The trouble with bringing down home prices by building homes rather than the current strategy of either ignoring the problem or blaming greedy developers is that it has run into apparently insurmountable problems. On the one hand, acquiring land, hiring workers and buying materials is very expensive, so there are larger loans involved and rents or sale prices must be high in order to recover the costs, much less make even a small profit. On the other, getting basic permission to build is a laborious process, especially if, thanks to high construction and land costs, the new building needs to be much larger or taller than anything around it.

So the question is if any type of housing can be both cheap to build and acceptable to interest groups?

There may be: the trinity house. A vernacular architectural style from Philadelphia, trinity houses are small and simple, which should mean that they are fairly cheap to build and won’t overwhelm the neighbors.

A row of Philadelphia trinity houses, from this post about them.

According to Curbed, the least elaborate kind of trinity is known as a bandbox. They were built on narrow lots that were about 16 feet wide, 16 to 20 feet or so deep and two to three stories tall. What made them different from, say, a New York City brownstone, is not just the smallness, but that the Philadelphia trinity had only one room on each floor, connected by a narrow spiral staircase. Most trinity houses appear to have one bathroom, which is usually the result of a modern partition, since most they were built before indoor plumbing.

The simplicity and smallness of the trinity house meant that it was very affordable. According to The Encyclopedia of Greater Philadelphia, a trinity house built for the World’s Columbian Exhibition in Chicago cost $2500. According to Kenneth T Jackson in The Crabgrass Frontier, Philadelphia’s working classes were unique for their level of homeownership.

Smallness and simplicity mean that the design can be flexible. In this day and age, one could imagine them being shared by housemates or used as starter homes for new families. They are also small enough to be used as accessory dwelling units. Many of Boston’s outer neighborhoods, like Allston-Brighton, Dorchester, Hyde Park, Roslindale, West Roxbury, Jamaica Plain and Roxbury feature houses on sometimes generous lots, so it would be possible to add these small houses to existing properties without demolishing existing homes.

This is a very traditional way of adding homes in a city. In Boston, these sorts of “laneway”, “infill” or “rear lot” houses can be seen in the North End, Beacon Hill, the South End and South Boston. Trinity houses actually developed in Philadelphia this way: as the city boomed to become the most important town in colonial North America the houses on generous plots were replaced with ample row houses, but there was still a need for housing for the middle and lower classes. Hence the large lots between houses and streets were crisscrossed with alleys and courtyards and the remaining space was maximized with the cheapest homes that could be built.

Trinity houses definitely aren’t for everyone — the elderly and the disabled would find them especially difficult — but as a low cost, high volume option they could provide an affordable by design home, reducing rents and freeing up larger triple deckers for people with children.