In older industrial cities—commonly known as legacy cities—most housing affordability is embedded in buildings that already exist. These buildings were constructed decades before the emergence of modern housing finance tools, energy codes, and development subsidies. Continued affordability in these cities depends less on what gets built next than on whether this older stock survives.
Durability, in other words, is housing policy.
A Gap in Housing Policy
I’ve seen firsthand how housing policy underestimates the importance of durability. For years, while managing historic tax credit investments and other tax credit financing for a national investor, I evaluated rehabilitation and affordable housing projects across multiple markets. Those programs move significant capital, but they reach only a small share of the housing stock. Most older buildings never enter those pipelines. Seeing that from the inside made clear how much of the question of affordability sits outside the tools that housers talk about most.
Later, while working in Philadelphia on strategies to address vacant properties and neighborhood stabilization, I came to understand that housing doesn’t fail all at once. Vacancy has a lifecycle, and the stage where intervention is still possible and affordable receives the least attention. Deferred maintenance accumulates quietly over decades before a building becomes distressed enough to trigger any formal response. By the time preservation tools or development finance appear, the window for low-cost stabilization has often closed.
More recently, while leading the civic technology initiative Clean & Green Philly, my work focused on making complex housing and land-use data legible enough for organizations and residents to act on it. That experience clarified something for me: what holds back efforts to extend housing durability usually isn’t a lack of knowledge; it’s that knowledge exists in one institutional lane while decisions are made in another.
Viewed through these lenses, the gap becomes hard to ignore. The technical understanding of how older buildings function, how they fail, and in what sequence, exists inside preservation practice, building science research, and the experience of seasoned tradespeople. But this hasn’t been translated into the systems where repair decisions are made.
A Study from Philadelphia
Philadelphia illustrates the challenge. Sixty-seven percent of the city’s residential buildings were built before 1950, according to a recent study commissioned by the Preservation Alliance for Greater Philadelphia and authored by PlaceEconomics. Median gross rents in these buildings are 9 percent lower than in newer construction, and monthly owner costs are 11 percent lower.
Rehabilitation through historic tax credit projects has leveraged billions of dollars in investment and produced thousands of housing units. But only a small fraction of city buildings will gain a historic designation or benefit from tax credit financing. Most are simply part of an aging housing system that predates modern housing policy.
The report’s most important insight is therefore not about preservation incentives; it is about where affordability already exists—and who is most exposed when it disappears.
Black and Latine Philadelphians are more likely to live in older housing. In neighborhoods with more pre-1950 buildings, rates of Black homeownership are also higher. This means that the structural vulnerability of aging housing is not a generic affordability issue. When older buildings deteriorate because maintenance decisions go wrong or repair knowledge is absent, the households most likely to lose affordable housing and accumulated equity are disproportionately households of color.
Durability, Equity, and Affordability
Durability is both a housing supply issue and an equity issue. Most older housing will never be designated as historic property, never receive tax credit equity, and never undergo formal historic review. It is not “historic” in a regulatory sense; it is simply old. And the survival of this housing depends less on formal incentives than on everyday repair decisions.
Housing policy discussions tend to focus on production—on how many units can be financed and built. Preservation debates often focus on designation or tax credit rehabilitation. Both matter. But neither addresses the larger question: How does existing housing perform over time?
The technical knowledge required to maintain older buildings is not scarce. Preservation professionals understand how traditional masonry walls manage moisture and why incompatible materials can trap vapor. Building science research documents the risks of air sealing without ventilation and the consequences of mis-sequenced retrofits. Federal research has long warned that envelope stabilization must precede interior efficiency upgrades in older buildings.
What is scarce, across all of this, is not expertise but integration.
Preservation practices developed within regulatory frameworks, while energy retrofit programs grew within utility incentive structures. Housing repair programs took shape through municipal departments and nonprofit intermediaries. Each field developed its own body of technical knowledge, and those bodies of knowledge rarely converge around the common housing types that make up most legacy cities.
Emerging Policy Options
Some programs have started to bridge this gap. In Philadelphia, the Built to Last initiative integrates whole-home assessment, structural repair, health and safety stabilization, and energy upgrades into a single intervention. Roof and envelope integrity are addressed before efficiency upgrades. Ventilation is considered when air sealing increases building tightness. Moisture mitigation is prioritized before cosmetic improvements. This sequencing makes a crucial difference: Durability risks can be managed when building science and housing repair programs operate together.
But programs like Built to Last are limited by budgets and capacity. Most aging housing is maintained outside structured frameworks, through decisions made by homeowners, small landlords, contractors, and neighborhood organizations responding to visible problems with limited guidance. These decisions determine whether buildings are stabilized or building decay accelerates.
Housing in legacy cities was often built using specific, repeatedly employed building types. Philadelphia’s masonry row houses and streetcar-era twins are one example; Boston’s triple-deckers, Cincinnati’s brick row houses, and Midwestern worker cottages are others. These housing types were constructed with consistent assemblies and predictable material behavior. Because of this, their failure patterns can also be predicted, which means repair guidance can be organized around building type rather than evaluated on a building-by-building basis.
Philadelphia has done some of this work. The city’s Rowhouse Manual, produced in partnership with the National Trust for Historic Preservation and the city, classifies row house stock into distinct archetypes by construction era and documents their structural characteristics and common maintenance problems. In a typical masonry row house, flat roofs tend to fail before structural walls show distress, porch assemblies fatigue under predictable load cycles, and masonry responds to moisture in ways that experienced tradespeople recognize immediately. That knowledge exists. What has yet to be developed is operational guidance that moves across the housing programs, lenders, retrofit administrators, and contractors to shape everyday repair decisions.
In the United Kingdom, the National Retrofit Hub has published archetype-specific retrofit pattern books for common housing types, including guides for flat-fronted Victorian terraced houses aimed at homeowners, landlords, and contractors. The guides explain how each housing type was constructed, where it typically fails, and how repairs should be sequenced. Westminster City Council’s Retrofit Taskforce and other London Councils boroughs have adopted this methodology. The framework is oriented toward energy retrofits, but the logic holds for structural durability.
The masonry row houses and streetcar-era twins of American legacy cities are no less legible as building types, and their failure patterns are no less predictable. What is missing is any actor currently funded or positioned to connect what is already known to the places where repair decisions are made.
In practice, responsibility for housing durability is distributed across a fragmented ecosystem. Community development corporations manage rehabilitation projects and small development pipelines. Municipal and nonprofit repair programs finance basic systems stabilization when roofs fail or structural problems emerge. Energy retrofit administrators oversee weatherization and efficiency upgrades. Lenders and small-scale developers make underwriting decisions about older buildings. Contractors determine the sequence of repairs on the ground. Each of these actors encounters the same housing stock from a different vantage point, often with only partial information about how these buildings function and where their vulnerabilities lie.
Different actors encounter durability risks at different points in the housing system. Community development corporations and neighborhood housing organizations often manage small rehabilitation programs or homeowner repair grants. Lenders evaluate collateral risk when financing the acquisition or rehabilitation of older buildings. Energy retrofit administrators oversee upgrades that can inadvertently accelerate deterioration if building assemblies are misunderstood. Small-scale developers and contractors make sequencing decisions during renovations that determine whether moisture problems are solved or compounded. Archetype-based guidance would allow each of these actors to recognize structural vulnerabilities earlier and to align interventions before deterioration accelerates.
Centering Building Archetype in Housing Preservation Policy
When the technical understanding of older building types is not shared across these layers, repair decisions become fragmented. Historic preservation, institutionally, focuses on designation, review, and incentive tools. Housing preservation—the work of keeping existing housing structurally viable and affordable—is a broader concern. Most older housing will never be classified as historic; yet, it still requires preservation intelligence to survive.
Archetype-based guidance offers one pathway. Within public programs, this guidance could standardize intake assessments, align retrofit protocols with building behavior, and ensure that structural stabilization precedes efficiency upgrades. For lenders and small-scale developers, it could clarify durability risks that affect renovation financing. For contractors and retrofit administrators, it could guide repair sequencing that prevents moisture and structural failures. And for homeowners and small landlords managing one or two units, it could provide a practical framework for deciding which repairs are urgent and which can wait.
The problem is not a lack of knowledge about how older buildings work, but rather the absence of systems to translate that knowledge into everyday housing decisions.
Legacy cities depend on aging housing stock to sustain lower-cost housing. If that stock deteriorates unnecessarily because technical knowledge remains siloed, the consequences are borne by households, neighborhoods, and housing systems alike. Repair financing cannot compensate for mis-sequenced interventions. Tax credit rehabilitation cannot replace preventive maintenance for hundreds of thousands of homes.
Housing durability sits at the center of affordability policy, not at its periphery. Across many legacy cities, a significant stock of affordable housing already exists. The question is whether housing systems will steward it appropriately.
Author’s note: Details of the Built to Last program were confirmed through correspondence with Philadelphia Energy Authority staff in February 2026.
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While I understand the importance of preservation of older housing stock, as an accessibility advocate, I’m keenly aware of how inaccessible many older buildings are for people with disabilities, particularly mobility disabilities. I’d rather see public resources spent on buildings and units that can be accessible. If the older building can be made accessible, great. If not, we should think about if homes that exclude a significant portion of the population is worthy of preservation.