The sev­en prin­ci­ples of the Allen­town Preser­va­tion League’s man­i­festo are not a list of inde­pen­dent com­mit­ments. They are a sys­tem — inter­con­nect­ed, mutu­al­ly rein­forc­ing, and col­lec­tive­ly con­sti­tut­ing a the­o­ry of what makes urban life good. The holis­tic liv­abil­i­ty sec­tion of the man­i­festo makes this argu­ment explic­it­ly, but the under­ly­ing research base for it is rich­er than the man­i­festo’s com­pressed prose can con­vey. What fol­lows attempts to unpack the sys­tems-lev­el case for a com­pre­hen­sive preser­va­tion practice.

The rela­tion­ship between build­ing preser­va­tion and walk­a­bil­i­ty is struc­tur­al: his­toric build­ing types cre­ate the con­di­tions for walk­a­ble urban life by pro­duc­ing con­tin­u­ous street­walls, mixed uses, and pedes­tri­an-scaled den­si­ty. The rela­tion­ship between walk­a­bil­i­ty and urban ecol­o­gy is equal­ly struc­tur­al: walk­a­ble neigh­bor­hoods have low­er per-capi­ta vehi­cle miles trav­eled, low­er green­house gas emis­sions from trans­porta­tion, low­er sur­face heat island effects (because imper­vi­ous sur­faces are dis­trib­uted across more fine-grained lots with more tree cov­er between them), and high­er rates of active trans­porta­tion that sup­port pop­u­la­tion health. The rela­tion­ship between urban ecol­o­gy and build­ing preser­va­tion clos­es the loop: a neigh­bor­hood with healthy tree canopy has low­er cool­ing loads on its build­ings, slow­er UV degra­da­tion of exte­ri­or mate­ri­als, and low­er mois­ture stress on mason­ry and wood assem­blies, extend­ing main­te­nance inter­vals and reduc­ing life­cy­cle costs.

These feed­back loops are not mere­ly the­o­ret­i­cal. The PlaceEco­nom­ics research has doc­u­ment­ed them empir­i­cal­ly in the con­sis­tent find­ing that neigh­bor­hoods with intact his­toric fab­ric — which tend also to be neigh­bor­hoods with more street trees, more walk­a­ble infra­struc­ture, and more mixed uses — out­per­form com­pa­ra­ble neigh­bor­hoods that have lost their fab­ric on vir­tu­al­ly every mea­sure of urban vital­i­ty, from busi­ness sur­vival rates to res­i­den­tial sta­bil­i­ty to tax rev­enue per acre of land. The cor­re­la­tion is not coin­ci­den­tal. It reflects the fact that the phys­i­cal con­di­tions that sup­port his­toric build­ing fab­ric — fine-grained lot struc­ture, mixed use, pedes­tri­an scale — are the same con­di­tions that sup­port walk­a­bil­i­ty, urban ecol­o­gy, and eco­nom­ic resilience. These are not sep­a­rate prop­er­ties of dif­fer­ent urban sys­tems. They are facets of the same inte­grat­ed system.

The lan­guage of the com­mons — resources shared by a com­mu­ni­ty, whose val­ue is pro­duced col­lec­tive­ly and whose degra­da­tion is a col­lec­tive loss — applies to urban neigh­bor­hoods with par­tic­u­lar force. A block of his­toric build­ings is a col­lec­tive good in the pre­cise eco­nom­ic sense: the char­ac­ter of the street, which pro­vides the con­text with­in which each indi­vid­ual build­ing oper­ates and from which each indi­vid­ual own­er ben­e­fits, is pro­duced joint­ly by all the build­ings on the block and can­not be ful­ly cap­tured by any indi­vid­ual own­er. The own­er of a well-main­tained his­toric build­ing ben­e­fits from the char­ac­ter of the street that the neigh­bor­ing build­ings help cre­ate; if neigh­bor­ing own­ers neglect their build­ings or demol­ish them for sur­face park­ing, the char­ac­ter — and with it the val­ue of all the remain­ing build­ings — is diminished.

This is the struc­ture of a com­mons prob­lem, and like all com­mons prob­lems, it is not solved by indi­vid­ual ratio­nal choice alone. Each indi­vid­ual build­ing own­er, mak­ing ratio­nal deci­sions from the stand­point of their indi­vid­ual inter­ests, may choose to defer main­te­nance (cap­tur­ing short-term cost sav­ings while shar­ing the long-term cost of neigh­bor­hood dete­ri­o­ra­tion with neigh­bors), to demol­ish (cap­tur­ing the devel­op­ment val­ue of a con­sol­i­dat­ed par­cel while destroy­ing the con­text on which the val­ue of neigh­bor­ing parcels depends), or to con­vert to car stor­age (cap­tur­ing the park­ing rev­enue while elim­i­nat­ing the street-lev­el activ­i­ty that makes the sur­round­ing blocks com­mer­cial­ly viable). The aggre­ga­tion of indi­vid­u­al­ly ratio­nal deci­sions pro­duces col­lec­tive­ly irra­tional out­comes — which is pre­cise­ly the def­i­n­i­tion of a com­mons failure.

The appro­pri­ate response to com­mons fail­ures is col­lec­tive gov­er­nance — insti­tu­tions, norms, and reg­u­la­tions that align indi­vid­ual incen­tives with col­lec­tive inter­ests. His­toric preser­va­tion reg­u­la­tion, at its best, is exact­ly this: a sys­tem of col­lec­tive gov­er­nance that pre­vents indi­vid­ual build­ing own­ers from mak­ing deci­sions whose costs fall pri­mar­i­ly on the col­lec­tive rather than on them­selves. The objec­tion that preser­va­tion reg­u­la­tion vio­lates prop­er­ty rights mis­un­der­stands the eco­nom­ics of the sit­u­a­tion: the prop­er­ty rights of his­toric build­ing own­ers are them­selves depen­dent on the col­lec­tive char­ac­ter of the neigh­bor­hood, which is a col­lec­tive­ly pro­duced good that can­not be sus­tained with­out col­lec­tive governance.

The con­cept of urban liv­abil­i­ty has attract­ed sub­stan­tial empir­i­cal research atten­tion in the past two decades, and the find­ings are remark­ably con­sis­tent in iden­ti­fy­ing the built envi­ron­ment con­di­tions that pro­duce it. The clas­sic work is Don­ald App­le­yard’s 1981 Liv­able Streets, which doc­u­ment­ed — through field research in San Fran­cis­co neigh­bor­hoods — that res­i­dents of streets with low vehi­cle traf­fic had, on aver­age, three times as many friends and twice as many acquain­tances in their neigh­bor­hood as res­i­dents of com­pa­ra­ble streets with high vehi­cle traf­fic. The mech­a­nism is straight­for­ward: walk­a­ble, traf­fic-calmed streets pro­duce the casu­al, repeat­ed encoun­ters between neigh­bors that gen­er­ate social trust and com­mu­ni­ty cohe­sion; high-speed arte­r­i­al streets pro­duce isolation.

More recent research has extend­ed and refined this find­ing. The Hap­py City research by Charles Mont­gomery (2013) syn­the­sized the urban design research on the rela­tion­ship between built envi­ron­ment and sub­jec­tive well­be­ing, find­ing con­sis­tent evi­dence that walk­a­ble, mixed-use, human-scaled envi­ron­ments pro­duce high­er lev­els of report­ed life sat­is­fac­tion than car-depen­dent envi­ron­ments, con­trol­ling for income and oth­er fac­tors. The mech­a­nism involves both the direct health ben­e­fits of active trans­porta­tion and the indi­rect social ben­e­fits of high­er rates of com­mu­ni­ty encounter — the inci­den­tal inter­ac­tions that gen­er­ate the social cap­i­tal on which com­mu­ni­ty resilience depends.

For Allen­town, the liv­abil­i­ty research base points con­sis­tent­ly toward the same set of built envi­ron­ment con­di­tions that the man­i­festo advo­cates pre­serv­ing: the walk­a­ble street grid, the mixed-use build­ing fab­ric, the human scale of the his­toric lot struc­ture, the tree canopy, and the neigh­bor­hood com­mer­cial activ­i­ty that pro­vides both dai­ly goods and social gath­er­ing points. These con­di­tions were not designed with liv­abil­i­ty research in mind; they were designed for an econ­o­my and a trans­porta­tion sys­tem that no longer exist in their orig­i­nal form. But they hap­pen to pro­duce the built envi­ron­ment con­di­tions that the research now iden­ti­fies as most con­ducive to human flour­ish­ing — which is, in its way, a remark­able vin­di­ca­tion of the intu­itions that drove their orig­i­nal design.

The impli­ca­tion of the sys­tems view is that preser­va­tion orga­ni­za­tions can­not be sole­ly or even pri­mar­i­ly in the busi­ness of pro­tect­ing indi­vid­ual build­ings, how­ev­er sig­nif­i­cant. They must be in the busi­ness of pro­tect­ing the con­di­tions — mate­r­i­al, reg­u­la­to­ry, social, eco­log­i­cal — under which build­ings, neigh­bor­hoods, and the peo­ple with­in them can flour­ish togeth­er. This means engag­ing with the full range of plan­ning and pol­i­cy deci­sions that shape those con­di­tions: zon­ing, infra­struc­ture invest­ment, trans­porta­tion pol­i­cy, tree man­age­ment, code enforce­ment, devel­op­ment incentives.

This com­pre­hen­sive prac­tice is what the man­i­festo’s eighth prin­ci­ple — holis­tic liv­abil­i­ty — describes, and it is not an expan­sion of preser­va­tion’s mis­sion beyond its prop­er scope. It is the recog­ni­tion that the prop­er scope of preser­va­tion has always been the built com­mons, and that the built com­mons is not mere­ly the sum of its indi­vid­ual his­toric struc­tures. It is the sys­tem with­in which those struc­tures oper­ate — the street, the block, the neigh­bor­hood, the city — whose coher­ence and qual­i­ty is pro­duced and sus­tained col­lec­tive­ly, and whose pro­tec­tion requires the same col­lec­tive atten­tion and gov­er­nance that the pro­tec­tion of indi­vid­ual build­ings requires, applied at a larg­er scale and across a broad­er range of insti­tu­tion­al actors.

The goal, as the man­i­festo states plain­ly, is not to freeze Allen­town in a par­tic­u­lar his­tor­i­cal moment or to pro­tect the built envi­ron­ment from change. It is to ensure that the changes made to that envi­ron­ment are informed by an hon­est account­ing of what is being trad­ed — what is being giv­en up as well as what is being gained — and that the bur­den of proof falls appro­pri­ate­ly on the inter­ven­tions that are irre­versible rather than on the inter­ven­tions that pre­serve options for the future. The green­est build­ing is the one that already exists. The most liv­able neigh­bor­hood is the one that has retained the con­di­tions that make it liv­able. The most equi­table city is the one that has main­tained the infra­struc­ture — build­ings, streets, trees, tran­sit, mixed uses — that allows its res­i­dents to flour­ish with­out a car, with­out a large trans­porta­tion bud­get, and with­out displacement.

We are not argu­ing for the past. We are argu­ing for what works — which hap­pens, more often than we usu­al­ly acknowl­edge, to be what was built before we con­vinced our­selves that the uni­ver­sal, the stan­dard­ized, and the new were nec­es­sar­i­ly improve­ments on the local, the par­tic­u­lar, and the already-built.

Mont­gomery, Charles. Hap­py City: Trans­form­ing Our Lives Through Urban Design. New York: Far­rar, Straus and Giroux, 2013.

Jacobs, Jane. The Death and Life of Great Amer­i­can Cities. New York: Ran­dom House, 1961.

App­le­yard, Don­ald. Liv­able Streets. Berke­ley: Uni­ver­si­ty of Cal­i­for­nia Press, 1981.

PlaceEco­nom­ics. Old­er, Small­er, Bet­ter (see above).

India-Aldana, S., et al. ‘Neigh­bor­hood walk­a­bil­i­ty and risk of obe­si­ty-relat­ed can­cers.’ Amer­i­can Jour­nal of Pre­ven­tive Med­i­cine (2023).

Coun­ty Health Rank­ings & Roadmaps. Mixed-Use Devel­op­ment Evi­dence Sum­ma­ry. Robert Wood John­son Foun­da­tion, cur­rent edition.