Energy-efficient homes as a rodent-control strategy in cities

A systems view of housing, public health, and integrated pest management

City rat problems are often framed as sanitation failures or as a need for more aggressive control. Those factors matter, but they are not the whole story.

A growing body of work is pointing at something less obvious and harder to fix: the home itself. The gaps that leak heat, moisture, and air also leak food access, nesting space, and safe harborage for rodents. In other words, the “building shell” is part of the ecology.

 

A 2024 study by Gadsen, et al., modeled this idea directly by asking a practical question: What happens to urban rat populations when more homes are sealed to high energy-efficiency standards, and when retrofits roll out over time?

This pillar article summarizes what that study did, what it found, what it did not claim, and how the EUREKA team can use the same logic to shape future field work, logging standards, and cross-sector pilots.

Why housing belongs in rodent control

Rodents thrive in cities because the built environment is an engine for survival: reliable food, reliable shelter, fewer predators in many settings, and constant opportunities to move between private and public spaces. Municipal programs can spend heavily on mitigation, yet infestations remain common and distressing.

Most rodent policy attention goes to outdoor drivers: trash, vacant lots, and sanitation codes. Those drivers are real, but rodents also exploit what the paper calls the “indoor table,” and indoor sightings are widespread.

The paper points to evidence that housing disrepair correlates strongly with indoor pest problems. Examples include:

structurally compromised homes with gaps in foundations, doors, walls, and facades;

homes with little insulation that provide space for nesting and breeding;

survey findings associating certain visible disrepair (like broken windows or sagging roofs) with higher reported rodent sightings.

This matters because structural interventions behave differently than typical control tactics:

They do not depend on changing resident behavior to the same degree.

They can reduce reliance on toxic tools.

They potentially persist for years, instead of resetting every service cycle.

The challenge is that the field rarely gets long, consistent datasets that link “building condition changes” to “rodent outcomes” over time. The study leans into that gap by using modeling to explore what the relationship could look like at neighborhood scale.

What “energy efficiency” means in this study

The term “energy efficiency” is sometimes misunderstood as appliance upgrades or “green” add-ons.

In this study, efficiency is used as a proxy for building envelope integrity. Standard energy-efficiency scoring systems account for insulation values (windows, doors, walls) and often reflect age, upkeep, and local climate.

The retrofits modeled here are explicitly described as home-envelope repairs, not cosmetic upgrades or appliance swaps.

That framing is important for rodent control because sealing, insulation, and envelope quality are directly tied to:

entry-point reduction,

reduced interior nesting space,

reduced access to indoor food resources, and

altered movement and risk exposure (including predation) when rodents are pushed out of structures.

What the study modeled

The study built a spatially explicit agent-based model (ABM) that includes:

urban brown rats (Rattus norvegicus), and

one natural predator used as a realistic mesocarnivore: the red fox (Vulpes vulpes).

The model was parameterized using literature plus the research team’s trapping and field observations. It was implemented in NetLogo and run across simulated time horizons of 1, 5, and 10 years.

Why include predators?

The model assumes that predator–prey dynamics still matter in cities under the right conditions, even if predators are not abundant everywhere. The paper notes that red foxes are one of the few mammalian predators of brown rats, while other common urban carnivores (such as domestic cats) may not reliably suppress rat populations.

Why Philadelphia?

The study uses three Philadelphia neighborhoods as distinct “cityscape types,” chosen to reflect variation in:

greenspace and park access,

commercial activity and food resources,

housing stock age and condition.

The neighborhoods modeled were:

Chestnut Hill (largest, most greenspace),

Olney (highest density),

Cobbs Creek (older housing stock; high share built before 1939).

What did “efficient vs inefficient homes” mean in the model?

Efficiency changes patch access. In simplified terms:

Inefficient homes were easier for rodents to enter and use.

Efficient homes were treated as sealed, with very low wildlife access (the model describes efficient housing as having ~5% access to wildlife).

The model also assumed that retrofits for “deep efficiency” were done using state-of-the-art pest exclusion methods, which is a strong assumption and is discussed later under limitations.

What scenarios were tested?

The study varied three major levers:

Initial housing conditions
Neighborhoods started with different proportions of homes that were already energy efficient (e.g., 25%, 50%, 75%, up to fully efficient).

Active retrofitting
Inefficient homes were converted to efficient homes over time (one randomly selected inefficient home retrofitted every ~30 “ticks/days” in the model).

Duration of the retrofit scheme
Simulations were run across different durations (up to 10 years), allowing the model to explore long-run effects.

Key findings

The headline result is simple: housing conditions and retrofitting were associated with lower modeled rat populations, but effects varied by neighborhood type and program design.

1) Starting conditions mattered

Across neighborhoods, higher proportions of efficient housing at the start corresponded to proportional reductions in rat populations over time.

This is a “systems” message. It suggests that cities with higher baseline building integrity are playing on easier difficulty settings. It also implies that targeted improvements to baseline housing conditions could be a form of upstream prevention.

2) Active retrofitting generally reduced rats, but not uniformly

The study found that periodic retrofitting showed statistically significant reductions in rat populations in some modeled neighborhoods (e.g., Cobbs Creek and Chestnut Hill), but not in Olney under the same model structure.

That does not mean retrofitting “doesn’t work” in dense areas. It suggests that in some landscapes, the effect size of a slow retrofit cadence may be smaller relative to other drivers, such as commercial food resources, density, and resource regeneration.

3) Where retrofits worked best

The model indicates retrofitting was most effective for rat reduction in neighborhoods with:

extensive park access, and

low commercial activity.

One interpretation consistent with the model’s structure is that greenspace and predator access can make housing exclusion more potent, because rodents pushed out of buildings face higher predation pressure and fewer safe alternatives.

4) Program design matters: big pushes may outperform slow drip

The paper reports that “single large efficiency initiatives” (large-scale retrofitting schemes) showed greater potential for rat reduction than gradual, single-home retrofits, even compared against low-to-moderate initial efficiency scenarios.

For program design, that is a concrete insight:

A slow, scattered retrofit rollout can be diluted by ongoing reproduction, movement, and resource availability.

A concentrated retrofit push may create a stronger shift in neighborhood-wide carrying capacity.

The model does not eliminate rats to zero, but it supports the idea that “structural step-changes” can matter more than incremental tweaks.

What the cost comparison suggests (and what it does not)

The paper includes a straightforward cost comparison intended to answer a practical question: Are large-scale retrofits “financially in the same universe” as what cities already spend on health outcomes linked to poor housing and pests?

Key inputs used include:

an example average retrofit cost per home in the Philadelphia metro area based on a set of common exterior projects (garage door, windows, siding, roof, entry door replacement),

tiered pricing to reflect varied home conditions, and

an estimate of per-household healthcare costs projected across a 10-year period.

The paper concludes that large-scale retrofit costs can be comparable to 10-year public health spending, and that if health costs are meaningfully reduced, retrofitting has the potential to offset near-term costs.

This is not a full economic evaluation. It is a signal that the conversation is not purely aspirational. Structural prevention may be expensive, but it is competing with expensive, recurring costs already embedded in the system.

For EUREKA, the message is operational: if structural investments are going to be justified, they will need:

credible measurements of rodent outcomes,

credible measurements of housing condition change,

and shared metrics across sectors.

That is a data problem the team can help solve.

What this means for integrated pest management in cities

The study’s core contribution is to expand the scope of IPM thinking. It treats housing efficiency retrofits as part of a broader urban health system, not as a niche “green building” topic.

A few practical implications follow.

Structural prevention changes the time horizon

Typical control efforts are judged on short windows: days, weeks, maybe a quarter. Structural changes operate on years.

That suggests a different evaluation approach:

baseline conditions measured consistently,

outcomes tracked over seasons,

and metrics designed to detect sustained reductions rather than short-term knockdowns.

Exclusion quality matters

The model assumes deep retrofits are done using rodent-proof materials and methods. The discussion section flags that real-world retrofits often do not use materials tested for wildlife exclusion, and not all inefficiencies are fixed simultaneously.

So “energy retrofit” does not automatically equal “rodent-proofing.” Programs need standards, procurement specs, and inspection criteria that are rodent-aware.

Sanitation still matters

The model does not include every driver (sanitation is explicitly mentioned as one of the factors not fully represented). That likely contributes to the model’s inability to bring rodent populations to zero.

The takeaway is not “retrofit instead of sanitation.” It is “retrofit plus sanitation plus smarter targeting.”

How the EUREKA team can use this study

This paper is a modeling study. Its job is to create testable hypotheses and program design ideas when field data is hard to gather.

EUREKA’s job is to make field data easier to gather.

Here are a few direct ways the team can operationalize the study’s logic.

1) Add “building envelope” signals to rodent logging

Rodent logs often capture devices, captures, and sightings. They should also capture the structural signals that predict rebound:

door sweeps missing,

foundation gaps visible,

utility penetrations unsealed,

ventilation openings,

insulation voids and crawlspace conditions (where observable and safe).

This does not require turning field work into a housing inspection. It requires a small, structured checklist that produces consistent data.

2) Build pilots that mirror the model’s contrasts

The model suggests effects vary by neighborhood configuration (greenspace vs commercial activity).

A practical pilot design could test:

one neighborhood type with higher greenspace access,

one dense commercial corridor,

and one mixed area.

Then compare outcomes across:

focused retrofit “push” blocks,

versus slower incremental retrofits.

3) Measure outcomes that matter to multiple sectors

Housing teams care about energy, comfort, and durability. Public health teams care about risk, stress, and injury exposure. Pest teams care about signs, captures, and service pressure.

A shared measurement set could include:

rodent sign indices and service frequency,

resident-reported sightings (with clear survey design),

building envelope condition scoring,

and retrofit intervention metadata (what was done, when, and to what standard).

4) Use data to justify integration, not just messaging

The paper notes there is a lack of discussion between urban wildlife management, public health, and the energy sector.

EUREKA can be the practical connector by producing datasets and case studies that show:

where structural improvements changed rodent trajectories,

and where they did not, and why.

That evidence is what turns cross-sector collaboration from goodwill into repeatable policy.

Limitations and what to test next

The study is careful about limitations. Several are directly relevant for interpreting results and designing pilots.

Key ones:

The model assumes deep retrofits with high-quality exclusion materials, which may not reflect typical retrofit practice.

The model is based on one U.S. city; results should be applied cautiously elsewhere.

Renters may be excluded from retrofit benefits depending on how programs are designed, which affects equity and implementation feasibility.

Predator dynamics are simplified; real urban predator diets and behaviors can change with anthropogenic food access.

For EUREKA, these limitations are a roadmap:

build pilots that record retrofit quality, not just “retrofit happened,”

track who benefits (owners vs renters),

and record sanitation/food access signals alongside housing changes.

Closing

This 2024 study makes a strong case that housing integrity and energy-efficiency retrofits belong inside the urban rodent toolbox. Not as a replacement for IPM, but as a structural layer that can shift carrying capacity over long time horizons.

It also makes a strong case that city rat control is not just a pest problem. It is a coupled housing–public health–infrastructure problem.

That is exactly the kind of problem EUREKA was built to handle.

 

Disclaimer:
This project was funded by the Department of Pesticide Regulation. The contents may not necessarily reflect the official views or policies of the State of California.