Beyond the LMI Map: Using Slum and Blight Studies to Maximize CDBG Coverage

Community Development Block Grant (CDBG) funding is built around one core idea: directing federal dollars to the people and places that need them most. 

For most jurisdictions, HUD's Low-to-Moderate Income (LMI) objective covers the bulk of that work — and in some communities, it covers nearly everything. But what happens when a jurisdiction has a clearly deteriorating neighborhood that doesn't happen to be majority LMI? What about a historic commercial corridor with crumbling infrastructure, or a mixed-income block dragged down by abandoned properties?

In 30 jurisdictions in the US, over 70% of block groups qualify as LMI under HUD's Low-to-Moderate Income Summary Data (LMISD). But even in these jurisdictions, some areas fall outside that threshold. For those neighborhoods, and for the hundreds of other jurisdictions where LMI data isn't enough to cover every deteriorating block, the Slum and Blight Study (also called a Deterioration Study) is one tool to help jurisdictions target the funds where they’re needed the most, even if the area doesn’t qualify under the standard rule. 

That's where the Slum and Blight National Objective comes in — and the Slum and Blight Study is the legal documentation that unlocks it.

Think of it as a "legal shield": a formally documented case that justifies spending federal CDBG dollars in an area based on physical conditions rather than resident income alone.

This guide explains what the study is, when you need one, and how it helps grantees maximize CDBG coverage across their entire jurisdiction.

What Is a Slum and Blight Study?

Under 24 CFR 570.208(b), HUD defines an area as qualifying under the Slum and Blight National Objective when it meets three conditions:

1. It meets a state or local legal definition of a slum, blighted, deteriorated, or deteriorating area.

2. It meets at least one physical threshold — either 25% of properties in the area exhibit deterioration, abandonment, high vacancy, significant property value decline, or environmental contamination, or public improvements throughout the area are in a general state of deterioration.

3. The assisted activity directly addresses one or more of the conditions that contributed to the area's deterioration.

The Slum and Blight Study — sometimes called a Deterioration Study — is the formal documentation a grantee prepares to prove all three conditions are met. It establishes the area boundary, records the conditions found, and creates the compliance record HUD requires grantees to maintain for the life of the designation.

When Do You Actually Need One?

Not every CDBG project requires a blight study. You only need one when you're using the Slum/Blight National Objective instead of the LMI benefit objective.

Here's a practical breakdown:

You Do NOT Need a Study If...

Your project is located in a neighborhood where 51% or more of residents are LMI. In that case, you simply use Census data or an income survey to establish the LMI National Objective. No additional study required.

And if your service area spans multiple block groups that don't individually hit 51%, it's worth running the composite calculation first. By aggregating raw LMI population figures across all block groups in your service area — rather than averaging percentages — some areas that appear to fall short will actually qualify. Only after exhausting your LMI options should you turn to the Slum and Blight National Objective.

You DO Need a Full Area Study If...

You want to run a program — code enforcement, sidewalk repair, infrastructure upgrades — across an entire neighborhood that isn't 51% LMI. This is called the Area Basis, and it requires a complete neighborhood-level Slum and Blight Study.

You Need Only a "Spot" File If...

You're addressing a single blighted property (demolishing one abandoned house, for example) in an otherwise stable neighborhood. This is called the Spot Basis, and it requires much less documentation — just property-specific evidence like photos, citations, or a structural engineer's report.

What Does a Full Area Study Include?

To qualify an entire neighborhood under the Slum and Blight National Objective, your study must prove two things:

1. The area meets the definition of a slum or blighted area under state or local law.

Every state has its own statutory definition of blight. Your study must cite and satisfy the applicable state or local standard. This is step one, and skipping it is a common mistake.

2. The area meets at least one of HUD's physical deterioration thresholds:

• The 25% Rule: At least 25% of properties in the defined area exhibit physical deterioration, abandonment, chronic vacancy, or environmental contamination.

• The Public Improvement Rule: Public infrastructure throughout the area — streets, lighting, sewers — is in a general state of deterioration.

What the Study Document Should Contain

A well-prepared Slum and Blight Study typically includes:

• Defined Boundaries: A precise map of the target area, with clear justification for why those boundaries were chosen.

• Physical Inspection Records: A lot-by-lot (parcel-by-parcel) survey of every property within the boundary. Every property should be assessed individually.

• Photographic Evidence: High-quality photos documenting deterioration — peeling paint, crumbling foundations, boarded windows, buckled pavement, and similar conditions.

• Data Analysis: A spreadsheet or database that tallies inspection results, identifies which properties failed and why, and calculates the overall deterioration percentage.

The more methodical and thorough this documentation, the stronger your position during a HUD monitoring review.

How Long Does the Designation Last?

Once an area is formally designated as Slum/Blight, that designation is valid for 10 years under HUD rules.

This is important: jurisdictions can fund multiple CDBG projects in the same designated area throughout the decade without repeating the full study process each time. That's a significant return on the upfront investment of conducting the study.

After 10 years, the jurisdiction must redetermine whether the area still qualifies. If neighborhood conditions have improved substantially (which is the goal!), and the area no longer meets the 25% deterioration threshold, the Slum/Blight National Objective can no longer be used there.

The Spot Basis: A Simpler Path for Single Properties

If your project focuses on one specific blighted property rather than an entire neighborhood, the Spot Basis is a more streamlined route.

What you need: Documentation of the specific blight conditions affecting that single property. This might include:

• Photographs of structural deficiencies

• A structural engineer's assessment

• Health department citations

• Building code violation records

What you can do with it: The Spot Basis is more restricted than the Area Basis. It applies only to:

• Acquisition

• Clearance (demolition)

• Relocation

• Historic preservation

• Rehabilitation — but only to the extent necessary to eliminate specific public health and safety threats (a dangerous gas line, a collapsing roof section, etc.)

The Spot Basis is not a shortcut for general neighborhood revitalization. It's a targeted tool for targeted problems.

Quick Reference: Which Path Is Right for Your Project?

Why This Matters for Your CDBG Program

Jurisdictions often focus exclusively on LMI-benefit projects because that's the most familiar path. But the Slum and Blight National Objective exists precisely because physical decay is a community-wide problem that harms property values, public health, economic development, and the quality of life for residents at every income level.

A well-executed Slum and Blight Study lets your jurisdiction:

• Expand your eligible project geography beyond LMI census tracts

• Fund infrastructure and code enforcement in mixed-income areas that are visibly deteriorating

• Justify CDBG investment in commercial corridors, historic districts, and transitional neighborhoods

• Build a defensible HUD compliance record that holds up during monitoring

The study itself is an investment of time and professional resources. But the payoff is a 10-year designation that unlocks CDBG eligibility across an entire neighborhood. This can be a valuable return on investment.

Getting Started

If your jurisdiction has neighborhoods that are deteriorating but don't qualify under the standard LMI objective, it's worth evaluating whether a Slum and Blight Study makes sense. Start by:

1. Reviewing your state's statutory definition of blight — your jurisdiction attorney or state CDBG program office can help locate the applicable standard.

2. Identifying candidate areas where physical conditions are visibly poor but LMI percentages fall below 51%.

3. Consulting your HUD Field Office or state CDBG administrator before investing in the study, to confirm your approach.

With the right documentation in place, the Slum and Blight National Objective can be one of the most flexible and powerful tools in your CDBG toolkit.

Conducting a Slum and Blight Study doesn't have to mean months of manual data collection. See how PASS AI® simplifies the process — from property inspection to HUD-compliant documentation — so your city can move faster on the projects that matter.