Valuation glossary
External obsolescence: when an outside influence reduces property value
A house can be well maintained and still lose value because of what happens around it. The key is to identify the outside influence, then establish how buyers or tenants respond to it.
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The short answer
External obsolescence is a loss in property value caused by negative influences outside the property. It may be temporary or permanent. Economic obsolescence is often used as another name for the same concept. Examples can include a harmful change in nearby land use or weaker local demand, but the influence must actually reduce value. An airport, highway or shopping center does not carry an automatic percentage deduction.
Reviewed for October 2026. PSI places economic principles and valuation approaches within the national Valuation category, which has 8 of the 100 scored broker questions. That is not a quota for external obsolescence. These original examples teach classification and stated calculation assumptions, not an appraisal of a real property or a new Illinois disclosure rule.
Four questions that keep the concept clear
- Where does the cause originate? Outside the property points toward external obsolescence. Wear in a component is physical deterioration; an inadequate layout or design is functional obsolescence. An owner being unable to afford a repair does not change the cause of the loss.
- What evidence shows a value effect? Look for relevant sales, rents, vacancy, operating results or other market evidence. A nearby use can help some properties and hurt others. Describe the influence and the market response rather than assuming a neighborhood label proves depreciation.
- How long is the effect expected to last? A temporary road closure and a lasting loss of demand require different assumptions. A loss the individual owner cannot economically cure can still end when outside conditions change.
- Where has the loss already been counted? Check the site estimate, improvement depreciation, comparable-sale adjustments and income assumptions. An approach should reflect the relevant influence without deducting the same effect twice.
| Stated cause | Likely classification | Question to ask |
|---|---|---|
| Worn roof covering | Physical deterioration | What component has deteriorated? |
| Poor internal layout | Functional obsolescence | What design or utility problem exists? |
| Outside noise that demonstrably reduces demand | External obsolescence | What market evidence establishes the loss? |
| Owner lacks funds to repair a roof | Still physical deterioration | Has the cause changed, or only the owner's finances? |
| Temporary access disruption | Potential temporary external obsolescence | What duration and value effect are supported? |
| Economic obsolescence | Often another name for external obsolescence | How is the source using the term? |
The distinctions that matter
| Distinction | How it works | What to notice |
|---|---|---|
| External and economic obsolescence | IAAO uses economic obsolescence as a synonym for external obsolescence. Local surroundings and wider economic conditions are useful examples, not universally separate categories. | Do not reject economic obsolescence solely because the cause is nearby. |
| External and functional obsolescence | Outside influences differ from a design or utility deficiency in the improvement. | A bad floor plan remains functional even if buyers dislike it. |
| Incurable and permanent | Economic curability concerns whether a correction is justified. Duration concerns how long the loss lasts. | The owner may be unable to cure a temporary outside problem. |
| External cause and external damage | A storm comes from outside, but its damage to a roof is physical deterioration. | Classify the actual loss described, not the direction from which an event arrived. |
| Land and improvement effects | External influences can affect land and improvements. The relevant allocation depends on the valuation evidence. | Do not treat external loss as exclusively building depreciation or deduct a site loss twice. |
| Market evidence and assumptions | A simplified exam problem supplies facts that a real appraisal would have to establish. | A dollar difference is not automatically proof of one outside cause. |
Work through the facts
Noise with an established market response
Otherwise comparable homes exposed to persistent outside noise sell for less. Assume the evidence supports that noise, rather than another difference, as the cause.
- The cause is outside the subject property.
- The stated evidence establishes a negative market effect.
Answer: Classify the supported loss as external obsolescence. Do not invent a standard airport or traffic deduction.
An owner cannot afford the roof repair
A roof is worn out. Its owner cannot afford replacement.
- The loss arises from wear in a building component.
- The owner's limited funds do not move the cause outside the property.
Answer: This is physical deterioration. Curability requires its own economic analysis.
The road reopens
A temporary outside access disruption reduces net operating income by $20,000 at each year-end for two years. Assume no continuing loss after year two and a 10% annual discount rate.
- Discount the first loss: $20,000 / 1.10.
- Discount the second loss: $20,000 / 1.10². Carry full precision before adding and rounding.
Answer: The combined present value is $34,710.74, or $34,711 to the nearest dollar. To the nearest hundred dollars, it is $34,700. Do not capitalize a two-year loss as if it continued indefinitely, or mix different rounding instructions.
An ongoing income penalty
Assume a supported ongoing annual net operating income loss of $30,000 and an appropriate, consistently applied 10% capitalization rate. The exercise asks for a simplified direct-capitalization indication.
- Use net operating income loss, not an unexplained gross-rent figure.
- $30,000 / 0.10 = $300,000.
Answer: The stipulated indication is $300,000. The rate, duration and income assumptions must be justified in an actual assignment.
Do not deduct the site loss again
A cost problem gives current affected site value of $90,000, improvement cost new of $300,000, physical depreciation of $45,000, functional depreciation of $15,000 and separately supported improvement external loss of $20,000. The site value already reflects its $10,000 outside-influence discount.
- Calculate $90,000 + $300,000 - $45,000 - $15,000 - $20,000.
- Do not also deduct the site's already reflected $10,000 from the improvements.
Answer: The indicated value is $310,000. This is a stated allocation, not a universal rule assigning external loss between land and buildings.
The shopping center is not the answer by itself
Two houses back onto a shopping center. The available evidence shows no adverse value effect for one and a supported noise-related loss for the other.
- The neighboring use alone is not proof of equal harm.
- Market response and the subject's actual exposure matter.
Answer: The stated market evidence supports different conclusions. In its own lending guidance, Fannie Mae uses shopping-center adjacency as an example for which lenders should expect an external-depreciation amount when reviewing a completed cost approach. That example does not establish a universal percentage or replace property-specific market evidence.
Two problems can coexist
A home has an awkward pass-through bedroom and a separate, supported value loss from outside industrial noise.
- The layout is a functional issue.
- The noise influence is external.
Answer: Identify both causes, then check that the valuation does not count the same market effect twice.
A controlled sales comparison
Assume reliable analysis controls other relevant differences. An unaffected comparable indicates $400,000 and the otherwise equivalent affected property indicates $370,000.
- The supported difference is $30,000.
- $30,000 / $400,000 = 7.5%.
Answer: The stipulated loss is 7.5% of the unaffected indication. Two raw sale prices without controls would not by themselves establish that conclusion.
Mistakes to avoid
- Calling every loss beyond the owner's budget external. Identify its cause first.
- Treating economic obsolescence as necessarily different from external obsolescence.. Identify the supported cause, assumptions and market effect before choosing a deduction.
- Equating generally incurable with permanent. Outside conditions can change.
- Using a gross-rent reduction as an NOI reduction without accounting for expenses or other effects.. Identify the supported cause, assumptions and market effect before choosing a deduction.
- Rounding intermediate present values and unintentionally changing the final cents.. Identify the supported cause, assumptions and market effect before choosing a deduction.
- Assigning a standard deduction to an airport, school, road or shopping center without market support.. Identify the supported cause, assumptions and market effect before choosing a deduction.
- Using protected characteristics or unsupported neighborhood stereotypes as valuation factors.. Identify the supported cause, assumptions and market effect before choosing a deduction.
- Subtracting an external effect already reflected in the current site value or another adjustment.. Identify the supported cause, assumptions and market effect before choosing a deduction.
Check your understanding
These are original teaching questions, not recalled or predicted PSI questions. Answer first, then explain why the other choices fail.
1. Supported value loss results from an outside industrial operation, while the building is sound. Which label best fits?
- A repair reserve
- External obsolescence
- Physical deterioration
- Functional obsolescence
Show answer and explanation
Answer: B. External obsolescence
The stipulated negative influence originates outside the property. Sound physical condition does not rule out external loss.
2. A worn roof cannot be repaired because the owner lacks money. What is the cause-based classification?
- Economic obsolescence in every case
- Functional because repairs cost money
- Physical deterioration
- External because the owner cannot pay
Show answer and explanation
Answer: C. Physical deterioration
The roof has deteriorated physically. The owner's finances do not change the cause.
3. How does the IAAO glossary relate economic obsolescence to external obsolescence?
- Economic loss excludes local influences
- They can never overlap
- It directs the reader to external obsolescence
- Economic loss must be national in scope
Show answer and explanation
Answer: C. It directs the reader to external obsolescence
IAAO treats economic obsolescence as another name for external obsolescence. Do not impose a universal local-versus-regional split.
4. A temporary road closure causes a supported value loss the individual owner cannot economically remove. Which statement is sound?
- It must be physical deterioration
- Temporary external loss can still be beyond the owner's economic ability to cure
- Incurable always means permanent
- It cannot be external because it ends
Show answer and explanation
Answer: B. Temporary external loss can still be beyond the owner's economic ability to cure
Duration and curability answer different questions. The outside condition can end without an owner-funded cure.
5. Under the stated simplified ongoing model, annual NOI loss is $30,000 and the appropriate capitalization rate is 10%. What is the indicated loss?
- $3,000
- $300,000
- $330,000
- $30,000
Show answer and explanation
Answer: B. $300,000
Divide $30,000 by 0.10. This uses the stipulated NOI and ongoing direct-capitalization assumptions, not a universal deduction.
6. A $20,000 year-end NOI loss lasts exactly two years. Discount each loss at 10%. What is their combined present value to the nearest dollar?
- $40,000
- $36,364
- $200,000
- $34,711
Show answer and explanation
Answer: D. $34,711
$20,000 / 1.10 + $20,000 / 1.10² = $34,710.7438 before final rounding. $200,000 incorrectly treats the loss as ongoing under a different model.
7. The current site estimate already includes a $10,000 external discount. What should the analyst avoid?
- Studying improvement effects
- Subtracting that same site loss a second time
- Checking current land sales
- Documenting an allocation
Show answer and explanation
Answer: B. Subtracting that same site loss a second time
External effects may affect both land and improvements. An allocation must prevent counting one effect twice.
8. A house backs onto a shopping center. No evidence of an adverse value effect has been supplied. What follows?
- All such houses are unmarketable
- The building must have functional obsolescence
- A mandatory 10% deduction
- The adjacency alone does not establish an external loss amount
Show answer and explanation
Answer: D. The adjacency alone does not establish an external loss amount
The analysis needs the relevant market response. The label of the neighboring use is not a universal value adjustment.
9. A storm has damaged roof shingles. The question asks how to classify the damaged component. What fits?
- External because the storm began outside
- Physical deterioration
- Economic because weather affects demand
- Functional because shingles serve a function
Show answer and explanation
Answer: B. Physical deterioration
The stated component damage is physical. Do not confuse the external origin of an event with external obsolescence.
10. A controlled comparison supports a $30,000 external loss from an unaffected value of $400,000. What percentage uses that stated base?
- 13.333%
- 7.5%
- 30%
- 8.108%
Show answer and explanation
Answer: B. 7.5%
$30,000 / $400,000 = 0.075. Use the specified unaffected base, rather than dividing by the affected $370,000.
Common questions
What is external obsolescence in plain English?
It is a reduction in property value caused by negative influences outside the property. A sound building can suffer it. Identify both the outside cause and a supported negative market effect.
Is economic obsolescence the same thing?
Often, yes. The IAAO glossary directs economic obsolescence to external obsolescence. Some teaching materials distinguish wider economic changes from nearby location influences, but that is not a universal separation of mutually exclusive categories.
Is external obsolescence always permanent?
No. IAAO expressly includes temporary and permanent loss. Estimate the period of the effect from supported facts; do not assume that a condition is permanent merely because the owner cannot cure it.
Why is external obsolescence often described as incurable?
An individual owner usually cannot economically remove the outside cause, such as a wider loss of demand. In appraisal teaching, an economic cure requires a justified correction, not simply an owner who has cash available. Curability and duration are separate: an outside influence may end or be mitigated without the owner removing its cause.
How is it different from functional obsolescence?
Functional obsolescence concerns a deficiency in an improvement's design or utility. External obsolescence concerns outside influences. A property can have both; keep their supported effects separate.
Does it affect land or only buildings?
It can affect land and improvements. Current land evidence may already reflect the influence. Any separate improvement deduction must have support and avoid repeating a loss already counted elsewhere.
Does a nearby airport automatically reduce value?
No. Exposure, access benefits, noise and market response vary. Support the effect for the property being valued. Do not invent an airport percentage or substitute a neighborhood stereotype for evidence.
Can an outside influence increase value instead?
Yes, surroundings can benefit a property. That benefit is not obsolescence, because obsolescence describes a loss. An amenity may benefit one property while causing a supported adverse effect for another.
How do you calculate external obsolescence?
There is no single mandatory formula. Depending on the assignment and evidence, the analysis may use controlled sales comparisons, supported income effects or a cost-approach depreciation analysis. The calculation must match the income definition, duration, rate, effective date and allocation assumptions.
How do temporary income losses change the calculation?
Use the stipulated timing and discounting assumptions. In the two-year example, discount each $20,000 year-end NOI loss separately and add the unrounded results. Round the final total to the requested unit. A permanent-income shortcut would answer a different question.
Is this the same as tax depreciation?
No. This page concerns appraisal loss in value. Tax depreciation is a separate deduction system with its own rules. An appraisal category does not itself establish a tax deduction or a tax recovery period.
What should I remember for the Illinois broker exam?
Start with cause: wear, design or an outside influence. Then check actual value effect, duration and double counting. PSI identifies economic principles and valuation approaches in its outline, but does not promise a fixed number of questions on this term. All questions here are original practice.
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Official sources and scope
IAAO supplies the glossary terminology. The California DRE chapter is used for general valuation teaching, not Illinois licensing law or a current USPAP edition. Fannie Mae supplies lender-program examples and evidence principles, not a universal percentage deduction or a requirement to use every approach in every assignment. Its displayed topic dates are June 4, 2025; the guide navigation identifies an October 7, 2026 publication. The calculations are original exercises with stated assumptions.
- California DRE Reference Book, chapter 15, printed pages 406-412: general cost approach, depreciation and age-life teaching
- IAAO Glossary, third edition: external, economic and functional obsolescence
- IRS Publication 946, 2025 edition, chapter 1: tax depreciation as cost recovery; used only for that distinction
- PSI June 24, 2026: national Valuation outline
- Fannie Mae B4-1.3-10: cost and income approaches
- Fannie Mae B4-1.3-03: neighborhood influences and objective analysis
- Fannie Mae B4-1.3-09: market-supported comparable adjustments
This is exam preparation, not advice for a specific transaction. State law and the applicable facts control. Our editorial and corrections process explains how to report an issue.