Real Estate Comping

Real Estate Comping Skill

Perform appraiser-grade property valuations using the Two-Bucket method for disclosure states or the Triangulation method for non-disclosure states. This skill is strictly about comparable sales analysis and ARV determination — it does not estimate rehab costs, renovation budgets, or scope of work. If the user needs rehab cost estimation, direct them to the appropriate skill for that.

Workflow Overview

1. Identify property location → Determine state from address
2. Route to correct methodology → Disclosure or Non-Disclosure framework
3. Execute 9-step analysis → Follow the appropriate prompt framework
4. Generate deliverables → PDF summary report + Excel breakdown + comps table

Comp Data Acquisition (before any analysis)

Primary path: the Zillow /search API pull. If an OpenWeb Ninja Real-Time Zillow Data key is available (OPENWEBNINJA_API_KEY env var), pull the comp universe programmatically instead of browsing listing sites. The companion comp-package skill ships the full contract and a self-contained puller script. The load-bearing facts:

• /search with home_status=RECENTLY_SOLD (exact enum; other casings return 400) for solds, FOR_SALE for actives
• Every search caps at 41 rows (about 5 weeks of sales in an active zip): partition by min_price/max_price bands and recursively split any band returning 41 (recovers 12-24 months per zip)
• price_min/price_max are silently ignored; confirm every filter against the echoed parameters object
• dateSold is epoch milliseconds; use unformattedPrice, not the soldPrice display string
• Clip to the target pocket with a lat/lon bounding box AND a street-name whitelist; verify LOT-type or missing-sqft surprises against the county card (often teardown sales or new builds)
• The API is MLS-only: auction, wholesale, and off-market transfers come from county records

Fallback path: no API key, or the user prefers manual comping: browse Zillow/Redfin/MLS exactly as the framework references describe. The methodology below is identical either way; only data acquisition changes.

Bedroom-band rule (both paths): when the subject's bedroom count is below the comp set (especially 2-bed vs 3-bed), run a dual-track ARV: the base case is valued ONLY against same-bed comps, clamped to that band's median price (extra sqft does not escape the band); reconfig to more bedrooms is a labeled upside credited only after a walkthrough verifies the layout converts. Underwrite off the base track, and project future value on the same-bed curve.

State Detection & Routing

Determine state type from property address:

• Non-Disclosure States (sold prices not publicly recorded): TX, UT, WY, NM, ID, MT, ND, AK, KS, MS, LA, MO
• Disclosure States: All other US states

Routing:

• Non-disclosure state → Read references/non-disclosure-prompt.md
• Disclosure state → Read references/disclosure-prompt.md

Quick Reference

Core Comping Rules (Both Frameworks)

These rules apply regardless of disclosure status:

GLA Definition

GLA = Gross Living Area = above-grade finished living space.

GLA is the single most important measurement in comparable sales analysis. Misidentifying GLA leads to incorrect PPSF calculations and unreliable ARVs.

Included in GLA:

• All finished rooms above grade (living rooms, bedrooms, kitchens, bathrooms, hallways)
• Second/third stories above grade
• Finished basement with separate exterior entrance at grade level (walkout basement)

Excluded from GLA:

• Unfinished basement (any portion below grade)
• Finished basement without separate exterior entrance (value separately, see Basement rules)
• Garage (attached or detached)
• Covered porches, screened porches, patios
• Attic space (unless finished with permanent stairs and standard ceiling height)
• Carports, breezeways, storage sheds

Basement valuation (not GLA but has value):

• Finished to same quality as main floor: value at ~50% of above-grade PPSF
• Finished with drop ceilings/inferior finishes: value at ~35-40% of above-grade PPSF
• Partially finished: value at ~25-35% of above-grade PPSF
• Unfinished: value at ~10-15% of above-grade PPSF (storage/utility value only)

Discrepancy protocol: When public records GLA differs from MLS GLA by >5%, flag it. Public records often include non-GLA space. Use MLS GLA as primary, cross-reference with county assessor measurements.

Comp Selection Filters

• Age: ≤90 days preferred, 6 months max
• Subdivision: Same micro-pocket, do not cross major roads
• GLA: ±100 sqft ideal, ±250 sqft outer bound
• Property type: Match elevation style (ranch to ranch, 2-story to 2-story)
• Build year: ±10 years

Outlier Detection

After gathering comps, screen for PPSF outliers before bucket analysis:

1. Calculate median PPSF of all comps in the set
2. Calculate standard deviation of comp PPSF values
3. Flag any comp >2 standard deviations from the median PPSF
4. Apply exclusion rules:
   • If 5+ comps total and one is an outlier: exclude it and note the exclusion with reason
   • If only 3-4 comps total and one is an outlier: keep it but flag it with notation in the analysis (too few comps to discard)
   • If 2+ outliers in a small set: re-examine comp selection criteria — the set may be too heterogeneous

Common outlier causes to document:

• Estate/distress sale (below market)
• REO/bank-owned (typically 10-15% below market)
• Major unreported renovation (above market)
• Seller concessions not reflected in price
• Related-party transaction (non-arm's-length)

Market Sentiment Assessment

Assess market conditions using quantitative indicators before applying sentiment adjustments:

Data sources for market sentiment:

• Redfin market tracker (monthly updates, metro and zip level)
• Zillow Home Value Index (ZHVI) for YoY price trends
• Local MLS statistics (DOM, inventory, sale-to-list)
• County assessor recent sale volumes

Apply the sentiment adjustment in Step 9 (Final ARV Assembly), not during comp selection.

Recent Renovation Handling (Bucket Classification)

When classifying comps into Bucket A (unrenovated) or Bucket B (renovated), apply these rules for properties with known renovation history:

Key indicator: A significant price jump between the last two sales of the same property (e.g., bought for $150K, sold 18 months later for $260K) strongly suggests a flip/renovation. Cross-reference with permit history and listing photos.

Definition of "substantial renovation":

• Kitchen + at least 1 full bathroom remodel (minimum ~$15K combined spend)
• OR full kitchen gut (cabinets + countertops + appliances replaced)
• Cosmetic-only (paint + flooring only) does NOT qualify — classify as Bucket A
• Paint + flooring + fixture updates = borderline — classify as Bucket A unless listing explicitly says "renovated" or "remodeled"

If renovation scope is unknown: Default to listing photos and remarks. "Updated," "remodeled," or "new kitchen/bath" language = Bucket B. "Original," "vintage," "needs TLC" = Bucket A.

Feature Adjustments (by price tier)

See references/adjustment-cheatsheet.md for complete adjustment values.

Quick reference (aligned with comp_analyzer.py source):

Unusual Feature Adjustments

Pool condition matters:

• Updated pool with modern finishes: full value
• Dated pool needing resurface: 50% of value
• Pool needing major repairs: may be net negative (removal cost $10,000-$15,000)

Basement/ADU Rules

• Basements: Not counted as GLA; value at ~50% of above-grade PPSF if finished (see GLA Definition section for full breakdown)
• ADUs: 50% value if not separately deeded; 100% if separately titled

Two-Bucket Methodology (Core of This Skill)

The Two-Bucket method separates comps into unrenovated (Bucket A) and renovated (Bucket B) to derive the market premium that renovation commands. This is a market-derived metric, not a rehab cost estimate.

Bucket Spread Sanity Check

The spread between Bucket A and Bucket B PPSF values tells you what the market pays for renovation in that micro-market.

• 5-30% spread: Normal range. Proceed with analysis.
• <5% spread: Suspect — unrenovated comps may be mispriced, or the market doesn't reward renovation strongly. Re-examine Bucket A comp conditions.
• >30% spread: Suspect — Bucket A comps may include distressed sales, or Bucket B comps may be ultra-luxury renovations beyond typical flip quality. Re-examine both buckets.

Worked Example: Two-Bucket Spread Analysis

Subject property: 1,500 SF ranch, 3 bed/2 bath, built 1978, dated condition, Knoxville TN

Bucket A (as-is/dated) — 5 comps:

Median PPSF_A: $120.20

Bucket B (renovated) — 5 comps:

Median PPSF_B: $165.56

Spread calculation:

Market Premium = ($165.56 - $120.20) / $120.20 x 100% = 37.7%

Sanity check: 37.7% exceeds the normal 5-30% range. Investigation needed:

• Check if Bucket A comps include any distress/estate sales pulling the average down
• Verify Bucket B comps are standard flips, not ultra-luxury renovations
• Check if subject micro-market has high renovation demand (near university, hospital, etc.)

If comps check out, proceed but note the elevated spread and widen confidence band to +/-5%.

Value calculations:

• As-is value: $120.20 x 1,500 SF = $180,300
• ARV (after renovation): $165.56 x 1,500 SF = $248,340
• Market premium from renovation: $248,340 - $180,300 = $68,040

Rehab budget sanity check: Rehab budget should be 40-70% of the market premium to maintain deal economics:

• Rehab range: $27,216 to $47,628
• If rehab estimate exceeds $47,628, the deal margin is thin — re-evaluate

Maximum Allowable Offer (MAO) check:

• MAO = ARV x 70% - Rehab = $248,340 x 0.70 - $35,000 (est. rehab) = $138,838
• Compare MAO to as-is value ($180,300) — if as-is value > MAO, the deal likely does not work as a wholesale flip

Required Deliverables

Every comp analysis MUST produce these two outputs:

1. Excel Breakdown Workbook

Comprehensive multi-sheet workbook with:

• Executive Summary sheet: Quick-view of key findings
• Subject Property sheet: All property details
• Comparable Sales sheet: Full comps table with bucket analysis
• Adjustments Detail sheet: Line-by-line adjustment breakdown
• Market Analysis sheet: Market metrics and trends
• ARV Calculation sheet: Step-by-step ARV math
• Sources & Notes sheet: Data sources, parameters, recommendations

Generate using: scripts/generate_excel_report.py

2. In-Context Analysis

The detailed analysis text with tables shown directly in the conversation, including:

• Step-by-Step ARV Breakdown (Base PPSF → Adjustments → Final ARV)
• Comps Summary Table (Address, Sale Date, Price, GLA, Beds/Baths, Year, Condition, Adjustments, Final Adjusted Value)
• Outlier Screening Results (any comps flagged or excluded, with reasons)
• Market Overview (Median price, PPSF, DOM, sale-to-list ratio, market phase, sentiment assessment)
• Sources & Assumptions (Data sources, time window, radius constraints)
• Recommendations & Caveats (Verification steps, risk factors, disclaimer)

Output Generation Instructions

Data Structure for Report Generation

Prepare analysis data as JSON with this structure:

{
    "subject_property": {
        "address": "123 Main St",
        "city": "Austin",
        "state": "TX",
        "zip": "78701",
        "county": "Travis",
        "subdivision": "Downtown",
        "property_type": "Single Family",
        "gla": 1850,
        "lot_size": 6500,
        "beds": 3,
        "baths": 2,
        "year_built": 1985,
        "condition": "Dated"
    },
    "comps": [
        {
            "address": "456 Oak Ave",
            "sale_date": "2025-12-15",
            "sale_price": 485000,
            "gla": 1780,
            "ppsf": 272.47,
            "beds": 3,
            "baths": 2,
            "year_built": 1982,
            "condition": "Renovated",
            "distance": 0.3,
            "total_adjustments": -5000,
            "adjusted_value": 480000,
            "outlier_flag": false,
            "outlier_reason": null
        }
    ],
    "outlier_screening": {
        "median_ppsf": 255.00,
        "std_dev_ppsf": 18.50,
        "threshold_low": 218.00,
        "threshold_high": 292.00,
        "excluded_comps": [],
        "flagged_comps": []
    },
    "bucket_analysis": {
        "unrenovated": { "count": 2, "median_ppsf": 235.20, "avg_ppsf": 235.20 },
        "renovated": { "count": 2, "median_ppsf": 257.33, "avg_ppsf": 257.33 },
        "market_premium_pct": 9.4,
        "spread_sanity": "normal"
    },
    "market_sentiment": {
        "dom_trend": "stable",
        "inventory_months": 4.2,
        "yoy_price_change_pct": 2.1,
        "sale_to_list_ratio": 0.98,
        "classification": "balanced",
        "sentiment_adjustment_pct": 3.5
    },
    "market_overview": {
        "market_phase": "Balanced",
        "median_price": 455000,
        "median_ppsf": 248.50,
        "avg_dom": 28,
        "sale_to_list_ratio": 0.98,
        "active_count": 45,
        "pending_count": 22,
        "notes": ["Market observations..."]
    },
    "arv_calculation": {
        "base_ppsf": 235.20,
        "market_premium_pct": 9.4,
        "renovated_ppsf": 257.33,
        "subject_gla": 1850,
        "base_arv": 476061,
        "feature_adjustments": -5000,
        "sentiment_adjustment_pct": 3.5,
        "final_arv": 471000,
        "confidence_level": "Moderate",
        "confidence_band_pct": 5.0,
        "arv_low": 447450,
        "arv_high": 494550
    },
    "adjustments_applied": [
        {
            "comp_number": 1,
            "comp_address": "456 Oak Ave",
            "adjustment_type": "GLA",
            "reason": "Subject 70 sqft larger",
            "amount": -5000
        }
    ],
    "sources": ["MLS", "County Records", "Zillow"],
    "search_parameters": {
        "time_window": "90 days",
        "radius": "0.5 miles",
        "gla_range": "1600-2100 sqft"
    },
    "recommendations": ["Verification steps..."],
    "caveats": ["Disclaimers..."]
}

Generate Reports

1. Save the analysis data to a JSON file
2. Run the Excel generator:

   python scripts/generate_excel_report.py output_report.xlsx data.json
   

Execution Instructions

1. Gather property address from user
2. Identify state and determine disclosure status
3. Load appropriate framework:
   • Disclosure: references/disclosure-prompt.md
   • Non-Disclosure: references/non-disclosure-prompt.md
4. Add property context (if provided): current condition, seller notes, known issues
5. Optional boundary drawing: For block-by-block markets, use Zillow boundary tool
6. Execute analysis following the 9-step framework
7. Screen for outliers after gathering comps, before bucket classification
8. Assess market sentiment using quantitative indicators
9. Classify recent renovations properly into buckets
10. Verify results: Cross-reference with market knowledge
11. Prepare data structure: Compile all analysis into JSON format
12. Generate deliverables:
    • Run generate_excel_report.py for Excel breakdown
13. Deliver all outputs to user: Excel and in-context analysis

Special Considerations

Non-Disclosure State Caveats

• Wider confidence bands (+/-5-7% vs +/-2-5%)
• Must derive sold prices using triangulation methods
• Recommend "Option Period Verification" once under contract

Source Code Alignment (comp_analyzer.py)

The following adjustment values are calibrated for the Knoxville, TN regional market and are used in the automated comp analyzer:

These are conservative Knoxville-calibrated values. For higher-value markets (>$500K), use the scaled values in the adjustment cheatsheet.