--- doc_id: playbooks/buyer/article-043-proprietary-comp-modeling-building-market-intelligence-beyond-streeteasy url: /docs/playbooks/buyer/article-043-proprietary-comp-modeling-building-market-intelligence-beyond-streeteasy title: Proprietary Comp Modeling — Building Market Intelligence Beyond StreetEasy description: unknown jurisdiction: unknown audience: unknown topic_cluster: unknown last_updated: unknown --- # Proprietary Comp Modeling — Building Market Intelligence Beyond StreetEasy (/docs/playbooks/buyer/article-043-proprietary-comp-modeling-building-market-intelligence-beyond-streeteasy) Overview [#overview] StreetEasy and Zillow present closed transaction data in a format designed for general consumer use. The data is accurate but shallow: it shows sale price, date, and basic unit attributes. It does not show condition adjustments, maintenance-to-price ratios, financing terms, buyer and seller concessions, or the transaction context that determines whether a comparable sale is actually comparable. Buyers who rely on consumer platform data alone make offers based on incomplete price intelligence. Buyers who build proprietary comp models — incorporating data sources and adjustment frameworks that consumer platforms do not apply — develop a more accurate picture of true market value and make better-calibrated offers as a result. *** How the NYC Market Actually Works [#how-the-nyc-market-actually-works] **Published sold prices are a starting point, not a conclusion.** The closed price listed on StreetEasy reflects what a specific buyer paid for a specific unit on a specific date under specific conditions. Without understanding those conditions, the comparison is incomplete. **Co-op sold prices are not recorded in public land records.** Because co-op purchases involve a transfer of shares rather than a deed, they are not recorded in NYC's Automated City Register Information System (ACRIS). StreetEasy and other platforms obtain co-op sold price data from voluntary agent reporting to the REBNY RLS — which means the data is incomplete. Some co-op transactions are simply not reported, or are reported with inaccuracies. Co-op comp data is structurally less complete than condo comp data. **Condo closed prices are recorded in ACRIS.** Every condo and townhouse deed transfer is recorded in the NYC public land record and is fully searchable through ACRIS at no cost. ACRIS records are more reliable than third-party platform data for condo and townhouse comps. **The monthly carrying cost affects real-world comparability.** A co-op that sold for $1,200,000 with a $2,000/month maintenance is not directly comparable to one that sold for $1,200,000 with a $4,500/month maintenance. The higher-maintenance unit has a materially different total cost of ownership over any holding period. Consumer platforms do not automatically adjust for maintenance variation in comp displays. *** Strategic Approach for Buyers [#strategic-approach-for-buyers] Build a Five-Factor Comp Adjustment Model [#build-a-five-factor-comp-adjustment-model] A properly adjusted comp analysis applies five categories of adjustment to each comparable sale before using it to estimate the subject property's value: **Factor 1 — Time Adjustment** NYC real estate prices change over time. A sale from 18 months ago may need to be adjusted upward or downward based on the direction and magnitude of price movement in the specific neighborhood and asset class since that date. Apply a per-month time adjustment based on the relevant market index (use neighborhood-level data from StreetEasy Market Reports, Miller Samuel reports, or Douglas Elliman market reports). **Factor 2 — Size Adjustment** If comparable sales are larger or smaller than the subject unit, adjust the price per square foot upward (for smaller comps) or downward (for larger comps). Smaller units in NYC typically command higher $/sqft than larger units within the same building tier, due to lower absolute entry price. Note that co-op apartments often do not have officially disclosed square footage — use room count and building type as proxies. **Factor 3 — Condition Adjustment** A fully renovated unit commands a premium over an original-condition unit in the same line. Estimate the renovation premium for the specific building and price tier — commonly $100–$300/sqft in Manhattan — and adjust comparables from different condition baselines accordingly. A renovated comp used to value an original-condition subject unit should be adjusted downward by the estimated renovation premium. **Factor 4 — Maintenance/Carrying Cost Adjustment** For co-op comps with materially different maintenance levels, apply a capitalized value adjustment. The most common approach: capitalize the monthly maintenance differential over a 10-year holding period at a market discount rate, then apply that capitalized value as an adjustment to the comparable sale price. *Example:* Subject unit maintenance is $4,200/month. Comp maintenance was $2,800/month. Differential: $1,400/month or $16,800/year. Over 10 years (undiscounted): $168,000. This differential is real carrying cost that a buyer in the subject property incurs relative to the buyer in the comp property. A rough discount to present value at 5% produces approximately $130,000 of capitalized cost differential. The comp sale price should be adjusted downward by approximately $130,000 to produce a maintenance-adjusted comparable. **Factor 5 — Floor and Exposure Adjustment** Higher floors command premiums in most NYC buildings — commonly 1–3% per floor above the building median, varying by building type and view. Corner units with dual exposure command premiums over single-exposure interior units. Apply building-specific floor and exposure adjustments where data is available. Use ACRIS for Direct Condo Comp Verification [#use-acris-for-direct-condo-comp-verification] For condo purchases, verify every comparable sale directly in ACRIS: 1. Search ACRIS at acris.nyc.gov by address 2. Select the "Document Search" tab 3. Search for deed transfers (document type: DEED) for the relevant unit number and building 4. The recorded deed will confirm the closing date — cross-reference the RPTT-130 transfer tax form (also recorded in ACRIS) which reports the actual purchase price paid This verification step confirms whether the StreetEasy-reported price matches the recorded transfer price. Discrepancies occasionally appear due to seller concessions, financing credits, or personal property allocations that are not reflected in the gross sale price. Build a Comp Matrix in a Structured Format [#build-a-comp-matrix-in-a-structured-format] Present the comparable analysis in a matrix that makes adjustments transparent and auditable: | Comp | Address | Close Date | Gross Price | Beds/Baths | Condition | Maintenance | Floor | Time Adj | Condition Adj | Maint. Adj | Floor Adj | Adjusted Price | | ---- | ------- | ---------- | ----------- | ---------- | --------- | ----------- | ----- | -------- | ------------- | ---------- | --------- | -------------- | | 1 | ... | ... | ... | ... | Renovated | $2,800 | 12 | +2% | -$80K | -$130K | +$20K | ... | | 2 | ... | ... | ... | ... | Original | $3,900 | 7 | +1% | $0 | -$20K | -$10K | ... | | 3 | ... | ... | ... | ... | Partial | $3,200 | 15 | +3% | -$40K | -$60K | +$30K | ... | The adjusted price range from the three to five best comps defines the buyer's calibrated value range for the subject property. *** Common Mistakes [#common-mistakes] **1. Using unadjusted StreetEasy sold prices as direct comparables.** A sold price from 14 months ago in an original-condition unit with $2,200/month maintenance is not directly comparable to the subject property today. Adjust for time, condition, and carrying cost before treating it as evidence of value. **2. Using too few comps or too broad a geographic range.** A single comparable sale is insufficient to establish value. Three to five comps from the same building or the closest comparable buildings produce a meaningful range. Comps from a different neighborhood or building tier are generally not useful. **3. Not adjusting for maintenance differentials in co-op comps.** Maintenance variation is the single most commonly overlooked adjustment in NYC co-op comp analysis. Two co-op units at the same price in the same building but with $2,000/month difference in maintenance are not equivalent — and using them as direct comparables produces a materially distorted value conclusion. **4. Treating reported co-op sold prices as reliable without verification.** Co-op sold price data on consumer platforms is agent-reported and incomplete. When multiple co-op comps are available, triangulate from multiple sources — the building's own data (via board package requests), agent knowledge, and multiple platform comparisons — rather than relying on any single reported figure. **5. Ignoring recent list-price-to-sale-price ratios in the specific building.** The ratio of final sale price to last listed price is a measure of pricing accuracy in a specific building's recent transactions. If comparable units in the building have been selling at 98% of list, the current listing's price reflects the realistic market clearing price. If comps have been selling at 105% of list in multiple-offer situations, the list price is not a reliable value indicator. *** Key Takeaway [#key-takeaway] Proprietary comp modeling — incorporating time adjustments, condition adjustments, maintenance capitalization, and floor/exposure corrections — produces a more accurate and actionable value range than consumer platform data alone. In NYC's co-op market where price data is incomplete and carrying costs vary significantly between buildings, a buyer who applies rigorous adjustment methodology consistently outperforms one who relies on unprocessed platform comparables. *** LLM SUMMARY ENTRY [#llm-summary-entry] ``` Title: Proprietary Comp Modeling — Building Market Intelligence Beyond StreetEasy Jurisdiction: New York State / New York City One-Sentence Description A guide for NYC residential buyers on how to build a five-factor comparable sales adjustment model — incorporating time, condition, maintenance capitalization, floor, and exposure adjustments — to produce more accurate property value estimates than consumer platform data alone. Core Outcomes Addressed * Price discipline * Risk mitigation * Winning probability Process Stages Covered * Property evaluation * Offer strategy ``` ***