NYC Condo Alteration Agreement Guide — RPL Article 9-B, DOB ALT-2, Local Law 97

NYC condos and co-ops both hand you an alteration agreement, but the legal structure underneath is very different — and missing that difference is how first-time NYC renovators lose $20K-$80K to process friction that a properly-scoped project avoids entirely. This pillar is the condo-specific playbook: what the board can and cannot require under Real Property Law Article 9-B, how the DOB ALT-2 filing works, what Local Law 97 means for your renovation (short version: less than co-op owners assume), and the document sequence that keeps a $250K bathroom from turning into a 14-month litigation exposure.

For the co-op variant (which is actually the more complex document), see the NYC Co-op Alteration Agreement Guide. For Brooklyn brownstone renovations, see Brooklyn Brownstone Whole-Home Renovation. This page is scoped to the Manhattan + Brooklyn + Queens condo interior renovation.

The core legal distinction — condo vs co-op

Under New York Real Property Law Article 9-B,¹ a condominium is real property: you own the interior of your unit, a proportional share of the common elements (hallways, lobby, facade, roof), and the deed is recorded with the City Register. The condo board is an elected body with authority defined by the Condominium Declaration and Bylaws — documents filed with the register at building formation and amendable only with supermajority unitowner approval.

This matters for renovations in specific ways:

• The condo board cannot arbitrarily deny a renovation that stays within the unit's legal boundaries and doesn't affect common elements. The Declaration defines what's common vs limited-common vs unit-owner property.
• Waterproofing, structural, and plumbing-stack connections are typically common element — the condo board has legitimate authority to review these scopes.
• Interior finishes, appliances, layout within the unit, and non-structural walls are unit property — the board's authority is limited.
• The ADA-like "no unreasonable interference" standard applies. The board can require noise hours, reasonable insurance, compliance with DOB filings, and a proper alteration agreement — they cannot require arbitrary design standards on unit interior.

The co-op alteration agreement by contrast is grounded in a proprietary lease and shareholder relationship; co-op boards have vastly broader discretion. If you're in a condo, your alteration agreement is real but narrower.

What a typical NYC condo alteration agreement actually contains

Most condo alteration agreements in 2026 are 12-30 pages (vs 40-80 for co-op agreements). Core provisions:

• Scope definition — exact drawings and specifications the unit owner submits and the board approves. Out-of-scope work is not authorized; mid-project scope changes require re-approval.
• Insurance requirements — the unit owner (via the contractor) must carry general liability typically $2M-$5M per occurrence, workers' compensation, and sometimes a separate alteration bond.
• Indemnification — the unit owner indemnifies the condo against damage to common elements and neighboring units.
• Architect / engineer sign-off — any scope touching plumbing, electrical, or structural elements requires a licensed architect (RA) or professional engineer (PE) stamp on the plans.
• DOB filing coordination — the condo board typically requires ALT-2 filing at DOB for any scope beyond "cosmetic" (see next section).
• Noise and work hours — typical restriction: 8 AM-5 PM weekdays, no weekend work, no noise work (demolition, hammer drills) before 9 AM.
• Security deposit or escrow — $2K-$15K held against damage to common elements, refunded post-completion.
• Completion timeline — most agreements cap project duration at 90-180 days with extensions requiring written approval.
• Wet-over-dry restrictions — you cannot locate a new wet room (kitchen, bath, laundry) over a downstairs neighbor's bedroom or living room without either written consent or board-approved mitigation (sound and moisture membranes).
• Post-completion inspection — after DOB sign-off, the building engineer or managing agent inspects the work; final security-deposit release is contingent.

A typical NYC condo alteration agreement should be reviewed by a real estate attorney before signing — standard cost $800-$2,000 and worth every dollar. A contractor who pushes you to sign without attorney review is signaling they intend to work the gaps, not close them.

DOB ALT-2 filing — what it is, when you need it

The NYC Department of Buildings classifies residential renovation filings into three main categories:²

• NB (New Building) — ground-up construction; not your condo renovation.
• ALT-1 — major alteration changing use, occupancy, or adding square footage. Rare for condo interior work; typical for adding a second floor or changing C of O.
• ALT-2 — alteration that doesn't change use, occupancy, or square footage but involves scope that requires DOB review. The dominant filing for serious condo renovations.
• ALT-3 (now DOB NOW: Directive 14 minor work) — cosmetic or minor work under thresholds. For true finish-only work (paint, flooring, cabinet reface in existing footprint, fixture one-for-one swap).

ALT-2 is required when renovation scope includes:

• New or relocated plumbing fixtures
• Electrical scope beyond one-for-one fixture replacement
• HVAC equipment additions or relocations
• Structural changes (load-bearing walls, new openings in structural elements)
• Changes to egress, windows, or façade
• Wet-over-dry room additions
• Any scope touching common elements

The ALT-2 filing path:

1. Design + pre-filing review — 4-8 weeks for architect/engineer to develop plans, run any required structural analysis.
2. DOB ALT-2 filing via DOB NOW — the online portal, submitted by the registered design professional.
3. Plan examination — DOB plan examiner review, typically 4-10 weeks. Objections are common on first review; revise + resubmit 1-3 times typical.
4. Permit issuance — after plan approval, general contractor pulls the work permit.
5. Construction — start only after permit issued; any work before permit is illegal and triggers DOB stop-work orders and fines.
6. Inspections — rough inspections at plumbing-rough, electrical-rough, framing (if applicable). Finals at completion.
7. Sign-off — DOB sign-off closes the permit; required before condo board final release.

Local Law 97 — the reality for condo owners

Local Law 97 (enacted 2019, compliance period starting 2024)³ gets enormous airtime in NYC renovation conversations. Here's what it actually means for a condo interior renovation:

LL97 applies to buildings, not units. The building's carbon emissions are tracked and capped; emissions exceeding the cap result in a building-wide fine, typically paid through common charges. Unit owners do not individually comply with LL97.

Your interior renovation doesn't directly trigger LL97 filings. The law targets HVAC electrification, building envelope, and major systems — a unit-scale alteration agreement doesn't create an LL97 compliance obligation for you.

Where LL97 affects your renovation: if your building is approaching emissions cap and starting to pay fines, building-wide projects (facade, roof, common HVAC) will become priority capital projects. Your condo common charges will rise to fund them, and some buildings will push for unit-level HVAC electrification (swapping gas-fired through-wall units for electric heat pumps) as part of the compliance strategy.

When your renovation interacts directly with LL97: if you're replacing through-wall HVAC as part of your renovation, specifying electric heat-pump equipment (instead of gas-fired packaged terminal air conditioners) contributes to building-level compliance. Some condo boards now require or strongly encourage electric heat-pump installation at any HVAC replacement.

Wet-over-dry and building moisture rules

The NYC DOB enforces specific rules on "wet rooms" (bathrooms, kitchens, laundry) and their location relative to "dry rooms" below:⁴

• Prohibited stacking — a new wet room cannot be placed over a downstairs neighbor's living room, bedroom, or home office (dry rooms) without either written consent from that neighbor OR board-approved waterproofing mitigation (continuous waterproof membrane, drain pan, moisture detection).
• Expanding an existing wet footprint — adding a bathroom to a bedroom wall is often approvable; creating a new bathroom in a location that has no upstairs or downstairs wet-room alignment usually requires explicit mitigation plans.
• Kitchen relocations — moving a kitchen to a formerly-dry area (dining room, family room) is a common renovation scope and requires compliance with wet-over-dry rules.

The technical solution is NBC (New Building Code) compliant waterproofing: full-shower Schluter or equivalent, drain pan under kitchen appliances with leak detection, Uponor or equivalent pressurized-line routing with accessible shutoffs.

NYC DEP backflow and plumbing modernization

New York City Department of Environmental Protection enforces plumbing code through the licensed master plumber filing system. Any renovation touching water supply or waste lines requires:

• Licensed master plumber with NYC DEP license, pulling the plumbing permit
• Backflow prevention — any new fixture on a potable water line must meet backflow-prevention code (check valves, atmospheric vacuum breakers, RPZ where required)
• Pressure testing — new DWV (drain-waste-vent) runs require a DEP-witnessed pressure test before concealment
• Water-saving fixture compliance — NYC plumbing code requires WaterSense-rated fixtures; 1.28 gpf toilets, 1.5 gpm showerheads, 1.2 gpm bath faucets

Scope tiers — what a 2026 NYC condo renovation actually costs

Light cosmetic — $80K-$150K Paint, flooring refinish or replacement in existing footprint, cabinet reface, appliance swap, fixture one-for-one swap. Typically no ALT-2 required. 6-8 week project. 1-2 bedroom condo.

Mid-range kitchen + bath — $150K-$400K Kitchen gut in existing footprint (new cabinets, counters, appliances, electrical), 1-2 bathroom gut renovations, some wall reconfiguration. ALT-2 filed. 3-5 month project. Typical Manhattan 1-bedroom to Brooklyn 2-bedroom scope.

Full condo gut renovation — $400K-$900K Every room renovated, typically with wall reconfigurations, all new MEP in the unit, custom cabinetry throughout, high-end appliances and fixtures, hardwood refinish or replacement. ALT-2 filed. 6-10 month project. Typical Manhattan 2-3 bedroom scope.

Premium architectural renovation — $900K-$1.5M+ Architect-led design, structural modifications, combined-unit scenarios, premium materials throughout (natural stone slabs, custom millwork, specified lighting, integrated smart-home), extensive HVAC reconfiguration. ALT-2 or ALT-1. 10-16 month project. Typical Manhattan 3-4 bedroom or combined-unit scope.

What Baily verifies before matching you with an NYC condo renovation GC

1. NY State Department of State home improvement contractor (HIC) registration — NYC specifically enforces NYC Consumer Affairs HIC licensing for $200+ residential work.
2. DOB-tracked permit history — real ALT-2 and ALT-3 closures in the last 24 months, NOT just "we do NYC work."
3. $2M general liability minimum with condo / co-op specific endorsement.
4. Workers' compensation current with NY State Workers' Compensation Board.
5. Licensed master plumber partner with NYC DEP license.
6. Licensed master electrician partner with NYC DOB license.
7. Registered architect or professional engineer on retainer for ALT-2 filings.
8. Complaint review — no open DOB violations or consumer complaints in the last 24 months.
9. Bond / Alteration bond when the building requires it.
10. Insurance naming — your specific condo association named as additional insured on the contractor's policy.

One lead, one contractor. Not 12.

Frequently asked questions

What's the difference between a condo alteration agreement and a co-op alteration agreement?

Condos are real property under NY Real Property Law Article 9-B; you own your unit, the board's authority is defined by the Condominium Declaration and Bylaws, and their discretion over your renovation is narrower than a co-op's. Co-ops are corporations — you own shares and hold a proprietary lease, and the board's discretion is vastly broader. Practically: condo alteration agreements are 12-30 pages and focus on scope + insurance + common-element protection. Co-op agreements run 40-80 pages and impose extensive design and material approval authority. Know which regime applies before you sign.

When does my condo renovation require a DOB ALT-2 filing?

ALT-2 is required whenever renovation scope includes new or relocated plumbing fixtures, electrical work beyond one-for-one fixture replacement, HVAC additions, structural changes, egress changes, wet-over-dry room additions, or any work touching building common elements. A pure cosmetic scope (paint, flooring, cabinet reface, one-for-one fixture swap) typically doesn't need ALT-2. Most meaningful renovations (kitchen with any MEP change, any bathroom gut, any layout change) do. Your registered architect or engineer files ALT-2 through DOB NOW; plan examination runs 4-10 weeks typical before permit issuance.

Does Local Law 97 affect my condo interior renovation?

Indirectly, not directly. LL97 regulates building-level emissions, not unit-level. Your interior renovation doesn't create a compliance obligation for you. It can affect you through (1) rising common charges if your building starts paying LL97 fines and funds mitigation through assessments, and (2) some condo boards now requiring electric heat-pump HVAC equipment at any replacement to support building-level compliance. If you're replacing through-wall HVAC as part of your renovation, electric heat-pump equipment is both LL97-aligned and often better-performing than legacy gas-fired PTAC equipment.

What does wet-over-dry mean and how does it affect my bathroom renovation?

NYC DOB enforces a rule that new wet rooms (bathrooms, kitchens, laundry) cannot sit over downstairs dry rooms (bedrooms, living rooms) without either written consent from the downstairs neighbor or board-approved waterproofing mitigation. Moving a bathroom or adding one in a location that wasn't previously wet is the classic trigger. Resolution options: (1) keep the new wet room in the existing wet footprint (stacked over the existing wet below), (2) get written consent from the downstairs unit owner, or (3) implement full continuous-membrane waterproofing with drain pans and leak detection, documented in your ALT-2 filing and approved by the board.

What insurance does my contractor need for a NYC condo renovation?

Minimum: $2M general liability per occurrence (many condos require $5M), workers' compensation current with NY State, and an alteration bond if the building requires one (typical $10K-$50K bond on projects >$200K). Your specific condo association must be named as additional insured on the contractor's GL policy — a named-insured endorsement, not just a certificate. A contractor who provides only a $1M certificate without the additional-insured endorsement is not adequately covered; a claim from a neighboring unit could bypass the contractor and hit you directly. Verify the endorsement documents before the project starts.

How long does a full NYC condo renovation actually take?

Design + alteration agreement + ALT-2 filing: 3-5 months. Plan examination at DOB: 4-10 weeks running in parallel. Permit issuance: 1-2 weeks after approval. Construction: 2-10 months depending on scope (mid-range gut ~4-5 months, full gut ~6-10 months, premium architectural ~10-16 months). DOB inspections and sign-off: 2-4 weeks at completion. Condo board final release: 2-4 weeks after DOB sign-off. Total end-to-end: 8-24 months from first design meeting to fully closed project. Starting construction before permit is legally risky; starting without a signed alteration agreement is commercially reckless.

---

Sources

Footnotes

1. New York Real Property Law Article 9-B (Condominium Act) — https://www.nysenate.gov/legislation/laws/RPP/A9-B. Establishes condominium ownership structure, board authority, and unit-owner rights. ↩

2. NYC Department of Buildings — Alteration Type 2 (ALT-2) filing requirements and DOB NOW filing portal — https://www.nyc.gov/site/buildings/index.page. Application categories and plan-examination process. ↩

3. NYC Local Law 97 of 2019 — Climate Mobilization Act emissions framework — https://www.nyc.gov/site/sustainablebuildings/ll97/local-law-97.page. Building emissions caps and compliance penalties. ↩

4. NYC Construction Codes Title 28 and referenced Residential Code — wet-over-dry and waterproofing requirements — https://www1.nyc.gov/site/buildings/codes/construction-codes.page. ↩