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Resource · Law & complianceMold Remediation vs DIY Removal: What NYC Law Actually Requires
Landlords who exceed the threshold without a licensed contractor face HPD exposure.
Reading time 5 minutes · Legal explainer
Under 10 Square Feet, DIY Is Legal. At or Above It, a Licensed Contractor Is Required.
New York law defines exactly where DIY ends and licensed remediation begins.
That boundary is 10 square feet. Under it, a property owner or tenant can legally clean mold themselves. At or above it, a licensed mold remediation contractor is required — someone holding a current NY State Mold Remediation Contractor License. There are no exceptions for residential buildings and none based on mold type.
The licensing requirement comes from Article 32 of NY State Labor Law, administered by the NY State Department of Labor mold program. Article 32 also separates the roles: the company that assesses a mold problem cannot be the company that remediates it on the same project, and the post-remediation clearance assessment must be performed by an independent licensed assessor.
On top of that sits the city layer. NYC’s Local Law 55 of 2018 — the Asthma-Free Housing Act, codified at Admin Code §27-2017.1 and following — makes indoor mold an owner responsibility in multiple dwellings and gives HPD its enforcement powers. Owners of buildings with ten or more units must engage a licensed assessor and a licensed remediator, independent of each other, whenever more than 10 square feet of mold is present. HPD’s adopted rules set out the work practices.
The number is 10 square feet. Everything on this page builds from it.
Where the 10 Square Foot Rule Applies in NYC’s Rental Housing Stock
The threshold applies to the total affected area — not just what is visible on the surface.
A bathroom wall with visible mold covering 8 square feet may look like a DIY situation. If there is additional growth behind the drywall — which moisture meter readings frequently reveal — the combined area crosses the threshold. The requirement applies to what exists, not to what is visible.
Mold Water Remediation dispatches from 1419 Coney Island Ave in Brooklyn. That puts the crew within direct reach of Brooklyn, Queens and Manhattan, where rental housing density is highest and where tenants and landlords most frequently face this exact question.
NYC’s pre-war building stock, with its plaster-and-lath walls, means the gap between surface mold and actual mold extent is often significant. Plaster retains moisture longer than modern drywall and conceals what is behind it. The visible patch is rarely the full picture — which is what moisture detection is for.
From the field
Know the Legal Threshold Before You Spend a Saturday on the Wrong Solution
“The surface looked clean when they finished. Three or four weeks later the mold came back — same spots, plus new growth along the baseboard.
I have been running Mold Water Remediation since 2016. Here is a situation I see regularly. Someone spent a weekend cleaning mold off a bathroom wall with a spray product from a hardware store. What happened next comes down to three things, and they almost always happen together.
First, the moisture source inside the wall was never addressed. The surface cleaning removed visible colonies. The conditions that fed those colonies — elevated humidity inside the wall cavity, a slow drip from an aging pipe joint, inadequate exhaust ventilation — remained exactly as they were.
Second, there was no containment. Containment is the physical step that separates licensed removal from a cleaning attempt, and its absence is the main way DIY work spreads contamination into areas that were clean before the project started. When you clean mold without it, you disturb the colony and spore dispersal deposits growth elsewhere.
Third, the affected area was larger than the surface suggested. The wall mold was the visible result of growth that had already extended behind the drywall paper. A surface clean does not reach that material.
When we get called after a DIY attempt, I start from scratch. New moisture readings across the full zone, new surface assessment, and documentation of what the prior effort produced. The written work plan we submit before remediation reflects current conditions — which is exactly what the law requires. That documentation trail is something no cleaning attempt can produce, and it is what matters during an HPD review or an insurance evaluation.
How Licensed Remediation Handles What DIY Cleaning Cannot
Landlord exposure is real, and it surfaces specifically at HPD re-inspection.
Here is how it typically plays out. A tenant in a Queens rental reports mold to HPD. The landlord sends a building employee to clean it. The area is above 10 square feet. HPD re-inspects and the violation stays open, because the condition was addressed by an unlicensed person.
The exposure does not arise from the cleaning itself. It arises from the documentation gap. There is no work plan. There is no clearance record. There is nothing an inspector can review to confirm the condition was properly remediated.
HPD classifies mold conditions by severity, and the most serious class carries a correction period measured in weeks, with civil penalties attached to violations that stay open. A cleaning attempt, however thorough, does not close one of those violations. It can extend it.
The licensed path produces documentation. The DIY path does not. Beyond the physical work itself, that is the practical difference between the two — and it is why licensed mold remediation is scoped the way it is.
What Licensed Mold Remediation Actually Involves
Mold Water Remediation Corp holds NY State Mold Remediation Contractor License #24-6A4P4-SHMO, issued July 2, 2024 by the Division of Safety and Health in Albany.
- Written work plan submitted before work begins — documenting the affected area, containment design, removal methods and verification standard
- Physical containment installed before any mold is disturbed — preventing spore dispersal into adjacent spaces
- Moisture source identification included in scope — removal without addressing the source produces the same result as a surface clean
- Licensed removal to the boundary the moisture data shows — not where the mold is visible, but where the readings confirm it has reached
- Independent post-remediation clearance — air sampling by a licensed assessor who is not us, as Article 32 requires
- Post-remediation documentation — a written record of the completed scope, available for HPD response or an insurance file
Every seam sealed. Every step documented.
What Shapes the Decision Between DIY and Licensed Remediation
Four variables determine whether DIY is a legal and practical option for your situation.
Total affected area
Measure the full zone, not just what is visible. If any portion sits behind a wall or ceiling surface, the true area is likely larger than the surface reading. At or above 10 square feet, the decision is made by law rather than by preference.
Moisture source status
If the source has not been fixed, neither cleaning nor licensed remediation produces a lasting result. Remediation includes source identification. A cleaning attempt typically does not.
Building type and wall construction
Plaster-and-lath walls in pre-war NYC buildings retain moisture behind the surface far longer than drywall. The same surface pattern means something different in a 1920 Brooklyn brownstone than in 1990 construction.
Documentation need
With an open HPD violation, a pending insurance claim, or a landlord-tenant dispute, a written work plan and clearance record are not optional. They are what closes the violation and supports the claim.
Areas We Serve
Mold Water Remediation serves all five NYC boroughs from our Brooklyn dispatch base.
Neighborhoods we regularly work in include Flatbush, Crown Heights, Park Slope, Astoria, Jackson Heights, Harlem, Washington Heights, the South Bronx and Bay Ridge. If the mold area is at or above 10 square feet, we are licensed to address it.
Not Sure Which Side of the Line You Are On?
Call and describe the space — size, building type, borough. We will measure what is actually there and tell you exactly where the legal requirement applies.
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