IICRC S520: The Mold Remediation Standard Explained

Quick answer

The ANSI/IICRC S520 Mold Remediation Standard, formally the Standard for Professional Mold Remediation, is a voluntary, consensus-based industry standard from the Institute of Inspection, Cleaning and Restoration Certification that describes the procedures and precautions for remediating mold in buildings and their contents.

The IICRC lists the Fourth Edition, 2024, as the current edition. S520 covers remediation only. It is not a licence, it is not a law and it cannot tell you a building is free of mold. State rules on mold vary, and some states license the work.

Quick facts

The key facts about ANSI/IICRC S520 Mold Remediation Standard, with sources:

Full title: ANSI/IICRC S520, Standard for Professional Mold Remediation ¹
Current edition: Fourth Edition, 2024; earlier editions are 2015, 2008 and 2003 ¹
Scope: Mold remediation in buildings and their contents, including cleaners, antimicrobial chemicals, coatings, HVAC, structural and contents remediation and post-remediation verification ¹
Written for: People involved in the mold remediation industry ¹
Nature: Voluntary standard; not a law or a licence ³
Federal limits: EPA says there are no federal limits for mold, so a sample cannot be checked against a standard ⁷
State rules: Vary; some states license mold work and keep assessor and remediator separate ¹⁰¹¹

Key takeaways

S520 is the main industry standard for professional mold remediation. It is voluntary and sold, not free.
The current edition is the Fourth Edition, 2024, which the IICRC says is available on its webstore.
S520 covers remediation. It is not a licence, and it does not replace a state rule where one exists.
No federal limits for mold exist, so no sample can prove a building is mold-free or compliant.
Moisture comes first. Mold work that does not fix the water problem is likely to come back.

S520 in plain English

S520 is the written procedure that mold remediation professionals use as a reference.

The IICRC says it describes the procedures to be followed and the precautions to be taken when remediating mold in buildings and their contents.

It also covers mold cleaners, antimicrobial chemicals, coatings, HVAC, structural and contents remediation, and post-remediation verification, among other topics ¹.

The IICRC says the standard is written for use by those involved in the mold remediation industry, and that it was developed with input from microbiologists, public health professionals, industrial hygienists, remediation contractors and training schools ¹.

That mix of experts is the reason a standard like this exists: mold work touches health, building science and contracting at once.

Remediation means cleaning up and removing mold and moldy materials in a way that limits the spread of spores. It is a different job from inspecting or testing. A related IICRC standard, S530, is listed for indoor environment assessment of suspected mold-contaminated structures and carries a BSR/ prefix on the IICRC page ².

For the broader context, see IICRC standards in restoration, and for the service itself read mold remediation.

How mold remediation is planned, as public guidance describes it

Mold remediation steps follow EPA’s public guidance on remediation plans, not the text of S520. They show the logic any standard-based job follows.

Fix the moisture problem. EPA’s remediation chapter says the water or moisture problem must be completely fixed, or the mold problem may reoccur ⁷.
Write a plan. The plan should cover steps to fix the moisture, use of protective equipment, and steps to contain and remove moldy materials without spreading mold ⁷.
Protect the workers and the home. The plan should cover the use of appropriate personal protective equipment ⁷. Larger or contaminated projects need containment.
Remove and clean. EPA says dead mold may still cause allergic reactions in some people, so it is not enough to kill it; it must also be removed ⁵.
Revise if facts change. If hidden mold is found, EPA says to revise the plan to cover the whole affected area ⁷.
Check the result. EPA says visible mold, mold-damaged materials and moldy odors should not be present after cleanup, and calls the final judgment a judgment call ⁷.
Verify. S520 addresses post-remediation verification ¹. A professional assesses the work, and a sample does not by itself prove a building is clear.

Process The order of a mold remediation job

Fix the moisture sourceWithout this, mold returns
Plan the workProtection, containment and removal steps in writing
Contain and removeTake out mold and mold-damaged material without spreading it
CleanRemove remaining residue; killing mold alone is not enough
CheckNo visible mold, damaged material or odor; judgment, not a single test

Order follows EPA’s public remediation guidance. S520 adds detailed procedures that we have not reviewed. Source: [7] [5]

The order matters. Fixing moisture comes first, removal second, checking last. A job that starts with spraying and ends with a certificate has skipped the first step.

What S520 covers and what it does not

Topics are from the IICRC S520 page. "Not covered" items are the boundary of this standard, not a criticism of it.
Topic	Covered by S520?	Where to read more
Procedures and precautions for mold remediation in buildings and contents	Yes ¹	This page
Mold cleaners, antimicrobial chemicals and coatings	Yes ¹	EPA says routine use of biocides such as bleach is not recommended ⁵
HVAC, structural and contents remediation	Yes ¹	Contents restoration
Post-remediation verification	Yes ¹	The related list below
Indoor environment assessment of suspected mold	Separate standard, S530, listed with a BSR/ prefix ²	Assessor or remediator tool
Water damage restoration	No; that is S500	S500
Licensing and who may do the work	No; set by states ¹²	How we vet
Coverage by your policy	No	What is covered

Assessment and remediation are different jobs

Some states keep the person who assesses mold separate from the company that removes it. Florida bars a mold assessor from performing remediation on a structure the assessor assessed within the last 12 months, with an exception for certain contractors ¹¹. Texas licenses assessors and remediators separately ¹⁰.

Example: S520 editions over time

The IICRC page lists four editions of S520. The table and chart below show the gaps between them as simple arithmetic on those years. The gaps are our calculation, shown to make one point: standards are revised on their own schedules, so an older guide may cite an older edition ¹.

Edition	Year the IICRC lists	Years since the previous edition
First	2003	Not applicable
Second	2008	5
Third	2015	7
Fourth	2024	9

Chart Years between S520 editions

The IICRC lists S520 editions in 2003, 2008, 2015 and 2024, which puts 5, 7 and 9 years between each edition and the one before.

Years between S520 editions (years since the previous edition)
Item	Value (years since the previous edition)
Second (2008)	5 yrs
Third (2015)	7 yrs
Fourth (2024)	9 yrs

Data period: Edition years as listed on the IICRC S520 page, read 2026-10-14; the gaps are arithmetic by HyreRestore

Source: [1]

A guide written between 2015 and 2024 may cite the Third Edition, as the NIH 2023 procedure does when it lists S520-2015 ⁸. Northwestern University’s 2025 guide cites the 2024 edition ⁹. When a company says it works to S520, ask which edition.

Where S520 shows up in your project

In a remediation proposal. Mold companies may say they work to S520. Ask what that means for your job. See choosing a restoration company.

In institutional rules. Northwestern University’s guide says mold remediation must be conducted in accordance with the 2024 S520, and says projects larger than about 10 square feet should be addressed by a contractor ⁹. The NIH procedure names S520 as one of two standards at the foundation of its program ⁸.

In EPA’s advice. EPA tells readers that if mold covers more than about 10 square feet or there has been significant water damage, they should consider a professional, and to ask the contractor to follow EPA guidance or other guidelines from professional or government organizations ⁵.

In a verification step. Some jobs end with a professional check. S520 covers post-remediation verification ¹.

In state mold law. Some states write their own mold rules. See the section on state variation below.

What S520 does for a mold job, and what it cannot do

What it does

Gives remediation companies a common procedure drawn from many disciplines ¹.
Gives owners a vocabulary: remediation, verification, containment.
Gives institutions a reference to require in contracts ⁹⁸.
Supports the EPA principle that moisture control is the key to mold control ⁵.

What it cannot do

The S520 standard cannot make a company follow it. It is voluntary ³.
It cannot prove a building is mold-free. EPA says it is impossible to eliminate all mold and mold spores indoors ⁶.
It cannot replace a state licence or a state rule.
It cannot set a pass number for a sample, because no federal limits exist ⁷.
It cannot diagnose illness.

Limits of S520 and of this page

S520 is a purchased standard written for professionals. We have not reviewed it in full, and this page describes only what the IICRC and public guidance state. Where we cite a guide that follows S520, the guide’s wording is its own.

The standard does not make a building mold-free. EPA says it is impossible to eliminate all mold and mold spores in the indoor environment, and that mold growth can be controlled indoors by controlling moisture ⁶. A well-run job removes the mold and fixes the cause. It does not promise zero.

Testing has its own limits. EPA says that in most cases, if visible mold growth is present, sampling is unnecessary, and that a sample cannot be checked against a standard because there are no federal limits ⁵⁷.

EPA also warns that poorly planned sampling can produce misleading results ⁷. A single test cannot certify a building mold-free.

No certified industrial hygienist, mold assessor or IICRC-certified remediator has signed this entry. We do not diagnose illness or recommend any treatment.

Source and scope

HyreRestore is independent of the IICRC. Nothing here is an IICRC endorsement of this site or any company. S520 is not a licence, and state rules vary.

What drives the cost of work done to S520

We publish no restoration prices. Work to a mold standard costs more than a quick wipe-down for specific reasons: written planning, protective equipment, containment, careful removal and disposal of materials, cleaning, and verification. The size of the affected area and the type of material move the total most.

Whether a mold project needs outside help at all is the biggest swing. EPA says that if the moldy area is less than about 10 square feet, in most cases you can handle the job yourself ⁵. Larger areas, or areas with significant water damage, are where a professional enters.

Two other drivers matter. First, the moisture source: fixing it may be a plumbing or roofing cost outside the mold job. Second, verification: if your state or lender requires an assessor, that is a separate line. See the restoration cost guide and the cost estimator.

S520 has no warranty. A company’s workmanship warranty, if any, is in your contract. Read it and ask what happens if mold returns because moisture came back.

How to use S520 when you hire a mold company

A homeowner does not need to read the S520 standard. You need a short list of questions.

Find the moisture source first, and ask who will fix it and when.
Ask whether your state licenses mold work and whether the company holds the state license. Check the board directly ¹⁰¹².
Ask which edition of S520 the company works to.
Ask for a written remediation plan covering moisture, protection, containment and removal ⁷.
Ask how the company will confirm the work is done, and who does the checking. If your state separates assessor and remediator, see the assessor or remediator tool.
Ask how any change will be approved. See change orders.
Keep the plan, photos and invoices. See photo documentation.

After mold remediation: what keeps it from returning

Mold needs moisture. After remediation, the job is to keep moisture out.

Watch humidity. EPA advises keeping indoor humidity below 60 percent, ideally between 30 and 50 percent ⁵.
Dry water events within 24 to 48 hours. EPA says that in most cases mold will not grow if wet materials are dried in that window ⁵.
Fix leaks promptly. The moisture source is the cause.
Revisit the area. EPA recommends revisiting the site shortly after cleanup and checking for no signs of water damage or mold growth ⁷.
Keep the file. A buyer or insurer may ask what was done.

Warning signs in mold work

No plan on paper. EPA expects a plan that covers moisture, protection and containment ⁷.
Moisture not addressed. If no one fixes the source, mold returns.
Bleach or biocide as the main method. EPA says chlorine bleach and similar biocides are not recommended as a routine practice during mold cleanup ⁵.
A promise that mold will be gone. EPA says it is impossible to eliminate all indoor mold ⁶.
A single air test as proof. No federal limit exists to compare it against ⁷.
The same company assesses and removes without disclosure. Some states bar it; where none does, managing the conflict is your job ¹¹.

Safety and risk

Do not disturb a large area of mold, enter a space with suspected sewage or floodwater, or use fogging, ozone or chemical treatments in an occupied home. People with asthma, allergies or weakened immunity should leave remediation to professionals. This page is not medical advice; speak to a clinician about symptoms.

S520 as a standard: authority, edition and state law

Authority and edition. ANSI/IICRC S520, Standard for Professional Mold Remediation, is published by the IICRC. The IICRC lists the Fourth Edition, 2024 as available, with earlier editions in 2015, 2008 and 2003 ¹. The IICRC says it is a standards-developing organization accredited through ANSI ⁴.

Voluntary, not law. The IICRC describes its standards as voluntary consensus-based standards ³.

Federal position. EPA says there are no federal limits for mold ⁷. The NIH procedure says there are no federal regulations from OSHA, NIOSH or EPA for airborne concentrations of mold spores ⁸.

State law. Rules differ. Texas licenses mold assessors and remediators under Occupations Code Chapter 1958, administered by the Texas Department of Licensing and Regulation ¹⁰.

Florida’s statute 468.8419 bars a mold assessor from remediating a structure the assessor assessed within 12 months, bars accepting or offering referral compensation with a remediator, and bars inspecting for a fee a property in which the assessor has a financial interest ¹¹. A state with no mold licensing has no such rule.

Contract and policy. A contract or insurer can require S520. Read both. This is general information, not legal advice.

S520 vs S500 vs a licence vs EPA guidance

Item	What it covers	Nature	Who controls it
ANSI/IICRC S520	Mold remediation procedures ¹	Voluntary standard	IICRC consensus body
ANSI/IICRC S500	Water damage restoration	Voluntary standard	IICRC consensus body
State mold licence	Who may assess or remediate mold ¹⁰	Law, where the state has one	State agency
EPA guidance	Moisture control and cleanup advice ⁵	Federal guidance, not a rule	EPA
Your remediation contract	The work agreed	Contract	You and the company
Your insurance policy	What the insurer pays	Contract	You and the insurer

Common S520 and mold remediation myths

Myth S520 is a licence.: Reality It is a standard. The IICRC describes its standards as voluntary ³. State boards issue licences ¹⁰.
Myth A clean test proves the home is mold-free.: Reality EPA says no federal limits exist, so a sample cannot be checked against a standard, and that it is impossible to eliminate all mold ⁷⁶.
Myth Bleach is the right fix.: Reality EPA says chlorine bleach is not recommended as a routine practice during mold cleanup ⁵.
Myth Killing mold is enough.: Reality EPA says dead mold may still cause allergic reactions in some people, so it must also be removed ⁵.
Myth Any restoration company can do mold work in any state.: Reality Some states license it. Check your state ¹⁰¹².
Myth Following S520 means the IICRC endorses the company.: Reality Nothing we found says so, and nothing here implies it.

What varies by state: mold licensing and the assessor-remediator split

Mold rules are state law, not national law. Texas licenses mold assessors and remediators separately ¹⁰.

Florida bars a mold assessor from performing remediation on a structure the assessor assessed within the previous 12 months, with an exception for a certified Division I contractor, who may have to disclose the right to request competitive bids ¹¹.

Other states may license neither role, so check yours. Where no law names the conflict of interest, managing it is up to you. NASCLA’s directory compares contractor licensing across states ¹².

When S520 matters most, and your next step

S520 matters most for larger areas of mold, mold after significant water damage, and any job where a lender, insurer or state rule asks for a written protocol. For a small patch on a hard surface, EPA’s guidance for small areas may be enough, as the service guide explains.

Your next step is to find and fix the water source, then ask any company three questions: which edition of S520, what is in the written plan and who will check the result. Read what a restoration contractor is before comparing bids.

Decision guide S520 decision guide

If Mold area is small and on a hard surface: Then Follow EPA’s small-area guidance; S520 may not be needed
If Mold area is large or follows significant water damage: Then Ask a professional; ask for a written plan and the S520 edition
If A company offers a single air test as proof: Then Ask what it is compared to; no federal limit exists
If Your state licenses mold work: Then Check the license with the state board before you sign

Questions about ANSI/IICRC S520 Mold Remediation Standard

What is IICRC S520?

ANSI/IICRC S520 is the Standard for Professional Mold Remediation. It describes the procedures and precautions for remediating mold in buildings and their contents. The IICRC lists the Fourth Edition, 2024 as available. It is voluntary, it is sold by the IICRC and it is not a licence or a law.

What edition of S520 is current?

The IICRC says the ANSI/IICRC S520 Fourth Edition, 2024 is available on its webstore. Earlier editions are listed as 2015, 2008 and 2003. Some public guides still cite the 2015 edition, so ask any company which edition it uses and note the answer.

Is S520 a license to remove mold?

No. S520 is a standard. A licence is permission from a state board. Some states license mold assessors and remediators, such as Texas, and others do not. Check your state licensing board and ask the company for its license number where one is required.

Does following S520 mean mold will not come back?

No. Mold needs moisture, and EPA says the water or moisture problem must be fixed or the mold problem may reoccur. A job to S520 should include a plan to fix the source. EPA also says it is impossible to remove every mold spore from indoor air.

Can a mold test prove my home is clean?

No. EPA says there are no federal limits for mold, so a sample cannot be checked against a standard, and that sampling is unnecessary in most cases when visible mold is present. A single test cannot certify a building mold-free. A professional checks the work, and the result is a judgment.

Should I use bleach on mold?

EPA says chlorine bleach and similar biocides are not recommended as a routine practice during mold cleanup, and that dead mold may still cause allergic reactions, so mold must be removed. For small areas, follow EPA’s guidance. For larger areas, hire a professional.

How big a mold area can I handle myself?

EPA says that if the moldy area is less than about 10 square feet, roughly a 3 foot by 3 foot patch, in most cases you can handle the job yourself.

Larger areas or significant water damage call for a professional. Do not disturb mold if anyone in the home has asthma or a weak immune system.

Does the same company inspect and remove mold?

In some states that is restricted. Florida bars a mold assessor from remediating a structure assessed within the last 12 months, with an exception for certain contractors. Texas licenses the two roles separately. In states with no rule, ask whether the company that tests will also bill for the removal.

Do I have to buy the S520 standard?

No. The IICRC sells it through its webstore. You can hire a company without buying it. Ask the company which edition it uses and ask for a written plan that covers fixing moisture, protection, containment and removal, as EPA’s guidance describes.

Sources

IICRC, S520 standard page (Fourth Edition 2024, scope, edition history), retrieved October 14, 2026.
IICRC, IICRC Standards (list of standards and field guides), retrieved October 14, 2026.
IICRC, Standards FAQs, retrieved October 14, 2026.
IICRC press release, S500 Consensus Body position statement (March 16, 2026), About the IICRC paragraph, retrieved October 14, 2026.
U.S. EPA, A Brief Guide to Mold, Moisture and Your Home, retrieved October 14, 2026.
U.S. EPA, Mold Remediation in Schools and Commercial Buildings, Chapter 1, retrieved October 14, 2026.
U.S. EPA, Mold Remediation in Schools and Commercial Buildings, Chapter 3 (remediation plan, success criteria, sampling), retrieved October 14, 2026.
National Institutes of Health, Moisture and Mold Remediation Standard Operating Procedures (2023), retrieved October 14, 2026.
Northwestern University Environmental Health and Safety, Water Intrusion Guide (September 2025), retrieved October 14, 2026.
Texas Department of Licensing and Regulation, Mold Assessors and Remediators laws and rules (Occupations Code Chapter 1958), retrieved October 14, 2026.
Florida Legislature, Fla. Stat. 468.8419 Prohibited acts (mold assessors), retrieved October 14, 2026.
NASCLA, Contractor State Licensing Information Directory (CSLID), retrieved October 14, 2026.

Expert review

Written by the HyreRestore Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.

How the numbers were checked: Edition, scope and audience come from the IICRC S520 page. Remediation sequence, success and sampling statements come from EPA’s Mold Remediation in Schools and Commercial Buildings and EPA’s Brief Guide.

Florida and Texas rules were read from the Florida Legislature page and the TDLR rules page. S520 is a paid standard; no text or tables are reproduced and it was not reviewed in full.

No certified industrial hygienist, mold assessor or IICRC-certified reviewer has signed this page. No prices or timelines are given, and nothing is medical advice.

Suggest a correction. We fix errors and say what changed.