What Are IICRC S520 Standards for Mold Remediation?

The Rulebook Nobody Gave You — But Your Contractor Supposedly Follows

If you've hired a mold remediation company — or you're about to — you've probably heard them mention "IICRC S520" like it's common knowledge. They might have said they're "S520 certified" or that they "follow S520 protocols." And you nodded, because what else are you going to do? Ask them to explain a 200-page technical document while you're standing in your moldy basement trying not to breathe too deeply?

Here's the thing: you don't need to read the whole standard. I've read it. Multiple times. In roughly the same way I used to read clinical protocols in nursing — carefully, skeptically, and with an eye toward what actually matters in the field versus what looks good in a document.

What you need is to understand the core principles. Because once you know those, you can tell the difference between quality remediation and expensive theater. One costs the same as the other. Only one of them actually works.

What Is IICRC S520?

The IICRC (Institute of Inspection, Cleaning and Restoration Certification) develops standards for the cleaning and restoration industry. S520 is their standard specifically for professional mold remediation — the closest thing the industry has to a consensus on how mold work should be done.

It's not a law. There's no federal regulation that says remediation companies must follow it. Oklahoma doesn't have state mold remediation licensing that requires S520 compliance. But it's the benchmark that insurance companies, courts, and professional associations reference when evaluating whether work was done correctly.

Think of it as the standard of care. In nursing, the "standard of care" isn't always written law either. But if you deviate from it and something goes wrong, you'd better have a very good explanation. Same concept.

The Three Conditions — The Classification System

S520 classifies mold contamination into three conditions. Understanding these is like understanding the triage system in an ER — it tells you the severity, the response required, and the goal of treatment.

Remediation moves spaces from Condition 3 (or 2) back to Condition 1. That's the measurable goal that clearance testing verifies. When I do post-remediation verification, I'm specifically determining: has this space achieved Condition 1?

The Core Principle: Source Removal — Not Chemical Warfare

Here's the most important thing S520 says. And it's the one that a lot of remediation companies would prefer you didn't know:

"You can't spray your way out of a mold problem. Dead mold can still make you sick. The standard says remove it — not kill it, not encapsulate it, not fog it into submission."

The fundamental principle of S520 is source removal — physically removing mold-contaminated materials and cleaning surfaces. Not killing mold. Not encapsulating it. Not treating it with chemicals and calling it done.

Why? Because dead mold can still cause health effects. Mold fragments and spores are allergenic whether the organism is alive or not. Spraying bleach on mold doesn't remove the problem — it just makes the mold quieter while leaving the contamination in place. It's cosmetic, not clinical.

In nursing, we had a similar principle. You don't treat a wound by covering it with something pretty and hoping the infection resolves itself. You debride. You clean. You remove the source. And then you cover it. Same logical sequence, different context.

S520 is clear: antimicrobial chemicals and coatings are supplements to physical removal, not replacements for it. They should be used "judiciously" and cannot substitute for actually removing the contaminated material.

So when a remediation company shows up with a fogger and tells you they're going to "treat" the mold — ask them about source removal. Ask them what's getting physically taken out. If the answer is "nothing, we're just treating it" — that's a deviation from the industry standard, and you should know that going in.

Independent Assessment and Verification

S520 has something important to say about who should be evaluating remediation work, and this is the part that matters most to you as a homeowner trying to figure out who's telling you the truth:

An Indoor Environmental Professional (IEP) conducting assessment or post-remediation verification should be independent from the remediation company. If they're not — if the same company doing the work is also verifying the work — that deviation from the standard must be disclosed in writing to the client.

Read that again. The standard itself acknowledges that having the same company do both the work and the verification is a deviation. They don't prohibit it, but they flag it. And they require disclosure. Because the conflict of interest is obvious enough that the standard's authors felt it needed to be called out explicitly.

This is exactly the business model I work under. I don't do remediation. I can't profit from failing you or from passing you. I'm the independent verification the standard is talking about — not as a marketing position, but as a structural characteristic of how I operate.

What S520 Requires for Post-Remediation Verification

According to the standard, proper verification includes:

• Visual inspection — confirming visible mold has been removed and surfaces are properly cleaned. Not "looks okay" — actually documenting the state of every treated area.
• Air sampling — comparing indoor spore levels to outdoor baseline to verify Condition 1. Numbers compared to numbers, species identified, methodology documented.
• Moisture assessment — verifying that moisture sources have been addressed to prevent recurrence. Because getting to Condition 1 today and Condition 3 next month isn't success.
• Documentation — written report with findings and a clear determination of whether clearance was achieved. A report that insurance companies can evaluate, that you can keep for future reference, that means something.

This is what proper clearance testing includes. If your remediation company is doing something less than this — or doing it themselves rather than engaging an independent IEP — that's a deviation from the industry standard. They might have good reasons. But you should know it's a deviation.

Why This Matters to You

You're not going to memorize S520. That's not the point. The point is understanding four things that give you the ability to evaluate whether you're getting quality work:

1. There IS a standard — professional mold remediation isn't just "whatever the company decides to do." There's a documented consensus on proper practices. Remediation companies that claim to follow it should be able to explain how.
2. Source removal is non-negotiable — if a company is primarily "treating" mold with chemicals rather than removing it, they're not following the standard. Ask questions. Understand the approach.
3. Independence matters — the standard specifically recommends independent verification. Companies that certify their own work are deviating from industry consensus. They might do great work. But you're taking their word for it without the safeguard the standard recommends.
4. Condition 1 is the goal — remediation should return your space to normal fungal ecology. That's measurable. That's verifiable. And you should require verification.

How I Use S520

When I do post-remediation verification, I'm applying S520 principles. Not because the law requires it — Oklahoma doesn't mandate S520 compliance — but because the standard represents the best available consensus on how this work should be done. And when a homeowner hires me, they're hiring the standard, not just a person with a moisture meter.

I'm independent from the remediation contractor. I do visual inspection, air sampling, and moisture assessment. I verify whether Condition 1 has been achieved. I provide written documentation of my findings. If the work passes, you have documentation that the remediation met industry standards. If it fails, you know what still needs to be addressed — before you pay the contractor and close the wall back up.

You're free to decide this level of verification isn't necessary. That's your right. But now you know what the standard says, and you know what the alternative looks like.