Today

Over 100 square feet: full containment, professional only

At this size the EPA's remediation guide calls for full containment under negative pressure. That much growth also means a lot of water went somewhere, and it may still be there.

What is probably happening

A long running leak, a flood that was not dried within 24 to 48 hours, or a building wide humidity problem.
Growth this widespread is usually inside wall cavities and under flooring, not just on the surface.
If the HVAC ran while this grew, the system may be carrying it too.

Do this in the next five minutes

Anyone with asthma, allergies, lung disease or a weak immune system should sleep elsewhere until a contractor has looked.
Turn the HVAC off if the mold is near a return or the smell is stronger when it runs. The EPA says not to run a system you suspect is contaminated.
Photograph everything. Measure. Note where water stains are.
Call your insurer and ask whether the cause is a covered event. Do it before signing anything.
Get a written protocol from an independent assessor before any remediator bids. That is the law in Texas and New York, and good practice everywhere.

Do not

Do not start pulling materials out. Full containment exists so the rest of the house does not get seeded.
Do not sign an Assignment of Benefits at the door.
Do not accept a quote that skips the moisture source. The EPA: if the moisture is not corrected, mold growth will recur.

Who to call

A mold remediation contractor working to an independent protocol

The assessor writes the scope and verifies the result. The remediator does the removal. Keeping those two apart is what stops the scope from growing to fit the invoice.

Also: Water damage. If anything is still damp, or you cannot say where the water came from, call restoration first. Drying comes before removal. Questions for that call ›

Get a free shortlist The seven questions for this trade

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What it should cost

$10,000 to $30,000

Whole house remediation. Wall mold alone runs $1,000 to $20,000. Most jobs charge $10 to $25 per square foot

Source: Angi, mold remediation cost, July 2026. View source

National published range, not a quote for your job. The full cost table for this trade is on the mold page.

Ask this contractor, on the phone, before anyone comes out

Tap each one as you ask it.

Who wrote the protocol, and are they independent of your company?
Describe the containment: sheeting, negative air machines, decontamination chamber?
What is the moisture source, and who is fixing it?
Who does the post remediation verification and what does pass look like?
What is your state mold license number, if my state has one?

End the call if

The same company tests, writes the scope, removes and clears. Texas, Florida and New York all bar that.
A price per square foot with no square footage on the paper.
An Assignment of Benefits pushed at you on the spot.

Insurance. Mold is generally covered only when it follows a covered sudden water loss. Report hidden water damage within days of finding it, and mitigate. Gradual leaks, seepage and flood are excluded. (Texas Department of Insurance)

Where this comes from

Not my problem, tap through instead Every mold answer