The Mold Inspection Checklist You Can Run Yourself

Run this before you pay anybody. It takes about an hour, it costs nothing, and in Arizona homes it finds the problem most of the time.

Take a torch, a phone for photos, and something to write on.

1. The AC closet or air handler (start here)

The single most likely location in any Arizona house.

Smell inside the closet, then run the system and smell again. Stronger with the system running is the classic sign.
Look at the floor and the bottom few inches of drywall around and behind the unit.
Look in the drain pan. Standing water means the condensate line is not draining.
Find where the condensate line discharges and check it drips when the system runs.
Check the secondary pan’s float switch is present and connected.
Look for anything stored in there, especially cardboard.

Any water or staining here is your answer. See mold in the AC closet.

2. Every supply line under a sink

Open every cabinet under every sink and smell inside.
Run a hand along the supply lines and the trap.
Feel the cabinet floor: stained, swollen, or soft.
Look at the back corners, where a slow leak collects.

3. Behind and under the water heater

Look at the pan, the floor, and the wall behind.
Check the age on the label. Past about ten to twelve years, it is living on time.

4. The laundry

Behind the washing machine: hoses, especially rubber ones.
The floor and the wall behind the machines.
If there is a drain pan, look in it.

5. Bathrooms

Ceiling above the shower: fine speckling is usually surface mildew from weak ventilation, not a remediation.
Test the exhaust fan by holding a square of toilet paper to the grille. If it does not hold, the fan is not moving air.
Grout and caulk at the tub and shower, especially at the base.
The wall on the other side of the shower: press the drywall at the base.
Under the vanity, and around the toilet base.

6. The floor, in bare feet

Walk the whole house. A warm patch on a slab floor is a hot-water slab leak.
Look for cupping, staining, or soft spots in wood, laminate, or LVP.
Look at the base of walls and at baseboards for staining or swelling.

7. The water meter

Shut off every fixture and appliance, including the ice maker.
Read the meter, wait an hour, read again.
Movement means water is escaping. That is a plumber’s call and it is one of the most useful hours you can spend.

8. The attic

With a torch, look at the insulation under any suspect ceiling area.
Look at the sheathing for staining, and at the underside of the roof around penetrations.
Check where the bathroom fans exhaust. A fan ducted into the attic instead of outside is very common here and it puts every shower’s moisture into your attic.
Look at the ducting for damage or disconnections.

9. Windows and doors

Sills and the wall below them, particularly on the weather side.
Condensation staining at the bottom corners.
Any window that has been replaced: the flashing detail is where problems start.

10. The roof and the exterior

From the ground, look at the roofline, any flat sections, parapets, and scuppers.
Look at the grade around the house: does it fall away or toward?
Look at where sprinklers hit. Irrigation against a wall is a slow, permanent problem.
Check where downspouts discharge, if there are any.

11. The whole-house smell test

Walk each room and score the musty smell out of five.
Turn the AC off for a few hours, then on, and see whether anything changes.
Smell at floor level and at nose height: low points at a slab or floor source, high at a ceiling or attic one.
Open every cabinet and closet and smell inside.

What the findings mean

What you found	What it points at
Water in the AC drain pan	Condensate overflow, the most common cause here
Warm spot on the floor, meter moving	Slab leak. Plumber first
Fine speckling on a bathroom ceiling, drywall firm	Surface mildew and a weak fan, usually not a remediation
Soft or spongy drywall anywhere	Water has been in the material. Get it looked at
Staining that returns after cleaning	An active water source above or behind it
Musty smell, nothing visible	The case where testing genuinely earns its fee
Wet insulation in the attic	A roof leak. Roofer plus dry-out
Nothing at all, but a smell persists	Check dry P-traps in unused bathrooms before assuming mould

The one that is not mould

Before spending anything on a persistent smell: run water in every rarely-used sink, shower, and floor drain for a minute. A dry P-trap lets sewer gas into the house, and it is mistaken for mould constantly, especially in guest bathrooms and in homes that sit empty part of the year.

Also worth ruling out: a failed plumbing vent, a dead rodent in a wall or attic, and old carpet pad.

When to call

The visual assessment is free, so there is no cost to being told it is nothing. Worth calling when you find a musty smell with no source, soft drywall, returning stains, anything around the air handler, or a meter that moves with everything off.

Inspection with sampling and independent lab analysis: $300–$700. Clearance testing: $250–$500. The remediation process page explains what happens if it turns out to be real, and the pricing page publishes every range.

We serve Glendale, Peoria, Sun City, El Mirage, and Youngtown.

Frequently Asked Questions

Can I inspect for mold myself?

The visual and smell part, yes, and most problems in Arizona homes are found exactly this way. What you cannot do yourself is see inside a wall, which is what a moisture meter and thermal imaging are for. Run this checklist first: it either finds it or tells you that you need the meter.

What is the number one place to check in an Arizona home?

The AC closet. The air handler condenses water out of the air all summer, that water drains through a condensate line, and a clogged line overflows the pan onto drywall in an enclosed space. It is the most predictable mould location in this valley and almost nobody looks there until there is a smell.

When should I stop and call someone?

When you find a musty smell with no visible source, soft or spongy drywall, staining that keeps returning, or anything in or around the air handler. Also when the water bill has moved with no explanation, which points at a slab leak. The visual assessment is free, so there is no cost to being told it is nothing.

How much does a professional inspection cost?

Visual assessment free. Inspection with air and surface sampling and independent lab analysis $300–$700. Clearance testing after a remediation $250–$500.