Attic mold in Glendale: the evaporative cooler question

Attic mould in Glendale surprises people, because everything about the climate says it should not happen. They are right, and that is the point: attic mould here is not humidity, it is a moisture source you have not found.

A Glendale attic in July is extremely hot and very dry. Nothing grows in that. So something is putting water up there, and in this city there is one candidate that does not exist in newer suburbs.

The evaporative cooler

A swamp cooler is the only appliance in a desert home whose entire purpose is to add moisture to the air. Glendale’s older housing stock has a lot of them, some in use, many sitting disused on a roof.

The ways one wets an attic:

A float valve or overflow that leaks. The unit holds water and sits on the roof, usually right above the attic. A failed float or blocked overflow puts water where the unit is.

Running while the house is shut up. A swamp cooler needs open windows to work; run it in a closed house and you are pushing moist air into a space with nowhere to vent, which raises indoor humidity substantially and finds cold surfaces.

Unsealed ducting. The cooler’s duct drops through the roof and into the ceiling. Where that transition is not properly sealed, moist air goes into the attic instead of into the room.

A disused unit nobody decommissioned. This is the one people forget. An abandoned cooler is a roof penetration that nobody maintains, often with its supply line still connected and its duct still open into the house. Either seal and decommission it properly or take it off.

Our swamp cooler mould guide covers the indoor side of this.

The other three sources

A bathroom or laundry fan venting into the attic. The duct terminates in the attic rather than through the roof, or fell off the roof jack. Every shower pushes warm wet air onto the roof deck underside. Mould concentrated above a bathroom points here.

Refrigerated air ducts sweating. On homes converted to or built with refrigerated air, cold ducts in a very hot attic condense wherever their insulation is compressed, torn or degraded. A duct that has come apart dumps conditioned air into the attic and makes it much worse, while also raising the power bill.

A roof leak, found after monsoon. Storms from mid-June through September drive water under tiles and through flashing that is fine in ordinary rain. The tell is a defined path down rafters and sheathing rather than a general bloom. On a house with an old cooler on the roof, that penetration is a prime suspect.

Why it matters when nobody goes up there

Air moves between attic and house through can lights, fan housings, duct boots and the attic hatch. What grows up there does not stay up there.

The roof structure is up there. Sustained moisture on sheathing is a wood problem before it is an air quality problem, and sheathing costs far more than insulation.

What a proper job looks like

1. Fix the water first. Cooler repaired, decommissioned or removed; fan ducted outside; duct reconnected and insulated; roof repaired. Remediation before this is money spent twice.
2. Contain the area.
3. Remove affected insulation, usually the largest single cost.
4. Treat and clean sheathing and framing.
5. Check the sheathing is sound.
6. Replace insulation.
7. Verify before closing up.

What it costs

Affected area and insulation removal are the two variables. The remediation cost calculator prices it from the same table as the pricing page.

Get a quote

Tell us whether the house has an evaporative cooler, in use or abandoned, whether the mould is above a bathroom, and whether there has been a monsoon leak. We cover Glendale, Peoria, Sun City, El Mirage, and Youngtown.