Mold Guides · Room-Specific & Commercial Mold

Mold in the Garage: Causes and What to Check

The garage is a room that is often treated as outside the house, and that is exactly why mold grows there. It is not heated or cooled like the rest of the home, it is not ventilated, and it is full of damp items: a car that comes in wet from the rain, boxes stored on the floor, tools, paint, and old furniture. The garage is also the room where leaks are noticed last, because no one lives in it and no one looks at it closely.

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This guide covers the causes of garage mold, what to check, and what an inspection looks at. Our mold removal page covers the service, and homes in Baton Rouge and across Louisiana share the same garage conditions.

Why garages grow mold

Garages grow mold because they are damp, unventilated and full of things that hold moisture. A car that comes in wet from the rain drips water onto the floor, and the floor stays damp because the garage is not heated and the air does not move. Boxes stored on the floor absorb that moisture, and the cardboard holds it, so the boxes and the floor beneath them stay damp. Tools, paint, old furniture and stored clothes add more material that absorbs moisture and holds it.

In a garage, a leaking roof or a wall that lets rain through adds steady moisture to everything stored inside. A roof leak over the garage, a wall that lets rain in, or a door that does not seal can let water into the garage, and because no one lives in the garage, the leak can go unnoticed for months. The garage is also often the lowest part of the house, so water from the yard can run into it, and the floor can stay damp after every heavy rain. In a Louisiana home, where the rain is frequent and the humidity is high, a garage can stay damp for much of the year.

Where garage mold appears

Garage mold appears on the walls, especially near the floor and in the corners, on the ceiling, on the stored items, and on the floor itself. The walls near the floor are the most common place, because water that comes in under the door or through the wall pools at the base of the wall and soaks into the drywall or the wood. The ceiling is the next most common, because a roof leak drips onto it, and the growth follows the moisture.

Stored items are the other place to look. Boxes that have been on the floor for a long time, especially cardboard boxes, can grow mold on the bottom and the sides, and the growth can spread to the items inside. Old furniture, stored clothes and tools can all grow mold if they have been damp for long enough. The pattern of where the growth appears often points to the cause: growth near the floor points to water coming in at ground level, growth on the ceiling points to a roof leak, and growth on stored items points to damp that has been there for a long time.

Mold in the Garage: Causes and What to Check — Louisiana mold guide

Stored damp items

Stored damp items are the main source of garage mold that homeowners control directly. Boxes stored on the floor absorb moisture from the concrete, and the cardboard holds it, so the boxes and the floor beneath them stay damp. Items stored in the garage after a flood, or after being rained on, bring moisture into the space, and if they are not dried before they are stored, they stay damp and the growth follows.

The habit to change is simple: store items off the floor, on shelves or pallets, so that air can move beneath them and the floor can dry. Do not store items in the garage that are wet, and do not store cardboard boxes directly on the concrete floor. Keep the garage reasonably clear, so that you can see the floor and the walls, and so that a leak can be noticed before it becomes a problem.

Ventilation and drainage

Ventilation in a garage is often poor, because the garage is not designed as a living space. The door is closed most of the time, there are no windows, or the windows are small, and the air does not move. Opening the garage door for a while on a dry day, or opening a window where the garage has one, lets air move through the space and dries it out. A garage that is never opened stays damp, and the damp stays.

Drainage outside the garage matters too. If the ground around the garage slopes towards it, rainwater runs into the garage under the door, and the floor stays damp after every storm. Keeping the grading sloping away from the garage, and keeping the gutters and downspouts clear, keeps water away from the building. These are general points, not a repair plan, and a professional inspection can show which of them applies to your garage.

What an inspection checks

An inspection of a garage checks the walls, the ceiling, the floor, the stored items, and the roof and the drainage outside. The inspector looks for staining, damp, a musty smell, and the signs of water entry, and uses moisture readings in the walls and the floor to map how far the damp has spread. The inspector also looks for the source: a roof leak, water coming in under the door, or damp stored items, and explains what the next steps are.

Homes in Shreveport and Alexandria follow the same steps, and the mold inspection and testing page explains the first stage. The garage is not a living space, but it is part of the house, and what grows in it can affect the rooms next to it. A regular look at the garage, especially after heavy rain, is one of the simplest habits a Louisiana homeowner can keep.

The garage through the wet season

The garage through the wet season is the garage at its dampest, because the rain is frequent, the car comes in wet, and the air is humid. The floor stays damp, the boxes on the floor absorb moisture, and the walls near the floor stay wet. A garage that is checked after every storm, and that is ventilated on dry days, will stay drier than a garage that is never opened and never looked at. The habit of opening the garage door on a dry day, and of looking at the floor and the walls after a storm, is the habit that keeps a garage dry through the wet season.

The wet season is also the time to check the things that keep water out of the garage: the roof, the door seal, and the grading around the building. A roof that leaks over the garage, a door that does not seal, or ground that slopes towards the garage will all let water in, and the wet season is when they show themselves. A garage that is checked through the wet season is a garage whose problems are caught early, when they are a roof repair or a door seal, rather than late, when they are a floor full of growth.

Key Takeaways

Garages grow mold because they are damp, unventilated and full of things that hold moisture.
Garage mold appears on the walls, especially near the floor and in the corners, on the ceiling, on the stored items, and on the floor itself.
Stored damp items are the main source of garage mold that homeowners control directly.
Ventilation in a garage is often poor, because the garage is not designed as a living space.
An inspection of a garage checks the walls, the ceiling, the floor, the stored items, and the roof and the drainage outside.
The garage through the wet season is the garage at its dampest, because the rain is frequent, the car comes in wet, and the air is humid.

Questions About Mold in the Garage: Causes and What to Check

Why does mold grow in garages?

Garages are damp, unventilated and full of items that hold moisture. A wet car drips onto the floor, boxes stored on the floor absorb moisture, and leaks from the roof or under the door go unnoticed because no one lives in the garage.

Where does garage mold usually appear?

On the walls near the floor and in the corners, on the ceiling where a roof leak drips, on stored items, and on the floor itself. Growth near the floor points to water at ground level, growth on the ceiling points to a roof leak.

How can I prevent mold in the garage?

Store items off the floor on shelves or pallets, do not store wet items or cardboard boxes directly on concrete, open the garage door or a window on dry days to ventilate, and keep grading sloping away from the garage.

What does an inspection check in a garage?

It checks the walls, ceiling, floor, stored items, and the roof and drainage outside, using visual signs and moisture readings to map the damp and find the source, whether that is a roof leak, water under the door, or damp stored items.

Your Next Step

If this guide matches what you found at home, the next step is a visit — not a guess. Call and describe what you found, and the visit is arranged from what you describe. The Mold Removal page explains what that service covers, and the mold remediation page explains how the full sequence works when mold has spread to more than one room.

Do not enter flooded rooms while you wait, and if water is leaking, turn off the shut-off valve for that fixture where you can reach it safely from dry ground.

Keep the guides on this site bookmarked: the first guide, the signs guide, and the preparation guide cover the checks worth repeating — after moving in, and after bringing used fixtures home.

Mold help is available across Louisiana. See mold remediation in Mandeville, LA for one local example, or find your town on the service areas page.