How it works: where basement and crawl space odors come from

Not every bad basement smell is mildew. Learn to separate a musty odor from sewer gas and from a natural gas leak, because each one has a different cause, a different urgency and a different person to call.

Lakewood has thousands of split-level and tri-level homes whose family room sits partly below grade. That design creates a cool, humid pocket in summer. Here is why it smells and what actually fixes it.

In a single-story ranch over a crawl space, the bedrooms sit directly on top of the problem. This guide traces the air paths from soil to pillow and explains which gaps matter most.

An evaporative cooler cools by adding water to the air. In a dry Colorado summer that works well upstairs, but the extra moisture can settle into a cool basement and feed the very smell you are fighting.

Colorado's dry air evaporates the water seal in an unused floor drain faster than many people expect. When that seal is gone, sewer gas comes straight up into the basement. The fix is often a bucket of water.

Fans can dry the surface of a carpet in a day, but the pad and the concrete underneath can stay wet much longer. That hidden moisture is why a basement can smell musty long after a leak looked finished.

Window wells are the low point of many Lakewood foundations. When they fill with leaves, snow or hail-storm runoff, water finds the window frame and the wall below it, and the smell follows.

Insulation stapled between floor joists was meant to keep a ranch's floors warm. Decades later, many batts have sagged onto the dirt, absorbed moisture or become nesting material, and they can be a major odor reservoir.

Soil under a house releases moisture every day, even in a dry climate. A ground cover keeps that moisture out of the crawl space air. Here is how the options differ and what separates a good installation from a sheet of plastic.

Colorado has widespread elevated radon, and many Jefferson County homes have a mitigation fan on the side of the house. That system does not remove odor, but the sealing it involves can change how a basement smells.

A crowded storage room can create its own musty smell even when the walls and floor are dry. Cardboard, paper and fabric soak up humidity, block airflow and give mildew plenty of surface to grow on.

Many Lakewood basements were finished decades ago with thin paneling over furring strips and a suspended tile ceiling. These materials can hide damp concrete, old leaks and mildew that keep a room smelling musty.

When a basement smells, the first instinct is to buy something that promises to kill the odor. Some of those products mask it, some cause new problems, and none of them dries a wet wall.

Deodorizing a basement before the moisture is fixed and any growth is removed is the most common way to waste money on a musty smell. Here is the sequence that tends to stick, and how to tell which stage you are at.

In a semi-arid place like Lakewood, much of the water against a foundation is put there by people: sprinkler heads, short downspouts and flower beds. Fixing the outside is often cheaper than fighting the smell inside.

Many mid-century houses in the west metro were connected to the sewer with clay tile or cast iron pipe. Decades of tree roots and shifting soil can open joints, and the result can be an odor that no amount of cleaning fixes.

A faint musty smell in a listing's lower level can mean anything from a dry drain to years of seepage. Buyers have a short window to find out which. This guide covers what to look for, ask and request.

Basement and garden-level units are common in Lakewood rentals, from duplex lower levels to older apartment buildings. When the air smells musty, some fixes are in the tenant's hands and others belong to the owner.