What Causes Mold Around the House

Knowing what causes mold to grow indoors can help you spot mold problem well before it gets out of hand, as well as effectively prevent mold contamination from happening in the first place.

Mold spreads around by releasing microscopic airborne spores which at some point can end up inside of your house. Once the spore lands on wet surface and certain conditions are met, it will start growing.

Mold needs these to grow

Mold Spores

Invisible to the naked eye, mold spores usually get inside your house from outdoor.


Prolonged exposure to wet conditions is required in order for mold to start growing.

A food source

The abundance of organic materials makes indoors a perfect breeding ground for mold.


A steady supply of oxygen plays a vital part in mold growth and reproduction cycle.

Lack of Sunlight

Direct exposure to sunlight is deadly to mold, that’s why it prefers to grow in the dark.

Optimal Temperature

Temperature levels of residential houses create optimal conditions for mold to grow.

So what exactly causes mold in a house?

In every major area of the house, there are plenty of possibilities for mold spores to flourish. Anything, from a plumbing problem to a lack of proper ventilation could lead to creating optimal conditions for mold to start growing indoors.

To learn more about what causes mold to grow in particular areas of your house, check out our detailed illustrations below.

Causes of Mold in Attic

Causes of mold in an attic.
  1. Minor and Major Roof Leaks
  2. Faulty or Missing Insulation
  3. Ice and Snow Damming Problems
  4. Improperly exhausted Dryer, Bathroom and Kitchen vents
  1. Heaters and Furnaces in the attic
  2. Condensation Effect during the cold season
  3. Improper Ventilation or lack of it

Causes of Mold in Basement

Causes of mold in a basement.
  1. Leaking plumbing pipes
  2. Flooding (nature or plumbing caused)
  3. Broken, clogged or sagged gutters or downspouts
  4. Clogged/Faulty footer drains
  5. Sump Pump failures
  6. Sloping grounds/ groundwaters
  1. Cracks in Foundation and Foundation Walls
  2. Rain and Melting Snow from windows
  3. Water Condensation on cold surfaces
  4. Lots of materials mold loves to grow on
  5. Dust and dirt accumulated with time
  6. Poor Air Ventilation / Circulation

Click here to learn more about how you can remove mold from your basement.

Causes of Mold in Crawl Space

Causes of mold in a crawl space.
  1. Bare earth floor with porous soil near foundation
  2. Missing or damaged Vapor Barrier
  3. Ground water due to high water tables
  4. Rain and Flood water
  5. Cracks in Foundation and Foundation Walls
  6. Plumbing related problems
  1. Faulty or missing Air Duct Insulation Materials
  2. Poor Ventilation or Lack of it
  3. Outdoor air getting into crawl space from outside
  4. Water Evaporation leading to condensation
  5. Exposed Plumbing Pipes and Joists

Click here to learn more about how you can remove mold from your crawl space.

Causes of Mold in Bathroom

Causes of mold in a bathroom.
  1. Plumbing Problems (Leaks & Overflows)
  2. Water Condensation on walls & ceiling
  3. Water Evaporation
  4. Frequently running watter
  5. Wet surfaces after showering
  1. Wet surfaces from Hot Steam
  2. Water Puddles on the floor and around sink
  3. Broken toilet and bathtub seals
  4. Poor Ventilation / Air Circulation
  5. Failed grout and/or caulking between tiles

Read more on our guide on how to remove mold from the bathroom.

Causes of Mold in Kitchen

Causes of mold in a kitchen.
  1. Water Leaks from Sink and Dishwasher
  2. Plumbing Problems (Leaks & Overflows)
  3. Water spills / Running tap water
  4. Condensation on plumbing pipes
  1. Steam from boiling water / cooking
  2. Steam from Dishwasher
  3. Plenty of food molds loves to grow on
  4. Poor Ventilation / Air Circulation

Read more on our guide on how to remove mold from the kitchen.

Causes of Mold in Air Ducts

Causes of mold inside an air duct or HVAC.
  1. Dust, dirt, debris and pet hair collected in the vent
  2. Clogged air duct filters
  3. Using basic fiberglass filters in houses with pets and other sources of micro-particles
  4. Leaks around duct joints
  5. Wetted fiberglass-lined ductwork surfaces
  6. Damaged or missing air duct insulation
  1. Damaged or missing foil vapor barrier
  2. Condensation on metal parts of HVAC units
  3. Improper use or absence of Drain Pans
  4. Improper mixing of outside and inside air
  5. Saturated air coming from air conditioner evaporator
  6. Weak (slow) air flow coming out of the grill

Read more on our guide on how to remove mold from the air ducts.

Causes of Mold on Outside the House

Causes of mold on the exterior of a building.
  1. The nearly constant presence of moisture
  2. Rainwater running down the wall surface
  3. Downspouts emptying next to the wall
  4. Siding made of porous materials such as wood, stucco, etc
  5. Vines and shrubs growing along the side of your house
  6. Broken, clogged or sagged gutters or downspouts
  1. Leaks and condensation from air conditioner drain lines
  2. Incorrectly placed sprinklers system
  3. Water wicking into the foundation from the sloping ground
  4. Poor ventilation in tight areas along the walls
  5. Abundance of organic materials mold loves to grow on


Need our services? At Above & Beyond, we offer a range of services including mold inspection and mold remediation to our customers in New Jersey and New York. Call now for free consultation @ (732) 490-5900.

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