Please ensure Javascript is enabled for purposes of website accessibility
top of page

How does moisture get into the house?

how does moisture get into the house?

Moisture intrusion can be the cause of building defects, as well as health ailments for the building's occupants.

Some common moisture-related problems include:

  • structural wood decay;

  • high indoor humidity and resulting condensation;

  • expansive soil, which may crack the foundation through changes in volume, or softened soil, which may lose its ability to support an overlying structure;

  • undermined foundations;

  • metal corrosion; and

  • mold growth. Mold can only grow in the presence of high levels of moisture. People who suffer from the following conditions can be seriously (even fatally) harmed if exposed to elevated levels of airborne mold spores:

    • asthma;

    • allergies;

    • lung disease; and/or

    • compromised immune systems.

Note: People who do not suffer from these ailments may still be harmed by elevated levels of airborne mold spores.

How does moisture get into the house?

Moisture or water vapor moves into a house in the following ways:

  • air infiltration. Air movement accounts for more than 98% of all water vapor movement in building cavities. Air naturally moves from high-pressure areas to lower ones by the easiest path possible, such as a hole or crack in the building envelope. Moisture transfer by air currents is very fast (in the range of several hundred cubic feet of air per minute). Replacement air will infiltrate through the building envelope unless unintended air paths are carefully and permanently sealed;

  • by diffusion through building material. Most building materials slow moisture diffusion, to a large degree, although they never stop it completely;

  • leaks from the roof;

  • plumbing leaks;

  • flooding, which can be caused by seepage from runoff or rising groundwater; it may be seasonal or catastrophic; and

  • human activities, including bathing, cooking, dishwashing, and washing clothes. Indoor plants, too, may be a significant source of high levels of humidity.

Climate Zones

Post Storm Roof Inspection

In the northern U.S., moisture vapor problems are driven primarily by high indoor relative humidity levels, combined with low outdoor temperatures during the winter. In the southern U.S. (especially the southeast), the problem is largely driven by high outdoor humidity and low indoor temperatures during summer months. Mixed climates are exposed to both conditions and can experience both types of problems. Humid climates, in general, will be more of a problem than dry climates. Wind-driven rain is the main cause of leaks through the building envelope.

A good inspector should check for moisture intrusion in the roof, plumbing, utility rooms, attic, and foundations. We will discuss roofs and attics in this article.

roof shingles


A roof leak may lead to the growth of visible mold colonies in the attic that can grow unnoticed. Roof penetrations increase the likelihood of water leaks due to failed gaskets, sealants, and flashing. The number of roof penetrations may be reduced by a variety of technologies and strategies, including:

  • consolidation of vent stacks below the roof;

  • exhaust fan caps routed through walls instead of the roof;

  • high-efficiency combustion appliances, which can be sidewall-vented;

  • electrically powered HVAC equipment and hot water heaters that do not require flue; and

  • adequate flashing. Oftentimes, inspectors discover missing, incorrectly installed, or corroded flashing pipes.



  • Look for stains or discolorations at all roof penetrations. Chimneys, plumbing vents, and skylight wells are common places where moisture may pass through the roof. Any such locations must be inspected for wetness, a musty smell, and/or visible signs of mold.

  • Are there areas of the insulation that appear unusually thin?

  • Rust or corrosion around recessed lights are signs of a potential electrical hazard.

Moisture Intrusion Inspector Logo

Ensure your roof inspector is Moisture Intrusion Certified.

Moisture intrusion into a building can cause major structural damage and can threaten the safety of its occupants. Most Errors & omissions (E&O) insurance claims in the inspection industry involve moisture intrusion.

Remember, a leaky roof can damage ceilings, walls, and furnishings. To protect buildings and their contents from water damage, roofers repair and install roofs made of tar or asphalt and gravel; rubber or thermoplastic; metal; or shingles made of asphalt, slate, fiberglass, wood, tile, or other material. Roofers also may waterproof foundation walls and floors.

The solution? Proactive roof maintenance.

little roof damage

Proactive maintenance means recurring visual checks, an annual inspection, and promptly fixing any LITTLE problems which you find during these activities before they become BIG problems.

Smooth Skies Services takes the guesswork out of protecting your biggest investment - your home or your business.

Smooth Skies Services

Protect your finances and skip the hassle. Our drone inspections are fast, cost-effective, and safe. The icing on the cake? You don't even have to be home for the inspection to take place!

Don't wait until a crisis when you're forced to make big, expensive decisions fast.

Then, give us a call so we can personalize a proactive plan for you.

As an engineer, I decided to create Smooth Skies Services so you don’t have to invest time in learning about roof components, materials, inspections, weather patterns, aerodynamics, air spaces, radio communications, and more.

Let's Fly.


Some of the content in this blog is posted with granted permission by InterNACHI. Additional information can be located at their website


Recent Posts

See All




bottom of page