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Winter: It’s that time of year in the Northeast when we see many homeowners with moisture and mold in attics and every year we see the same thing. Insurance companies get calls from homeowners who are saying “I have roof leak” or “There is water dripping under the roof in my attic” or “There is mold on the sheathing.”

Well, it could be, but it probably isn’t a roof leak. When the moisture is spread out throughout the attic, chances are it is a moisture condensation issue.

Condensation in attics can occur in all types of homes, old or new. This article will cover our experiences with mold and condensation issues in attics. Insurance Restoration Specialists, Inc. (IRS) is a full-service disaster recovery firm based in central New Jersey. We service the insurance industry and commercial properties throughout the state.

attic mold

The Inspection

Most attic entries are through a small hatch or via pull-down stairs. In many instances, the homeowner just had a home inspection or were just in the attic and reported that they saw mold. We have seen moisture, ice crystals and mold in the winter; in the summer, you just see dry, stained wood. Using a high-powered LED flashlight is the best way to assess attic conditions. All attic areas should be inspected to determine if there is a pattern of staining or a pattern of moisture.

Is the staining only on one side of the roof? It is common to see only one side of the roof impacted – guess which side it would be? In most cases, it is the north side of the house. Why? The north side is the coldest side and gets the least amount of sun during the winter months. The south side gets more sunlight, is warmer and dries out.

It is a good practice to inspect the roof a day or two after a snowfall. Where the snow stays on the roof the longest is the coldest side of the house, the shady side. That’s where you’ll see the most moisture and mold on the inside of the house in the attic.

Inspect the attic to look for and document the conditions that would contribute to moisture in the attic. Look at the condition of the insulation, look for soffit vents, ridge vents and gable vents, look for bathroom exhaust, chimney, ductwork, inspect the stairs and hatches.

attic mold

Dark water stains, mold and frost on the underside of the roof.

attic mold

Severe dark staining of the underside of the roof, black in color from long-term moisture issues; truss framing covered with a light-colored mold.

testing wood

Wet and stained wood; elevated moisture content over 61%. Normal plywood moisture content is 10 – 15%.

attic mold

Ice and water stains from condensation.

Even though there is foam baffle in the soffit, it still may not be adequate ventilation; foam spacers need to be properly installed.

What’s Going On? Why Now?

Again, this a winter issue; when the roof is cold and the heat is on in the home, hot air rises from the home and comes in contact with the cold roof. If the warm air is carrying moisture and warm air rises, then there will be condensation moisture on the cold surface, the underside of the roof.

The image below shows natural convection of the warm air stack effect in a home.

air flow diagram

Physics Rule

Heat rises – no, warm air rises. Heat itself moves by conduction, convection and radiation. In the winter, stack effect heat rises because it is moving with warm air that is less dense than the cold air. A positive pressure area is created in the upper section of a building compared to the lower sections of a building that can be a pressure negative.

So, warm air rises, but where is the moisture coming from? The answer is, moisture is coming from the house itself.


  • Occupants. As we breathe, we give off carbon dioxide and water vapor. The more people who reside in a house means more moisture is generated from respiration.
  • Related to the occupants are showers, bathroom use and cooking. The more occupants in the home means more showers and more cooking, activities that produce moisture.
  • Basements and crawlspaces. If you have a damp basement and crawlspace, that moisture will evaporate and rise through the house up into the attic.
  • Humidifiers. People purposely add moisture in a home during winter months for comfort by using portable humidifiers or humidifiers in the central heating system which, many times, add too much moisture to the house.
  • Other appliances: Coffee pots, irons, clothes steamers, microwave ovens, carpet cleaners, crock pots, hair driers, dish washers and laundry machines and plants all add moisture to the home as well.

Pathways For Moisture to Get to the Attic

There are multiple sources of moisture in the home but why do some homes have moisture and mold problems in the attic while other homes do not? As described above, there can be varying sources of moisture in a home and every house has different conditions and pathways that will allow the moisture to rise up to the attic. What are some of the main pathways?

  • Attic hatches or attic pull-down stairs
  • Recessed light fixtures or even regular light fixtures
  • Ductwork and ceiling vent covers
  • Bathroom exhaust fans
  • Whole house fans in the ceiling
  • Wall outlets – wall cavities


Address the sources of moisture and try to keep the relative humidity in the winter (RH) between 20-30%. The normal range of relative humidity in buildings is commonly stated to be 30 – 50%. If you suspect your home has moisture issues in the attic, I would try to keep the %RH as low as possible.

Don’t Intentionally Add Moisture to Your House


Photo from EPA website.

Moisture on the inside of windows is a sign of elevated moisture in your home. More information can be obtained in the EPA document; Brief Guide Mold, Moisture and Your Home:

Address the Air Pathways

  • Insulate and/or use weather sealer gaskets around attic stairs or hatches. I have seen people create an insulating cover above the access door or hatch and some can be purchased on-line. Insulated zipper covers or foam block covers can be purchased or self-made.
  • Seal light fixtures with a gasket, not always easy to do. Caulk around the fixtures in the attic or use insulated recessed lights. Caution – some recessed lights are not designed to be covered; they get hot and are not supposed to be covered.
  • Bathroom and kitchen exhausts should be directed and ducted to the outside and not into the attic.
  • Seal off vents and fan covers in the ceiling if they are not being used in the winter. Many times, air conditioning units in the attic are not being used. Warm air can rise up into the ducts and cause moisture and mold issues in the attic and in the ducting. I recommend closing the vents and even sealing them with tape and plastic or magnetic sheets.
  • Make sure there is no air leakage from ducting located in the attic that is being used to supply heat.

Tom’s Simple Solution to the Problem: “Control the moisture in the house and control the pathways of warm air. If there is no moisture in the home, then there is no moisture in the attic.”

Address The Attic

There is moisture and mold in the attic, now what do we do? If insulation is old and matted down, it is time to remove and replace it.

poor insulation

Old matted down insulation in the attic has minimal R-Rating which will result in heat loss.

Carefully remove the insulation. Have dust control measures in place. Put all old insulation in bags, seal the bags with tape and carry out clean bags through the house. Dust control and personal protective equipment is recommended.

Safety Tip: In many cases there is no flooring in the attic and you may need to add some temporary planking or plywood to stand on so you don’t accidentally step onto the sheetrock and have your foot go through, causing damage to rooms located below the attic.

Do a detailed cleaning of the attic using HEPA vacuums and wipe down with detergent. Some stain-removing detergents can be used on the wood. Thoroughly scrub the wood areas with brushes – multiple applications is needed. Cleaning the attic can be very difficult and time consuming.


Inspect after remediation – wood should be clean, no insulation, no dust left behind. Note: Heavy staining cannot always be removed.

air vent

light fixture

Air-seal around vents and light fixtures when insulation is removed.

Some contractors will treat the attic space with an anti-microbial paint coating. This is an acceptable practice as long as the wood has been cleaned properly and is dry before painting. Note: there are contractors that don’t clean well and like to paint over mold – that is not acceptable!

attic mold

Correct example of attic wood painted with white antimicrobial coating after mold remediation was performed.

Moisture and Ventilation Check List

Now that the attic has been cleaned and treated for mold and a visual inspection confirmed that there is no sign of mold or remaining dust in the attic, it is time to re-insulate. But wait, did we correct the moisture and ventilation problems?

Check List

  • There are no room or chimney leaks
  • Air sealing around fixtures done
  • Weather seal or insulation of access points done
  • Ducts and connections of ducts are good
  • Bathroom exhaust vented to the outside; connections are good
  • Soffit Vents
  • Gable Vents
  • Ridge Vents


The basic construction of attic ventilation should include soffit vents and a ridge vent. If you can’t do a ridge vent, then be sure to have gable vents. Some experts say, don’t do both ridge vents and gable vents.

How much venting is needed? The standard building code states that there should be one square foot (144 inches squared) of free vent area for every 300 square feet (1/300) of attic space. Some may err on the side of caution and use 1/150 square feet of space.

The free vent area should be more dominant in the soffit than in the ridge; a 60 to 40 ratio is recommended. 60% of the free vent area along the soffits and 40% vent area on the ridge will create a better air flow.

attic mold

Correct example of attic wood painted with white antimicrobial coating after mold remediation was performed.


Mold in attics is due to moisture in the attic. The source of moisture in the attic is from moisture in the home. If the attic is not properly vented to allow the moisture to escape, moisture will build up and condensation will occur on the underside of a cold roof in the winter.

Mold remediation services are needed to address the contamination but improvements must be made to prevent this from occurring again. Improvements to the attic include, preventing heat and moisture from entering the attic, increasing the ventilation with soffit and ridge vents and adding adequate insulation.

IRS has performed many mold remediation projects in attics and we keep seeing the same issue year after year. This document is to serve as some guidance in identifying and correcting problems in attics. Every building and situation is different and there may be other solutions to solving your specific problem. Do more research on your end to help prevent a moisture problem and loss of energy in your attic.

IRS has restoration experts to do inspections for the insurance companies. I have inspected hundreds of attics over the last 20 years. I am always trying to pass on my knowledge and experiences to others, which is the purpose of this article.

Tom Peter, Certified Industrial Hygienist, Mold and Moisture Expert for Insurance Restoration Specialists, Inc. (IRS);

Tom has over 30 years of experience with indoor environmental and indoor air quality issues. Now CEO of IRS, he manages a team of experts to address mold and moisture issues in buildings.

About Insurance Restoration Specialists, Inc.

Insurance Restoration Specialists, Inc. (IRS) is a premier provider of disaster recovery mitigation, environmental remediation, biohazard emergency response and HVAC inspection and cleaning in the New Jersey-Philadelphia-New York City area. IRS is certified by NADCA and have Certified Air Systems Cleaning Technicians and a Certified Ventilation System Inspector on staff. Services include mold removal,water damage restoration, fire damage restoration, flood damage cleanup, smoke damage remediation, and biohazard remediation.