Mold in New Home Construction

It seems like builders are stuck in the 80's when it comes to mold prevention.  Haven't they read anything about what causes mold?  Or, is this just another cost that they would prefer to avoid by covering it up with the newly installed insulation and drywall?  After all, no one will see this mildew once they cover it up.  And, it may take a while before any harm comes to the homeowner.  It is unnerving to see builders seal active mildew inside newly constructed homes.  The nature of construction is such that rain and moisture are a part of the construction process.  All materials are exposed to the wet Florida climate until the roof is dried-in (water-tight).

Mold scientists could do their experiments right on job sites.  Just drive around and look at newly constructed homes for yourself.  Black and green active mildew is crawling over the interior surfaces caused by rain during construction.  The amazing and disgusting thing is that builders, after seeing this obvious growth, just seal right over the mold as if it is going to miraculously disappear once the insulation is installed and permanently covered by ½ wall board.  The fact is mold is alive behind the walls.  Some of this dangerous mildew will die as the home dries out and some will live on behind the walls.

Builders should treat the affected areas with 10% bleach and water solution a few days before installation of insulation.  These areas should then be allowed to dry for two days, followed by the application of Fiberlock6040 mildew sealer.

Air Conditioning plays an important role in preventing mildew.  An undersized or over-sized unit can cause moisture build-up that can cause a serious mildew problem.  Air conditioning units are not better because they are bigger.  The specific tonnage needs to be calculated by a licensed air conditioning or mechanical engineer.  Building plans should be checked by a structural engineer, an HVAC (air conditioning) engineer and an electrical engineer. 

Just as important as the size of the a/c is the air return and supply ducting.  Building codes in most municipalities now require all bedrooms to have their own a/c supply and return.  This helps keep moisture from building up in areas that have inadequate air circulation.  A mildew breakout will likely be caused by moisture penetrating the home from the outside or moisture not being removed by a properly installed air conditioning system.  An exhaust fan can pull hot humid air from the attic and cause mildew as well. 

Factors to consider:

  •        Protect as much of the building materials from rain as possible during construction.
  •        Dry-in the roof immediately with 30 lb. felt-paper to lock out as much water as possible.
  •        Once the home is dried-in, use 10% bleach to water solution and spray down the interior of the home on a Sunday morning when the construction crew is off.  Use a high-pressure type of system.  This will kill surface mold and help control the spread of active mold.  This might even kill some of the crews' germs!
  •        Do the same 10% bleach-water solution again, just before installation of interior insulation.
  •        Seal the interior of the home with a product called Fiberlock 6040 (see below for more information)

·       Have a licensed a/c mechanical engineer review your existing home or new construction to ensure the effectiveness of the a/c system.  Have air returns and supplies in every room. Consider two systems for efficiency and effectiveness.

·       Have the HVAC engineer design a Replacement Air System to control unwanted attic pollutants from being drawn into the home.

·       Request a "French Drain" to take rainwater away from the house.  A French drain is a PVC plastic pipe about 4 inches wide connected to the gutter system that takes rainwater underground and away from the foundation towards a retention area.

  •        Be cautious about landscaping, too. Keep all vegetation 36 inches away from the house or more.
  • A new trend that is likely to become mandated by code is a required Replacement Air System installed along side the standard air conditioning ducts.  This system is inexpensive and allows outside air to be used to replace air that is sent outside via exhaust fans and dynamic air pressures.  There are vacuum pressures created inside a home due to exhaust fans, kitchen vents or doors opening and closing.  Have you ever noticed the mildew around exhaust fans? Have you ever felt pressure on your inner ear when a door shuts?  When air is sent out of a home via an exhaust fan, where does the air come from to replace the air that was just sent outside?  The air comes from the easiest route, which is the attic. The problem is that the attic air is moist and undesirable.  Typically this attic air is drawn into the air conditioned space through openings into the attic like pocket doors, light fixtures such as recessed cans in the ceiling or just about any penetration from the a/c space into the attic space.  Attic air is a direct cause of mildew and is filled with contaminates like fiberglass insulation fibers, rodent droppings, dirt, dust and insect droppings.  To avoid pulling attic air into the living space, you must create an outside source of air called a Replacement Air System so when air is needed it comes from a clean source.

  • Exhaust, Ventilation and Moisture Prevention
    By Bryan Ligman, PE, and Malou Hughes, MBA
  • Kitchens and Bathrooms Can Be Trouble Spots for Indoor Air Quality

  • Due to higher humidity levels, bathrooms are conducive to mold growth. Proper exhaust, ventilation and moisture prevention are essential to preventing mold problems. Photo courtesy of Air Quality Sciences, 2004.

  • Kitchens and bathrooms are two major sources of pollutants in both commercial and residential buildings.  Cooking releases heat, smoke (containing both particulate matter and gaseous pollutants) and moisture, all of which can negatively impact the quality of the indoor air.  In bathrooms, the use of hot water can generate steam, increasing humidity and creating conditions conducive to mold growth.  These locations are equipped with extensive plumbing, making them more susceptible to water intrusion and ultimately mold growth due to leaks if plumbing systems are not carefully monitored and maintained.
  • For these reasons, architects, designers, construction professionals and occupants should take steps to ensure that kitchens and bathrooms contribute minimally to indoor air pollution. Three primary activities can help reduce the negative impact these areas may have on indoor air: exhaust, ventilation and moisture prevention.
  • Exhaust
    Exhaust systems are important because they carry pollutants from the source directly outside, which keeps them from migrating into other areas of the building from entering the heating ventilating and air conditioning (HVAC) system and being circulated throughout the building.  Exhaust and ventilation guidelines for residential buildings are recommended in the newly-released American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE) ventilation standard 62.2, Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings.
  • This minimum standard recommends local mechanical exhaust for all kitchen and bathrooms.  These exhaust systems may be operated intermittently or continuously.  Residential intermittent local exhaust is to be occupant controlled (i.e. operation of the exhaust fans is determined by the occupants).  Continuous exhaust systems are similar to those required in most commercial buildings with the exhaust system being part of an overall balanced mechanical system.
  • In kitchens, it is important to select and install ducted fans that exhaust pollutants directly outdoors. In many cases, kitchens have non-ducted fans designed simply to filter out airborne grease and then re-circulate the air back into the kitchen.  This type of "exhaust" is not recommended as it will not reduce or remove moisture or gaseous pollutants, which contribute to poor indoor air quality (IAQ).  The ASHRAE standard also has recommendations for whole house ventilation systems for controlling unavoidable pollutants associated with building occupants and general living processes.  Detailed information on requirements and use of such a system is presented in the 62.2 standard.
  • Ventilation
    Properly designed and installed exhaust systems in kitchens and bathrooms are extremely effective in removing pollutants from the building at their sources. However, they can also dramatically impact airflows within the building, triggering other potential IAQ and HVAC issues.  Exhaust fans carry pollutants as well as relatively large volumes of air out of the building, creating potential negative pressures in the building resulting in unplanned airflows.  If replacement air is not directed into the building, it will be pulled in through various pathways that pose least resistance to airflow such as down chimneys, through cracks or holes, under doorways, etc.  If left to drift in from any source, air may reintroduce pollutants potentially causing life-threatening conditions such as a back-drafting furnace, water heater or fireplace.  By managing ventilation, construction and HVAC professionals can use the HVAC system to pull in fresh, outdoor replacement air into the building to compensate for air lost through the exhaust system.
  • Moisture Control
    Moisture control is critical in kitchens and bathrooms in order to prevent mold growth.  Generally, bathrooms that include showers and/or bathtubs intermittently have mold growth in the shower or on the ceiling above the shower.  In these areas, mold management is largely a household cleaning issue.  The moldy areas should be cleaned regularly with a disinfectant solution such as one-part bleach to nine-part water.  The basic rule for preventing significant mold problems is to ensure that pipes are correctly installed and that water systems are tested before turning over the building for occupancy.  This allows plumbing professionals to address or correct any plumbing problems that may result in water leakage and ultimately mold growth.
  • These measures should help minimize the negative impact of pollutants generated in kitchens and bathrooms, protecting occupants, and making for a more comfortable environment.
  • Experts are saying…
  • Bryan Ligman is a senior engineer with over 15 years of experience in building science. Ligman is director of technical operations for the Building Consulting Group at Air Quality Sciences. Malou Hughes is marketing manager at Air Quality Sciences. Hughes has a Masters in Business Administration and has conducted extensive research on indoor air quality.
  • Brian L'Hommedieu of Microscope, a Fort Myers firm that specializes in removing mold and fungus from homes and buildings, said business has picked up substantially lately.  He said changes in construction methods are causing mold to breed more often.
  • L'Hommedieu said the problem could have resulted from a leak from another unit in Weis's building.
  • "The cabinets are actually sagging off the wall... The condo was not saturated.  It was an ambient humidity in the home."
  • Ken Plonski, a WCI vice-president of public relations, said it is unclear whether it is WCI's fault or Weis was negligent.  He said there is a question whether Weis had the air conditioning turned off while the unit sat empty for several months.  That could add humidity inside of a unit, which helps breed mold.
  • WCI has brought in several environmental inspectors who are trying to determine what has happened, Plonski said.  He said when there is a complaint, WCI will immediately respond.  WCI will fix the problem if it is the company's fault, he said.
  • San Marino, a new apartment complex off Collier Boulevard, has also had mold problems.  Mold was growing on the walls of an unoccupied first-floor unit in a building, and tenants living directly above were concerned that they were being exposed to it.  Rebecca Robbins, the general manager of the complex, said the mold problem has been taken care of.
  • She said the landscaping around the building was initially graded improperly, and that caused rainwater to leak into the first floor of the building. The problem has been fixed and the mold is gone, she said.
  • But Stephanie Christensen disagrees.  She and a roommate live in an apartment on the second floor of the building.
  • Phares Heindl, an Altamonte Springs lawyer who has handled several mold cases, said he has been representing clients in these cases for four years, and he typically would get a call about once a month from a person soliciting his help.
  • Fred Sylvester, owner of Accredited Building Consultants in Fort Myers, said in the 1930s and 1940s, mold was not a major problem in homes because they were not as well insulated as they are today.  He also said building materials such as vinyl-backed wallpaper contribute to the mold problem. "You take that vinyl and peel it off the wall, and that drywall is black with mold," he said. He said all homes leak, but mold results when a home is not allowed to breathe. "It's what you do with that moisture where you get into problems. We call it a drainage plane," he said.
  • "If these (building) materials get wet and then dry out, mold won't grow on them," he said. "It may grow temporarily, but it will dry out. Let me put it this way: If you have a small, leaking window, and it gets wet and dries out, mold doesn't grow.
  • "There are other things that will happen, but mold doesn't grow. If it constantly gets wet, then mold will grow. This is not rocket science.
  • "The Readers Digest version of this is: We built houses in the '20s, '30s, and '40s, even up to the '70s and '80s (that were able to breathe). And in the '90s they started building really, really tight houses with a lot of insulation. A lot of plastic materials were starting to be introduced in the building business. The moisture vapor doesn't pass through (these materials)."

  • Products to help lock out mold

  • Seal the exterior block walls with a product called Fiberlock IAQ 3000It is a high quality interior and exterior block filler formulated to fill small imperfections and pinholes in masonry block and porous concrete before top-coating.  This product contains mineral-type fillers and fine silica aggregates which fill voids in masonry surfaces.  This 100% acrylic block filler is easy to apply, alkali resistant and provides a uniform surface capable of receiving all types of finish coats.  Fiberlock IAQ 3000 is not water sensitive after application and its flexibility and durability are the best available for a block filler, far superior to cementitious and PVA types.

  • Lock out moisture and mold with a Mold-Resistant Masonry Waterproofer IAQ9000.  Being that moisture is one accelerant to mold, it would make more sense to seal out moisture and retard mildew growth.  Fiberlock IAQ 9000 is a low-odor waterproofing coating that is specially formulated to stop water from penetrating through a variety of interior and exterior surfaces including above or below grade masonry walls, cinder and concrete block, stucco, brick, retaining walls, and foundations.  This latex based formula stops 10 psi of water pressure and reduces radon gas penetration.  Fiberlock IAQ 9000 contains an EPA-registered fungicide to help prevent mold from growing on the surface of the cured film.  This fast-drying formula may be applied easily with a brush and/or roller on dry surfaces and cleans up easily with soap and water.

  • Interior surfaces should be treated with Fiberlock IAQ 6040. This low viscosity, translucent violet sealant is designed to seal new construction materials and resist fungal growth. This specially formulated, water-based coating contains EPA-registered antimicrobials that inhibit the growth of mold on the surface of the cured film.  The low-viscosity 100% acrylic formula is easy to apply, and the translucent finish will not block the appearance of treated building materials. Fiberlock IAQ 6040 can be used on wood, OSB, wallboard, concrete and other construction materials to withstand the moist, humid conditions that provide the ideal environment for fungal growth.

  • Air conditioning Duct Liner can be pre-treated for mildew using another Fiberlock product called IAQ 7000™.  It encapsulates the surface of the duct.  The installation instructions are as follows: Carefully remove all mold, dust and other particulate from lining within air duct.  Ensure that surface of insulation is intact.  If necessary, bind insulation together with Fiberlock IAQ 8000™ Duct Liner Insulation Sealer/Adhesive/Basecoat.  Apply Fiberlock IAQ 7000 to all surfaces of duct liner insulation by brush or airless spray.  Application rate will vary depending on porosity of the insulation.  Apply one coat by airless spray, or two coats by brush.  Porous surfaces may require additional coats.  Ensure that surfaces are completely sealed.  Circulate fresh air through the HVAC system to help dry the coating.  Exhaust air outside the building.  DESCRIPTION Product No.: 8370 White Fiberlock IAQ 7000 is a quick drying water-based adhesive coating/encapsulant for use on duct liner insulation surfaces.  Fiberlock IAQ 7000 dries to form a durable, flexible, moisture-resistant protective coating on the duct liner insulation material.  Its semi gloss finish minimizes dirt buildup on the coating surface, which provides nutrients that feed mold colonies.  Fiberlock IAQ 7000 also contains an EPA registered fungicide to resist mold growth on the cured film surface.  Fiberlock IAQ 7000 can be used in residential, commercial, or industrial facilities requiring maximum moisture and mold resistance.  Fiberlock IAQ 7000 is acceptable for use over faced or unfaced fiberglass duct liner insulation, and unfaced fiberglass duct board insulation.

  • Mold in Existing Construction

  • AfterShock is supplied ready to use.  Stir thoroughly.  Do not mix with other coatings, solvents or colors in oil.  Remove damaged materials and clean surfaces.  Surface must be free of dust, mildew, mold, dirt, grease, loose paint, oil, glue size, calcimine, wax, soap and other surface contamination.  Patch surface irregularities with an appropriate patching compound.  AfterShock is self-priming over bare gypsum drywall, composition board, ceiling tile and concrete.  Do not apply when air or surface temperature is below 50°F or when drying conditions are poor.  Use adequate ventilation during application. Drywall - Joint cement should be sanded smooth, but avoid abrading the paper.  Ferrous Metal - Clean, then prime with Fiberlock IAQ™ 4000 acrylic DTM primer.  Wood - Seal knots and stains with Fiberlock IAQ 5000 stain-blocking primer.  Masonry Block - Apply one coat of Fiberlock IAQ 3000 acrylic block filler if a denser surface is desired.  DESCRIPTION Product No.: 8390 White AfterShock is an EPA-registered antimicrobial coating designed to kill residual mold and mildew remaining after pre-cleaning contaminated surfaces.  AfterShock also inhibits the future growth and spread of mold and mildew on the cured film surface in residential and institutional buildings.  AfterShock is recommended for use on interior wall surfaces such as plaster, wallboard, drywall, concrete, masonry block, wood, primed metal and galvanized metal.  AfterShock is also recommended for use on interior wood framing, primed metal, concrete, and wallboard inside the wall cavity. Do not use for HVAC system applications.

  • More information can be found at

  • 150 Dascomb Road
  • Andover, MA 01810 U.S.A.
  • Toll Free: (800) 342-3755
  • Tel.: (978) 623-9987 Fax: (978) 475-6205