Photograph of severe mold and flood lines in a basement (C) Daniel Friedman Mold-resistant Construction Products & Practices

  • MOLD RESISTANT CONSTRUCTION - CONTENTS: Priorities for Preventing Indoor Mold Contamination in Buildings following flooding or storm damage. How to respond quickly to building floods to avoid a mold problem: what steps to take, in what priority. How to move furnishings or possessions from a flooded home to a new or temporary location without bringing along a mold or contamination issue. How to recognize cosmetic molds to avoid unnecessary mold remediation cost. CONSTRUCTION DETAILS TO AVOID MOLD in a new or flood-repaired building and Interior Maintenance to Avoid Mold - Building maintenance tips to avoid indoor toxic mold contamination. How to prevent mold in buildings - construction details and choices of materials to prevent toxic mold. Building and HVAC recommendations to minimize mold problems in hot humid climates
  • POST a QUESTION or READ FAQs about how to build or repair a building to resist mold contamination
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Mold resistant construction practices: clean up existing mold, repair & build to avoid future mold problems: this article describes how to prevent mold growth in buildings. We discuss priorities of action to avoid indoor mold contamination after building flooding or wetting from roof or plumbing leaks.

We distinguish between harmless cosmetic mold and mold that needs to be removed, and we outline both construction and building maintenance details that will help prevent future mold growth in a building.

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Priorities for Preventing Indoor Mold Contamination in Buildings

Photograph of flooded file cabinetsAll mold is everywhere, all the time, according to one of our mold mentors, an experienced mycologist. So how do we prevent a mold problem in a building? We avoid or quickly correct conditions that invite problem mold colonies from growing indoors.

In areas subject to high humidity, wet soils, rain, freezing weather, or other conditions that encourage high indoor humidity, building leaks, poor building ventilation, or other conditions that tend to produce indoor mold and its potential harmful effects and high costs, it is possible to reduce the chances of a future mold problem.

Article Contents

BUILDING FLOODS - Building Leak or Emergency Flood Response Procedures to Avoid Mold

Here are our recommendations for emergency response to building floods, burst pipes, sewer backups, roof blow-offs or other sudden catastrophic soaking of buildings.

These suggestions are based on 30 years of experience in construction, construction inspection, and our indoor air quality and mold investigations and laboratory testing. Additions, corrections, and content suggestions for this list are invited.

  1. Respond immediately to building leaks and floods. This means within 24-48 hours all of the critical steps need to be taken if you want to maximize the chance of avoiding a costly mold cleanup project. This topic will be expanded in detail at this website (coming). Basically:
    • Before entering a building that has been flooded review
      FIRST PRIORITIES: What to Do After a Building Has Been Flooded to address life, health, and safety concerns.
    • Stop the water entry
    • Remove standing water
    • Remove wet carpets, furniture, and boxes of wet stored items
    • Remove floor trim and lower portions of walls (such as drywall or paneling) (at least 12") and any wall insulation, in rooms where the floors were wet or flooded.
    • Remove upper portions of wall coverings (drywall or paneling) higher than 12" if these areas are wet, or if water entered the wall cavity from above.
    • Remove ceilings that have been flooded from above
    • Remove wet materials (such as areas listed above) until you find a 12" or greater area of dry clean margin.
    • Use dehumidifiers, fans, heaters, to dry the exposed building areas and surfaces.
    • If mold is already visible or suspected, use containment to avoid air movement from the damaged (moldy) area to other building areas. Containment generally means negative air and poly plastic barriers.
    • Read: Mold Action Guide after Flooding: How to Minimize Mold Damage After a Building Flood
    • Read: Flood Response for Septic Systems what to do after a septic system has been exposed to flooding
  2. Keep unwanted outside water out of the building. This means attention to the roof drainage system (gutters and leaders), surface drainage, and at some sites, unusual levels of ground water. In buildings where we find recurrent basement water entry, most of the time the underlying cause is inadequate maintenance of gutters and downspouts, with roof spillage against the foundation.

    Preventing indoor mold by keeping outside water out also means proper construction of all exterior components, roofing, siding, windows, doors, trim, steps, patios, exterior light fixtures, even downspout straps, to keep water out of building walls and cavities.

    See vapor barriers for a discussion of vapor barriers behind vinyl siding. The importance of flashing and house wrap on conventional construction pales next to the importance of property detailing when problem-prone building exteriors such as EIFS Synthetic Stucco are used since if workmanship is not exactly correct with those materials leaks into the building cavities trap water and often lead to costly damage, rot, or mold.

    See Exteriors, Landscaping, & Siding - Inspection, Repairs, Product Failures for a discussion of exterior building materials and defects.
  3. Humidity: Maintain Proper Indoor Humidity Levels to avoid mold. See What indoor humidity should we maintain in order to avoid a mold problem? Also see VENTILATION in BUILDINGS.
  4. Leak Prevention: proper roofing and flashing details are critical to avoid longer term building leaks at the roof and at other building penetrations such as windows, doors, plumbing vents. Indoors, replace corroded plumbing traps, use burst-resistant washing machine hoses and fixture supply risers. When possible, turn off water when leaving a building vacant for some time.
  5. Mold-resistant Building Materials: should be used where possible, especially in high-risk areas such as basements and bathrooms.
    See Mold proof drywall ? You Must Be Kidding!
  6. Mold-Friendly Building Materials: should be avoided in high risk areas. Do not put mold-friendly construction materials (stuff on which mold grows readily) into damp areas. In our experience this means the items listed at Interior Construction Product Installation Details below
  7. Ventilation: to avoid indoor mold, proper venting avoids build-up of high moisture in building cavities and avoids, in freezing climates, leaks into building cavities from ice dams. See our discussion of attic venting and under-roof ventilation
    at Detecting and Correcting Attic Condensation and Preventing Ice Dam Leaks in Buildings

    and see our discussion of bathroom ventilation fans, ducts, and indoor moisture control

    Crawl space ventilation and dryout steps are discussed at How to Dry Out a Crawl Space.

    Also see VENTILATION in BUILDINGS - our home page for this topic.

IMPORTING MOLD - How to Avoid Bringing Problem Mold Into a Building

How to move furnishings or possessions from a flooded home to a new or temporary location

If you are moving items out of a home that has been flooded and if that building has become visibly mold-contaminated, there is a significant risk that you will be bringing mold-contaminated dust or even active mold colonies from the flooded building into the new one.

The best approach is to remove moldy furnishings or other possessions from the flooded building, have them cleaned, and then bring them into the new building.

Pressure Treated lumber" which is sold as resistant to rot and resistant to wood destroying insects is very often not only wet when purchased, but is often mold contaminated with several species of Penicillium sp. or Aspergillus sp. We confirmed this condition by a survey of building materials at several lumber suppliers in New York, using tape samples of visible mold on the surfaces of these products.

When using pressure-treated lumber for interior framing, clean off any visible mold. Simple power-washing would suffice. This step is not necessary and would be inappropriate for the same lumber when used outdoors, such as for a deck or an entry stair.

But inside, such lumber may be used for sill plates or in some cases I've seen it used to re-frame a rotted floor over a wet crawl space. Importing a large Aspergillus sp. colony on the floor framing surface over a crawl space provided an immediately-detectable high level of airborne Aspergillus sp. in the room above this area, as these spores move easily in convection air currents moving from the crawl area up through the building.

COSMETIC MOLDS - How to Avoid Unnecessary Mold Cleanup Expenses

As long as we are discussing not bringing mold into a building, it's important to warn against unnecessary expenses cleaning up "cosmetic-only" molds such as black mold commonly found on kiln-dried lumber which has been exposed to wetting in transit or storage.

Usually this is a cosmetic-only mold in the Ceratocystis/Ophistoma bluestain group. However in a few cases where this "black mold" on lumber was on wood framing later exposed to flood basements or crawl spaces, I've also found problematic mold growing mixed with this cosmetic inhabitant.

See Stuff that is Not Mold or Harmless Mold and review Harmless Cosmetic Molds in that document.

CONSTRUCTION DETAILS - Interior Construction Product Installation Details to Reduce Mold-Risk

MAINTENANCE - Interior Maintenance to Avoid Mold Suggestions from the U.S. EPA

This list based on a shorter EPA list, with additions and edits by the author.

-- Initial Source: Mold Prevention Tips U.S. EPA.


The following mold resistant construction advice is from OSHA Guide to Workplace Mold.

Moisture control is the key to mold control. When water leaks or spills occur indoors - act promptly. Any initial water infiltration should be stopped and cleaned promptly. A prompt response (within 24-48 hours) and thorough clean- up, drying, and/or removal of water-damaged materials will prevent or limit mold growth.

Mold prevention tips include:

Questions That May Assist in Determining Whether a Mold Problem Currently Exists

Always consider consulting a health professional to address any employee health concerns.

Flood damage & mold cleanup guides


Continue reading at ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUPdiscusses the initial response to building flooding, and in more depth, building methods and materials useful for improving the mold-resistance of new construction, renovated buildings, and repairs after mold remediation in buildings.

Suggested citation for this web page

MOLD RESISTANT CONSTRUCTION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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