Mold-resistant Construction Products & Practices
InspectAPedia® -
How to prevent mold in buildings - construction details and choices of materials to prevent toxic mold
How to respond quickly to building floods to avoid a mold problem: what steps to take, in what priority
How to avoid importing problem mold into a building on contaminated materials
Recognize cosmetic molds to avoid unnecessary mold remediation cost
Building maintenance tips to avoid indoor toxic mold contamination
Questions & answers about preventing mold growth on or in buildings
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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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.
Priorities for Preventing Indoor Mold Contamination in Buildings
All 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.
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.
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:
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.
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.
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. See WATER ENTRY in BUILDINGS.
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!
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
IMPORTING MOLD - How to Avoid Bringing Problem Mold Into a 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.
CONSTRUCTION DETAILS - Interior Construction Product Installation Details to Reduce Mold-Risk
Avoiding Mold Growth on Drywall: when installing drywall in basements or in any location where a floor is at extra risk of becoming wet, keep the bottom edge
of drywall at least 1/2" off of the floor. Avoiding floor contact means that a small spill which wets the floor, if cleaned up promptly,
will not soak up into the drywall itself. We 'm not sure it's cost effective but you might want to consider using mold resistant drywall.
Avoiding Mold Growth on Wood paneling: use the same floor clearance detail for wood paneling. We find severe mold not only on the exposed
side of wood paneling but often, even if no mold is visible on the room side, the un-coated back surface of this material supports mold growth in
buildings which have been wet or subject to high moisture.
Avoiding Mold Growth on and Behind Floor trim:
Even weeks after a "water damage company" had reported that they had "fully dried out a building" by "extracting the water" in it, we found very
high moisture in the lower portion of the building walls.
Pulling off floor trim showed (in several investigations) that the back of the
wall/floor trim was not only still wet with visible water droplets, but it had already become moldy. The drywall behind the this trim, and the
wall cavity itself as well as insulation in it were also quite wet and moldy.
When installing floor trim in a basement below grade, or in a bathroom or kitchen where spills are likely, I
back-prime and end-prime all trim boards.
In bathrooms we caulk the trim to the floor, putting a small bead of caulk on the under-side of the trim
boards as they are placed. The caulk won't be visible, but it'll reduce the chances of a small spill sending water into the wall cavity.
Avoiding Mold Growth on Floor cabinets in Bathrooms and Kitchens: When we are installing them, we spray the under-side and backs of floor cabinets with
clear lacquer before installing them. This takes
only a few moments, as the lacquer dries almost immediately. (Proper venting needed.) By sealing these surfaces we reduce the rapidity of moisture
up-take into them in damp or wet conditions. Reducing the moisture uptake in these materials reduces potential mold growth on these hidden
surfaces and gives more time for building dry-out after a wetting event. In bathrooms we caulk the junction of the exposed cabinet bottom and the floor
after the cabinet is in place.
Avoiding Mold Reservoirs in Fiberglass insulation: Don't put fiberglass insulation under floors over damp or wet crawl spaces - we are conducting a study of this topic. See INSULATION MOLD for details.
Preliminary data shows that
very often we find sever Aspergillus sp. or Penicillium sp. infection of fiberglass over damp crawl spaces and in damp building
walls against below-grade foundations, even when there is no mold actually visible on the insulation or its kraft paper facing.
Avoiding Mold Reservoirs in Indoor Carpeting: wall-to-wall indoor carpeting which has been wet should be discarded. We have never seen
a successful clean-up of this material in place after flooding. Carpets form a particle reservoir, including allergens, mold, mites, etc. in buildings
which can be a problem especially in basement areas which can be expected to be damp even when there is no water entry.
We advise against using
carpeting in these areas at all. If basement carpeting in a building has been wet, remove and discard it promptly. After building dry-out and cleanup
have been completed, install a hard surface flooring or simply paint the exposed concrete slab with an epoxy paint. Nicer surfaces such as ceramic
or vinyl tile work well. (Sheet vinyl may become moldy on its backside if the floor or slab below are damp.) If you are concerned about making
a warmer or more quiet surface, use area carpets which can be sent out for regular cleaning.
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.
Fix leaky plumbing ... This means watching for corroded sink and tub traps and replacing them
before they leak into the floor; find and fix loose toilets; use burst-proof washing machine hoses - this failure has led to some serious
building floods. Insulate cold water lines to avoid condensation leaks into building cavities, basements, crawl spaces. ... and leaks in the building envelope as soon as possible - this means noticing roof leaks, roof flashing leaks, soffit leaks,
leaks at windows, doors, plumbing vents, leaks where decks or patios abut the building wall.
Watch for condensation and wet spots. Fix source(s) of moisture problem(s) as soon as possible. This means looking in your basement
and crawl space for signs of water entry - which we discussed above.
Prevent moisture due to condensation by increasing surface temperature or reducing the moisture level in air (humidity). - This means
that you may find condensation on walls in cool closets or behind pictures hung on cool walls - places where air is not circulating. Heavy drapes in some buildings
lead to mold on the walls behind them. To increase surface temperature, insulate or increase air circulation.
To reduce the moisture level in air, repair leaks, increase ventilation (if outside air is cold and dry), or
dehumidify (if outdoor air is warm and humid).
Keep heating, ventilation, and air conditioning (HVAC) drip pans clean, flowing properly, and unobstructed. - we often
find A/C condensate leaking into building walls and floors when drains are clogged. In climates where A/C systems remove a large amount
of moisture from building air, watch for water blowing out of the condensate tray right into the blower assembly or even into
ducts downstream in the air handler system - a common source of mold in air conditioning duct work.
Vent moisture-generating appliances, such as dryers, to the outside where possible. Venting dryers into attics, basements, crawl spaces
is a bad idea. If those areas are seasonally too dry, use a humidifier with a humidistat. When showering, use the vent fan - install one
if there is none.
Perform regular building/HVAC inspections and maintenance as scheduled. - Change air filters monthly when these systems are in use, and
at that time, inspect for condensate leaks.
Don't let foundations stay wet. Provide drainage and slope the ground away from the foundation. -- But remember our advice from above. -
most wet basements and crawl spaces are in that condition because of outside gutter and leader defects.
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:
Repairing plumbing leaks and leaks in the building structure as soon as possible.
Looking for condensation and wet spots. Fix source(s) of moisture incursion problem(s) as soon as possible.
Preventing moisture from condensing by increasing surface temperature or reducing the moisture level in the air (humidity). To increase surface temperature, insulate or increase air circulation. To reduce the moisture level in the air, repair leaks, increase ventilation (if outside air is cold and dry), or dehumidify (if outdoor air is warm and humid).
Keeping HVAC drip pans clean, flowing properly, and unobstructed.
Performing regularly scheduled building/ HVAC inspections and maintenance, including filter changes.
Venting moisture-generating appliances, such as dryers, to the outside where possible.
Venting kitchens (cooking areas) and bathrooms according to local code requirements.
Cleaning and drying wet or damp spots as soon as possible, but no more than 48 hours after discovery.
Providing adequate drainage around buildings and sloping the ground away from building foundations. Follow all local building codes.
Pinpointing areas where leaks have occurred, identifying the causes, and taking preventive action to ensure that they do not reoccur.
Questions That May Assist in Determining Whether a Mold Problem Currently Exists
Are building materials or furnishings visibly moisture damaged?
Have building materials been wet more than 48 hours?
Are there existing moisture problems in the building?
Are building occupants reporting musty or moldy odors?
Are building occupants reporting health problems that they think are related to mold in the indoor environment?
Has the building been recently remodeled or has the building use changed?
Has routine maintenance been delayed or the maintenance plan been altered?
Always consider consulting a health professional to address any employee health concerns.
Questions & Answers regarding this article
Questions & answers about preventing mold growth on or in buildings
Question: Best plan for removing mold on wood flooring and ceilings & preventing its reappearance
Our builder is constructing a log cabin for us during the hot, moist summer months. The roof has not been fully completed so the interior structure has been exposed to many afternoon rains (as of August 15, 2011).
Tongue and groove eastern white pine flooring provides the flooring for 2nd floor as well as ceiling for 1st floor. Both sides of the T & G will be visible in the completed log cabin. Dark staining and spotting from mold/mildew growth has appeared on the T & G flooring in many, repeat...many, places and needs to be addressed in a timely and correct manner.
The metal roof will be installed in one week. Windows and doors are not installed yet. What is your recommendation as to the best procedure and plan of action to remediate this unsightly, unhealthy, and disturbing occurrence? - Brenda Eller
Reply: After Building Dry-In, Use Sanding, HEPA Vacuuming, Media Blasting, Use of Clear Fungicidal Sealants & Floor Coatings to remove mold and prevent future mold growth
Brenda you're right that white pine T&G flooring easily supports mold growth, particularly when wet and before it has received any finish coating.
The building has to be at the dry-in state so that you can dry out all interior materials and keep them dry, else cleaning costs and effort may be wasted.
If the upper side of your T&G flooring is to be sanded before finishing, that'll do the trick to remove problem mold on the upper floor surfaces.
The under-side can also be wiped, & HEPA vacuumed, but I suspect that won't remove stains nor even mold left in hard-to-reach crevices. If mold is left in flooring crevices it will sometimes reappear below a coating, making future cleaning still tougher.
So you might want to consider cleaning the underside as well as other irregular surfaces that are moldy using media blasting.
When surfaces are clean if you coat them with two or even three layers of clear polyurethane that will reduce moisture up-take in the wood and thus resist future mold appearance. If wood is to be stained of course you'll do that before applying poly.
There are also clear sealants used by some mold remediation companies that might work well on the under-side of floors (ceilings) where the wood is to be left exposed. I wouldn't use those on the walk-on surfaces unless the manufacturer agrees that their sealant is hard enough for floor traffic.
Clear fungicidal sealants suitable for use where wood ceilings or framing are to be left exposed are illustrated at FUNGICIDAL SPRAY & SEALANT USE GUIDE
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328
This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
"Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
"A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
"Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
"Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
"When Block Foundations go Bad," Fine Homebuilding, June/July 1998
Masonry structures: The Masonry House, Home Inspection of a Masonry Building & Systems, Stephen Showalter (director, actor), DVD, Quoting: Movie Guide Experienced home inspectors and new home inspectors alike are sure to learn invaluable tips in this release designed to take viewers step-by-step through the home inspection process. In addition to being the former president of the National Association of Home Inspectors (NAHI), a longstanding member of the NAHI, the American Society of Home Inspectors (ASHI), and the Environmental Standard Organization (IESO), host Stephen Showalter has performed over 8000 building inspections - including environmental assessments. Now, the founder of a national home inspection school and inspection training curriculum shares his extensive experience in the inspection industry with everyday viewers looking to learn more about the process of evaluating homes. Topics covered in this release include: evaluation of masonry walls; detection of spalling from rebar failure; inspection of air conditioning systems; grounds and landscaping; electric systems and panel; plumbing supply and distribution; plumbing fixtures; electric furnaces; appliances; evaluation of electric water heaters; and safety techniques. Jason Buchanan --Jason Buchanan, All Movie Review
Masonry Structures: Behavior and Design, Robert G. Drysdale, Ahmid A. Hamid, Lawrie R. Baker, The Masonry Society; 2nd edition (1999), ISBN-10: 1929081014, ISBN-13: 978-1929081011
Straw Bale Home Design, U.S. Department of Energy provides information on strawbale home construction - original source at http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10350
More Straw Bale Building: A Complete Guide to Designing and Building with Straw (Mother Earth News Wiser Living Series), Chris Magwood, Peter Mack, New Society Publishers (February 1, 2005), ISBN-10: 0865715181 ISBN-13: 978-0865715189 - Quoting: Straw bale houses are easy to build, affordable, super energy efficient, environmentally friendly, attractive, and can be designed to match the builder’s personal space needs, esthetics and budget. Despite mushrooming interest in the technique, however, most straw bale books focus on “selling” the dream of straw bale building, but don’t adequately address the most critical issues faced by bale house builders. Moreover, since many developments in this field are recent, few books are completely up to date with the latest techniques. More Straw Bale Building is designed to fill this gap. A completely rewritten edition of the 20,000-copy best--selling original, it leads the potential builder through the entire process of building a bale structure, tackling all the practical issues: finding and choosing bales; developing sound building plans; roofing; electrical, plumbing, and heating systems; building code compliance; and special concerns for builders in northern climates.
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