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Mold Occurrence in New Construction

Mold Occurrence in New Construction
Posted in: Building Codes
Jan 12, 2005 - 6:22:00 PM

Mold Occurrence Influenced By Building Inspection Practice

"Fifty percent [50%] of homes contain problem molds. A new MAYO Clinic medical study attributes nearly 100% of chronic sinus infections to mold. A 300% increase in the asthma rate over the past 20 years has been linked to molds," Source: USA WEEKEND, Dec. 3-5, 1999

Mold occurrence in new homes has become so endemic that builder's liability insurance coverage limits the insurance carrier's liability to a few thousand dollars, if it covers mold issues at all. Homeowner's insurance policies are similarly affected, with insurance carriers limiting their liability to not more than five thousand dollars in most instances. Financially sound insurers, with hundreds of billions of dollars in assets, say they cannot afford to write insurance policies covering mold. Many states are limiting their own liability for failure to properly inspect homes to prevent conditions that contribute to mold propagation. Mold related health issues stand to cause as serious an economic impact on the US economy as have asbestos related issues and lead paint related issues.

When mold becomes an issue, tens of thousands of dollars must often be expended to address the conditions which allow mold growth and tens of thousands more to repair cosmetic and structural damage to the home. Many health care organizations and respiratory experts attribute a number of illnesses to spores and airborne toxins directly attributable to mold colonization in the living environment. While insurers say they are not able to afford the cost, homeowners and builders are probably not prepared for the significant price of mold remediation and control either.

The increasing incidence of mold problems in residential construction has been attributed to many different factors including less air exchange between the treated inside air and unconditioned outside air, poor Heating, Ventilation, Air Conditioning, (HVAC) planning, the changing nature of building materials, poorer site location as prime building sites become more scarce, and a host of other potential causes. It is often claimed that through simply controlling the relative humidity and allowing for sufficient air exchange, mold incidence can be completely controlled. The prevailing wisdom is that when relative humidity is held to below 60%, mold will not even be an issue.

In reality, the most expensive mold problems are those that exist in areas not often visited and in concealed areas that cannot be easily inspected. These are the areas wherein humidity is not ever controlled. These areas, including inside the stud cavity and on the floor joists and decking above the crawl space or basement have humidity levels that are not affected by adjustments to the HVAC, system. By comparison, mold issues inside the living area are more easily addressed and fairly obvious solutions and treatments are available.

Elimination of conditions conducive to mold growth inside the wall cavity can very often be accomplished by simple application of materials required by the Model Energy Code, (MEC) and the International Residential Code, (IRC). The MEC requires sealing the building envelope to restrict air leakage, (caulking, sealing, and weather-stripping at all penetrations and joints). The IRC requires in section 602.8, Item 4, that the material used in annular spaces around wires and pipes be an approved fireblocking caulk. Use of fibrous materials, foams (including fire retardant foams), or noncombustible fill materials do not meet the requirements of these overlapping code requirements. An elastomeric caulk, fire rated in accordance with the testing protocol of ASTM E119 and/or ASTM E-814 does meet both requirements. The application of an elastomeric fire rated caulk at all penetrations between the ground level floor and the crawl space can prevent mold spores from penetrating into the stud cavity from ground level contributing to mold growth inside the cavity on wood and/or on drywall materials.

Existing homes can also be treated from the crawlspace or basement wherever pipes, wires, or other penetrants break the thermal barrier between the living area and the unheated crawlspace or basement. Application is much more difficult in existing structures because insulation materials are present and are an obstacle to accessibility to the annular spaces around the penetrants.

Recommendations to builders should include that instructions for proper fill of the annular spaces be strictly followed and steps should be taken beyond current Building Code requirements. These steps should include but not be limited to caulking with an approved, elastomeric sealing caulk rated to last 35 years or more, at every annular space wherever any wire, pipe, or other penetrating item passes through any wood, even where fire caulking is not required. Sealing each cavity from the adjacent cavity serves to prevent the lateral movement of mold spores and insures that any mold problem that occurs will be more isolated in scope and less costly to address.

In addition to proper sealing and fire caulking, a number of new products have been introduced to combat mold in new residential and commercial construction during recent years. One very promising approach involves utilization of biocide free coatings that are sprayed on the masonry walls of the crawlspace, on the floor joists in the crawlspace area, and on the floor deck below the first floor. These coatings are formulated to be so smooth that spores cannot stay on them long enough to germinate and even if the spore does germinate, it cannot utilize the organics in the wood as a food source. These coatings usually incorporate ingredients found in non-stick cookware to accomplish mold resistance. Some mold barrier sprays also utilize generally mild biocides such as Sodium Chloride, (table salt), or Copper Sulfate, (a swimming pool water treatment). A lower cost and equally promising product utilizes graphite as its base material, the graphite based products can score a perfect 10 when tested in accordance with the recognized mold resistance protocol of ASTM D-3273. Other non-stick formulations can also score at that level but current information indicates that in terms of cost to provide the protection, the newer graphite based formulations work at least as well as others and they do so at far lower cost of manufacture, which results in lower costs to the builder.

Some builders, especially those who have experienced mold issues in previous construction, are anxious for answers to their mold related concerns and have embraced a pro-active approach to building mold free homes. Building Inspectors serve the builder and the homebuyer well when enforcing building codes regulations during each construction phase that severely curtail or eliminate the possibility of mold growth.

Some of the elastomeric Fire Rated Caulks that comply with IRC code provisions and also meet current Energy Code requirements include:

Product Trade Name Manufacturer Telephone
Elastomeric Fire Rated Caulks:
Metacaulk 66303 Rectorseal 713-263-8001
FireLockRi Protective Chemicals Corp. 828-966-9213
Firetemp™ CI Caulk Johns Manville 888-322-1129
3M™ Fire Barrier CP 25WB+ 3M Corporation 800-328-1687
Mold Barrier Coatings:
E-Coat EnviroCare® Corporation 877-463-2628
Steri Shield Somay® 305-633-6333
Foster Products H.B. Fuller 800-231-9541
Mold-Ban Protective Coatings Corp. 828-883-5865
FiberLock®IAQ™ Fiberlock Technologies, Inc. 978-623-9987


A mold free environment for many families can only be accomplished through good building code wording and enforcement. Responsible code enforcement personnel and responsible builders are the homeowners only line of defense against health problems resulting from molds, spores, and airborne toxins associated with mold in the home environment.


1.) Vigorously enforce building code requirements relating to fire caulking at the plate between the "ground" floor and the basement and/or crawlspace area.

2.) Allow only flexible elastomeric fire caulking, tested in accordance with ASTM E-119 and/or ASTM E-814, (fire rated caulking is required in this application in accordance with the IRC, section 608, item 4), to be used as a fire barrier in the annular spaces around wires or pipes at the ground floor level, (elastomeric fillers create the tightest seal). Require "intumescent" fire caulk around plastic vent or drain pipes, (intumescent fillers grow with heat to close off the fire path when a penetrant melts from the heat). Many foam products, even those that are "fire-rated," release cyanide gas under fire conditions and melt at such low temperatures as to be ineffective under actual fire conditions. Fibrous materials allow for the passage of moisture, mold spores, and, under fire conditions, toxic gases. "Noncombustibles" tested in accordance with ASTM E-136 often shrink during cure and allow for the passage of spores and gases.

3.) Modify building codes by local amendment or at the code development level to include treatment with an approved mold barrier spray on crawl space or basement walls and on the floor deck below the first floor.

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