Checklist: Checklist for Minimizing Mold Risk
BUILDING ENVELOPE
Provide dampproofing and drainage plane on foundation wall: With full basements, dampproofing should be applied to the outside of the foundation wall. A free-drainage layer should be provided next to the foundation wall surface (a layer of drainage mat or free-draining insulation plus backfilling with crushed stone is preferable, but just the drainage layer or porous backfilling is often adequate). Provide drainage tile at foundation footings: Perforated perimeter drainage pipe should be installed with a minimum slope of 1⁄2” in 10 feet (13 mm in 3 m). The pipe should be located below the floor level but not extend below the bottom of the footing—so that soil is not disturbed. It should drain to daylight or to a sump. The drain pipe should be surrounded with crushed stone and the layer of stone protected with filter fabric to keep fines out. Provide capillary break on footing: A capillary break, either dampproofing or a membrane, should be installed between the footing and foundation wall, crawlspace stem wall, or perimeter foundation for slab-on-grade. Provide polyethylene vapor retarder under floor slab: With either slab-on-grade construction or with a full basement and poured basement floor, provide either a layer of polyethylene (6-mil minimum) or rigid insulation under the slab. This will block capillary movement (wicking) of moisture into the slab from below. If both rigid insulation and a polyethylene vapor retarder are used, install poly next to the concrete—not vice versa—so that a reservoir of standing water cannot be created. With a monolithic slab-on-grade, the poly vapor retarder should extend beneath the grade beam. Avoid a layer of sand between the poly and the concrete—this can provide a mold reservoir. Provide drainage away from building: The grade around a building should slope away from the building at a minimum grade of 5% (6” in 10’, or 5 cm in 1 m) for at least 10 feet (3 m). Provide low-permeability soil cap near building: Within a few feet (1 m) of the building, provide a low-permeability soil mix (high clay content) to minimize infiltration of rainwater right next to the building. Provide a roof overhang: A roof overhang will help keep rain and splashback off of the building walls—where it can be absorbed and migrate into the wall cavity. Install gutters and downspouts: Gutters and downspouts should be used to collect rainwater and carry it away from the building. Consider a rainwater catchment system to capture that rainwater for reuse. Provide a drainage plane in the wall system: A drainage plane is a layer that allows water entering the wall system to drain to the ground. This can be provided with overlapping layers of asphalt-impregnated felt paper, or with a permeable house-wrap product (though water resistance of plastic house-wrap products may deteriorate if in contact with a surfactant, such as oil from cedar siding). Provide a rain screen with any absorbent siding: A rain screen (air space between the siding/cladding and drainage plane) should be provided with any porous or absorptive siding or cladding (clapboard, shingle, board-and-batten, brick veneer, stucco, etc.). A rain screen can be provided with strapping or a wire drainage mat (e.g., CedarBreather®) between the exterior sheathing and siding. With stucco or brick facing, an air space and weepage openings are required. Provide flashing to prevent migration of moisture into building: Step flashing should be used to shed water, keeping it out of rigid insulation, sill, band joists, window trim, and other locations, particularly where dissimilar materials meet. At foundations, this flashing can also help protect against termite entry. Provide proper flashing when installing windows: Proper flashing at window rough openings is critical to avoid moisture migration into the building from the exterior. The EEBA Builder Guide series of books by Joe Lstiburek provide very good detailing options. Determine where in the envelope design the vapor retarder should go based on location and building use: Deciding where a vapor diffusion retarder should be placed depends on the climate (whether it is primarily a heating climate or a cooling climate) and how the building is likely to be operated (especially whether or not air conditioning will be used). In general, the vapor retarder should go on the warm side of the wall—in cold climates this is on the interior; in hot climates (especially with air conditioning), it is on the exterior. Provide drying potential in the envelope design: Make sure that moisture in a wall or ceiling cavity has an escape route. The direction of drying potential is determined by relative temperature differences, so it is important to design the envelope layers accordingly. In hot-humid climates, the drying potential should be toward the interior (i.e., interior layers should be more permeable). Specify high-performance windows with warm-edge spacers: In high-humidity conditions, condensation on window surfaces during winter months can be a significant problem relative to mold. Condensation can generally be prevented by the use of high-performance glazings and low-conductivity glazing spacers.MECHANICAL AND PLUMBING SYSTEMS
Seal all ducts: Failure to seal ducts, plenums, distribution box connections, duct collars, return-air duct collars, and air-supply registers may allow dirt, dust, and other debris to enter the air distribution system, providing media for mold. Seal ducts with mastic, not duct tape. Insulate all cold components of cooling equipment: To prevent condensation on cold surfaces, insulate cold components (ducts and pipes) of air conditioning equipment. Insulate cold-water pipes: In climates with moderate to high summer humidity, insulate cold-water supply pipes to prevent condensation. Condensate dripping off cold-water pipes is a common source of moisture for mold growth. Make plumbing easy to inspect and repair: When possible, avoid plumbing in exterior walls or concrete slabs, and provide access points to inspect and repair. Avoid depressurization: Design HVAC systems to avoid depressurization that can draw moist air into the building from the ground or crawl space. In humid climates, infiltration of outside air often accounts for the vast majority of moisture in buildings. Vent significant moisture sources to the outside: Always vent kitchen range hoods, bathrooms, and clothes dryers to the outside. Use quiet exhaust fans to increase the likelihood that homeowners will use them (bath fans rated at less than 1.5 sones, kitchen range hood fans with a low setting rated at less than 3.5 sones). Never install unvented gas heaters: “Vent-free” gas appliances contribute significant quantities of water vapor: as much as 7 gallons (26 l) per day for a typical residential gas space heater operating 50% of the time. (Water is a primary combustion product of natural gas.) Provide whole-building mechanical ventilation: Adequate fresh air supply and indoor air exhaust will help to avoid the buildup of humidity in most (but not all) climates. When outdoor air is very humid, moisture removal should accompany fresh-air delivery. Provide adequate dehumidification: In hot-humid climates, an energy-efficient building will require little air conditioning for the sensible load; most of the A/C load is for dehumidification (the latent load). Avoid oversizing A/C equipment, as that will reduce dehumidification performance. In some situations, it makes more sense to install dehumidifiers rather than air conditioners. Keep relative humidity below 50 to 60%. Locate ducts within conditioned envelope: This will reduce the likelihood of moisture condensing on the cold duct surfaces. Install properly draining condensate lines: With air conditioning and condensing heating or water heating equipment, provide condensate lines that drain to the outdoors or to a waste line, as specified by manufacturer. Provide proper slope and drainage of drain pans under unit air conditioners: Avoid situations in which water sits in drain pans—this is a prime environment for mold growth. Install floor drains beneath clothes washers: Install a good drain pan and floor drain(s) that can catch the wash water if a hose fails.Material Selection
Avoid carpeting on a concrete basement floor slab: Basement slab floors are likely to be damp and cool—posing risk of moisture condensation. Consider carpeting only if the floor slab is insulated and redundant measures have been used to prevent moisture leakage or diffusion through the foundation walls or floor. Install vapor-permeable carpet pad and carpeting: If carpeting or carpet pad gets wet, or if moisture gets underneath the carpet/carpet pad, it should be able to dry out. This strategy is most important for carpet in a basement floor location, but it is reasonable insurance for carpeting installed anywhere. Minimize the use of carpeting: Carpet can provide an environment where mold can grow. “Unless it’s kept clean,” says Terry Brennan, “a carpet is really a tilled garden waiting for rain.” Install track-off entryway systems to reduce dirt entry, and use quality vacuum cleaners regularly. Consider non-paper-faced gypsum board: U.S. Gypsum’s Fiberock, a relatively new wallboard product with cellulose fiber distributed uniformly through the material instead of as surface facings, offers much less cellulose media for mold growth (see EBN Vol. 9, No. 2). Avoid vinyl wallcoverings on exterior (perimeter) walls: Vinyl wallcoverings can trap moisture between the gypsum board and wallcovering. Avoid impermeable vinyl wallcoverings unless moisture dynamics and drying potential within the wall system have been carefully considered and determined to be adequate. Generally, in humid climates, vinyl wallcoverings should be limited to interior partition walls. Specify a ridge vent that will exclude rain and snow: For gable roofs, ridge vents are available that effectively block the entry of rain or snow—both of which can add unwanted moisture (and mold-growth potential) to an attic or roof assembly.Construction Practices
Protect building materials on the job site: Keep building materials off the ground and under cover until use. An investigation in North Carolina found that very high levels of mold contamination were common in framing lumber stacked on the job site. Remove wood and paper waste from the job site: Do not leave sawdust, wood chips, and other debris in wall cavities, crawl spaces, or other building cavities—it can provide food media for mold. When practical, do not operate the HVAC system during construction: Contamination of ducts, plenums, and warm-air registers occurs when HVAC equipment is operated before construction is completed. Accumulated dust and debris provides food media for mold. If HVAC equipment must be operated during construction, use special HEPA filters to keep dust out. Seal fan penetrations: During construction, seal all bathroom, kitchen, and dryer exhaust fan penetrations and ducts. Failure to do this often results in moist exhaust air leaking into a wall or ceiling cavity. Seal penetrations through the building envelope: Penetrations for windows, doors, wires, plumbing, exhaust vents, and so forth should be properly sealed to prevent rain penetration and air leakage.Building Operation
Clean or replace air filters: Air filters in forced-air heating systems, air conditioners, dehumidifiers, and other equipment should be cleaned or replaced as recommended by manufacturer. Instruct building occupants to use exhaust fans: Bathroom fans and kitchen exhaust fans should always be used when moisture is being generated. Avoid surrounding buildings with vegetation: Too much vegetation alongside or overhanging a building can prevent air circulation and shade the building. These conditions can result in wetter surfaces on the exterior of buildings and reduced drying of wall cavities—both of which can foster mold growth. Be on the lookout for signs of mold: Homeowners and commercial building maintenance personnel should be on the lookout for telltale signs of mold contamination: blotchy staining on walls, musty odors, dark “shadow” marks behind furniture, etc. When mold is found, proper mold remediation practices should be followed. Use night-flushing ventilation carefully: In humid and mixed climates, operate whole-building, night-flushing ventilation systems only when the outdoor relative humidity is not too high. Do not overcool buildings: In humid climates, the colder building interiors are maintained, the greater the likelihood of condensation and mold growth.
