Buildings should be designed and built to provide comfortable and healthy levels of relative humidity (40-55% relative humidity). They should also prevent both liquid water from migrating through building components and water vapor from being trapped in building assemblies, like walls.
Moisture prevention includes quality construction to shed water away from the building and its foundation; vapor (region dependent) and air barrier systems that hinder the flow of air infiltration and water vapor; quality building products and installation that can help reduce the chance of leaks; and cooling and heating systems designed to provide comfort throughout the year. The following checklist provides a list of actions that you and your builder can do, or install, in your home to make it less prone to moisture problems.
- Perms are a traditional unit of water vapor permeability. Is shows the ability of a material to permit the passage of water vapor.
- Understand the vapor openness of the materials:
< 0.1 perm
1.0 – 0.1 perm
Kraft- faced fiberglas
- No Class I on inside or outside of walls in mixed, humid climates
- All armored/metal hoses from service to appliance
- All Air Handler Units (AHUs) equipped with secondary drain pan and automatic shutoff
- Conduct a plumbing integrity test
Site / Elevation / Slab
- Finished floor level at least 12" above 100- year flood plain
- Grade level under floor (slab, stem wall, crawl space) is at least 8" above the surrounding finished grade, including landscaping
- Grade slopes away from building on all sides for proper drainage
- Drainage tile on and around top of footing.
- Drainage board for below grade walls
- Garage floor elevation and appropriate driveway slope
- 8" or greater clearance between building exterior cladding and final earth grade, including landscaping
- Siding and exterior trim primed on all sides
- All exterior flashing installed per manufacturer’s instructions and/or per Energy and Environmental Building Association’s Water Management Guide specifications
- Roof slope > 3-in-12
- Eaves at least 18" and rake (gable) at least 12"
- Secondary water protection installed on roof.
- Roof covering above and below flashing
- Rain gutters on eaves installed
- Downspouts discharge > 3' from building
- Drain in laundry and mechanical room(s).
- Splashboards/capillary break in laundry and mechanical room(s)
- Seal all top plate penetrations
- Capillary break between foundation and framing
Windows and Doors
- Avoid pocket doors in humid areas (suchas bathrooms)
- Avoid single pane aluminumwindows
- Faucets do not drip or leak upon occupancy
- Automatic water sensors / shutoff system installed
- Air admittance vents
- Gasketed access panels to plumbing fixtures
Heating, Ventilation & Air Conditioning
- Mechanical core with access to wet walls
- Sealed combustion furnace
- Whole house positive ventilation strategy.
- Condensate line(s) discharge >2 feet from house
- Bathroom ventilation fan with humidistat or timer vented to exterior
- Kitchen range hood vented to exterior
- Room by room load analysis including whole house latent load analysis
- Air handling unit in conditioned space
- Advanced humidity control HVAC system
- Water heater equipped with secondary drain pan
- Water heater equipped with shutoff
- User friendly washer water shutoffvalves
- Washer and dryer outside of conditioned space
- Drain pan under washer
- Dishwasher with condensing water drain
- Sealed water heater combustion, or isolated from conditioned area and power vented
- Landscape exists primarily on rainfall; no permanent irrigation system
- Plants minimum of 3' from foundation and when mature, won’t touch the structure
- Irrigation/sprinkler system located >2' from house; water does not hit house while operating
- Onsite designated retention area
Developed as part of the NASULGC/DOE Building Science Community of Practice. The factsheet editors are: Robert "Bobby" Grisso, Ph. D., Extension Engineer, Biological Systems Engineering; Martha A. Walker, Ph.D, Community Viability Specialist, Central District; Philip Agee, Ph. D., Assistant Professor, Department of Building Construction, and John Ignosh, Extension Specialist, Biological Systems Engineering, Virginia Tech.
DISCLAIMER – This piece is intended to give the reader only general factual information current at the time of publication. This piece is not a substitute for professional advice and should not be used for guidance or decisions related to a specific design or construction project. This piece is not intended to reflect the opinion of any of the entities, agencies or organizations identified in the materials and, if any opinions appear, are those of the individual author and should not be relied upon in any event.
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February 26, 2020