State and local housing, property maintenance, and building codes contain a wide array of legal requirements pertaining to housing construction and maintenance. Below are listed provisions found in model codes that address water and moisture control. The opening file on Housing and Building Codes features a chart listing code provisions on several healthy home attributes. IPMC § 302.2: Grading and Drainage. Premises must be graded to prevent the accumulation of stagnant water on the premises or within the building. (Stagnant water can provide a breeding ground for mosquitoes and other insects and also can lead to mold growth.) IPMC § 303.6: Exterior Walls. Exterior walls must be maintained free from holes and must be weatherproof. (Exterior walls must be capable of preventing dampness or water from entering the structure.) IPMC § 303.7: Roofs and Drainage. The roof and flashing must not have defects that admit rain. Roof drainage must be adequate to prevent dampness in the walls or interior of the home, and roof drains and gutters must be in good repair and free of obstruction. IPMC § 303.13: Window, Skylight, and Door Frames. Windows, skylights, and door frames must be in good repair and weather tight. (If not weather tight, moisture problems can result.) IPMC § 303.13.1: Glazing. Glazing materials must be free from cracks and holes. (Holes in glass can admit moisture and pests.) IPMC § 303.16: Basement Hatchways. Basement hatchways must be maintained to prevent the entry of rodents, rain, and surface drainage water. IPMC § 403.2: Ventilation/Bathrooms and Toilet Rooms. Bathrooms and toilet rooms must have at least one openable window, unless equipped with a mechanical ventilation system. Mechanical ventilation systems must discharge air to the outside and may not recirculate the air. (Bathroom ventilation is important due to high humidity levels associated with baths and showers.) IPMC § 403.5: Clothes Dryer Exhaust. Clothes dryer exhaust systems must be independent of other systems and must be exhausted in accordance with the manufacturer’s instructions. (Clothes dryers should vent to the outside to prevent excessive humidity levels.) IPMC § 504.1: Plumbing Systems and Fixtures/General. Plumbing fixtures must be properly installed and maintained in working order and free of leaks, obstructions, and defects. (Plumbing leaks can cause moisture problems, which can lead to mold growth.) IPMC § 506.1: Sanitary Drainage System/Maintenance. Every plumbing stack, vent, waste, and sewer line must function properly and be free of leaks and obstructions. (Plumbing leaks can cause moisture problems, which can lead to mold growth.) IRC § 307.2: Bathtub and Shower Spaces. Bathtub and shower floors, walls above bathtubs with installed showerheads, and shower compartments must be finished with a non-absorbent surface. Wall surfaces must extend to at least six feet above the floor. IRC § 322.1: Moisture Vapor Retarders/Moisture Control. In all framed walls, floors, roofs, and ceilings making up the building thermal envelope, a vapor retarder must be installed on the warm-in-winter side of the insulation, unless the framed area is ventilated to allow moisture to escape. (Vapor retarders are designed to prevent the movement of moisture-laden air from the warm side of the wall to the cool side. In temperate climates, vapor retarders are placed on the interior (warm in winter) side of the wall cavity; in hot, humid climates, they are placed on the exterior (warm) side of the wall cavity. According to the Asthma Regional Coordinating Council of New England, walls should be designed to dry to both the interior and the exterior and basements should be designed to dry to the interior. Installing vapor barriers interferes with the ability of walls to dry in both directions, so their use should be limited to severely cold climates. Paper-faced cavity insulation should be used in place of plastic interior vapor barriers.) IRC § 401.3: Foundations/Drainage. Surface water must be diverted to a storm sewer or other approved point of collection. Lots must be graded to enable surface water to drain away from foundation walls. The minimum slope away from the foundation must be six inches fall within the first 10 feet. However, if this is not possible, drains and swales may be used to ensure drainage away from the structure. (Proper drainage is important in preventing wet basements, damp crawl spaces, and possible failure of the foundation.) IRC § 405.1: Foundation Drainage/Concrete or Masonry Foundations. Drainage tiles, gravel drains, or perforated pipe must be installed around all concrete or masonry foundations that retain earth and enclose habitable space located below grade, and must discharge by gravity or mechanical means to an approved drainage system. A drainage system is not required in well-drained ground. (This enables groundwater to drain away from the foundation, and prevents water from leaking into habitable space.) IRC § 405.2.1: Wood Foundations/Base. A minimum 4-inch thick, porous layer of gravel, stone, or course sand must be placed under the basement floor. (This facilitates drainage under the floor, and can serve as a capillary break under a concrete floor slab, preventing groundwater from reaching the slab, where it could be wicked up into the interior.) IRC § 405.2.2: Wood Foundations/Moisture Barrier. A 6-mil-thick polyethylene moisture barrier must be applied over the porous layer required under IRC § 405.2.1, with the basement floor constructed over the polyethylene. (This prevents groundwater from penetrating the basement floor.) IRC § 405.2.3: Wood Foundations/Drainage System. Except in well-drained soils, a sump must be provided to drain the porous layer and the footings. The sump must extend at least 24 inches below the bottom of the basement floor and be capable of gravity or mechanical drainage to a sewer system or to daylight. IRC § 406.1: Concrete and Masonry Foundation Dampproofing. Unless waterproofed, foundation walls that retain earth and enclose habitable space located below grade must be dampproofed from the top of the footing to the finished grade by applying a bituminous coating or other listed waterproofing material to the outside of the foundation wall. (The dampproofing material fills the pores in the concrete, and prevents groundwater from entering the interior through capillary action. According to the Asthma Regional Coordinating Council of New England, the top of the footing also should be dampproofed, in order to prevent water from rising up from the footing into the foundation.) IRC § 406.2: Concrete and Masonry Foundation Waterproofing. In areas with a high water table or other severe soil-water conditions, foundation walls that retain earth and enclose habitable space located below grade must be waterproofed with one of several listed impervious membranes from the top of the footing to the finished grade. IRC § 406.3: Dampproofing for Wood Foundations. Wood foundations that retain earth and enclose habitable space located below grade must be dampproofed by sealing plywood panel joints with caulking, installing a below-grade moisture barrier on exterior foundation walls, and backfilling with porous fill adjacent to the foundation wall. (Dampproofing measures detailed in § 406.3.1 – 406.3.4.) IRC § 408.1: Under-Floor Space/Ventilation. The crawl space between the floor joists and the earth under the building must be provided with ventilation openings. (The IRC recommends ventilating the crawl space to control condensation and reduce dry rot, unless the ground is covered with a vapor retarder, the perimeter walls are insulated, and the space is supplied with conditioned air. (See IRC § 408.2.) The Asthma Regional Coordinating Council of New England (ARC) prefers this alternative approach. ARC recommends that crawl spaces be designed and constructed as mini-basements in order to limit indoor humidity and airborne contaminants: without vents to the exterior, insulated along the perimeter, with a continuous ground cover such as polyethylene.) IRC § 408.4: Under-Floor Space/Removal of Debris. The under-floor grade must be cleared of all vegetation, organic material, and construction materials. (These materials can create pockets for water to accumulate, and disturb the drainage plan as they decay.) IRC § 408.5: Under-Floor Space/Finished Grade. If the groundwater table can rise to within 6 inches of the finished floor elevation, or surface water does not readily drain from the site, the grade in the crawl space must be as high as the finished grade outside the building, unless a drainage system is installed. (These measures will prevent moisture from accumulating in the crawl space.) IRC § 504.2.1: Pressure Treated Wood Floors (On Ground)/Base. A minimum 4- inch thick base of gravel or crushed stone must be placed over the compacted earth underlying the floor. (The base provides a capillary stop for water rising up through the soil and into the slab.) IRC § 504.2.2: Pressure Treated Wood Floors (On Ground)/Moisture Barrier. Polyethylene sheeting must be placed over the granular base. (This can help to minimize moisture problems associated with slab-on-ground construction.) IRC § 506.2.2: Concrete Floors (On Ground)/Base. A minimum 4-inch base course of sand, gravel, or crushed stone must be placed on the subgrade when the concrete slab is below grade, except on well-drained soil. IRC § 506.2.3: Concrete Floors (On Ground)/Vapor Retarder. An approved vapor retarder must be placed between the concrete slab and the base course (or subgrade where no base course exists). IBC § 1202.2: Ventilation/Attic Spaces. Ventilation openings must be protected against the entry of snow and rain (to prevent the entry of moisture). IBC § 1202.4.2.1: Ventilation/Bathrooms. Rooms containing bathtubs, showers, and similar fixtures must be mechanically vented in accordance with the International Mechanical Code. IBC § 1209.3: Surrounding Materials/Showers. Shower compartments and walls above bathtubs with installed shower heads must be finished with a smooth, non-absorbent surface up to a height of at least 70 inches above the drain. IBC § 1209.4: Waterproof joints. Built-in tubs with showers must have waterproofed joints between the tub and adjacent wall (to keep water and moisture from getting into the supporting floor and framing). IBC § 1403.2: Weather protection. Exterior walls must provide the building with a weather resistant exterior wall envelope, and must include flashing, except for concrete or masonry walls. The exterior wall envelope must be constructed so as to prevent water from accumulating within the wall assembly by providing a water-resistant barrier behind the exterior veneer, and a means for draining any water that enters. The wall assembly must be protected against condensation in accordance with the International Energy Conservation Code. IBC § 1403.3: Vapor retarder. An interior non-corrodible vapor retarder must be provided. IBC § 1404.2: Water-resistive barrier. At least one layer of asphalt felt must be attached to the sheathing, with flashing, to provide a continuous water-resistant barrier behind the exterior wall veneer. IBC § 1405.3: Flashing. Flashing must be installed so as to prevent moisture from entering the through top and sides of exterior window and door openings; at the intersection of chimneys and frame walls; under and at the ends of copings and sills; above projecting wood trim; at the intersection of exterior walls and porches or decks; at wall-roof intersections; and at built-in gutters. (Flashing protects walls and roofs from moisture by preventing water from entering at points where water is most likely to intrude.) IBC § 1405.3.1: Exterior wall pockets. Wall pockets or crevices in which moisture can accumulate in exterior walls should be avoided or protected with caps, covers, flashing, or other means to prevent water damage. IBC § 1405.3.2: Masonry. Flashing and weepholes must be located in masonry above ground level to prevent water from penetrating the wall, and provide a means for moisture to escape. IBC § 1503.1: Weather Protection/General. Roof decks must be covered with roof coverings and designed, installed, and maintained to protect the building. (Roofing protects the building from water intrusion. Historically, the roof system is one of the most problematic areas of a building.) IBC § 1503.2: Flashing. Flashing must be installed to prevent moisture from entering the wall through the joints in the coping, through moisture-permeable material, at intersections with the roof plane, or at parapet wall penetrations. IBC § 1503.2.1: Flashing/Locations. Flashing must be installed at wall and roof intersections; at gutters; where the roof changes slope or direction; and around roof openings. Where flashing is metal, it must be corrosion-resistant. IBC § 1503.4: Roof Drainage. Design and installation of roof drainage systems must comply with the International Plumbing Code. IBC § 1504: Roof Assemblies and Rooftop Structures/Performance Requirements. Roof decks and roof coverings must be wind and impact resistant. IBC § 1507: Requirements for Roof Coverings. This section specifies the installation requirements for several types of roof coverings: asphalt shingles, clay and concrete tiles, metal roof panels, slate shingles, wood shingles, wood shakes, built-up roofs (e.g., coal-tar roofs), modified bitumen roofing, and others. Each type of roofing has a corresponding minimum slope requirement, to ensure adequate drainage, as well as minimum deck requirements such as solid wood sheathing or spaced sheathing. Underlayment also is specified for each type of covering. Underlayment serves to separate the roof deck from the roof covering, and provides additional protection against rain and moisture. Appropriate fasteners and proper attachment of roof coverings is specified. Ice dam protection is required in cold climates for some roof types. Flashing requirements also are specified. IBC § 1510.3: Reroofing/Recovering vs. Replacement. New roof coverings must not be installed without first removing the existing roof coverings if the existing roof is water soaked or has deteriorated to the point that it does not provide an adequate base for additional roofing. (An existing roof must be allowed to dry completely before new roof covering is applied, in order to avoid trapping moisture below the new layer of covering which could lead to deterioration of the new roof covering as well as the existing sheathing.) IBC § 1510.6: Reroofing/Flashings. Flashings must be reconstructed during reroofing. IBC § 1803.3: Site Grading. The ground immediately adjacent to the foundation must be sloped away from the building at a five percent incline for a distance of ten feet, or an appropriate method for diverting water away from the building must be used. (Grading prevents the accumulation of water around and under a building. In arid climates, grading requirements may be reduced.) IBC § 1805.3.4: Foundation elevation. On graded sites, the top of the exterior foundation must extend above the elevation of the street gutter at the point of discharge or the inlet of an approved drainage device a minimum of 12 inches. (This protects the building from flooding due to heavy rain.) IBC § 1806.1: Damp-proofing and Waterproofing/Where Required. Walls that retain earth and enclose interior spaces and floors below grade must be waterproofed or damp-proofed. (Damp-proofing is the application of coatings or other materials in order to prevent the passage of water under slight hydrostatic pressure; waterproofing is required to prevent the passage of water or water vapor under significant pressure.) IBC § 1806.2: Damp-proofing Required. Where hydrostatic pressure will not occur, damp-proofing for walls and floors is required. IBC § 1806.2.1: Damp-proofing Required/Floors. Damp-proofing materials must be installed between the floor and the base course (gravel), unless a separate floor is installed above the concrete slab, in which case the damp-proofing can be applied above the concrete slab. Where applied below the slab, damp-proofing should consist of 6-mil polyethylene or other approved material; above the slab, 4-mil polyethylene is acceptable. (This prevents moisture from entering below-ground spaces. Rigid insulation would be preferable.) IBC § 1806.2.2: Damp-proofing Required/Walls. Damp-proofing materials for walls must be installed on the exterior surface of the wall, and extend from the top of the footing to above ground level. IBC § 1806.3: Waterproofing Required. Where hydrostatic pressure exists, walls and floors must be waterproofed if the design does not include a groundwater control system. IBC § 1806.3.1: Waterproofing Required/Floors. Floors requiring waterproofing must be concrete and designed to resist maximum hydrostatic pressures to which the floor will be subjected. Waterproofing is accomplished by placing a membrane underneath the concrete slab. IBC § 1806.3.2: Waterproofing Required/Walls. Walls requiring waterproofing must be waterproofed from the bottom of the wall to at least 12 inches above the maximum ground water level. The remainder of the wall must be damp-proofed. IBC § 1806.3.3: Waterproofing Required/Joints and Penetrations. Joints in walls and floors, joints between the wall and floor, and penetrations of the wall and floor must be made watertight (to ensure the effectiveness of waterproofing, and prevent water from entering the building or becoming trapped in the foundation walls or floor slab). IBC § 1806.4: Subsoil Drainage System. Where hydrostatic pressure does not exist, damp-proofing must be applied, and a base installed under the floor, as well as a drain around the foundation perimeter. IBC § 1806.4.1: Floor Base Course. Floors of basements must be placed over a floor base course at least 4 inches thick consisting of gravel or crushed stone. (The gravel or stone provides a capillary break so that moisture from the soil below will not rise to the underside of the floor. It can also act as a drainage system for water under the slab.) IBC § 1806.4.2: Foundation Drain. A drain must be placed around the perimeter of a foundation consisting of gravel or crushed stone. IBC § 1911.1: Minimum Slab Provisions/General. Floor slabs placed directly on the ground must be at least 3½ inches thick. A polyethylene vapor retarder or other approved material must be placed between the base course or subgrade and the concrete floor slab. IBC § 2104.1.8: Masonry Construction/Weep Holes. In masonry construction, walls must be provided with weep holes. (Because masonry is not water tight, small holes are necessary to allow water to drain from masonry walls.) IBC § 2509.2: Gypsum Board in Showers and Water Closets/Base for Tile. When gypsum board is used as a base for tile and wall panels in showers and tubs, water resistant gypsum backing board is required. (Ideally, gypsum board should not be used at all in wet areas. The backing paper on gypsum board provides excellent food for mold to grow. Alternatives to gypsum board include concrete masonry, ceramic tile on cement backer board, or cement plaster, which perform well in high-moisture areas.) IBC § 2509.3: Gypsum Board in Showers and Water Closets/Limitations. Gypsum board, including water-resistant gypsum backing board may not be used over a vapor retarder in a shower or bathtub. (Although water-resistant gypsum board is required when used as a base for tiles or wall panels in showers and tubs, in extreme conditions, even water-resistant gypsum board will not provide an adequate level of moisture protection. Installing water-resistant gypsum board over a vapor retarder would create a waterproof membrane on both sides of the gypsum board. Moisture would become trapped in the gypsum board, causing it to fail. Ideally, gypsum board should not be used at all in wet areas.) IBC § 2512.1.2: Exterior Plaster/Weep Screeds. For exterior plaster walls, a corrosion-resistant weep screed with a vertical attachment flange must be provided at the base of the exterior walls. The attachment flange must overlap the base of the water-resistant barrier on the wall cavity. (This will allow water that becomes trapped behind the plaster wall to run down the water-resistant barrier behind the exterior plaster, over the attachment flange, and drain to the exterior, not the interior, of the building.) IECC § 502.1.1: Building Envelope Requirements/Moisture Control. In residential buildings of less than 4 stories, the building design must not create conditions of accelerated condensation. All framed walls, floors, and ceilings not ventilated to allow moisture to escape must be provided with a vapor retarder on the warm-in-winter side of the insulation. (See parenthetical to IBC § 1403.3 above for a cautionary note regarding vapor barriers.) IECC § 503.3.3.5: Mechanical Ventilation. Automatic or gravity dampers that close when the HVAC system is not operating must be provided for outdoor air intake and exhausts. (This is intended to reduce air infiltration when the system is not operating. Air infiltration could lead to condensation, if, for example, warm moist air meets cooler air.) IECC § 602.1.5: Basement Walls. Where the basement is not considered a conditioned space (heated or cooled), either the basement wall or the basement ceiling should be insulated. (According to the Asthma Regional Coordinating Council of New England, basements should be designed to be conditioned and dry, and should be insulated around their perimeters, not between floors. Insulating the basement ceiling impedes the ability of the basement to dry.) IECC § 802.1.2: Building Envelope Requirements/Moisture Control. In residential buildings of 4 or more stories, all framed walls, floors, and ceilings not ventilated to allow moisture to escape must be provided with a vapor retarder on the warm-in-winter side of the insulation. (See parenthetical to IBC § 1403.3 above for a cautionary note regarding vapor barriers.) IMC § 307.1: Condensate Disposal/Fuel-Burning Appliances. Liquid combustion products must be collected and discharged to an approved plumbing fixture or disposal area in accordance with the manufacturer’s instructions. (Some appliances produce liquid by-products, which must be disposed of.) IMC § 504.1: Clothes Dryer Exhaust/Installation. Clothes dryers must be exhausted in accordance with the manufacturer’s instructions, be independent of all other systems, and convey any moisture and combustion products to the outside. (Clothes dryers emit high levels of moisture, which could lead to mold growth and building deterioration if vented to the indoors.) IMC § 406.1: Ventilation of Uninhabited Spaces/General. Crawl spaces and attics must be provided with natural or mechanical ventilation. A mechanical system must be automatically controlled to operate when the relative humidity of the space exceeds 60 percent. (This can prevent excess moisture from building up in enclosed spaces. However, if the outdoor air has a higher relative humidity than the air in the enclosed space, the system would run continuously, and possibly increase humidity levels in the enclosed space.) IMC § 603.4.1: Duct Construction and Installation/Gypsum Ducts. The use of gypsum boards to form ducts is limited to return air systems where the board surface temperature is maintained above the air stream dew point temperature. Gypsum board ducts may not be used in air handling systems using evaporative coolers. (If the surface temperature of the gypsum board is lower than the air stream dew point temperature, water will condense on the surface of the gypsum board, causing it to deteriorate. Evaporative cooling equipment uses water as a cooling agent, resulting in increased moisture in the air stream, which could lead to mold growth and deterioration of the gypsum board.) IMC § 603.11: Condensation. Provisions must be made to prevent the formation of condensation on the exterior of any duct. (Insulating ducts and covering them with a moisture barrier can prevent moisture vapor from condensing on the duct and insulation. Condensation on duct exteriors is typically a problem when ducts carrying cooled air pass through warm areas where humidity is not controlled. This provision does not address condensation on duct interiors, which can occur when ducts carrying warm, moist air pass through cooler areas.) IMC § 604.11: Vapor Retarders. Where ducts used for cooling are externally insulated, the insulation must be covered with a vapor retarder. (Insulation alone will not prevent condensation unless it is impervious to moisture.) IMC § 604.13: Internal Insulation. Internal insulation
that is not impervious to water may not be used to line ducts or plenums
from the exit of a cooling coil to the downstream end of the drain pan.
(Insulation in this location could easily become wet, which could lead
to mold growth.) About the Codes
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