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.)
IMC § 1002.1: Water Heaters/General. Water heaters
must be installed in accordance with the manufacturer’s directions.
(Ideally, hot water heaters should be installed in a room with a floor
drain, and should be equipped with a shut-off valve, to minimize damage
in the event of a leak.)
- The IPMC applies to existing residential and
commercial structures and premises.
- The IRC regulates the construction, alteration,
repair, use, and occupancy of detached one- and two-family dwellings
and townhouses not more than three stories high. While the section numbers
in the code are preceded by a letter, e.g., “R” for the
administrative, definitions, and building, planning, and construction
portions of the code, “N” for the energy conservation portion,
etc., those prefixes have been omitted from this document.
- The IBC governs new construction in residential
buildings four or more stories high.
- The IECC sets forth alternative compliance approaches
for new construction in both residential (one-and two-family buildings,
and multi-family buildings three or less stories in height) and commercial
buildings (including residential buildings four or more stories high).
For residential buildings, these approaches include a systems approach,
which considers the entire building and its energy-using systems as
a whole; an approach based on the performance of components in the building
envelope; an approach based upon the performance of the building envelope
as a whole; and others. Commercial buildings can comply using a prescriptive
approach, which sets standards for the building envelope, mechanical,
lighting, and service water-heating subsystems; a total building performance
approach; or an energy cost budget approach. Therefore, the code provisions
cited in this table may not be required in a particular building if
that building is constructed using an alternative approach to compliance.
- The IMC governs the design, installation, maintenance,
alteration, and inspection of permanently installed mechanical systems
used to control environmental conditions within buildings. The IMC does
not require the removal and replacement of existing mechanical systems,
although work performed on existing systems must conform to the code’s
requirements for new work.
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