Looking for Signs
Identifying the type of moisture damage and discovering its source or
sources usually involves the human senses of sight, smell, hearing, touch,
and taste combined with intuition. Some of the more common signs of visible
as well as hidden moisture damage, include:
- Presence of standing water, mold, fungus, or mildew
- Wet stains, eroding surfaces, or efflorescence (salt deposits) on interior
and exterior surfaces
- Flaking paint and plaster, peeling wallpaper, or moisture blisters
on finished surfaces
- Dank, musty smells in areas of high humidity or poorly ventilated spaces
- Rust and corrosion stains on metal elements, such as anchorage systems
and protruding roof nails in the attic
- Cupped, warped, cracked, or rotted wood
- Spalled, cracked masonry or eroded mortar joints
- Faulty roofs and gutters including missing roofing slates, tiles, or
shingles and poor condition of flashing or gutters
- Condensation on window and wall surfaces
- Ice dams in gutters, on roofs, or moisture in attics
Uncovering
and Analyzing Moisture Problems
Moisture comes from a variety of external sources. Most problems begin
as a result of the weather in the form of rain or snow, from high ambient
relative humidity, or from high water tables. But some of the most troublesome
moisture damage in older buildings may be from internal sources, such as
leaking plumbing pipes, components of heating, cooling, and climate control
systems, as well as sources related to use or occupancy of the building.
In some cases, moisture damage may be the result of poorly designed original
details, such as projecting outriggers in rustic structures that are vulnerable
to rotting, and may require special treatment. The five most common sources
of unwanted moisture include:
- Above grade exterior moisture entering the building
- Below grade ground moisture entering the building
- Leaking plumbing pipes and mechanical equipment
- Interior moisture from household use and climate control systems
- Water used in maintenance and construction materials.
Above grade exterior moisture generally results from weather
related moisture entering through deteriorating materials as a result of
deferred maintenance, structural settlement cracks, or damage from high
winds or storms.
 Damp interior plaster around windows generally indicates moisture has entered from the outside. Photo: NPS files. |
Such sources as faulty roofs, cracks in walls,
and open joints around window and door openings can be corrected through
either repair or limited replacement. Due to their age, historic buildings
are notoriously "drafty," allowing rain, wind, and damp air to
enter through missing mortar joints; around cracks in windows, doors, and
wood siding; and into uninsulated attics. In some cases, excessively absorbent
materials, such as soft sandstone, become saturated from rain or gutter
overflows, and can allow moisture to dampen interior surfaces. Vines or
other vegetative materials allowed to grow directly on building materials
without trellis or other framework can cause damage from roots eroding
mortar joints and foundations as well as dampness being held against surfaces.
In most cases, keeping vegetation off buildings, repairing damaged materials,
replacing flashings, rehanging gutters, repairing downspouts, repointing
mortar, caulking perimeter joints around windows and doors, and repainting
surfaces can alleviate most sources of unwanted exterior moisture from
entering a building above grade.
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"Controlling Unwanted Moisture" an Historic Preservation Brief
