“The physician can bury his mistakes, but the architect can only advise his
client to plant vines—so they should go as far as possible from home to build
their first buildings.”
Frank Lloyd Wright
New York Times, October 4, 1953
Introduction
Damaging moisture originates not only from outside
a home; it is created inside the home as well. Moisture is produced by smoking;
breathing; burning candles; washing and drying clothes; and using fireplaces, gas
stoves, furnaces, humidifiers, and air conditioning. Leaks from plumbing, unvented
bathrooms, dishwashers, sinks, toilets, and garbage disposal units also create moisture
problems because they are not always found before water damage or mold growth occurs.
Figure 7.1 provides an overview of the sources of moisture and types of
air pollutants that can enter a home.
Solving moisture problems is often expensive and time-consuming. The first step
is to do a moisture inventory to eliminate problems in their order of severity.
Problems that are easiest and least expensive to resolve should be addressed first.
For example, many basement leaks have been eliminated by making sure sump pumps
and downspouts drain away from the house. On the other hand, moisture seeping though
basement or foundation walls often is very expensive to repair. Eliminating such
moisture is seldom as simple as coating the interior wall, but often requires expert
consultation and excavating around the perimeter of the house to install or clean
clogged footing drains. Sealing the outside of the basement walls and coating the
exterior foundation wall with tar or other waterproofing compounds are often the
only solutions to eliminate moisture.
Moisture condensation occurs in both winter and summer. The following factors increase
the probability of condensation:
- Homes that are ineffectively insulated and
are not sealed against air infiltration in cold climates can result in major
moisture problems.
- Cool interior surfaces such as pipes, windows,
tile floors, and metal appliances; air conditioner coils with poor outside drainage;
masonry or concrete surfaces; toilet tanks; and, in the winter, outside walls
and ceilings can result in moisture buildup from condensation. If the temperature
of an interior surface is low enough to reach the dew point, moisture in the
air will condense on it and enhance the growth of mold.
- Dehumidifiers used in regions where outside
humidity levels are normally 80% or higher have a moisture-collecting tank that
should be cleaned and disinfected regularly to prevent the growth of mold and
bacteria. It is best if dehumidifiers have a drain line continuously discharging
directly to the outside or into a properly plumbed trap. This is also true in
climates where air conditioning units are used on a full-time or seasonal basis.
Their cooling pans provide an excellent environment for the growth of allergenic
or pathogenic organisms.
- Moisture removed from clothing by clothes
driers ends up in the dryer vent if it is clogged by lint or improperly configured.
Moisture buildup in this vent can result in mold growth and, if leakage occurs,
damage to the structure of the home. The vent over the cooking area of the kitchen
also should be checked routinely for moisture or grease buildup.
Roof
The control of moisture in a home is of paramount
importance. It is no surprise that moisture control begins with the design and integrity
of the roof. Many types of surfacing materials are used for roofs—stone, composition
asphalt, plastic, or metal, for example. Some have relatively short lives and some,
such as slate and tile, have extraordinarily long lives. As in nearly all construction
materials, tradeoffs must be made in terms of cost, thermal efficiency, and longevity.
However, all roofs have two things in common: the need to shed moisture and protect
the interior from the environment.
Click here for a list of roof inspection questions.
When evaluating the roof of a home, the first thing to observe is the roofline against
the sky to see if the roof’s ridge board is straight and level. If the roofline
is not straight, it could mean that serious deterioration has taken place in the
structure of the home as a result of improper construction, weight buildup, a deteriorated
or broken ridge beam, or rotting rafters. Whatever the cause, the focus of an inspection
must be to locate the extent of the damage.
The next area to inspect is around the flashing on the roof. Flashing is used around
any structure that penetrates the surface of a roof or where the roofline takes
another direction. These areas include chimneys, gas vents, attic vents, dormers,
and raised and lowered roof surfaces. One of the best ways to locate a leak around
flashing is to go into the attic and look carefully. Leaks often are discovered
when it rains; but if it is not raining, the underside of the roof can be examined
with the attic lights off for pinpoints of daylight.
Roofing material should lay relatively flat and should not wave or ripple. The roof
should be checked for missing or damaged shingles, areas where flashing should be
installed, elevation changes in roof surfaces, and evidence of decomposing or displaced
surfaces around the edge of the roof [1,
2, 3].
Insulation
A house must be able to breathe; therefore, air must not be trapped inside, but
must be allowed to exit the home with its moisture. Moisture buildup in the home
will lead to both mold and bacteria growth.
Figure 7.2 demonstrates insulation blown into an attic, to a depth of approximately
12 inches (Figure
7.3).
Figure 7.4 shows the area extending from a house under the roof, known as
the soffit. The soffit is perforated so that air can flow into the attic and up
through the ridge vents to ventilate the attic.
If insulation is too thick or installed improperly, it restricts proper air turnover
in the attic and moisture or extreme temperatures could result in mold or bacteria
growth, as well as delamination of the plywood and particleboards and premature
aging of the roof’s subsurface and shingles.
Care also must be taken in cold climates to ensure that the insulation has a vapor
barrier and that it is installed face down. When insulation is placed in the walls
of a home, a thin plastic vapor barrier should be placed over the insulation facing
the inside of the home. The purpose of this vapor barrier is to keep moisture produced
inside the house from compromising the insulation. If the barrier is not installed,
warm, moist air will move through the drywall and into the insulated wall cavity.
When the air cools, moisture will condense on the fibers of the insulation making
it wet; and, if it is cellulose insulation, it will absorb and hold the moisture.
Wetness reduces the effectiveness of the insulation and provides a favorable environment
for the growth of bacteria and mold [4, 5].
Siding
Good siding should be attractive, durable, insect- and vermin-resistant, waterproof,
and capable of holding a weather-resistant coating. Fire-resistant siding and roofing
are important in many areas where wildfires are common and are required by many
local building codes.
All exterior surfaces will eventually deteriorate, regardless of manufacturer warranties
or claims. Leaks in the home from the outside occur in many predictable locations.
The exterior siding or brick should be checked for cracks or gaps in protective
surfaces. Where plumbing, air vents, electrical outlets, or communication lines
extend through an exterior wall, they should be carefully checked to ensure an airtight
seal around those openings. The exterior surface of the home has doors, windows,
and other openings. These openings should be caulked routinely, and the drainage
gutters along the top should be checked to ensure that they drain properly.
Exterior surface materials include stucco, vinyl, asbestos shingles, brick, metal
(aluminum), cement, exterior plywood, hardwood, painted or coated wood, glass, and
tile, some of which are discussed in this chapter [6,
7].Fiber Cement
Fiber cement siding is engineered composite-material products that are extremely
stable and durable. Fiber cement siding is made from a combination of cellulose
fiber material, cement and silica sand, water, and other additives. Fiber cement
siding is fire resistant and useful in high-moisture areas.
The fiber cement mixture is formed into siding or individual boards, then dried
and cured using superheated steam under pressure. The drying and curing process
assures that the fiber cement siding has very low moisture content, which makes
the product is stable—no warping or excessive movement—and its surface good for
painting.
Weight is a minor concern with fiber cement products: they weigh about 1½ times
what comparably sized composite wood products do. Other concerns relate to cutting
fiber cement: cutting produces a fine dust with microscopic silica fibers, so personal
protective equipment (respirator and goggles) are necessary. In addition, special
tools are needed for cutting.
Brick
Brick homes may seem on the surface to be nearly maintenance free. This is true
in some cases, but, like all surfaces, brick also degrades. Although this degradation
takes longer in brick than in other materials, repairing brick is complex and quite
expensive. There are two basic types of brick homes. One is brick veneer, which
is a thin brick set to the outside of a wooden stud wall. The brick is not actually
the supporting wall. Brick veneer typically has the same pattern of bricks around
the doors and windows; a true brick wall will have brick arches or heavy steel plates
above the doors and other openings of the building. Some brick walls have wooden
studs behind the brick to provide an area for insulation, plumbing, vents, and wiring.
It is important that weep holes and flashing be installed in brick homes to control
moisture.
Improperly constructed building footers can result in major damage to the exterior
brick surface of a home by allowing moisture, insects, and vermin to enter. A crack,
such as the one in
Figure 7.5, is an example of such a failure. This type of damage will require
much more than just a mortar patch. Buildings constructed of concrete block also
experience footer failure. The damage is reason to not skimp when installing and
inspecting the footing and reinforces the need for appropriate concrete mix, rebar,
and footing drains.
Stucco
Synthetic stucco (exterior insulation and finish system; EIFS) is a multilayered
exterior finish that has been used in Europe since shortly after World War II, when
contractors found it to be a good repair choice for buildings damaged during the
war. North American builders began using EIFS in the 1980s, first in commercial
buildings, then as an exterior finish to wood frame houses.
EIFS has three layers:
- Inner layer—foam insulation board secured
to the exterior wall surface, often with adhesive;
- Middle layer—a polymer and cement base coat
applied to the top of the insulation, then reinforced with glass fiber mesh;
and
- Exterior layer—a textured finish coat.
EIFS layers bond to form a covering that does not
breathe. If moisture seeps in, it can become trapped behind the layers. With no
place to go, constant exposure to moisture can lead to rot in wood and other vulnerable
materials within the home. Ripples in the stucco could be a sign of a problem. On
the surface it may look like nothing is wrong, but beneath the surface, the stucco
may have cracked from settling of the house. With a properly installed moisture
barrier, no moisture should be able to seep behind the EIFS, including moisture
originating inside the home. Drains in the foundation can be designed to enable
moisture that does seep in to escape.
Other signs of problems are mold or mildew on the interior or exterior of the home,
swollen wood around door and window frames, blistered or peeling paint; and cracked
EIFS or cracked sealant.
Vinyl
Standard vinyl siding is made from thin, flexible sheets of plastic about 2 mm thick,
precolored and bent into shape during manufacturing. The sheets interlock as they
are placed above one another. Because temperature and sunlight cause vinyl to expand
and contract, it fits into deep channels at the corners and around windows and doors.
The channels are deep enough that as the siding contracts, it remains within the
channel.
Siding composed of either vinyl or aluminum will expand and contract in response
to temperature change. This requires careful attention to the manufacturer’s specifications
during application. Cutting the siding too short causes exposed surfaces when the
siding contracts, resulting in moisture damage and eventual leakage. Even small
cracks exposing the undersurface can create major damage.
Vinyl has some environmental and health concerns, as do most exterior treatments.
Vinyl chloride monomer, of which polyvinyl chloride siding is made, is a strong
carcinogen and, when heated, releases toxic gases and vapors. Under normal conditions,
significant exposures to vinyl chloride monomer are unlikely.
Asbestos
Older homes were often sided with composites containing asbestos. This type of siding
was very popular in the early 1940s. It was heavily used through the 1950s and decreasingly
used up until the early 1960s. The siding is typically white, although it may be
painted. It is often about ¼-inch thick and very brittle and was sold in sections
of about 12 x 18 inches. The composite is quite heavy and very slatelike in difficulty
of application. As it ages, it becomes even more brittle, and the surface erodes
and becomes powdery. This siding, when removed, must be disposed of in accordance
with local, state, and federal laws regulating the disposal of asbestos materials.
The workers and the site must be carefully managed and protected from contamination.
The composite had several virtues as siding. It was quite resistant to fire, was
not attractive to insects or vermin, provided very good insulation, and did not
grow mold readily. Because of its very brittle nature, it could be damaged by children
playing and, as a result, often was covered later with aluminum siding.
Metal
If metal siding is used, the mounting fasteners (nails
or screws) must be compatible with the metal composition of the siding, or the siding
or fasteners will corrode. This corrosion is due to galvanic response.
Click here for tips to prevent metal corrosion.
Galvanic response (corrosion) can produce devastating results that often are only
noticed when it is too late. It should always be considered in inspections and is
preventable in nearly all cases.
When two dissimilar metals, such as aluminum and steel, are coupled and subjected
to a corrosive environment (such as air, water, salt spray, or cleaning solutions),
the more active metal (aluminum) becomes an anode and corrodes through exfoliation
or pitting. This can happen with plumbing, roofing, siding, gutters, metal venting,
and heating and air conditioning systems.
When two metals are electrically connected to each other in a conductive environment,
electrons flow from the more active metal to the less active because of the difference
in the electrical potential, the so-called “driving force.” When the most active
metal (anode) supplies current, it will gradually dissolve into ions in the electrolyte
and, at the same time, produce electrons, which the least active (cathode) will
receive through the metallic connection with the anode. The result is that the cathode
will be negatively polarized and hence be protected against corrosion.
Thus, less noble metals are more susceptible to corrosion. An example of protecting
an appliance such as an iron-bodied water heater would be to ensure that piping
connections are of similar material when possible and follow the manufacturer’s
good practice and instructions on using dielectric (not conductors of electricity)
unions [8].
Figure 7.6 shows examples of electrochemical kinetics in pipes that were
connected to dissimilar metals.
References
- Lawrence Berkeley National
Laboratory. Cool roofing materials database. Berkeley, CA: Lawrence Berkeley
National Laboratory, Environmental Energy Technologies Division; 2000.
Available from URL:
http://eetd.lbl.gov/coolroof/.
- California Energy Commission.
Roofing. Sacramento: California Energy Commission; no date. Available from URL:
http://www.consumerenergycenter.org/coolroof/.
- Cazayoux EJ, Bilello RA.
Roof materials. Baton Rouge, LA: Louisiana State University; no date. Available
from URL:
http://www.leeric.lsu.edu/bgbb/7/ecep/carpntry/i/i.htm.
- Department of Energy.
Insulation fact sheet. Washington, DC: Department of Energy; 2002. Available
from URL:
http://www.ornl.gov/sci/roofs+walls/insulation/ins_01.htm.
- The Old House Web. Insulation:
stories and more from the Old House Web. Gardiner, ME: The Old House Web; no
date. Available from URL:
http://www.oldhouseweb.com/stories/How-To/HVAC_and_Insulation/Insulation/.
- The Old House Web. Siding:
stories and more from the Old House Web. Gardiner, ME: The Old House Web; no
date. Available from URL:
http://www.oldhouseweb.com/stories/How-To/Siding/.
- Vandervort D. House siding
and architectural details. Glendale, CA: Hometips.com; no date. Available from
URL:
http://www.hometips.com/home_improvement/siding.html.
- University of Wisconsin-Stevens
Point. Corrosion, lead, copper: in-home water supplies—are you at risk? Stevens
Point, WI: University of Wisconsin-Stevens Point; no date. Available from URL:
https://www.uwsp.edu/cnr/etf/corros.htm.