Chapter 7—Environmental Barriers

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-1

Roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2

Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-3

Siding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-3

Fiber Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-4

Brick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-4

Stucco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-4

Vinyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-5

Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-5

Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-5

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-6

Figure 7.1. Sources of Moisture and Air Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-1

Figure 7.2. Blown Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-3

Figure 7.3. Depth of Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-3

Figure 7.4. Attic Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-3

Figure 7.5. Brick Structural Defect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-4

Figure 7.6. Corrosion in Piping Resulting From Galvanic Response . . . . . . . . . . . . . . . . . . . . .7-5

Healthy Housing Reference Manual 1

Contents
“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 timeconsuming. 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.

Chapter 7: Environmental Barriers

Figure 7.1. Sources of Moisture and Air Pollutants [1]

Healthy Housing Reference Manual 7-1
• 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.

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 [1–3].

1) Is the roofline of the house straight?

2) Are there ripples or waves in the roof?

3) What is the condition of the gutters and downspouts?

4) What is the condition of the boards the gutters are attached to?

5) Does the flashing appear to be separated or damaged?

6) Is there any apparent damage in the attic or can sunlight be seen through the roof?

7) Is there mold or discoloration on the rafters or roof sheathing?

8) Is there evidence of corrosion between the gutter and downspouts and any metal roofing or 

aluminum siding?

9) Do the downspouts route the water away from the base or foundation of the home?

10) Are the gutters covered or free of leaves? Are they sagging or separating from the fascia?

11) Does the gutter provide a mosquito-breeding area by holding water?

Roof Inspection

7-2 Environmental Barriers
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

Healthy Housing Reference Manual 7-3

Figure 7.2. Blown Attic Insultation 

Figure 7.3. Depth of Attic Insulation 

Figure 7.4. Blown Attic Insultation 
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), fiber 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 11⁄2 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.

7-4 Environmental Barriers

Figure 7.5. Brick

Structural Defect
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 1⁄4-inch thick and very brittle and was sold in

sections of about 12×18 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.

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 ironbodied water heater would be to ensure that piping

Healthy Housing Reference Manual 7-5

Figure 7.6. Corrosion in Piping Resulting From Galvanic Response

1. Use like metals when possible

2. Use metals with similar electronegativity 

levels

3. Use dielectric unions for plumbing

4. Use anodes that are inexpensive to replace

Remember: Use metals with less susceptibility 

to protect metals that are more susceptible 

to corrosion.

Metal Corrosion Prevention
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

1. 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/.

2. California Energy Commission. Roofing.

Sacramento: California Energy Commission; no

date. Available from URL: http://www.consumerenergycenter.org/homeandwork/homes/

construction/roofing.html.

3. 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.

4. 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.

5. 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/HowTo/

HVAC_and_Insulation/Insulation/. 

6. 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/.

7. Vandervort D. House siding and architectural

details. Glendale, CA: Hometips.com; no date.

Available from URL: http://www.hometips.com/

home_improvement/siding.html.

8. University of Wisconsin-Stevens Point. Corrosion,

lead, copper: in-home water supplies—are you at

risk? Stevens Point, WI: University of WisconsinStevens Point; no date. Available from URL:

https://www.uwsp.edu/cnr/etf/corros.htm. 

7-6 Environmental Barriers