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Conserving Energy in Historic
Buildings
Baird M. Smith, AIA
With the dwindling supply of energy
resources and new efficiency demands placed on the existing building stock,
many owners of historic buildings and their architects are assessing the
ability of these buildings to conserve energy with an eye to improving
thermal performance. This brief has been developed to assist those persons
attempting energy conservation measures and weatherization improvements
such as adding insulation and storm windows or caulking of exterior building
joints. In historic buildings, many measures can result in the inappropriate
alteration of important architectural features, or, perhaps even worse,
cause serious damage to the historic building materials through unwanted
chemical reactions or moisture caused deterioration. This brief recommends
measures that will achieve the greatest energy savings with the least
alteration to the historic buildings, while using materials that do not
cause damage and that represent sound economic investments.
Inherent Energy Saving Characteristics of Historic Buildings
Many historic buildings have energy
saving physical features and devices that contribute to good thermal performance.
Studies by the Energy Research and Development Administration (see bibliography)
show that the buildings with the poorest energy efficiency are actually
those built between 1940 and 1975. Older buildings were found to use less
energy for heating and cooling and hence probably require fewer weatherization
improvements. They use less energy because they were built with a well-developed
sense of physical comfort and because they maximized the natural sources
of heating, lighting and ventilation. The historic building owner should
understand these inherent energy saving qualities.
The most obvious (and almost universal)
inherent energy saving characteristic was the use of operable windows
to provide natural ventilation and light. In addition, historic commercial
and public buildings often include interior light/ventilation courts,
rooftop ventilators, clerestories or skylights (fig. 1). These features
provide energy efficient fresh air and light, assuring that energy consuming
mechanical devices may be needed only to supplement the natural energy
sources. Any time the mechanical heating and air conditioning equipment
can be turned off and the windows opened, energy will be saved.
Early builders and architects dealt
with the poor thermal properties of windows in two ways. First, the number
of windows in a building was kept to only those necessary to provide adequate
light and ventilation. This differs from the approach in many modern buildings
where the percentage of windows in a wall can be nearly 100%. Historic
buildings where the ratio of glass to wall is often less than 20%, are
better energy conservers than most new buildings. Secondly, to minimize
the heat gain or loss from windows, historic buildings often include interior
or exterior shutters, interior venetian blinds, curtains and drapes, or
exterior awnings (fig. 2). Thus, a historic window could remain an energy
efficient component of a building.
There are other physical characteristics
that enable historic buildings to be energy efficient. For instance, in
the warmer climates of the United States, buildings were often built to
minimize the heat gain from the summer sun. This was accomplished by introducing
exterior balconies, porches, wide roof overhangs, awnings and shade trees.
In addition, many of these buildings were designed with the living spaces
on the second floor to catch breezes and to escape the radiant heat from
the earth's surface. Also, exterior walls were often painted light colors
to reflect the hot summer sun, resulting in cooler interior living spaces
(fig. 3).
Winter heat loss from buildings
in the northern climates was reduced by using heavy masonry walls, minimizing
the number and size of windows, and often using dark paint colors for
the exterior walls. The heavy masonry walls used so typically in the late
19th century and early 20th century, exhibit characteristics that improve
their thermal performance beyond that formerly recognized (fig. 4). It
has been determined that walls of large mass and weight (thick brick or
stone) have the advantage of high thermal inertia, also known as the "M
factor." This inertia modifies the thermal resistance (R factor) (1) of
the wall by lengthening the time scale of heat transmission. For instance,
a wall with high thermal inertia, subjected to solar radiation for an
hour, will absorb the heat at its outside surface, but transfer it to
the interior over a period as long as 6 hours. Conversely, a wall having
the same R factor, but low thermal inertia, will transfer the heat in
perhaps 2 hours. High thermal inertia is the reason many older public
and commercial buildings, without modern air conditioning, still feel
cool on the inside throughout the summer. The heat from the midday sun
does not penetrate the buildings until late afternoon and evening, when
it is unoccupied.
Although these characteristics may
not typify all historic buildings, the point is that historic buildings
often have thermal properties that need little improvement. One must understand
the inherent energy saving qualities of a building, and assure, by reopening
the windows for instance, that the building functions as it was intended.
To reduce heating and cooling expenditures
there are two broad courses of action that may be taken. First, begin
passive measures to assure that a building and its existing components
function as efficiently as possible without the necessity of making alterations
or adding new materials. The second course of action is preservation retrofitting,
which includes altering the building by making appropriate weatherization
measures to improve thermal performance. Undertaking the passive measures
and the preservation retrofitting recommended here could result in a 50%
decrease in energy expenditures in historic buildings.
Passive Measures
The first passive measures to utilize
are operational controls; that is, controlling how and when a building
is used. These controls incorporate programmatic planning and scheduling
efforts by the owner to minimize usage of energy-consuming equipment.
A building should survey and quantify all aspects of energy usage, by
evaluating the monies expended for electricity, gas, and fuel oil for
a year. and by surveying how and when each room is used. This will identify
ways of conserving energy by initiating operational controls such as:
- * lowering the thermostat in
the winter, raising it in the summer
- * controlling the temperature
in those rooms actually used
- * reducing the level of illumination
and number of lights (maximize natural light)
- * using operable windows, shutters,
awnings and vents as originally intended to control interior environment
(maximize fresh air)
- * having mechanical equipment
serviced regularly to ensure maximum efficiency
- * cleaning radiators and forced
air registers to ensure proper operation
The passive measures outlined above
can save as much as 30% of the energy used in a building. They should
be the first undertakings to save energy in any existing building and
are particularly appropriate for historic buildings because they do not
necessitate building alterations or the introduction of new materials
that may cause damage. Passive measures make energy sense, common sense,
and preservation sense!
Preservation Retrofitting
In addition to passive measures,
building owners may undertake certain retrofitting measures that will
not jeopardize the historic character of the building and can be accomplished
at a reasonable cost. Preservation retrofitting improves the thermal performance
of the building, resulting in another 20%30% reduction in energy.
When considering retrofitting measures,
historic building owners should keep in mind that there are no permanent
solutions. One can only meet the standards being applied today with today's
materials and techniques. In the future, it is likely that the standards
and the technologies will change and a whole new retrofitting plan may
be necessary. Thus, owners of historic buildings should limit retrofitting
measures to those that achieve reasonable energy savings, at reasonable
costs, with the least intrusion or impact on the character of the building.
Overzealous retrofitting, which introduces the risk of damage to historic
building materials, should not be undertaken.
The preservation retrofitting measures
presented here, were developed to address the three most common problems
in historic structures caused by some retrofitting actions. The first
problem concerns retrofitting actions that necessitated inappropriate
building alterations, such as the wholesale removal of historic windows,
or the addition of insulating aluminum siding, or installing dropped ceilings
in significant interior spaces. To avoid such alterations, refer to the
Secretary of the Interior's "Standards for Historic Preservation Projects"
which provide the philosophical and practical basis for all preservation
retrofitting measures (see last page).
The second problem area is to assure
that retrofitting measures do not create moisturerelated deterioration
problems. One must recognize that large quantities of moisture are present
on the interior of buildings.
In northern climates, the moisture
may be a problem during the winter when it condenses on cold surfaces
such as windows. As the moisture passes through the walls and roof it
may condense within these materials, creating the potential for deterioration.
The problem is avoided if a vapor barrier is added facing in (fig. 5).
In southern climates, insulation
and vapor barriers are handled quite differently because moisture problems
occur in the summer when the moist outside air is migrating to the interior
of the building. In these cases, the insulation is installed with the
vapor barrier facing out (opposite the treatment of northern climates).
Expert advice should be sought to avoid moisturerelated problems to insulation
and building materials in southern climates.
The third problem area involves
the avoidance of those materials that are chemically or physically incompatible
with existing materials, or that are improperly installed. A serious problem
exists with certain cellulose insulations that use ammonium or aluminum
sulfate as a fire retardant, rather than boric acid which causes no problems.
The sulfates react with moisture in the air forming sulfuric acid which
can cause damage to most metals (including plumbing and wiring), building
stones, brick and wood. In one instance, a metal building insulated with
cellulose of this type collapsed when the sulfuric acid weakened the structural
connections! To avoid problems such as these, refer to the recommendations
provided here, and consult with local officials, such as a building inspector,
the better business bureau, or a consumer protection agency.
Before a building owner or architect
can plan retrofitting measures, some of the existing physical conditions
of the building should be investigated. The basic building components
(attic, roof, walls and basement) should be checked to determine the methods
of construction used and the presence of insulation. Check the insulation
for full coverage and whether there is a vapor barrier. This inspection
will aid in determining the need for additional insulation, what type
of insulation to use (batt, blownin, or poured), and where to install
it. In addition, sources of air infiltration should be checked at doors,
windows, or where floor and ceiling systems meet the walls. Lastly, it
is important to check the condition of the exterior wall materials, such
as painted wooden siding or brick, and the condition of the roof, to determine
the weather tightness of the building. A building owner must assure that
rain and snow are kept out of the building before expending money for
weatherization improvements.
Retrofitting Measures
The following listing includes the
most common retrofitting measures; some measures are highly recommended
for a preservation retrofitting plan, but, as will be explained, others
are less beneficial or even harmful to the historic building:
- Air Infiltration
- Attic Insulation
- Storm Windows
- Basement and Crawl Space Insulation
- Duct and Pipe Insulation
- Awnings and Shading Devices
- Doors and Storm Doors
- Vestibules
- Replacement Windows
- Wall Insulation--Wood Frame
- Wall Insulation--Masonry Cavity
Walls
- Wall Insulation--Installed on
the Inside
- Wall Insulation--Installed on
the Outside
- Waterproof Coatings for Masonry
The recommended measures to preservation
retrofitting begin with those at the top of the list. The first ones are
the simplest, least expensive, and offer the highest potential for saving
energy. The remaining measures are not recommended for general use either
because of potential technical and preservation problems, or because of
the costs outweighing the anticipated energy savings. Specific solutions
must be determined based on the facts and circumstances of the particular
problem; therefore, advice from professionals experienced in historic
preservation, such as, architects, engineers and mechanical contractors
should be solicited.
Air Infiltration: Substantial heat
loss occurs because cold outside air infiltrates the building through
loose windows, doors, and cracks in the outside shell of the building.
Adding weatherstripping to doors and windows, and caulking of open cracks
and joints will substantially reduce this infiltration. Care should be
taken not to reduce infiltration to the point where the building is completely
sealed and moisture migration is prevented. Without some infiltration,
condensation problems could occur throughout the building. Avoid caulking
and weatherstripping materials that, when applied, introduce inappropriate
colors or otherwise visually impair the architectural character of the
building. Reducing air infiltration should be the first priority of a
preservation retrofitting plan. The cost is low, little skill is required,
and the benefits are substantial.
Attic Insulation: Heat rising through
the attic and roof is a major source of heat loss, and reducing this heat
loss should be one of the highest priorities in preservation retrofitting.
Adding insulation in accessible attic spaces is very effective in saving
energy and is generally accomplished at a reasonable cost, requiring little
skill to install. The most common attic insulations include blankets of
fiberglass and mineral wool, blownin cellulose (treated with boric acid
only), blowing wool, vermiculite, and blown fiberglass. If the attic is
unheated (not used for habitation), then the insulation is placed between
the floor joists with the vapor barrier facing down. If flooring is present,
or if the attic is heated, the insulation is generally placed between
the roof rafters with the vapor barrier facing in. All should be installed
according to the manufacturer's recommendations. A weatherization manual
entitled, "In the Bank . . . or Up the Chimney" (see the bibliography)
provides detailed descriptions about a variety of installation methods
used for attic insulation. The manual also recommends the amount of attic
insulation used in various parts of the country. If the attic has some
insulation, add more (but without a vapor barrier) to reach the total
depth recommended.
Problems occur if the attic space
is not properly ventilated. This lack of ventilation will cause the insulation
to become saturated and lose its thermal effectiveness. The attic is adequately
ventilated when the net area of ventilation (free area of a louver or
vent) equals approximately 1/300 of the attic floor area. With adequate
attic ventilation, the addition of attic insulation should be one of the
highest priorities of a preservation retrofitting plan.
If the attic floor is inaccessible,
or if it is impossible to add insulation along the roof rafters, consider
attaching insulation to the ceilings of the rooms immediately below the
attic. Some insulations are manufactured specifically for these cases
and include a durable surface which becomes the new ceiling. This option
should not be considered if it causes irreparable damage to historic or
architectural spaces or features; however, in other cases, it could be
a recommended measure of a preservation retrofitting plan.
Storm Windows: Windows are a primary
source of heat loss because they are both a poor thermal barrier (R factor
of only 0.89) and often a source of air infiltration. Adding storm windows
greatly improves these poor characteristics. If a building has existing
storm windows (either wood or metal framed), they should be retained.
Assure they are tight fitting and in good working condition. If they are
not in place, it is a recommended measure of a preservation retrofitting
plan to add new metal framed windows on the exterior. This will result
in a window assembly (historic window plus storm window) with an R factor
of 1.79 which outperforms a double paned window assembly (with an air
space up to 1/2") that only has an R factor of 1.72. When installing the
storm windows, be careful not to damage the historic window frame. If
the metal frames visually impair the appearance of the building, it may
be necessary to paint them to match the color of the historic frame (see
figure 6).
Tripletrack metal storm windows
are recommended because they are readily available, in numerous sizes,
and at a reasonable cost. If a preassembled storm window is not available
for a particular window size, and a custommade storm window is required,
the cost can be very high. In this case, compare the cost of manufacture
and installation with the expected cost savings resulting from the increased
thermal efficiency. Generally, custom-made storm windows, of either wood
or metal frames, are not cost effective, and would not be recommended
in a preservation retrofitting plan.
Interior storm window installations
can be as thermally effective as exterior storm windows; however, there
is high potential for damage to the historic window and sill from condensation.
With storm windows on the interior, the outer sash (in this case the historic
sash) will be cold in the winter, and hence moisture may condense there.
This condensation often collects on the flat surface of the sash or window
sill causing paint to blister and the wood to begin to deteriorate. Rigid
plastic sheets are used as interior storm windows by attaching them directly
to the historic sash. They are not quite as effective as the storm windows
described previously because of the possibility of air infiltration around
the historic sash. If the rigid plastic sheets are used, assure that they
are installed with minimum damage to the historic sash, removed periodically
to allow the historic sash to dry, and that the historic frame and sash
are completely caulked and weatherstripped.
In most cases, interior storm windows
of either metal frames or of plastic sheets are not recommended for preservation
retrofitting because of the potential for damage to the historic window.
If interior storm windows are in place, the potential for moisture deterioration
can be lessened by opening (or removing, depending on the type) the storm
windows during the mild months allowing the historic window to dry thoroughly.
Basement and Crawl Space Insulation:
Substantial heat is lost through cold basements and crawl spaces. Adding
insulation in these locations is an effective preservation retrofitting
measure and should be a high priority action. It is complicated, however,
because of the excessive moisture that is often present. One must be aware
of this and assure that insulation is properly installed for the specific
location. For instance, in crawl spaces and certain unheated basements,
the insulation is generally placed between the first floor joists (the
ceiling of the basement) with the vapor barrier facing up. Do not staple
the insulation in place, because the staples often rust away. Use special
anchors developed for insulation in moist areas such as these.
In heated basements, or where the
basement contains the heating plant (furnace), or where there are exposed
water and sewer pipes, insulation should be installed against foundation
walls. Begin the insulation within the first floor joists, and proceed
down the wall to a point at least 3 feet below the exterior ground level
if possible, with the vapor barrier facing in. Use either batt or rigid
insulation.
Installing insulation in the basement
or crawl space should be a high priority of a preservation retrofitting
plan, as long as adequate provision is made to ventilate the unheated
space, perhaps even by installing an exhaust fan.
Duct and Pipe Insulation: Wrapping
insulation around heating and cooling ducts and hot water pipes, is a
recommended preservation retrofitting measure. Use insulation which is
intended for this use and install it according to manufacturer's recommendations.
Note that air conditioning ducts will be cold in the summer, and hence
moisture will condense there. Use insulation with the vapor barrier facing
out, away from the duct. These measures are inexpensive and have little
potential for damage to the historic building.
Awnings and Shading Devices: In
the past, awnings and trees were used extensively to provide shade to
keep buildings cooler in the summer. If awnings or trees are in place,
keep them in good condition, and take advantage of their energy-saving
contribution. Building owners may consider adding awnings or trees if
the summer cooling load is substantial. If awnings are added, assure that
they are installed without damaging the building or visually impairing
its architectural character (fig. 7). If trees are added, select deciduous
trees that provide shade in the summer but, after dropping their leaves,
would allow the sun to warm the building in the winter. When planting
trees, assure that they are no closer than 10 feet to the building to
avoid damage to the foundations. Adding either awnings or shade trees
may be expensive, but in hot climates, the benefits can justify the costs.
Doors and Storm Doors: Most historic
wooden doors, if they are solid wood or paneled, have fairly good thermal
properties and should not be replaced, especially if they are important
architectural features. Assure that the frames and doors have proper maintenance,
regular painting, and that caulking and weatherstripping is applied as
necessary.
A storm door would improve the thermal
performance of the historic door; however, recent studies indicate that
installing a storm door is not normally cost effective in residential
settings. The costs are high compared to the anticipated savings. Therefore,
storm doors should only be added to buildings in cold climates, and added
in such a way to minimize the visual impact on the building's appearance.
The storm door design should be compatible with the architectural character
of the building and may be painted to match the colors of the historic
door.
Vestibules: Vestibules create a
secondary air space at a doorway to reduce air infiltration occurring
while the primary door is open. If a vestibule is in place, retain it.
If not, adding a vestibule, either on the exterior or interior, should
be carefully considered to determine the possible visual impact on the
character of the building. The energy savings would be comparatively small
compared to construction costs. Adding a vestibule should be considered
in very cold climates, or where door use is very high, but in either case,
the additional question of visual intrusion must be resolved before it
is added. For most cases with historic buildings, adding a vestibule is
not recommended.
Replacement Windows: Unfortunately,
a common weatherization measure, especially in larger buildings, has been
the replacement of historic windows with modern double paned windows.
The intention was to improve the thermal performance of the existing windows
and to reduce longterm maintenance costs. The evidence is clear that adding
exterior storm windows is a viable alternative to replacing the historic
windows and it is the recommended approach in preservation retrofitting.
However, if the historic windows are severely deteriorated and their repair
would be impractical, or economically infeasible, then replacement windows
may be warranted. The new windows, of either wood or metal, should closely
match the historic windows in size, number of panes, muntin shape, frame,
color and reflective qualities of the glass.
Wall Insulation--Wood Frame: The
addition of wall insulation in a wood frame building is generally not
recommended as a preservation retrofitting measure because the costs are
high, and the potential for damage to historic building materials is even
higher. Also, wall insulation is not particularly effective for small
frame buildings (one story) because the heat loss from the uninsulated
walls is a relatively small percentage of the total, and part of that
can be attributed to infiltration. If, however, the historic building
is two or more stories, and is located in a cold climate, wall insulation
may be considered if extreme care (as explained later) is exercised with
its installation.
The installation of wall insulation
in historic frame buildings can result in serious technical and preservation
problems. As discussed before, insulation must be kept dry to function
properly, and requires a vapor barrier and some provision for air movement.
Introducing insulation in wall cavities, without a vapor barrier and some
ventilation can be disastrous. The insulation would become saturated,
losing its thermal properties, and in fact, actually increasing the heat
loss through the wall. Additionally, the moisture (in vapor form) may
condense into water droplets and begin serious deterioration of adjacent
building materials such as sills, window frames, framing and bracing.
The situation is greatly complicated, because correcting such problems
could necessitate the complete (and costly) dismantling of the exterior
or interior wall surfaces. It should be clear that adding wall insulation
has the potential for causing serious damage to historic building materials.
If adding wall insulation to frame
buildings is determined to be absolutely necessary, the first approach
should be to consider the careful removal of the exterior siding so that
it may later be reinstalled. Then introduce batt insulation with the vapor
barrier facing in into the now accessible wall cavity. The first step
in this approach is an investigation to determine if the siding can be
removed without causing serious damage.
If it is feasible, introducing insulation
in this fashion provides the best possible solution to insulating a wall,
and provides an excellent opportunity to view most of the structural system
for possible hidden structural problems or insect infestations. A building
owner should not consider this approach if it would result in substantial
damage to or loss of historic wooden siding. Most siding, however, would
probably withstand this method if reasonable care is exercised.
The second possible approach for
wall insulation involves injecting or blowing insulation into the wall
cavity. The common insulations are the loose fill types that can be blown
into the cavity, the poured types, or the injected types such as foam.
Obviously a vapor barrier cannot be simultaneously blown into the space.
However, an equivalent vapor barrier can be created by assuring that the
interior wall surfaces are covered with an impermeable paint layer. Two
layers of oil base paint or one layer of impermeable latex paint constitute
an acceptable vapor barrier. Naturally, for this to work, the
paint layer must cover all interior surfaces adjacent to the newly installed
wall insulation. Special attention should be given to rooms that are major
sources of interior moisture--the laundry room, the bathrooms and the
kitchen.
In addition to providing a vapor
barrier, make provisions for some air to circulate in the wall cavity
to help ventilate the insulation and the wall materials. This can be accomplished
in several ways. One method is to install small screened vents (about
2 inches in diameter) at the base of each stud cavity. If this option
is taken, the vents should be as inconspicuous as possible. A second venting
method can be used where the exterior siding is horizontally lapped. Assure
that each piece of siding is separated from the other, allowing some air
to pass between them. Successive exterior paint layers often seal the
joint between each piece of siding. Break the paint seal (carefully insert
a chisel and twist) between the sections of exterior siding to provide
the necessary ventilation for the insulation and wall materials.
With provisions for a vapor barrier
(interior paint layer) and wall ventilation (exterior vents) satisfied,
the appropriate type of wall insulation may then be selected. There are
three recommended types to consider: blown cellulose (with boric acid
as the fire retardant), vermiculite, or perlite. Cellulose is the preferred
wall insulation because of its higher R factor and its capability to flow
well into the various spaces within a wall cavity.
There are two insulation types that
are not recommended for wall insulation: ureaformaldehyde foams, and cellulose
which uses aluminum or ammonium sulfate instead of boric acid as a fire
retardant. The cellulose treated with the sulfates reacts with moisture
in the air and forms sulfuric acid which corrodes many metals and causes
building stones to slowly disintegrate. This insulation is not appropriate
for use in historic buildings.
Although ureaformaldehyde foams
appear to have potential as retrofit materials (they flow into any wall
cavity space and have a high R factor) their use is not recommended for
preservation retrofitting until some serious problems are corrected. The
major problem is that the injected material carries large quantities of
moisture into the wall system. As the foam cures, this moisture must be
absorbed into the adjacent materials. This process has caused interior
and exterior paint to blister, and caused water to actually puddle at
the base of a wall, creating the likelihood of serious deterioration to
the historic building materials. There are other problems that affect
both historic buildings and other existing buildings. Foams are a twopart
chemical installed by franchised contractors. To obtain the exact proportion
of the two parts, the foam must be mixed and installed under controlled
conditions of temperature and humidity. There are cases where the controls
were not followed and the foam either cured improperly, not attaining
the desired R factor, or the foam continued to emit a formaldehyde smell.
In addition, the advertised maximum shrinkage after curing (3%) has been
tested and found to be twice as high (see figure 8). Until this material
is further developed and the risks eliminated, it is clearly not an appropriate
material for preservation retrofitting.
Wall Insulation--Masonry Cavity
Walls: Some owners of historic buildings with masonry cavity wall construction
have attempted to introduce insulation into the cavity. This is not good
practice because it ignores the fact that masonry cavity walls normally
have acceptable thermal performance, needing no improvement. Additionally,
introducing insulation into the cavity will most likely result in condensation
problems and alter the intended function of the cavity. The air cavity
acts as a vapor barrier in that moist air passing through the inner wythe
of masonry meets the cold face of the outer wythe and condenses. Water
droplets form and fall to the bottom of the wall cavity where they are
channeled to the outside through weep holes. The air cavity also improves
the thermal performance of the wall because it slows the transfer of heat
or cold between the two wythes, causing the two wall masses to function
independently with a thermal cushion between them.
Adding insulation to this cavity
alters the vapor barrier and thermal cushion functions of the air space
and will likely clog the weep holes, causing the moisture to puddle at
the base of the wall. Also, the addition of insulation creates a situation
where the moisture dew point (where moisture condenses) moves from the
inner face of the outer wythe, into the outer wythe itself. Thus, during
a freeze, this condensation will freeze, causing spalling and severe deterioration.
The evidence is clear that introducing insulation, of any type, into a
masonry cavity wall is not recommended in a preservation retrofitting
plan.
Wall Insulation--Installed on the
Inside: Insulation could be added to a wall whether it be wooden or masonry,
by attaching the insulation to furring strips mounted on the interior
wall faces. Both rigid insulation, usually 1 or 2 inches thick, and batt
insulation, generally 3-1/2 inches thick, can be added in this fashion,
with the vapor barrier facing in. Extra caution must be exercised if rigid
plastic foam insulation is used because it can give off dense smoke and
rapidly spreading flame when burned. Therefore, it must be installed with
a fireproof covering, usually 1/2-inch gypsum wallboard. Insulation should
not be installed on the inside if it necessitates relocation or destruction
of important architectural decoration, such as cornices, chair rails,
or window trims, or causes the destruction of historic plaster or other
wall finishes. Insulation installed in this fashion would be expensive
and could only be a recommended preservation retrofitting measure if it
is a large building, located in a cold climate, and if the interior spaces
and features have little or no architectural significance.
Wall Insulation--Installed on the
Outside: There is a growing use of aluminum or vinyl siding installed
directly over historic wooden sidings, supposedly to reduce longterm maintenance
and to improve the thermal performance of the wall. From a preservation
viewpoint, this is a poor practice for several reasons. New siding covers
from view existing or potential deterioration problems or insect infestations.
Additionally, installation often results in damage or alteration to existing
decorative features such as beaded weatherboarding, window and door trim,
corner boards, cornices, or roof trim. The cost of installing the artificial
sidings compared with the modest increase, if any, in the thermal performance
of the wall does not add up to an effective energy-saving measure. The
use of artificial siding is not recommended in a preservation retrofitting
plan.
Good preservation practice would
assure regular maintenance of the existing siding through periodic painting
and caulking. Where deterioration is present, individual pieces of siding
should be removed and replaced with matching new ones. Refer to the earlier
sections of this brief for recommended retrofitting measures to improve
the thermal performance of wood frame walls.
Waterproof Coatings for Masonry:
Some owners of historic buildings use waterproof coatings on masonry believing
it would improve the thermal performance of the wall by keeping it dry
(dry masonry would have a better R factor than when wet). Application
of waterproof coatings is not recommended because the coatings actually
trap moisture within the masonry, and can cause spalling and severe deterioration
during a freezing cycle.
In cases where exterior brick is
painted, consider continued periodic painting and maintenance, since paints
are an excellent preservation treatment for brick. When repainting, a
building owner might consider choosing a light paint color in warm climates,
or a dark color in co!d climates, to gain some advantage over the summer
heat gain or winter heat loss, whichever the case may be. These colors
should match those used historically on the building or should match colors
available historically.
Mechanical Equipment
A detailed treatise of recommended
or not recommended heating or air conditioning equipment, or of alternative
energy sources such as solar energy or wind power, is beyond the scope
of this brief. The best advice concerning mechanical equipment in historic
buildings is to assure that the existing equipment works as efficiently
as possible. If the best professional advice recommends replacement of
existing equipment, a building owner should keep the following considerations
in mind. First, as technology advances in the coming years, the equipment
installed now will be outdated rapidly relative to the life of the historic
building. Therefore, it may be best to wait and watch, until new technologies
(such as solar energy) become more feasible, efficient, and inexpensive.
Secondly, do not install new equipment and ductwork in such a way that
its installation, or possible later removal, will cause irreversible damage
to significant historic building materials. The concept of complete invisibility,
which necessitates hiding piping and ductwork within wall and floor systems,
may not always be appropriate for historic buildings because of the damage
that often results. Every effort should be made to select a mechanical
system that will require the least intrusion into the historic fabric
of the building and that can be updated or altered without major intervention
into the wall and floor systems. These points should be considered when
weighing the decision to replace a less than efficient exiting system
with a costly new system, which may cause substantial damage to the historic
building materials and in turn may prove inefficient in the future.
Summary
The primary focus of this brief
has been to describe ways to achieve the maximum energy savings in historic
buildings without jeopardizing the architectural, cultural and historical
qualities for which the properties have been recognized. This can be accomplished
through undertaking the passive measures and the "recommended" preservation
retrofitting. Secondly, this brief has emphasized the benefits of undertaking
the retrofitting measures in phases so that the actual energy savings
anticipated from each retrofitting measure can be realized. Thus, the
"not recommended" retrofitting measures, with potential for damage or
alteration of historic building materials, would not have to be undertaken,
because the maximum feasible savings would have already been accomplished.
Lastly, and perhaps most important,
we must recognize that the technologies of retrofitting and weatherization
are relatively new. Unfortunately, most current research and product development
is directed toward new construction. It is hoped that reports such as
this, and the realization that fully 30% of all construction in the United
States now involves work on existing buildings, will stimulate the development
of new products that can be used with little hesitation in historic buildings.
Until that time, owners of historic buildings can undertake the preservation
retrofitting measures recommended here and greatly reduce the energy used
for heating and cooling, without destroying those historic and architectural
qualities that make the building worthy of preservation. Washington, D.C.
April, 1978
NOTE
(1) R factor is the measure of the
ability of insulation to decrease heat flow. The higher the factor, the
better the thermal performance of the material.
# # # # #
Bibliography
Recommended Weatherization Manuals
and Instruction Booklets
Nielsen, Sally E., ed. Insulating
the Old House. Portland, Maine: Greater Portland Landmarks, Inc., 1977.
Available from Greater Portland Landmarks, Inc., 165 State Street, Portland,
Maine.
Making the Most of Your Energy Dollars
in Home Heating and Cooling. Washington, D.C.:1975. National Bureau of
Standards, Consumer Information Series 8. Available from the Superintendent
of Documents, U.S. Government Printing Office, Washington, D.C. 20402.
Stock Number C13.53:8.
In the Bank . . . or Up the Chimney.
Washington, D.C.: April 1975. Available from the Superintendent of Documents,
U.S. Government Printing Office, Washington, D.C. 20402. Stock Number
023000002973 .
Other Suggested Readings
American Society of Heating, Refrigerating
and Air Conditioning Engineers, Inc. ASHRAE Handbook of Fundamentals.
New York: ASHRAE, 1972.
"Energy Conservation and Historic
Preservation," supplement to 11593, Vol. 2, No. 3. Washington, D.C.: Office
of Archeology and Historic Preservation, U.S. Department of the Interior,
June 1977.
General Services Administration.
Energy Conservation Guidelines for Existing Office Buildings. Washington,
D.C.: General Services Administration, February 1977.
"The Overselling of Insulation."
Consumer Reports, February 1978, pp. 6773.
Petersen, Stephen R. Retrofitting
Existing Housing for Energy Conservation: An Economic Analysis, Building
Science Series 64. Washington, D.C.: U.S. Government Printing Office,
December 1974.
Rossiter, Walter J., et al. UreaFormaldehyde
Based Foam Insulations: An Assessment of Their Properties and Performance.
National Bureau of Standards, Technical Note 946. Washington, D.C.: July
1977.
Smith, Baird M. "National Benefits
of Rehabilitating Existing Buildings," supplement to 11593, vol 2, No.
5. Washington, D.C.: Office of Archeology and Historic Preservation, U.S.
Department of the Interior, October 1977.
Thermal Transmission Corrections
for Dynamic Conditions--M Factor. Brick Institute of America, Technical
Notes on Brick Construction, 4 B, pp. 1-8. McLean, Virginia: March/April
1977.
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