|Table of Contents|
Table of Contents
Introduction to Thermal and Acoustic Insulation
March 10, 1977
Prof. Phil Wisely
Introduction.. .... ............ ... ...... p. 1
Historic Background of Thermal and Acoustic
Insulation p. 2
Thermal Insulation....... ........ ... ........ p. 9
Climate....... . ...... .. . ..... . p. 9
Heat Control....... ...... .. ....... p. 9
Heat Transmission............... ............ p. 10
Loose-Fill Insulation........................ p. 11
Flexible Insulation...... .... .... ....... .... p. 11
Rigid Insulation. .... ..... ....... .... ...... p. 11
Cements as Insulation..................... p. 12
Reflective Insulation........................ p. 12
Sprayed-On Insulation........................ p. 13
Corrugated Insulation.......................... p. 13
Acoustic Insulation ......................... p. 15
Acoustical Tile............................ p. 16
Assembled Units....... ...................... p. 16
Sprayed-On Acoustic Materials............... p. 17
Slide List. .......... ........... .. .. ..... p. 19
Footnotes ..... .............................. p. 20
Bibliography ........ ..... ...... ............ p. 21
This paper is intended to give the reader a
general understanding of the principles and materials
of insulation and acoustics. The first part of the
report deals with insulation and acoustics historically,
but,due to a lack of information and slow growth in
the fields is quite incomplete. The second part of
the report concerns itself with the basics of both
insulation and acoustics in the areas of principles
and materials. No attempt is made to go into the technical
aspects of either area due to the availability of
such information in texts and product reports.
Insulation (Thermal and Acoustic)
The use of certain materials for their insulative
values goes back to the time when man's primary concern
was to protect himself from the environment. The advantages
of heat insulation must have been known very early
in history. The comforts of fur clothing and snowhouses
of the eskimo, for example, certainly were realized
hundreds of years ago. Primitive Americans survived our
climate in the bark wigwams and log houses of the
Penobscots and Iroquois, the tipis of the Crows or the
adobe pueblos of the Southeastern Indians. In contrast
to the early experimentation by man with thermal
insulation, insulation from sound is relatively recent.
The first use of a material for insulation dates
back to primitive man when bark was stripped off of
cork oak trees and used as roofing for huts. Early man
most likely observed that cork oak trees were perfectly
protected from the tropical sun and the resultant severe
heat. In addition, the trees did not attract insects,
resisted fire and had a rugged character that allowed
them to resist the ravages of time and the elements. The
Romans also made use of the cork oak tree, as they made
cork oak boards with which they fabricated bee hives.
The cork oak, in this case, allowed the interior temp-
erature of the bee hives to remain constant during both
the summer and winter months. There is also evidence that
cork was used as a natural waterproofing agent by the
Romans. Cork is a material that has cell walls which
are composed of resin which keeps the cells tightly
sealed. This in essence keeps a "dead" air space in
each cell which acts as an insulator.
The first development of cork in sheet form
was in Germany. Cuttings of cork, which previously had
been considered waste, were ground to the proper size,
mixed with a clay binder, and molded into boards.
Later on, another method was developed where the cork
was granulated and then impregnated with asphalt or
pitch. The material was then formed into slabs and
proved to be an excellent insulator with the qualities
necessary for waterproofing. Another later development
allowed granular cork, when subjected to very high
temperatures, to form into sheets or blocks which did
not require pitch or asphalt as a binder. Due to the
lack of pitch, this new cork insulation was much less
of a fire hazard, was lighter and was easier to handle.
There are examples of thermal insulation in
some methods of construction in the Ukraine in log
and earth huts. The huts have foundations made up of
logs laid on blocks of wood, tree stumps and stones
which are placed at a slight deapth in the ground to
increase stability. With this method of construction
there is a danger of the foundation freezing. To
counteract this, the lower part of the wall is increased
in thickness by adding on a plinth made of planks or
brushwood. The plinth is then coated with clay and
the space is filled with rammed earth. This method
is known as Prisba construction.
There are three types of timber-clay insulation
used in wall construction. They are similar to the
wattle and daub method used in England and the colonies.
The structural system is timber post and beam with
spare timbers between the posts and straw mixed with
clay applied to both sides of the wall. This method
requires much wood and the clay tends to dry and fall
off. The second method alternates the layers of wood
and clay-straw mixture with a layer of clay applied
to the exterior. The third method has a layer of reeds
applied to the timber frame. The two inch thick layer
of reeds is then covered with clay.
The first evidence of sound insulation is
found in a British government report on housing
that dates from 1844. This report advocates the use
of lime-pugged floors, for sound insulation, in
working class houses. The use of pugged floors,
however, was not new, lime floors had replaced the
beaten earth floor of the Middle Ages and had been
in use for over two centuries. Clay and lime pugging,
sometimes mixed with twigs and moss, was put between
the timber floor joists as sound insulation. As a
further insulative measure, the cracks between the
floor boards were filled with either sand, a mud
and straw mixture or clay.
The simplest types of these floors consisted
of three or four inches of lime laid on fixed trays
between the joists. The lime was finished to a smooth
condition and was carried on interlaced hazel twigs.
Typical seventeenth century English examples had a
one inch quilt of thick reeds mixed with lime. When
boarding was laid upon this mattress of reeds a
system which corresponds to the modern floating
floor was obtained. Also in England, Christopher
Wren called for a system of cockle shell pugging on
sound boarding between floor joists. This is said
to be less effective than solid clay or lime filling.
In some instances moss was also used. Long moss was
6 gathered, dried and mixed with dry lime rubbish and
filled between joists. Violet le Duc used a solution
that called for a layer of rough mortar laid on top
of the floor joists, not between them like the previous
Shortly before the 1844 British government
report, in 1836, Her Majesty's Commissioners of
Prisons approached Dr Reid and Professor Faraday
seeking advice on how to construct walls that would
eliminate intelligible voice communication between
cells. Several experiments were conducted with varying
materials and wall thicknesses. The first prototype
consisted of two nine inch brick walls with a two and
a quarter inch space between filled with sand. This
attempt failed. The second prototype was based on the
theory that the inner part of the brick, if made jagged,
would disrupt the waves of sound. In this second
attempt, one of the nine inch brick walls was changed
to a thirteen inch jagged wall. This was an improvement
over the first attempt but still was not very good.
The third prototype had both of the walls thirteen
inches thick and jagged which was a further improvement.
The fourth prototype contained two thicknesses of
sail cloth between the jagged walls and improved the
insulation still further. The next attempt was to
achieve better results in a more permanent and less
costly way. This was done by creating two nine inch
brick walls with two and three-quarter inch spaces
and a four and a half inch brick wall in the center.
The central empty spaces were filled with sand.
Although Reid and Faraday learned what they had intended
to, they still did not acquire an understanding
of the nature of sound or sound waves. What they did
learn was only a small improvement over what mass
alone would have given them. In general, they seem
to have overlooked the possibility of indirect sound
transmission along side walls.
The inability of experimental techniques to
give quantitaive measurements of sound insulation was
a barrier to progress in this field but with the
introduction of soft materials between floor joists
and floor boards the basic principle of soundproofing
had been established. These soft materials could be
felt, paper, or kamptulicon, which was a preparation
of rubber and ground cork patented before 1848. Many
times these two systems would be applied simultaneously.
Also at this time, the architect A.J. Davis was
calling for sound deafening in his specifications as;
"deafening'; the first and second floors to be deafened
with hair, lime and sand mortar. Two inches thick and
lie close to the underside of floor; all solid without
hollows. It can be seen that the purpose of this
construction was to prevent or diminish the transmission
of sound through the floors. The addition of the two
extra inches of mortar was made possible by the insertion
of a sub-flooring between the floor joists. To accomplish
this, nailers were attached to the sides of the joists.
It appears that this type of floor insulation was very
common during the nineteenth century, for example, the
architect Renwick used a similar solution in the
Smithsonian building. Most improvements at this time were
of a more practical nature and were limited to small
additions. One of the best methods was the use of a
strip of soft material between the joists and the floor
This was, however, not the only improvement made
in the area of sound deafening. Complicated construction
using a free hanging ceiling which created a double layer
was also advocated. This space was often filled with
broken crockery as a sound deadening agent. The floor
itself then would have felt strips on the joists
but there also would be a layer of kamptulicon on the
floor boards underneath the carpet.
"With the introduction of soft materials between
floor joists, the basic principle of sound proofing
floors was established. It was possible to construct
a floor with reasonable sound insulation. The practice
of using "deafening", however, did not disappear until
well into the twentieth century. Part of the problem
was, of course, that research and understanding in
the scientific nature and behavior of sound did not
develop before the end of the nineteenth century
and the difference between contact and airborne sound
was not clearly recognized."1
"Two of the most interesting and extreme examples
of soundproofing occurred in music buildings built in
the 1900's, where many insulative materials were used
together. At the Institute of Musical Art in New York
the rooms were intended for private instruction and
designed to be soundproof. The floor is constructed
of hollow terra cotta tile arches supported by iron
I beams. On top of this is a layer of cinder concrete,
then sawdust mortar, and then cork flooring. Below
the reinforced concrete arches hang ceilings of plaster
on wire lath. The ceiling is supported by angle bars
which are supported by the I beams. In the air spaces
between the arches and the hung ceiling is a deadening
sheet. Despite all this, the construction was not
successful in securing the desired insulation.
At the School of Music at the University of
Illinois, Smith Memorial Hall, the framework of the
building is reinforced concrete with tile and concrete
joist floors, giving a massive, rigid construction not
easily affected by vibrations. The partitions are
three inch gypsum block separated by a two inch air space
that contains a layer of sound absorbing material. To
insure the preservation of the air space between the
block walls, one side was built up completely first. Both
three inch members rest on machinery cork and are
insulated from the floor above by hair felt. Contact
between partitions, columns, beams, etc., is avoided
by interposition of hair felt. The floor has a one inch
layer of dry sand over the concrete frame, two inches
of cinder concrete fill with a cement topping, a layer
of uncoated builder's felt, and finally linoleum. The sand
helps to break the continuity of the structure between
the finished floor and the structural floor."2
It was recognized at a very early time that these
methods of sound insulation were very limited. This
was due, at least in part, to the fact that all of
these attempts at sound insulation were based on
experience, not on direct observations of the behavior
"Although thermal insulation was man's earliest
accomplishment, for centuries he lost sight of its
importance. Other fields of science expanded, but
little was done to investigate the flow of heat until
the middle 1800's when Peclet presented the basic
laws and mathematics of heat flow through materials.
Still, few people were interested, and the science
of heat conservation turned over for another long sleep."3
The first attempt to apply the concepts of the science
of acoustics was made around 1895 by W.C. Sabine of
Harvard university in his study of the reverberation
time, that is, roughly speaking, the time required
for a given sound in a room, when its source is
stopped, to die away.
The extensive development and use of insulation
(both thermal and acoustic) dates from @ 1900.
Today something more is needed to stand between
the indoor climate we seek and the outdoor climate
served up to us daily. Something more than a good rain
shed, or a shield against wind.
As we grow technologically we have learned to
adopt ourselves to the extremes and we have learned
to create and maintain "indoor climates" which provide:
Man, by his very nature can not tolerate extreme
temperatures for extended periods of time. The degree
to which we maintain comfort during extremes of weather
is a measure of our standard of living. All of the
following should influence design and the use of materials:
air temperature (hot or cold)
sun and sky shine
The loss or gain of unwanted heat by humans is
touch or conduction
drafts, breezes, convection
respiration, breathing, ventilation
l Still air is a good insulator, but, is rarely
used due to convection. The job is to keep the air
still. This can be done with many materials. One
method is to enclose small particles of air within
closed cells, as in cork or cellular glass, or foamed
plastics. Another is to trap it in deep caves and
passageways between particles, as in granular materials
like pumice or vermiculite. Still another method is
to employ the principle that thin films of air cling
persistently to all surfaces and thus to use masses
of fine fibers which provide a tremendous surface area
to which air clings.
Fur, wool, feathers and mineral wool insulations
are examples. This thin film of air is so definitely
a heat barrier that it must be considered in all heat
transmission calculations. It must be remembered that
heat movement can not be stopped, but, it can be
Why different materials transmit heat at
the ability of the material forming the fibers
or cells to conduct heat along their length
the ability of adjacent fibers or cellular particles
to transmit heat by conduction
the orientation of these paths of heat flow
the size of the particles of trapped air and
the closeness of adjacent films of air on the
fibers or granules,
13 Heat insulations are available in a number of
shapes or structures, many of which are designed to
serve a specific use. Compositions are animal, vegetable
and mineral, and combinations of these types. Because of
(A the nature of the service for which insulating materials
are designed, most are relatively light in weight and
hence somewhat fragile. Except for specific forms such
as bricks, blocks, and boards that are known to possess
a definite physical strength, most insulations should
not be expected to provide much structural value.
Loose Fill Loose fill insulation usually is poured
or packed in bulk between confining structural
members. Loose-fill compositions used for specific
temperature requirements are asbestos powder,
cork granules, diatomaceous earth powder, powdered
gypsum, mineral wool (rock, slag or glass) pellets,
shredded paper, magnesia powder, silica-gel powder,
shredded wood fibres, vermiculite (expanded mica)
granules, pumice, pearlite, and lightweight slags.
Certain loose-fill insulations are used as aggregates
in lightweight concrete.
Flexible Flexible forms of insulation (blankets,
sheets, batts and felts) facilitate installation
by wrapping, nailing, or the use of adhesives.
They are well adapted for use on curved surfaces.
Flexible products are available in many compositions.
some of which incorporate surface-reinforcing
mediums of various types, materials include asbestos
felt, cane, cattle hair, cotten, hemp, jute,
kapok, mineral wool, paper, seaweed, rubber foam
and wood fibers.
Rigid Rigid insulation forms sometimes are classified
as blocks, boards, bricks, sheets or slabs. Many rigid
insulation products consist of combinations of
different raw materials, with or without internal
binders, air spaces, or surface treatments. Rigid
insulations are nailed or wired in place or
installed with adhesives. Their compositions
include asbestos, calcium-silicate, cellular
glass, cellulese acetate, cork, diatomaceous
earth, fire clay, gypsum, magnesia, cane, mineral
wool, paper, rubber foam, straw, vermiculite, and
wood. In the building field, insulation boards are
1i used as sheathing, as a plaster base material, and
for interior finish. Such uses may depend on their
structural strength, appearance, or acoustical
performance rather than on their thermal value.
Cements Insulating cements are furnished in dry powder
or pellet form and require only the addition of
sufficient water to mix to troweling consistency.
They are used on equipment having irregular
contours, such as valves, pipe fittings, etc., and
may be applied as a finish coat over other insulation
forms. Compositions include asbestos, diatomaceous
earth, magnesia, mineral wool, vermiculite and pearlite.
Reflective Reflective insulations effectively reduce
the transfer of radient heat when their low
emissivity adjoin an air space. Aluminum foil is
a widely used reflective type. It is furnished in
single and multi layer forms with or without a
paper backing and is used in combination with
insulation boards, flexible insulations, and pipe
insulation. Steel sheets approximately 0.006 in.
thick also are used as reflective insulation,
principally in refrigeration. Reflective insulation
is effective because it reflects a high percentage
of the radiation striking it and also emits a small
percentage of the amount of heat radiated by ordinary
(non-metallic) surfaces under the same temperature
conditions. Reflective insulation is based on entirely
different principles from those of conventional
Sprayed-on -"Several materials are used in this type of
application, one of them being the polyurethane foam
that can,be either foamed on or poured. Other common
ones are asbestos fiber mixed with inorganic binders,
vermiculite aggregate with a binder such as portland
cement or gypsum, and perlite aggregate using gypsum
as a binder. Machines are used for blowing these
insulations into place; as a result, the shape or
irregularity of the surface being insulated is of
Asbestos-fiber insulation is usually applied over
a base coat of some adhesive, often a laytex-type
water emulsion. The primer should be applied to only
as much of the surface as can be sprayed with fiber
while the adhesive is still tacky. Application direct to
metal lath does not require the primer adhesive.
This type of insulation also seals cracks and
crevices to prevent dust from sifting through and
eliminates joint and lap problems common to corrugated
building materials. It also tends to protect metal
from corrosive actions.
The other two insulations in this group mentioned
above can be sprayed over a base of gypsum lath, base
coat plaster, masonry surface, or metal lath."
Corrugated -"Corrugated insulation is usually made from
paper formed into shapes that produce enclosed air
pockets. One type is produced by shaping heavy paper
into a series of small regular semicircular corrugations
and covering both sides with a sheet of flat paper
to give strength and produce the air pockets. This
can be done using either single or multiple layers
of corrugated paper. This type of insulation is produced
either in sheets or rolls, depending on the thickness
of the mat, and is applied in strips fitting between
studs or in large sheets cemented to a flat surface.
A more rigid type of corrugated insulation is
made by forming a honeycomb-shaped mat with paper
and covering both sides with a flat paper sheet.
The whole thing is given its rigidity by spraying
with a thin coating of portland cement slurry or other
type of stiffener. The resulting paper mat,
from one to four inches thick, is quite strong and
may be used for nonbearing partitions, without further
support, plastered on both sides."5
Acoustics is a field that is concerned primarily
0 with the effects of sound and methods by which the effects
of sound can be controlled. In order to understand how we
can control sound, it is necessary to form a picture of
what happens to sound waves and the energy they contain
when sound is generated in a closed room.
When sound is produced by a sound source, waves
rravel outward in all directions radially from the source.
Variations in the speed of sound may result from differences
in atmospheric temperature. "When sound waves strike a
surface such as a wall or ceiling, they are reflected
and the reflected sound, as well as the original, is heard
4l by a listener, resulting in an increase in sound intensity.
While a sound source is operating, a room becomes filled
with reflected sound waves and when the source is stopped,
then reflected waves continue to travel back and forth
between room surfaces. As a listener picks up these reflected
waves, he hears them as the original sound being prolonged
and finally becoming inaudible as the reflected waves
gradually lose their energy by absorption. This prolongation
of sound is called reverberation.
A2 Control of increased intensity and of excessive
reverberation are two of the major problems of sound
engineering. Along with them are the problems of control
of unwanted sound and of transmission of sound from room
to room through walls, floors, and ceilings.
23 A large part of acoustical correction deals with the
improvement of hearing conditions and the reduction of
unwanted noise in rooms by reducing the energy of reflected
sound. this is done mainly by the use of acoustical materials,
materials which have a substantially greater ability to
absorb sound than such conventional ones as wood, glass,
hard plaster, or concrete.
The percentage of the energy absorbed by a material
when a sound wave is reflected from it is called the sound
absorption coefficient, or acoustical absorptivity. This
absorptivity coefficient depends on the nature of the material,
the frequency of the sound, and the angle at which the sound
wave strikes the material.
Acoustical Tiles "A majority of the tiles used for
acoustical purposes are made from wood, cane, or asbestos
fibres, matted and bonded into sheets of various
thicknesses, ranging from 3 sixteenths of an inch
to 1 and a quarter inches. The sheets are cut into
tiles of several sizes. The edges may be square cut,
beveled, or tongue and grooved.
These tiles are intended primarily for ceiling
applications. They can be applied to solid surfaces
with adhesives, nailed to furring strips attached
to a ceiling frame or the underside of a solid deck,
or installed in a suspended ceiling frame.
A great variety of designs, colors, and patterns
are available. The acoustic openings in the surface
of the tile in themselves provide many different
designs. The openings may be holes drilled in uniform
or random patterns or a combination of large drilled
holes and tiny punched ones. The openings may be slots,
straitions, or fissures, or the surface of the tile
may be sculptured in various patterns. All ceiling tile
comes with a factory painted surface so that it does
not require painting after installation. However,
fiber tile can be repainted with a nonbridging paint
without appreciable loss of acoustical properties."7
Assembled Units -"Assembled units usually consist of some
type of sound absorbing material such as a rock-wool
or fiber-glass blanket fastened to an acoustically
transparent facing. This facing is generally some
type of rigid board, such as hardboard or asbestos
board, or a metal sheet. The facings are preforated
to allow the penetration of sound waves.
Such acoustical panels can be fastened to a wall
over a framework of furring strips or suspended in
front of the wall by some mechanical framework. By
varying the thickness of the sound-absorbing element
and the spacing between the panels and the wall, some
variation in the overall absorption and the absorption
at different frequencies can be obtained. Sound-absorption
coefficients will vary with the thickness of the material,
the type of facing, and the size and number of the
perforations in the face."
Z7 Sprayed on Acoustic Materials "Two types of materials
are used for this kind of sound control application.
One type consists of plaster made with vermiculite or
perlite aggregate and the other of a coating of
mineral fiber mixed with an adhesive.
Vermiculite acoustical plaster is generally a
premixed product, requiring only the addition of
approximately 10 gallons of water per bag of mix.
The plaster can be applied by hand or by machine
spraying and will bond to any clean, firm, water
resistent surface such as base plaster, concrete,
or steel. When it is applied by hand, usually two coats
are used, a first coat at least three-eights of an
inch thick, and a finish coat at least one-eight of
an inch thick. When machine application is used, two,
three, or four thin coats are applied so that the total
thickness of plaster will be at least one half inch.
Perlite acoustical plaster is usually mixed on
the job, using calcined gypsum as the binder. It also
can be applied by hand or by machine. Sound-reduction
properties of perlite plaster are approximately the
same as those of vermiculite.
The main advantage of using machine spraying
as a means of application is that this method presents
no difficulties in plastering over irregularly shaped
Acoustical treatment with mineral fiber involves
the use of specially prepared mineral wool or asbestos
fibers and an adhesive to hold them to the surface.
The fibers are prepared and mixed with an inorganic
binding material, which helps to give them body, and
packed in bags ready for application. The area to be
covered is first primed with a thick coat of adhesive
and the fiber is then sprayed over the surface in one
or more coats. This depends on the thickness that is
required. For thicknesses over one half inch, at least
two coats are used. Each coat is tamped to consolidate
the fibers, the final surface can be sprayed with
sealer or color."9
- slide 1 from History of Techniques Regarding
Thermal and Acoustic Insulation and Fire
Protection, by William Warner
- slide 2, Ibid.
- slide 3, Ibid.
- slide 4, Ibid.
- slide 5, Ibid.
- slide 6, Ibid.
- slide 7, Ibid.
- slide 8, Ibid.
- page 52, Design of Insulated Buildings by Rot
- page 68, Ibid.
- page 84, Ibid.
- page 22, Ibid.
- page 18, Ibid.
- page 18, Ibid.
- page 18, Ibid.
- page 21, Ibid.
- page 345, Materials of Construction, Smith
- page 622, Time Savers Standards, Callender
- page 409, Materials of Construction, Smith
- page 975, Mechanical and Electrical Equipment
for Buildings, McGuinness
- page 983, Ibid.
- page 995, Ibid.
- page 635, Time Savers Standards, Callender
- page 637, Ibid.
- page 633, Ibid.
- page 991, Mechanical and Electrical Equipment
for Buildings, McGuinness
page 408, Materials of Construction, Smith
page 408., Materials of Construction, Smith
1 APT v.7, no.4, 1975, Sound Insulation; Some Historical Notes
2 History of techniques Regarding Thermal and Acoustic
Insulation and Fire Prevention, by William Warner, page 6.
3 Thermal Insulation, John F. Milloy, introduction.
4 Materials of Construction, Smith, page 350.
5 Ibid. page 350
6 Ibid. page 405
7 Ibid. page 405
8 Ibid. page 407
9 Ibid. page 407
APT v.5 no.1 1973
APT v.7 no.4 1975
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