Effect of Edge Insulation Upon Temperature

and Condensation on Concrete-Slab Floors

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 138
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UNITED STATES DEPARTMENT OF COMMERCE • Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Effect of Edge Insulation Upon Temperature

and Condensation on Concrete-Slab Floors

Harold R. Martin, Paul R. Achenbach, and Richard S. Dill

Building Materials and Structures Report 138

Issued October 9, 1953

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 2S, D. C. Price 20 cents
Contents

Page

1. Introduction 1

2. Test equipment 2

2.1. Test structure 2

2.2. Description of floor specimens 2

2.3. Heating equipment 4

2.4. Cooling equipment 5

2.5. Temperature measurements 5

3. Test procedure 6

4. Test results and discussion . 6

4.1. Approach to steady-state conditions 6

4.2. Floor-surface temperatures 8

4.3. Comparison of insulation methods 12

4.4. Effect of wall construction 14

4.5. Isotherms 15

4.6. Condensation 18

4.7. Aging of insulating materials 19

5. Conclusions 20

6. References 21
I

Effect of Edge Insulation Upon Temperature and Condensation

on Concrete-Slab Floors

Harold R. Martin, Paul R. Achenbach, and Richard S. Dill

By means of a special structure, with necessary refrigerating apparatus and auxiliary

equipment, nine concrete-slab floor specimens, each about 4J4 by ft, wore subjected to temperature conditions simulating those to which such floors in basementless houses are exposed during cold weather. As installed in the structure, the exposed edge of each speci- men abutted or overlapped a foundation typical of that around the perimeter of a house;

the other three edges were insulated to reduce the heat exchange to a negligible amount. The air in the structure above the specimen was maintained at about 70° F, and that above

the earth beyond the exposed edge was maintained at 32° F and 0° F for the different tests simulating winter conditions. The exposed edges of the several specimens were insulated

in different ways to determine the effect of edge insulation on floor-surface temperatures and

the possibility of condensation. It was found that the temperature of the floors with edge

insulation was from 9 to 13 deg F higher at a point 1 in. from the cold wall and the average temperature of the 30-in. border next to the cold wall from 3 to 5 deg F higher than that of the floor without edge insulation, the simulated outdoor temperature being about 0° F in both cases. Condensation, which probably would occur on uninsulated floors under certain conditions, can be prevented by the use of edge insulation. Some recommendations con- cerning types and arrangements of edge insulation are included for outdoor temperatures

as low as 0° F.

1. Introduction

I As a result of economic conditions and construction material scarcity, there has been a

j great increase in the number of basementless

j houses constructed in recent years. The floor

I most generally used in this type of house is the

ij concrete slab, sometimes placed on the ground

) but more often on a fill of gravel or similar material. Some low-cost houses have concrete floors

j containing heating pipes or ducts; others are

I equipped with space heaters or heating devices

I that deliver heat above the floor surface. Tests

'[ have been made on heated floors by others

I [1, 2, 3].^ The present experiments concern only

unheated floors,

i Past experience and experimental work [4] have

'\ shown that the heat loss of unheated concrete

floors on the ground is proportionately too small

: to be of material importance from an economic

j standpoint but that heat transfer in such floors

' merits consideration on account of its effect upon

; comfort and condensation. For this reason, no

attempt was made during these tests to measure

heat loss through the specimen floor, attention

being concentrated on the determination of the

effect of edge insulation on floor-surface temperatures for different outside temperatures.

1 Because concrete is a good conductor of heat,

j it can be expected that a floor constructed of this

I material will be relative^ cool in the region near

' This investigation was planned and conducted in cooperation with the Housing and Home Finance Agency, formerly the National Housing Authorty, as a study of methods for improving the acceptability of concrete floors for dwellings.

2 Numbers in brackets indicate the references at the end of this report.

the outside walls in cold weather. This cool

border area is often too chilly for the comfort of those who wish to occupy that part of the rooni.

Two methods are possible for bettering the condition: (1) to apply heat in the border area or (2) to increase the resistance of the heat path through

the concrete or through the earth beneath by

thermal insulation. This paper is concerned \vith

the latter method. It is well recognized that

such a floor, even if of the best construction possible, will still be chilly if the room does not have

the proper distribution of heat.

Water vapor will condense on any surface

colder than the dewpoint of the an- with which it

is in contact; for this reason, condensation sometimes occurs on concrete floors in the cold region near an outside wall. To prevent such condensation and promote comfort, the temperatm-es in

this region should be maintained at a higher level than those often found on uninsulated concrete

floors. Thermal insulation applied near the

outer, or exposed, edge of a concrete floor wfll reduce the heat flow and raise the floor-surface

temperatures.

In order to obtain more detailed information on

the arrangement and amount of insulation needed

for concrete floors, a special structure was erected

at the National Bureau of Standards in which

specimen floor sections could be exposed to simulated winter conditions. As it was impracticable

to test all conceivable edge arrangements for all climatic conditions, the present investigation was

planned to extend existing knowledge and to provide a basis for prediction of the performance

of floors with difterent edge arrangements in

climates of dift'erent degrees of severity.

1
2. Test Equipment

2.1. Test Structure

To obtain information on concrete-slab floors,

the structure shown in figure 1 was erected at the

National Bureau of Standards. This structure was a wood-frame building about 36 ft long and

12 ft wide attached to one wall of an existing in- sulated enclosure. The exposed walls and ceil- ings of the structure were filled with rock-wool

insulation, one layer SYs in. thick being used in the walls and twice this thickness in the ceilings, as sho\vn in figure 2. The buUding was divided

lengthwise into two nearly equal compartments

by a frame partition simulating an outside wall, as shown in figures 2 and 3. The 2- by 4-in. studs

of the wood-frame partition panels were faced

with K-in. plasterboard, and the stud spaces were

filled with 3% in. of rock wool. The partition

rested directly on the edge of the floor slab or on

a concrete-block wall, depending upon the design

of the particular specimen. For the tests, one of

these compartments was heated and the other

cooled. There were no windows in the structure,

and each compartment was made accessible by a

refrigerator-type door. The cold compartment

was not floored.

2.2. Description of Floor Specimens

The floor of the heated compartment consisted

of seven concrete slabs, each about 4^ ft in width

and 6K ft in length.

A 4-in. air space was provided between adjacent

floor test sections to diminish the passage of heat

between specimens. This air space was formed

between dams made of 1-in. boards nailed on 2- by 4-in. studs. These dams extended into the

earth 4 ft below the floor surface and were left in

place during the tests. The edges of the end

floors and the edges of all floors opposite the cold

space were similarly protected, as shown in flgure

2. It was expected that the air space, the wellinsulated structure, and the moderate temperature differentials involved would be such that heat

exchange between^oors and between floors and

the outside air and earth would be unimportant.

As an added precaution, test data were not taken on the floors at the two ends of the structure. Floors 1, 3, 4, and 5 shown in figure 4 each had

a partition simulating an insulated wood-frame

wall at the edge of the floor. Only floor 5 of this group was without edge insulation. Floor 2, shown in flgures 4 and 5, referred to hereinafter

as floor 2A for the first year's tests and floor 2B

for the second year's tests, and floors 6, 7, 8, and

9, also shown in figure 5, had concrete-block walls

with 2-in. wood furring strips and K-in. gypsum

wallboard extending 12 in. above the floor. For

these floors, the concrete-block walls were a continuation of the foundation construction for a

height of 12 in. above the floor. All floors in this

group were provided with edge insulation.

Floors 1, 2, 3, and 4, shown in flgure 4, were in- sulated with fiberboard dipped in coal-tar mastic.

The thermal conductivity of the fiberboard was

about 0.37 Btu/(hr) (sq ft) (deg F/in.). The edge

construction of these floors was as follows:

Floor 1. Fiberboard % in. thick was placed in an L-shape between the floor and foundation and

at the exposed edge of the floor. The insulation on the exposed edge was protected by a nominal

1- by 6-in. wood board.

Floor 2. A piece of flberboard 2 in. thick an

10 in. high was placed vertically to separate the

Figure 1. Exterior view of test structure.

-A—

I Rock Wool In 3'-0" Rofter Spoc^

Figure 2. Sectional view of test structure.
I'-M"

Fixed

Ponel L

5-0"

5 Insulaled Removable Panels

I

! 5'- O" . I

S'- 0' .1 5'— 0"

Cold Spoce

5'-0'

Tett Space

35'- 10"

Fixed Panel \_

Figure 3. Plan view of test structure.

FLOOR I FLOOR 2 FLOOR 3 FLOOR 4 FLOOR 5

rNSULATEO WALL PANEL INSULATED WALL PANEL

6" Gravel

Woterpoot Poper ^

Figure 4. Section showing construction details of floors tested in tests 1 and 2.

3
Figure 5. Section showing construction details of floors tested in tests 3 and 4-

foundation from the edge of the slab and the

gravel beneath it. Floor S. A piece of fiberboard IK in. thick and

14 in. high was affixed externally to cover the

exposed edge of the slab and the foundation and

extended to a depth of 2 in. into the ground.

Floor 4-- Fiberboard V/o in. thick was placed in an L-shape between the floor and foundation and

between the exposed edge of the floor and the

facing brick on which the wall rested. Floor 5. No insulation was used at the edge of

this floor. The concrete slab rested upon the

concrete-block foundation.

Floors 6, 7, 8, and 9 were insulated with rubberboard insulation having a thermal conductivity

of about 0.25 Btu/(hr)(sq ft)(deg F/in.). These

floors, shown in figure 5, were insulated with two

dift'erent thicknesses (% in. and 2 in.) and three

different depths (6 in., 10 in., and 18 in.) of rubber

board in order to study the effect of insulation

thickness and depth on the floor temperatures.

Floor 2, designated as specimen 2A for the tests made during the first year, was left intact during

the installation of floors 6, 7, 8, and 9, to provide

a comparison between the results obtained with

fibei'board and those obtained with rubber board.

The edge constructions of specimens 6, 7, 8, and

9 were similar in that the same type of insulation,

although of different thicknesses and depths, was

placed in a vertical position in each case between

the foundation and the slab and gravel. The

thicknesses and depths of the rubber board for the several sjjecimens were as follows:

Floor Thickness Depth

in. in. 6 2 18

7 % . 18

8 2 10

9 2 6

A view of the test space as arranged for tests

1 and 2 is shown in figure 6. Floors 1 to 5, inclusive, are shown in consecutive order, with floor 5 appearing in the foreground. A view of the

test space for tests 3 and 4 is shown in figure 7 and floors 6, 2, 7, 8, and 9 are shown in the order

mentioned, with floor 9 appearing in the

foreground.

2.3. Heating Equipment

The heating equipment shown in figures 6 and

7 was used in the heated compartment of the test structure to produce and maintain temperatures

simulating those in a house. The heater and dis- tribution system were designed to provide heating

almost entirely by convection and to provide uniform temperatures over all the test floors. The

heater consisted of resistance-type electric heating

elements mounted on the inside of a metal duct,

which in turn was connected to the outlet of a

centrifugal blower. The section of metal duct

containing the electric heating elements was well
Figure 6. View of floor specimens, wall construction, and

equipment in the test space for tests 1 and 2.

1

1 insulated to prevent appreciable radiation of heat.

The air uptake from the heater was connected

to a horizontal duct located about 7 ft above the

\ floor. The duct was provided with outlets on

, the upper side to distribute warm air throughout

the test space without creating high velocities

I near the floor. The heater was controlled autoI matically by a room thermostat and relay. The

J I thermostat, visible in figures 6 and 7, was of the

J bimetallic tj^pe, with a relatively long temperature-

,|j sensing element to provide greater sensitivity.

It was located at approximately the center of the

r heated compartment, 30 in. above the floor.

i 2.4. Cooling Equipment

I

I Cooling of the air in the cold compartment of

the test structure was effected by means of two

banks of iron-pipe refrigeration coils mounted

I longitudinally in the test space. These coils were

] enclosed in sheet-metal housings, which were open

; at the bottom to reduce the transfer of heat by

radiation yet permit forced circulation of air over

J them. A centrifugal blower was used to draw air

i over the coils and discharge it through a horizontal

distribution duct near the ceiling of the cold com1^ partment. Cooled air was discharged upward

through several outlets to eliminate high-velocity

air motion near the ground surface. The refrigI eration coils were operated on the flooded prinI ciple, employing an accumulator tank and float.

FiGUKK 7. View of floor specimens, ivall construction, and

equipment in the test space for tests 3 and 4.

An automatic pressure-regulating valve was provided in the suction line to maintain constant

pressures and temperatures in the coils at preselected values. With this equipment, nearly uniform temperatures were maintained in the cold

compartment of the test structure, with a minimum of air motion opposite the edges of the test floors and at the ground level, these being the zones of principal interest.

2.5. Temperature Measurements

Temperatures were measured with copperconstantan thermocouples placed in a vertical

plane passing through the center line of each floor specimen at selected stations indicated in figure

8 by small circles. A semiprecision potentiometer was used to measure the electromotive force developed by the thermocouples. Holes to the desired

depth were made by driving a i K-in. pipe into the

soil. Because of cave-ins, the thermocouple wires were placed in the ground before final removal of

the pipe. The thermocouples were enclosed in a rubber tube in order to protect them from dampness, and the tubes were filled with paraffin. The

rubber tube and the thermocouples were supported on sticks that were inserted into the pipes to the

desired level after sufficient earth had been re5
LlJ Xu

cc<

LUO

<u.q:3

V)o

z

62 50 38 26 14 0 6

DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES

Figure 8. Diagram of tetnperature stations for concrete-slab floor tests.

In the case of floors 5 and 9, which had slabs only 2 inches thick, the measurements were made on the surface and at depths of 2, 6, 12, 28, and 40 inches

instead of the stations shown. In addition to the stations shown, measurements were made on the surface of floors 1, 3, 4, and 5 at a distance of 6 inches from

the exterior of the cold wall and at a distance of 13 inches from the same reference for the other floors. In the case of floor 1, which had a wood protective board and floor 3, which had fiberboard over the outer edges of the floors, temperature measurements were made on the outer surface of these materials at the ex- tended centerline of the floor slab instead of on the outer surface of the edge of the wall.

moved from the holes. The pipe was then re- moved, and earth was tamped into the holes

around the sticks and the rubber tubes. Because

the wall of the rubber tube was thin and because

the earth was a considerably better conductor of

heat than either the tube, paraffin, or supportingstick, it was considered unlikely that these materials would cause significant error in the temperature measurements.

3. Test Procedure

The duration of the tests ranged from 25 to 37

days. Readings were taken at the start of each

test and daily thereafter throughout the week.

No readings were taken during weekends. The

"day of test" referred to in this report was the

elapsed time from the start of each test. A

comparison of the temperatures taken on successive days indicated that the 25-day test period

woidd be satisfactory because the heat flow had

closely approached the steady-state at the end of

this period of time. Two tests were made on the

fo'st set of floor specimens shown in figure 4. The

first test began May 6 and lasted 31 days, and the

second test began June 10 and lasted 37 days,

with the cold compartment maintained at about

0° F and 32° F, respectively. The following

year, two additional tests were made on the

second set of floor specimens shown in figure 5. The third test began on June 30 and lasted 25

days, and the fourth test began on July 29 and

lasted 25 days, with the cold compartment maintained at about 0° F and about 32° F, respectively.

The heated compartment, or test space, was maintained at about 70° F tliroughout all tests. Any

moisture condensation on the floors was noted.

4. Test Results and Discussion

4.1. Approach to Steady-State Conditions

The approach to steady-state conditions of heat

transfer was determined by plotting and com6
paring daily floor-surface temperatures, subsoil

temperatures, and other pertinent temperatures.

To illustrate this, data pertaining to floor 7 were

considered representative, and these data are shown graphicaflY in figures 9 and 10 for the test with temperatures in the cold space maintained

at about 0° F. Figure 9 shows the temperature gradient on

the surface of floor 7 for selected days from a point about 2 in. from the quarter round of the

mop board to a point 62 in. from the exterior of

the cold wall. The test was started with all parts of the floor and edge construction near the

surface at temperatures between 74° and 75° F. The changes in the temperatures on the floor

surface, in the cold space, and beneath the ground

surfaces in both the test space and the cold space

for floor 7 during the 25 days of test 3 are showni

in figure 10. It may be seen in this figure that

practically no change occurred in the temperature on the surface at either edge of the floor or on the

exterior surface of the cold wall at station E after the flrst 10 days of the test. The temperature in the earth at a depth of 28 in. below the surface in the cold space was still decreasing, though very

slowly, after 25 days of exposure. Figure lb

indicates that the decrease in floor-surface temperature shown in figure 9 between the 17th and

25th da3's probably resulted from variations in the air temperature in the test space.

250517—53 2 7
DAY OF TEST Figure 10. Variations of temperatures on floor 7 and in associated edge construction during 25 days of exposure in test 3.

4.2. Floor- Surface Temperatures

The heating and cooUng systems in the test structure were designed to produce uniform air temperatures in the test space over all the floor specimens and to expose all of the floor-edge constructions to the same temperature in the cold

space. The range of air temperature in the test space and in the cold space, as well as the range

in flooi'-surface temperatures on the 18th day for

all floors, are shown in table 1 for tests 1 to 4. Some of the more significant temperature dif- ferences in the test space are summarized in table 2 for tests 1 to 4. Table 1 shows that the air temperatures over

the five specimen floors dift'ered less than 1 deg

F at the 30-in. level for tests 1 and 2. The

differences in floor-surface temperature at dis- tances of 38 in. and 62 in. from the exterior side

of the cold wall were also less than 1 deg F for the five floors for these same tests. The air temperatures were not quite as unifoi'm for tests 3 and 4 as for the earlier tests. The difl'erences

in air temperature for the five floors were 1.5 deg F in test 3 and 1.7 deg F in test 4 at the 30-in.

level. Table 1 also shows that the average air and

floor-surface temperatures were 1 to 3 deg higher

for tests 3 and 4 than for tests 1 and 2. In the

cold space, the five floors were exposed to air temperatures difl'ering as little as 0.7 deg F in

test 2 and as much as 1.7 deg F in test 3. The vertical temperature differences in the

test space between the 2- and 30-in. levels were

relatively small, as shown in table 2. This

result is attributed to the well-insulated walls

and roof of the test space and to the fact that

heat was lost from the test space largely through one wall and the floor during most of each test period.

The floor temperatures along the center line of

the specimen floors on the 18th day of the tests are shown in figure 11 for tests 1 and 2 and in

figure 12 for tests 3 and 4. The floor-edge construction associated with each graph of floor- surface temperature is shown at the right in each

of these two flgures. Figures 11 and 12 show that

the temperature in the cold space had very little

8
Table 1. Temperatures at selected stations on 18th day Jor all floors

Tost 1 Test 2 Tests Test 4 Location of therniocouple junctions Maxi- Mini- Aver- Maxi- Mini- Aver- Maxi- Mini- Aver- Maxi- Mini- Aver- mum mum age mum mum age mum mum age mum mum age

Test space air: °F "F "F °F °F op "F op °F "F "F

30 in. above floor.. .-. 70.

1

69. 7 69.9 70. 2 09.5 69.8 73.9 72.4 72,9 71.9 70.2 70. 2 in. above floor 69.5 68.2 68.6 69.0 08.5 09.1 70.4 08.7 09.5 71.3 69.

7

70.

Floor surface: 62 in. from exterior of cold wall _ .- . 68. 5 68. 0 68. 1 68.7 08.

0

68.3 70.3 68.5 69.3 70. 7 68. 9 69. 38 in. from exterior of cold wall 66.8 60. n 06. 3 07.3 00.5 66.9 68.6 60.0 07. 1 09. 2 67.5 08. Cold space air: 1.6 0.1 1.1 34.9 34.2 34.4 2.5 0.8 1.4 33.

1

32.2 32.

Table 2. Temperature differences between selected stations in the test space on 18lh day for all floors

Test 1 Test 2 Test 3 Test 4 Location of thermocouple junctions Maxi- Mini- Aver- Maxi- Mini- Aver- Maxi- Mini- Aver- Maxi- Mini- Aver- mum mum age mum mum age mum mum age mum mum age op °F "F op °F OF "F °F °F

Test space air between 30 in. and 2 in. levels.. _ . 1.7 0.4 1.3 LO 0.4 0.7 3.8 2.8 3.4 0.6 0.2 0.5

Test space: Between 2 in. level and floor surface 38 in. from

cold wall - 2.7 1.9 2.3 2.6 1.9 2.2 2.8 1.8 2.4 3.0 2.

1

2.4 Between 2 in. level and floor surface 62 in. from

cold wall - -.- 1.0 0.2 0.5 1.0 0.4 0.8 0.5 -0.2 0.2 1.3 0.6 0.9 Between 30 in. level and floor surface 62 in. from

cold wall... _ 1.9 1.4 1.7 L7 1.3 1.5 4.0 3.3 3.6 1.9 L2 1.4

Table 3. Floor-surface temperatures on 18th day of tests

1 and 3 with cold space at 0° F±

Table 4. Floor-surface temperatures on 18th day of tests 2 and 4 with cold space at 32° F±

Floor Distance from exterior of cold wall Floor Distance from exterior of cold wall number number

62 in. 50 in. 38 in. 26 in. 14 in. 13 iu.i 6 in. 62 in. 50 in. 38 in. 26 in. 14 in. 13 in.i 6 in.

O p ° F 0 F

o F

o p

o po po po po p

0 p ° F » F » F

1 68.5 68.0 66.8 65.2 61.6 61.2 56.2 1 68.7 68.1 67.3 66.3 63.9 63.5 £8.4 2A 2 68.0 67.5 66.3 64.5 60.0 59.2 2A 2 68.1 67.5 66.5 6.5.0 61.3 60.8

3 68.0 67.5 66.6 65.5 62.5 62.0 56^6 3 68.0 67.6 66.9 66.1 64.1 63.8 60.3

4 68.0 67.1 66.0 64.4 61.9 61.6 59.4 4 68.3 67.5 66.7 65.6 64.4 64.2 63.0

5 68.2 67.2 66.0 64.4 58.8 57.9 46.8 5 68.6 67.9 67.2 65.7 62.2 61.6 54.6

6 69.7 68.8 67.7 66.0 01.6 60.7 6 69.2 68.6 68.0 67.2 64.9 64.1 2B 2 69.2 68. 5 66.9 65.2 59.7 59.3 2B 2 68.9 68.4 07.6 66.4 62.9 62.0

7 68.9 67.7 66.0 63.7 58.5 57.8 7 69.

1

68.4 67.5 66.0 63.0 62.3 8 68.5 67.8 66.4 63.8 58.5 57.7 8 69.4 68.5 67.7 66.2 63.5 63.0

9 70.3 69.7 68.6 66.3 60.0 58.8 9 70.7 70.

1

69.2 68.1 64.3 63.6

' Temperatures at this station vs^ere obtained by interpolation for floors

1, 3, 4, and 5.

2 Floor 2A (test 1) and floor 2B (test 3) are the same floor tested during

successive years.

' Temperatures at this station obtained by interpolation for floors 1, 3, 4, and 5.

2 Floor 2A (test 2) and floor 2B (test 4) are the same floor tested during

successive years.

effect on the floor-surface temperatures at dis- tances greater than 38 in. from the exterior of

the cold wall. Figure 11 reveals this result more

clearly than figure 12, because the air temperatures in the test space difl^ered only slightly for the five specimen floors for tests 1 and 2. At a

distance of 14 in. from the exterior of the cold wall,

the cold-space temperature did have a significant

efi^ect on the floor-sui-face temperature. Lowering the cold-space temperature from about 32°

F to a nominal value of 0° F lowered the floor- surface temperature at this station from 1.3 deg F to 3.4 deg F in tests 1 and 2 and from 3.2 deg F to 5.0 deg F in tests 3 and 4.

The surface temperatures of the floor specimens

shown in figures 11 and 12 are listed in tables

3 and 4. These tables summarize the temperatures for floors 1 to 9, inclusive, with floor 2, which was retained during tests 3 and 4 for comparison with tests 1 and 2, appearing twice,

thereby making a total of 10 elements. This

tabulation includes the floors with the insulated

frame walls and the floors with the uninsulated

concrete-block walls. Table 3 lists the floor- surface temperatures for a cold-space temperature

of 0° F, whereas table 4 lists the floor-surface

temperatures for a cold-space temperature of

32° F.

9
76 62 50 38 26 14 0

DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES Figure 11. Floor-surface temperatures on 18th day of tests 1 and

10
70

65

60

55

30 INCH BORDER

FLOOR 6 COLD SPACE TEMR

0° Fi 32° F' 13

70

65

60

55

76 62 50 38 26 14 0 1^ 30 INCH BORDER -|- 12 2

1 TRI

I

Ll. o

UJo

Q

UJ

FLO

GOLD SPfi CE TEMR

OR 2B

O'F' 32° F*

1 13

76 62 50 38 26

70

65

60

55

[^30 INCH BORDER f-—12 -

cr1-

LlO

UJ

UJ

FLO COLD SPt\CE TEMROR 7

0° F' 32° F*--

1 13

76 62 50 38 26 14

.— 30 INCH BORDER —

.

70 t65

60

55

i 5 . _ .

_ T 1

\

TRI k H

u.°

UJ

e)

(JUJ COLD SP/ CE TEMR

l-LUOM H

1 O^F* 32° F* 13

76 62 50 38 26 14

70

65

60

55

50

(—30 INCH BORDER —12 ~ ' -( t=

TRI

u.o

UJ QUJ

13

FLO COLD SPjfi\CE TEMROR 9

0°F' 32° F*

1

. -. -9 I- ,

2" X 10'-

FLOOR 8

FLOOR 9

FLOOR EDGE SECTIONS 76 62 50 38 26 14

DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES Figure 12. Floor-surface temperatures on 18th daxj of tests 3 and 4-

11
4.3. Comparison of Insulation Methods

The data in tables 1, 3, and 4 indicate that the

temperature of the air in the test space, which

differed somewhat between tests 1 and 3 and between tests 2 and 4, affected the floor-surface

temperatures. As shown in table 1, the floor- surface temperatm-es at a distance of 62 in. from

the exterior of the cold wall differed only slightly

for floors 1 to 5, inclusive, for cold-space temperatures of 0° F and 32° F when the air temperatures

in the test space above all floors were nearly uniform at the 30-in. level. For this reason, it was

considered desirable to use the floor-surface

temperature of each floor at a distance of 62 in. from the exterior of the cold wall as a basis for reference. The order of preference of the several

specimens was based upon the temperature dif- ference between this reference station and the

designated stations between it and the cold wall,

with the floor having the lowest temperature

difl'erence being rated the most desirable. The

results derived in this manner are given in tables

5 and 6. The floors with insulated frame walls

and those with uninsulated concrete-block walls are listed in separate groups. The difference in temperature between any given station and the

62-in. station for the same floor is recorded under

the distance of that station from the exterior of the cold wall. The magnitude of these temperature difl^erences was dependent upon the resistance

to heat flow within the floor and the earth beneath

it and was afl'ected by the distance of the station

from the cold wall and by the edge construction

of the floor. For floors 1, 3, 4, and 5 having insulated frame

waUs between the test space and the cold space, the station 6 in. from the exterior of the cold wall was about 1 in. from the inner surface of the cold

wall. The comparable temperature station on

the other floors having concrete-block walls was

the one 13 in. from the exterior of the cold wall

or 1 in. from the edge of the trim. The temperatures at these stations are of the greatest

importance insofar as condensation on the floor

is concerned. The likelihood of condensation on

the specimen floors will be discussed later. From

the standpoint of comfort, the temperatures of

the floor surface at distances greater than 1 in. from the interior surface of the cold wall ai"e of

interest.

It may be seen in tables 5 and 6 that the same

floor did not always appear in the same order of

preference at all distances from the cold wall in

either grouping and that there were some inconsistencies between the order of preference for

Table 5. Order of 'preference based on. temperature differences between reference and designated stations on the floor surface on 18th day of tests 1 and 3 with cold space at 0° F±

62 in. 50 in. 38 in 26 in. 14 in. 13 in. 6 in.

Distance from interior of cold wall

57 in. 45 in. 33 in. 21 in. 9 in. 8 in. 1 in.

Distance from exterior of cold wall

Temperature differences for floors with insulated frame wall

Floor Deg F Floor Deq F Floor Deq F Floor Deg F Floor Dig F Floor Deg F

1 '•0.5 3 1.4 3 2.5 3 5.5 3 " 6.0 4 8.6

3 <-. 5 1 1.7 1 3.3 4 6.1 4 ! 6.4 3 11.4

4 .9 4 2.0 4 3.6 1 6.9 1 * 7.3 1 12.3

5 1.0 5 2.2 5 3.8 5 9.4 5 ' 10.3 5 21.4

Surface temperature at this station used as

reference. Average temperature 68.2° F.

Distance from exterior of cold wall

62 in. 50 in. 38 in. 26 in. 14 in 13 in.

Distance from edge of trim

38 in. 26 in. 14 in. 2 in. 1 in.

Temperature differences for floors with uninsulated concrete block wall

Surface temperatures at this station used as

reference. Average temperature 69.1° F.

Floor '2A

9 '2B

86

7

Deg F

0.5

.6

".7

«. 7.9 1.2

Floor

9

fi8 '2B

Deg F

» 1.7

' 1.7 2.0

2.

1

2.3

2.9

Floor '2A

6 •2B

9

Deg F

3.5 3.7 "4.0

" 4.0

4.7

5. 2

Floor '2A

6 '2B

Deg F

8.0

8.

1

9.5

10.0

10.3 10.4

Floor <2A

^2B

Deg F

8.8

9.0

9.9

10.8

11.

1

11.5

" Designates different floors with equal temperature differences at a given station.

' Interpolated values.

« Floor 2A (test 1) and floor 2B (test 3) was the same floor tested in successive years. 12
temperatures of 0° F and 32° F in the cold space. In making comparisons, it is questionable whether

or not temperature differences of less than 1 deg

are significant from the standpoint of relative

comfort. B}" comparing floors 1, 3, 4, and 5 with

each other, all having insulated frame walls sep- arating the test space and cold space, floor 4 was

superior to floor 3 near the cold wall, but the

reverse was true for the stations farther from the

cold wall. This indicated that separation of the

concrete slab from the foundation by insulation

as in floor 4 was effective in raising the temperature

at the extreme edge of the concrete slab, but that

the greater depth of insulation applied to floor

3, together with the insulation in the voids of the

concrete block in the foundation, reduced the

heat transmission at distances of a foot or more

from the cold wall. The temperatvu-es of floor

1 near the cold wall, with thinner insulation between the concrete slab and foundation than floors

3 or 4, were lower than those of the latter floors; and floor 5, without edge insulation, was considerably colder than the other three floors at dis- tances of less than 2 ft from the cold wall. The average floor-surface temperature for a 30-in.-wide border adjoining the inside surface of

the cold wall was determined from the graph of

the floor-surface temperature for each specimen.

When a comparison was made of floors 1, 3, 4,

and 5, based upon the average temperatures

observed on this 30-in.-wide border, as shown in table 7, floors 3 and 4 were practically equivalent,

floor 1 rated third, and uninsulated floor 5 was

appreciably colder than the other specimens.

Concrete-slab floors 6, 7, 8, and 9 were separated from the concrete-block foundation walls

with dift'erent thicknesses and deptlis of rul)berboard insulation, as shown in figure 5. Floor 2, which was tested twice, was separated from the

foundation wall with a mopped-flberboard in- sulation. Based only upon the thickness, depth,

and thermal conductivity of the insulations

used with the several floors in this group, it was

expected that the sequence of the specimens in

order of decreasing merit would be 6, 8, and 9, with floor 6 being preferable to floor 7 and floors 6 and 8 being preferable to floor 2, but with floors 7 and 2 being indeterminate with respect to the

other floors, except by test. However, the data

summarized in tables 5 and 6 do not support

this expected order of merit in every respect.

Instead, they indicate that floor 6 (shown by data

in table 6) was superior to the other floors at the

stations near the cold wall when the cold-space

temperature was 32° F; whereas floor 6 (as shown

by data in table 5) was second in order of preferTable 6. Order of preference based on temperature difference between reference and designated stations on the floor surface on 18th day of tests 2 and 4 with cold space at S2° F±

Distance from exterior of cold wall

62 in. 50 in. 38 in. 26 in. 14 in.

1 13 in. 6 in.

Distance from interior of cold wall

57 in. 45 in. 33 in. 21 in. 9 in. 8 in. 1 in.

Order

of pref- erence

Temperature differences for floors with insulated frame wall

Surface temperatures at this station used as reference. Average temperature 68.4° F.

Floor Deo F Floor Deg F Floor Deg F Floor Dei F Floor Deg F Floor

3 0.4 3 1.

1

3 1.9 3 -.3. 9 4 >> 4. 1 4

1 .6 1 < 1. 4 1 2.4 4 3 ^ 4.2 3

5 .7 5 » 1.4 4 2.7 1 4.8 1

*• 5.2 1 4 .8 4 1.6 5 2.9 6.4 5 1-7.0 5

Deg F

5.3

7.7

10.3 14.0

Distance from exterior of cold wall

62 in. 50 in. 38 in. 26 in. 14 in. 13 in.

Distance from edge of trim

50 in. 38 in. 26 in. 14 in. 2 in. 1 in.

Temperature differences for floors with uninsulated concrete block wall

Surface temperatures at this station used as

reference. Average temperature 69.2° F.

Floor Deg F Floor Deg F Floor Deg F Floor Deg F Floor «2B 0.5 6 1.2 6 2.0 6 4.3 6 ^2A -.6 »2B 1.3 «2B 2.5 S 5.9 8

6 ".6 9 1.5 9 2.6 = 2B 6.0 7 9 ''.6 '2A ' 1.6 «2A -3.1 7 6.1 ' 2B

7 .7 7 "1.6 7 ' 3.

1

9 6.4 9

8 .9 8 1.7 8 3.2 =2A 6.8 =2A

Deg F

5.1

6.4 6.8

6.9

7.1 7.3

« Designates different floors with equal temperature differences at a given station.

' Interpolated values. ^

" Floor 2A (test 2) and floor 2B (test 4) was the same floor tested in successive years.

13
Table 7. Comparison of floors based upon the iemperahire

difference i^T) betiveen the 62-in. reference station and

the average temperature for the 30-in. border adjacent to the cold ivall

Cold-space tem- Cold-space temOrder of perature 32° F perature 0° F

Prefer- ence

Floor AT Floor AT

Floors with insulated frame wall

No. Deg F No. Deq F

1 4 3.4 3 5.0

2 3 3.5 4 5.1

3 1 4.5 I 5.8

4 5 6.2 5 9.1

Floors with uninsulated concrete bloek wall

1 6 2.4 2A 4.1

2 2B 3.0 6 4. 5

3 9 3.2 2B 4.6

4 8 3.4 9 4.9

5 7 3.5 8 5.2

6 2A 4.0 7 5.8

All floors

1 6 2.4 2A 4.

1

2 2B 3.0 6 4.5

3 9 3.2 2B 4.6

4 4 3.4 9 4.9

5 8 3.4 3 5.0

6 3 3.5 4 5.1

7 7 3.5 8 5.2

8 2A 4.0 7 5.8

9 1 4.5 1 5.8

10 5 6.2 5 9.1

ence at the same stations when the cold-space

temperature was 0° F. In the zone near the cold

wall, the data shown in table 5 indicate that floor 2A was the best of the group, whereas the data

for the same group in table 6 shows it to be the

floor of least merit.

The position of floor 2A relative to the other

floors in the order of preference at the stations 13

and 14 in. from the exterior of the cold wall was

considered uncertain because the thermocouples

at these stations were moperative on the 18th day

of tests 1 and 2, and the temperatures reported were obtained by extrapolation of the floor-surface

temperature curves. The data on floor 2B,

shown in table 5, at the same stations probably

provide the best indication of the relative merit

of floor 2 because reliable temperature data were

available for this observation. Therefore, it is possible that floor 6 was also better than any

other specimen investigated in tests 1 and 3 when

the cold-space temperature was 0° F. Comparing the floors having uninsulated concrete-block walls with each other, based on the

average floor temperatures of a 30-in. border

adjacent to the cold wall, it is shown in table 7 that, except for the gross inconsistency of floor 2A

for the two dift"erent cold-space temperatures,

the order of preference of the floors for both coldspace temperatures was 6, 2B, 9, 8, and 7. No

reason is apparent for floor 2B being superior to

floor 8, since the floor construction and edge

construction were the same for both floors, and

the only known difference was that the thermal' ^[ conductivity of the msulation in floor 8 was;

lower than that for floor 2. Possible reasons for! g the unexpected relation between these two floors . (j, are differences in moisture content of the earth | jjt beneath the floors or variations in the infiltration ' g of cold air thi'ough the concrete-block construe- .j, tion. Excepting floor 2A, tables 5 and 6 show ' floor 9 to be the one with, the least merit at the ; , stations adjacent to the cold waU. This result

J. jp would be expected because the insulation be- 1 \f tween the slab and the foundation was only 6 ,i in. deep for floor 9. However, at the 26- and 38- '

-j in. stations, floor 9 was superior to floors 7 and 8.

j

'y. This residt mdicated that the 4-in. hollow tile ^ used under the concrete slab in floor 9 ma}' have i been useful in reducing the heat transmission t

ij tlii-ough the floor as compared to the 6-in. gravel

fill used beneath the other floors.

, u 4.4 Effect of Wall Construction ;

From the data given in tables 5 and 6, dhect - comparisons regarding minunum floor tempera- f

' tures and the possibility of condensation near the '

' cold wall can be made between the floors constructed with insulated frame walls and those • constructed with uninsulated concrete-block walls,

although the wall constructions were of different : thicknesses. The 6-in. station on the floor surface r- of floors 1, 3, 4, and 5 was 1 in. from the interior '. side of the cold waU, whereas the 13-in. station was 1 in. from the edge of the trim for flooi-s 2, 6,

7, 8, and 9. All nine specimen floors can be compared for i comfort from the data in table 7. As shown in ! the last section of table 7, the inconsistenc}" of ' floor 2A is still apparent in the tests conducted

at two dift'erent temperatures in the cold space. With the exception of floor 2A, the order of pref- erence of the other floors is faii'ly consistent in the

tests made at dift'erent cold-space temperatures.

Floors 6, 2B, and 9 were consistenth' better than i' am' of the floors with insulated frame walls; floors

j 3, 4, and 8 were approximatel}' equal in average ,i surface temperatures; and floors 7 and 1 were

consistenth' colder than the other floors with in- ; sulated edges. Floor 5, without edge insulation, i was 3.3 deg colder than floor 1, the coldest of the j insulated floors for a cold-space temperature of 0° ;• F and 1.7 deg colder than floor 1, which was t again the coldest of the insulated floors, for a ^ cold-space temperature of 32° F. \ The comparison of test data on floors shown in table 7 may not reflect the effect of dift'erent . methods of edge insulation alone. The insulated ! frame wall used with floors 1, 3, 4, and 5 had a i heat transmission factor of approximately 0.08

Btu/(hr) (sq ft) (°F), Avhereas the concrete-block , wall with furring and plasterboard interior finish / used with floors 2, 6, 7, 8, and 9 had a heat- s transmission factor of about 0.34 Btu/(hr) (sq ft) , (°F). For a temperature diflerence of 70 deg F j 14
, between the test space and the cold space and

-with a cold-space temperature of 0° F, the tem1 perature of the interior surface of the insulated

' frame wall would be about 66.5° F, whereas the

'} interior surface temperature of the uninsulated

concrete-block wall would be about 55.5° F. In

] the former case, the descending stream of au* near

1 the cold wall would assist in heating the floor;

^ whereas in the latter case, the stream of air approaching the floor from the cold wall would not

' heat the floor and might even increase the cooling

' of the floor surface at the edge. In the test

' structure, this effect was not of great significance

i because the uninsulated concrete-block wall exI tended less than 2 ft above the surface of floors

2, 6, 7, 8, and 9. However, in an actual installation, uninsulated walls of normal height might

have an appreciable effect on the surface temperatures at the edges of the floor. The comparison

in table 7 of nine floors indicated that from the

standpoint of comfort the wall construction in the

I test structure did not significant^ affect the floor

II temperatures, because three of the floors with

,i uninsulated concrete-block walls were superior to

I the four floors with insulated frame walls.

1 Only approximate comparisons are possible

,| "between earlier data on concrete floors reported

ii hy Dni, Robinson, and Robinson [4] and the

i results obtained in this investigation because of

1 differences in floor and edge construction and

i| differences in the heating systems used in the

'! test space. Comparing floor 1 of the earlier in- vestigation [4] with floor 5 in the present study,

both of which were uninsulated, it will be noted

: that the surface temperatures at distances of 18

; and 36 in. from the exterior side of the cold wall

I were about 3 to 4 deg F higher on floor 5 for an

' outdoor temperature of about 32° F. However,

floor 5 had hollow clay tile under the slab, whereas

floor 1 in the earlier investigation had gravel under

the slab, and floor 1 had a thickened edge of con-

! crete at the cold edge, whereas floor 5 was of

uniform thickness edge to edge. These dif- ferences in construction would probably tend to make floor 1 a colder floor than floor 5.

j Comparing floor 3 in the earlier investigation

i [4] having 1 in. of fiberboard 6 in. deep separating

j the slab from the foundation with floor 1 in the

i present study for an outdoor temperature of about

I 32° F, it is seen that the surface temperatures 8

I in. from the exterior of the cold wall differed by

I less than one-half a degree but that floor 1 in the

present study was approximately 3 deg warmer at

distances of 24 and 40 in. from the same reference

point. These differences may represent real differences in heat transfer through the two floors and the earth beneath, or they may be accounted

for partly by the different heating systems used in

the test space. Forced circulation of air was used

in the present investigation, whereas cast-iron

radiators at the opposite side of the test space

with natural convection were used in the earlier investigation.

4.5. Isotherms

Temperatures were observed in the test space on the floor surface and below, and in the cold

space on the ground surface and below along the

center line of the floor specimens perpendicular to the cold wall. Representative isothermal curves below floor level in the test space and below ground

level in the cold space for floor specimens 2A and

3 are shown in figures 13 and 14, respectively, for

the 18th and the 31st days of tests 1 and 2. The

temperatures observed on the 18th day are in- dicated by the numbers above and to the left of

the corresponding grid intersections.

The temperature represented by each pair of

isothermal lines is identified by the underlined

number between or above the pairs. The dis- tance between any given pair of isothermal lines along the path perpendicular to them indicates

how much temperature change occurred after the

18th day of the test. The ground temperature

beneath the floors and in the cold space was stiU

increasing during tests 2 and 4 eighteen days

after changing the cold-space air temperature from

0° F to 32° F. This was undoubtedly the result of

performing the test with 32° F in the cold space

immediately after completing a test with 0° F

in the cold space. The results for test 2, as shown in figures 13 and 14, illustrate these

changing conditions.

The isothermal lines in the concrete floor slabs, in the gravel, and in the earth, shown in

figures 13 and 14, lie in the position and direction

that would be expected from theoretical analysis.

The changes in slope of the isotherms at the interface of the concrete and gravel and at the interface of the gravel and earth indicate the differ- ences in thermal conductivity of the adjacent

materials. The shape of the isotherms for these

floors indicated that all of the heat transmitted

through the floor surface flowed downward and

to the right through the slab, the gravel, and the

earth toward the foundation and footing. A

trace of the probable heat-flow path from the

floor surface at a distance of 76 in. from the

exterior of the cold waff toward the cold space

indicated that any heat that entered the earth

from outdoors at the left of the test space, as shown in figures 13 and 14, traveled a path below

the limits of the isotherms shown, and below the

footings. It is concluded, therefore, that any

heat transmitted from outdoors had little effect on the temperature distribution within the limits

of figures 13 and 14. A comparison of the isotherms in figures 13

and 14 reveals that the temperatures in the earth near the warm side of the foundation wall were

appreciabty lower for floor 2A than for floor 3. This result leads to the conclusion that the insulation in the voids of the concrete blocks of the

foundation wall of floor 3 was effective in reducing

the heat transmission through this floor as compared with floor 2A, having the foundation wall

15
COLD SPACE J2°F±

in

<

o

2

irV)o

a:

UJ

(_>

Q

62 50 38 26 14 0 6 DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES

Xo

<

Ll- O

O

cc

too

O

CO

62 50

DISTANCE FROM

38

EXTERIOR

26

OF COLD

Figure 13. Temperature pattern and isothermal lines during tests 1 and 2 for floor 2A, representing specimens

with uninsulated concrete-block wall.

16
76 62 50 38 26 14 6 0 6 18 DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES

62 50 38 26 14 6 0 6 DISTANCE FROM EXTERIOR OF COLD WALL IN INCHES

Figure 14. Temperature -pattern and isothermal lines during tests 1 and 2 for floor 3, representing specimens

insulated frame walls.

COIo

<

LUo

<Ll. IT

V)O

LlI o

<(-COo

with

17
unfilled. The unfilled voids in the foundation of

floor 2A would permit circulation of air in the

foundation wall in a clockwise direction as viewed

in figure 13. The portion of the concrete blocks

exposed to the cold outside air above the ground

level would produce a downward current of cold

air in the voids of these blocks that would continually remove heat by convection from the

earth on both sides of the foundation wall, but

with the greater amount being removed from the

warm side. Filling the voids with insulation

would prevent this circulation in the foundation

wall and diminish the heat transmission through

the foundation. It might also decrease the depth

of freezing of the earth in a given climate. The

frost line was about 3 in. deeper opposite floor 2A than opposite floor 3, as shown in figures 13

and 14, when the temperature in the cold space was 0° F. The spacing of the isotherms provides an approximate measure of the rate of heat fiow per

unit area in any given material or in materials of

comparable thermal conductivities. The time

rate of heat fiow through a material per unit area is given by the equation

where k is the thermal conductivity of the material, d is the thickness of the material, and AT

is the temperature dift'erence across the portion

under consideration.

Considering the earth between two isothermal

lines 5 deg apart, AT is a constant, and k can be

assumed to be nearly constant. Therefore, the

heat fiow is inversely proportional to the distance

between adjacent isothermal lines in the earth

beneath the concrete fioor. The convergence of

the isotherms below the fioor surface near the

cold wall indicates that the heat transmission

increased significantly in this zone. If the concrete fioor slab is considered as a heat-fiow meter

of low precision, and if the change in direction of

the heat fiow through the concrete is neglected,

the increase in temperature difference between

upper and lower surfaces of the concrete fioor

slab toward the cold wall is an approximate measure of the increase in the rate of heat flow

thi-ough the floor as the cold wall is approached.

The isotherms below ground level in the cold

space, indicated in figures 13 and 14, show that

the earth was frozen to a depth ranging from 13

to 16 in. below the surface at a distance of 6 in. from the foundation after 18 days of exposure to a cold-space temperature of 0° F. An additional

13 days of exposure, as in test 1, increased the

depth of frozen earth at this distance by 5 or 6

in. The depth of the frost line was probably

affected somewhat by the heat flow from outdoors.

4.6. Condensation | As previously stated, the floor-surface temper- | ature station 1 in. from the interior of the cold

wall was the most important insofar as surface

condensation on the floors is concerned. For

tests 1 and 3, with a cold-space temperature of 0°

F, the temperatures at this station ranged from

56.2° to 60.7° F for the insulated floors and was

46.8° F for the uninsulated floor. A photograph

of floors 4 and 5 and one of the protective end

slabs, in that ordei , with floor 4 in the foreground,

is shown in figure 15. This photograph shows

clearly the condensation at the edge of fioor 5 and

on the uninsulated protective end slab. Condensation did not occur on any of the insulated

fioors. Daily observations of the relative humidity in i ; the test space were taken with a sling psychrome- 1

' ter. As steady-state conditions were approached .

i with respect to fioor-surface temperatures, the

!

relative humidity was nearly constant in the test space at about 55 percent for tests 1, 2, and 3, i and at about 63 percent for test 4. The relative

humidity was not controlled during the tests but I was permitted to reach steady-state values, depending upon the rate of fiow of water vapor from i the outdoors to the test space and from the test space to the cold space. Daily variations in rel- ( ative humidity of 1 or 2 percent were sometimes

| recorded. i Because condensation occurred on uninsulated '> fioor 5 with a surface temperature of 46.8° F at the cold edge and did not occur on the coldest of

the insulated fioors with a surface temperature of I 56.2° F, it would follow that the relative humidity ' in the test space was in the range between 44

percent and 62 percent at the levels where the

dry-bulb temperature was 70° F. The observed

relative humidity for test 1 was within this range, i During the first week of test 2, begun only 3 or ' 4 days after ending test 1, which was perfoi'med

' at a lower cold-space temperature, condensation was observed at the edges of some of the insulated

fioors. However, as test 2 progressed toward ' steady-state conditions, aU condensation disap- ' peared. These results showed that the concrete ^ floors and earth beneath changed temperature so slowly that the rise in dewpoint temperature in

''• the test space that resulted from the changed conditions in the cold space caused condensation to " occur temporarily on floors with insulated edges.

| It is concluded that, during changing outdoor conditions, condensation might occur temporarily on

insulated concrete floors that would otherwise be - free of condensation. i. The ASHVE Guide [5] shows that condensation ' will occur on single-glass windows at an indoor

relative humiditj^ of about 16 percent for an out- ; door temperature of 0° F and at an indoor relative

humidity of about 39 percent for an outdoor tern-

^ perature of 32° F. These psychrometric conditions correspond to indoor dewpoint temperatures

18
FiGUBE 15. View of test space showing condensation on uninsulated floor 5, and -protective end slab during test 1 with

cold-space temperature at 0° F.

of about 23.5° F and 44° F, respectively. Hence,

it is unlikely that condensation would occur even

j on an uninsulated floor, such as floor 5, if it were

used in a structure with several single-glass windows. The ASHVE Guide also shows that con-

, densation will occur on double-glass windows at a

I relative humidity of about 42 percent for an out-

' door temperature of 0° F and at an indoor humid-

, ity of about 65 percent for an outdoor temperature

': of 32° F. These indoor conditions correspond to

I dewpoint temperatures of about 46° F and 58° F,

; respectively. Therefore, it is possible that an unI insulated floor like floor 5 would condense moisture

i| near the cold wall in a structure using double-glass

|i windows. On the other hand, surveys of humidi ities in residences by Phillips [6] and Teesdale [7] indicate that very few residences have interior

ji relative humidities and dewpoint temperatures

high enough to cause condensation on a doubleglass window or on the edge of a floor with temperatures equal to those observed on floor 5. The

greatest danger of condensation occurring on uninsulated concrete floors would probably be in

modern houses having low air infiltration or those

with automatically controlled humidity. Floor 5

! was covered with asphalt tile ]i in. thick, but it is improbable that this covering had a significant

effect on the floor-surface temperatures observed

thereon.

Floor-surface condensation would be highly improbable on concrete floors with edge constructions like any of the insulated specimens tested.

I With an outside temperature of 0° F and an inside

j temperature of 70° F, the maximum relative

j humidity that could be reached before condensation would occur on the floor surface at a distance

of 1 in. from the interior side of the cold wall

would range fi'om 62 percent for floor 1 to 70

percent for floor 4 with insulated frame walls and

j from 59 percent for floor 9 to 65 percent for floor

6 with uninsulated concrcte-f)lock walls, if {Uh)v

2A, whose thermocoupl(!s were inoptirativc at this station, and floor 5, which was uninsulated, are not included.

The possibility of condensation occurring on some of the floors directly under the sill of the

wall and consequent rotting of the sill should not

be overlooked. For example, for walls of floors 4

and 5, temperatures under the sills might be low

enough to allow condensation. Floors 1 and 3, with insulation protecting the area under the sills, would be expected to be relatively warmer and

would be less likely to have condensation occur under the sill. In the same way, floors 2, 6, 7, 8,

and 9 were reasonably well protected at the edges

( against temperatures likely to cause condensation on the floor under the baseboard.

The causes of condensation on concrete floors during summer and winter are different. Summer

condensation on a concrete floor under some at- mospheric conditions is caused by thermal lag

resulting from the heat capacity of the floor and

the earth underneath. When such a floor is subjected to a protracted period of cool weather

followed by warm humid weather, the floor and

the earth beneath it tend to remain cool for some

time, and condensation would occur on the surface

and would persist as long as the floor temperature was below the dewpoint of the air and would cease when the floor was warmed above this temperature

either by the air or other means. In whiter, con- densation in a heated house would be most likely

to occur near the outside or exposed walls ; whereas

in summer, it would be most likely to occur in

protected areas, such as in closets, under furniture, or under rugs. A rug on a concrete floor reduces

the heat flow from the air to the floor surface and

retards the warming of the floor. However, the

rug might be pervious to water vapor, and for

this reason a damp spot might exist underneath

it when the rest of the floor appeared to be dry.

Because the causes of condensation on concrete

floors in summer and winter are not the same,

different measures are required for the prevention

of condensation in these two seasons. To decrease

the probability of summer condensation, a conventional concrete floor should be as thin as practicable, and it should be insulated from the

earth beneath. The use of lightweight concretes

also performs the same function because of the

relatively low thermal conductivity and volumetric heat capacity of these materials. Condensation on concrete floors during the winter was shown to be highly improbable when the floor edges were insulated by any of the methods that

have been described.

4.7. Aging of Insulating Materials

Samples of the mopped fiberboard used in floor 2 and the rubber board used in floors 6, 7, 8, and 9 were removed for examination and determination

of moisture content. At the time of removal, the

19
Figure 16. Rubber board (above) and mopped fiberboard

(belo'w) after removal from test floors.

fiberboard liad been in place for 6 years and tlie rubber board for 5 years. The effect of aging on the insulating materials

while in the test floors, shown in figure 16, may be

seen in the front and side views of the 3- hy 6-in. portions taken from floors 2 and 8. It will be seen

that there was no noticeable deterioration in the

rubber board, whereas the mopped fiberboard

had disintegrated considerably. Several portions were removed from the insulating barriers within

the floor constructions and were immediately

weighed. These sections were then dried and

reweighed to determine the percentage of moisture

absorbed by each. The average moisture absorbed, based upon the weight of the dry samples,

for each of the insulating materials was as follows

:

Mopped fiberboard 28 percent and rubber board

9 percent. The relative amount of moisture

absorbed by the two insulating materials does not

provide any information, however, as to the moisture within the floors, gravel, or earth during the

tests. It is probable that the effectiveness of both of

these insulating materials decreased after installation because of the moisture absorbed from the

surrounding materials. The disintegration of the

mopped fiberboard was such that its use as an

insulating material for this type of construction

is considered undesirable. The rubber board

showed no apparent disintegration within the

observed period.

5. Conclusions

This report contains information on concrete

floors for buildings that are heated by systems

liberating heat above the floor surface only.

While some of the data may have application to heated concrete floors, such floors, in general,

require greater amounts of insulation to prevent

excessive heat loss to the earth and to the outdoor

air through the exposed edges.

This study of various methods of insulating the

edges of concrete floors laid on the ground leads

to several conclusions about the amount of insulation, the methods of construction, and the ) characteristics of the insulation that should be

used. These are as follows:

(a) The temperatures on the surface of the

concrete floors laid on the ground and insulated

at the edge reached nearly steady-state conditions

in 10 days for outdoor temperatures of 32° F

and 0° F. The temperatures in the earth outside of

the structure continued to decrease for at least 30 days after the start of the tests with the cold

space at 0° F, although the rate of change was

very slow after that period of time, averaging

about 0.15° F per 24 hr.

(b) Comparing the insulated floors with the

uninsulated floor for an outdoor temperature of

0° F, the surface temperatures 1 in. from the cold

wall ranged from 9 to 13 deg F higher on the 'i, insulated floors, the average surface temperatures

for a 30-in. border ranged from 3.3 to 5.0 deg , F higher for the insulated floors, and there was no , significant difference in surface temperature be- j, tween the insulated and uninsulated floors at distances of 3 ft or more from the cold edge.

(c) Floors having edge constructions protected

by 1/2 and 2-in. -thick insulation were consistently

warnler than those having %-in. msulation. The

best temperature distribution was obtained with

insulation 2 in. thick and 18 in. deep. Thicker

and deeper insulations would probably be still I- more effective.

j; (d) Filling the voids in the concrete-block

foundation wall with mineral wool appeared to increase floor-surface temperatures at distances ^ of 1 ft or more from the wall. A material not ' subject to damage by moisture should be used

for this purpose. An air space beneath the con- ' Crete floor slab, such as was provided by 4-in. 'I structural clay tfle, appeared to provide warmer ' floor-surface temperatures than a 6-in. layer »: of gravel below the slab for otherwise similar

conditions.

(e) No consistent increase in floor temperature was observed when using an insulation having a thermal conductivity of 0.25 Btu/(hr) (sq ft) (°F/in.) as compared with an insulation having a thermal conductivity of 0.37 Btu/(hr) (sq ft) (°F/in.) for floor-edge insulation. The moisture

content of the two materials was not known at the

time of the tests. However, the difference in

20
I absorbency of the materials would probably

increase the disparity in the insulating value of the two materials.

(f) It was evident that complete separation of

I the concrete slab from the foundation wall by an

insulating barrier was desirable. The results did

not indicate outstanding superiority for either the

"floating" floor with the slab entirely inside the

foundation wall or the concrete slab supported on the foundation wall,

i (g) Past experience indicates that the amount

' of insulation in the exterior walls of structures using concrete floor slabs aft'ects the temperatures

of the floor surfaces near the exterior walls. However, during the present tests no significant

j difference was observed between the specimen

j floors with insulated frame walls and those with

j uninsulated concrete-block walls that could be

attributed to the wall construction, possibly

because the concrete-block walls extended only a

short distance above the floor surface or possibly

because the greater thickness of those walls

' caused the useful portion of the floor surface to be more remote from the cold space.

(h) With the insulation methods used during

these tests, condensation would be expected to appear in cold weather on the windows of a house

before it would appear on the edges of concrete

floors. Condensation would probably occur on

I the edges of uninsulated concrete floors in humidiI fled houses or in houses with double-glazed win1 dows under some winter conditions.

(i) The deterioration of the fiberboard insula-

' tion dipped in coal-tar mastic during 6 years of

: exposure in the foundation construction indicates

,j the advisability of using materials for edge insulaI tion of unheated concrete floor slabs that are not

I damaged by moisture or that are adequately protected against damage by moisture. Other desirable characteristics would be: rigidity, relative

inertness, and low thermal conductivity.

(j) Existing concrete floors and foundation

walls supporting them could be protected by

covering the exposed edges of the floor and

jl foundation wall with insulation. Such applications should cover the exposed edge of the floor

slab, all of the exposed side of the foundation wall,

and should extend into the earth.

(k) An arrangement of the insulation made

up of a horizontal piece under the border of the

floor and a vertical piece separating the edge of the floor from the foundation wall should be as good as vertical insulation of equal thickness and

width placed against the foundation wall. A

horizontal layer of insulation might permit more

1 rapid changes in temperature of the concrete slab

because it would pai-tiaily isoliil(; ihc slal> lioiii the heat capacity cflects of the earth beneath.

On the other hand, a horizontal layer of insulation would pci-mit the frost liru; to ap[)roa(;h nc^arer

to the luuh'i' side of tlic. floor in severe cliniat es and

might incfease the |)i-()l)al)ilil \ of fi-ost heaving.

It shoidd be ])ointe(l out thai alllioiigli IIk; edge

constructions used foi' this invesligiilion are types

that have been used in the l)uil(liiig in(hiKtry,

the present study was planned to provide; ird'oi-ma- tion only on temperature distribution upon the

floor surfaces and susceptibility to condensation

thereon and was not intended to develop conclusions about the structural advantages or disadvantages of the several constructions.

6. References

References Cited in Text

[1] A. B. Algren, Ground temperature distribution with a floor panel heating system, Trans. Am. Soc. Heating and Ventilating Engineers (1948).

[2] J. R. Jamison, R. W. Roose, and S. Konzo, Warm

air perimeter heating. Heat losses from floor slabs. Part 3, Heating, Piping and Air Conditioning (Feb. 1952).

[3] C. M. Humphreys, C. V. Franks, and L. F. Schutrum,

Field studies of heat losses from concrete floor panels. Heating, Piping and Air Conditioning (Jan, 1951).

[4] R. S. Dill, W. C. Robinson, and H. E. Robinson, Measurements of heat losses from slab floors, NBS Building Materials and Structures Report

BMS103 (1945).

[5] American Society of Heating and Ventilating Engineers Guide, p. 200 (1952).

[6] T. D. Phillips, A survey of humidities in residences,

NBS Building Materials and Structures Report

BMS56 (1940).

[7] L. V. Teesdale, Remedial measures for building construction, IJ. S. Forest Products Laboratory

Report R1710 (1947). Additional References

L. Shuman, How to insulate concrete floors. Heating and

Ventilating (July 1948). H. D. Bareither, A. N. Fleming, and B. E. Alberty,

Temperature and heat loss characteristics of concrete

floors laid on the ground. University of Illinois, Small

Homes Council Technical Report. H. D. Bareither and J. T. Lendrum, Concrete floors for basementless houses. University of Illinois, Small

Homes Council Report No. F4.3. Federal Housing Administration, Minimum property

requirements for properties of one and two living units located in the territory covered by the District of Columbia Insuring Office, 406-E Concrete slabs on ground (July

1947). MPR. Revision No. 25, 406-E Concrete slabs on ground (Aug. 1951). Washington, February 16, 1953.

U. S. GOVERNMENT PRINTING OFFICE: 1953

21

BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association 15^ BMS33 Plastic Calking Materials... BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging * BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

With "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co.. 10^ BMS37 Structural Properties of "Palisade Homes" Constructions for Walls, Partitions, and

Floors, Sponsored by Palisade Homes

BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10j5 BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10^ BMS40 Structural Properties of a Wall Construction of "Knap Concrete Wall Units" Sponsored

by Knap America, Inc * BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls * BMS42 Structural Properties of Wood-Frame Wall and Partition Construction with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation * BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 * BMS44 Surface Treatment of Steel Prior to Painting * BMS45 Air Infiltration Through Windows 15^ BMS46 Structural Properties of "Scott-Bilt" Prefabricated Sheet-Steel Constructions for Walls,

Floors, and Roofs Sponsored by The Globe-Wernicke Co * BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20^ BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15^ BMS49 Metallic Roofing for Low-Cost House Construction 20jS BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging * BMS51 Structural Properties of "Tilecrete Tvpe A" Floor Construction Sponsored by the

Tilecrete Co 10^ BMS52 EfiFect of Ceiling Insulation Upon Summer Comfort ISji BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 10^ BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 10^ BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls * BMS56 A Survey of Humidities in Residences * BMS57 Roofing in the United States—Results of a Questionnaire * BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings * BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 30^ BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions. . * BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 15^ BMS63 Moisture Condensation in Building Walls ISjS BMS64 Solar Heating of Various Surfaces * BMS65 Methods of Estimating Loads in Plumbing Systems 15)i BMS66 Plumbing Manual 35(5 BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 20f5 BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10^ BMS70 Asphalt-Prepared Roll Roofings and Shingles 20^ BMS71 Fire Tests of Wood- and Metal-Framed Partitions * BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co . * BMS73 Indentation Characteristics of Floor Coverings 10^ BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 20^ BMS75 Survey of Roofing Materials in the North Central States 15j5 BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls * BMS77 Properties and Performance of Fiber Tile Boards * BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 25^ BMS79 Water-Distributing Systems for Buildings 20^ BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 15^ BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x 7>^ inches).. 30^

•Out o( print. [List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS82 Water Permeability of Walls Built of Masonry Units 25^

BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 15^ BMS84 Survey of Roofing Materials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

Temperature * BMS86 Structural, Heat-Transfer, and Water Permeability Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Products Corporation 15^ BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research,

Design, and Construction 20^ BMS88 Recommended Building Code Requirements for New Dwelling Construction With

Special Reference to War Housing * BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated

Wood-Frame Wall Construction Sponsored by the Homasote Co 15^ BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Coa';tructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15^ BMS91 A Glossary of Housing Terms . * BMS92 Fire-Resistance Classifications of Building Constructions 35^ BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure.. * BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls * BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 25<S BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 10^ BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board * BMS98 Phvsical Properties of Terrazzo Aggregates * BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 155^ BMSlOO Relative Slipperiness of Floor and Deck Surfaces * BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls * BMS102 Painting Steel 10(i BMS103 Measurements of Heat Losses From Slab Floors 15(i BMS104 Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

Partitions, Floors, and Roofs Sponsored by the Douglas Fir Plywood Association * BMS105 Paint Manual with particular reference to Federal Specifications $1. 25 BMS106 Laboratory Observations of Condensation in Wall Specimens 10^ BMS107 Building Code Requirements for New Dwelling Construction * BMS108 Temperature Distribution in a Test Bungalow With Various Heating Devices 15^ BMS109 Strength of Houses: Application of Engineering Principles to Structural Design $1. 60 BMS110 Paints for Exterior Masonry Walls 206

BMSIU Performance of a Coal-Fired Boiler Converted to Oil 15^ BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- Entraining Admixture ; lOp

BMS113 Fire Resistance of Structural Clay Tile Parti dons 15^ BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters 25i

BMS115 A Study of a Baseboard Convector Heating System in a Test Bungalow 20^ BMS116 Preparation and Revision of Building Codes 15^ B MSI 17 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 20(^ BMS118 Stack Venting of Plumbing Fixtures 15^ BMS119 Wet Venting of Plumbing Fixtures 2Q<t BMS120 Fire Resistance of Walls of Gravel- Aggregate Concrete Masonry Units 15^ BMS121 Investigation of Failures of White-Coat Plasters 25^ BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding 15^ BMS123 Fire Tests of Wood-Framed Walls and Partitions With Asbestos-Cement Facings 15^ BMS124 Fire Tests of Steel Columns Protected With Siliceous Aggregate Concrete 15^ BMS125 Stone Exposure Test Wall 30^ B MS126 The Self-Siphonage of Fixture Traps 20^ BMS127 Effect of Aging on the Soundness of Regularly Hydrated Dolomitic Lime Putties 15^ BMS128 Atmospheric Exposure Tests of Nailed Sheet Metal Building Materials 20^ BMS129 Fire Endurance of Shutters for Moving-Stairway Openings 10^ BMS130 Methods and Equipm.ent for Testing Printed-Enamel Feit-Base Floor Covering 15(i BMS131 Fire Tests of Gunite Slabs and Partitions . 15^ BMS132 Capacities of Plumbing Stacks in Buildings 20^ BMS133 Live Loads on Floors in Buildings 20^ B MS134 Fire Resistance of Concrete Floors 15^ BMS135 Fire Tests of Steel Columns Encased With Gypsum Lath and Plaster 16^ BMS136 Properties of Cavity Walls 15^ BMS137 Influence of the Wash From Bronze on the Weathering of Marble 15^ BMS138 Efifect of Edge Insulation Upon Temperature and Condensation on Concrete-Slab

Floors 20^

'Oot of print.