IP

National Bureau of Standards

MAR 3 0 1945

U. S. DEPARTMENT OF COMMERCE
BUILDING MATERIALS AND STRUCTURES REPORTS

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BMSl Research on Building Materials and Structures for Use in Low-Cost Housing 10^ BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions lOji BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 10^ BMS4 Accelerated Aging of Fiber Building Boards lOfi BMS5 Structural Properties of Six Masonry Wall Constructions 15ji BMS6 Survey of Roofing Materials in the Southeastern States 15ji BMS7 Water Permeability of Masonry Walls (*) BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10^ BMS9 Structural Properties of the Insulated Steel Construction Co.'s "Frameless-Steel" Constructions for V/alls, Partitions, Floors, and Roofs 10^. BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 10j5 BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 10j5 BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc 15(i BMS13 Properties of Some Fiber Building Boards of Current Manufacture 10^ BMS14 Indentation and Recovery of Low-Cost Floor Coverings 10j5 BMS15 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored by

the Wheeling Corrugating Co lOf^ BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 10(i BMS17 Sound Insulation of Wall and Floor Constructions 20^ Supplement to BMS 17, Sound Insulation of Wall and Floor Constructions 5|S BMS18 Structural Properties of "Pre-fab" Constructions for Walls, Partitions, and Floors Sponsored by the Harnischfeger Corporation 10{S

BMS19 Preparation and Revision of Building Codes 15^ BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors, Sponsored

by Connecticut Pre-Cast Buildings Corporation lOji BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association lOji BMS22 Structural Properties of " Dun-Ti-Stone" Wall Construction Sponsored by the W. E. Dunn Manufacturing Co lOjl BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc 10^ BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute 10^ BMS25 Structural Properties of Conventional Wood-Frame Constructions for Walls, Partitions,

Floors, and Roofs 15fS BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc lOji BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by the Bender Body Co 10^ BMS28 Backflow Prevention in Over-Rim Water Supplies 10^ BMS29 Survey of Roofing Materials in the Northeastern States 100 BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association 10j5 BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions Sponsored by The Insulite Co 16j5

[List continued on cover page in]

' Out of print.
UNITED STATES DEPARTMENT OF COMMERCE . Henry A. Wallace, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS*

and STRUCTURES

REPORT BMS103

Measurements of Heat Losses From Slab Floors

by

RICHARD S. DILL, WILLIAM C. ROBINSON

and HENRY E. ROBINSON

ISSUED MARCH 10, 1945

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I945

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, U. S. GOVERNMENT PRINTING OFFICE

WASHINGTON 2S, D. C. • PRICE 10 CENTS
F or ewor

Heat losses from slab floors is at all times of interest in connection

with low-cost housing, since it is essential that floors be satisfactory as well as inexpensive. In wartime, however, the subject is of more

importance than usual on account of the necessity for saving fuel,

and because only a minimum of critical materials is procurable for use in floor construction.

This paper presents the results of Bureau tests of eight floors. It gives quantitative information that may be used for estimating

heat losses through floors and by means of which typical floors can

be conipared on the basis of heat-transfer properties.

Lyman J. Briggs, Director.
Measurements of Heat Losses from Slab Floors

by RICHAED S. DILL, WILLIAM C. EOBINSON, and HENRY E. ROBINSON

CONTENTS

Page Foreword n

I. Introduction 1 II. Test equipment 2

III. Procedure and observations 7

1. Slab floors laid on the ground 8

ABSTRACT

Four concrete floors laid on the ground and three concrete and one wood floor laid over crawl spaces were

tested for heat-transfer properties in a special structure provided for the purpose.

It was found that the heat loss of the floors laid on

the ground was decreased by insulating the edges; that

the heat loss through the center of such floors is rela- tively small when the enclosing structure is continuously heated; that the edge loss for a wood floor laid over a crawl space is small ; and that the edge loss for an

insulated concrete floor laid over a crawl space was

considerable. Observed ground temperatures at various depths,

down to 13 ft below the surface, are reported in the paper and some factors are suggested for estimating

floor heat losses.

I. INTRODUCTION

Design of low-cost houses involves a compromise between the cost and the performance

of building elements. Therefore, information on the heat-transfer properties of floors should

be helpful to designers, especially in the lowcost housing field. Insofar as heat transfer is concerned, the desirable characteristics of a

floor are (1) low heat loss, considered as an

economic factor in heating the house, and (2)

warmth or a feeling of warmth to the touch, as

it affects comfort.

The two characteristics are related, inasmuch

as a floor with a high heat loss is normally ex- pected to be colder on the surface than a floor with a low heat loss. However, comfort does

not depend solely upon temperature; with the same surface temperature, materials of high

thermal conductivity and of high heat capacity

per unit volume feel colder to the touch than

others. For example, a concrete floor feels colder to the touch than a wood floor at the same temperature. Insulation in the form of

rugs on the floor tends to nullify this difference

Page

III. Procedure and observations—Continued.

2. Floors laid over crawl spaces 9

3. Temperature distribution 19

4. Condensation on the test floors 19

IV. Summary and conclusions 19

with floors at the same measured temperature.

Floors can be classified on the basis of ar- rangement as follows: Those laid over heated

basements or over other heated spaces, those

laid over unheated spaces, and those laid on

the ground.

In most houses having heating devices in

the basement, the heat loss through the floor

is practically negligible because the basement

is warmed by radiation and convection from

the heating device and from the pipes and

ducts. Very often the same condition is true

of floors laid over closed crawl spaces containing heating pipes and ducts. In many cases there is an actual gain of heat in the house from

the basement through the floor. This accidental effect probably accounts for the satis- factory performance of some heating systems

that would not otherwise provide uniform heat

in houses. In view of these facts, further consideration will not be given in this paper to

floors laid over heated spaces. The temperature at a given point or given

region of a floor ob\'iously depends upon the

rate at which heat is gained or lost at that point

or region. If the walls are poorly insulated,

the floors will be cold near the exposed walls

because a cold draft of air descends along the

surface of such waUs.

Floors gain and lose heat by radiation, convection, and conduction, and the radiant gain

is sometimes important. Floors laid over un- heated spaces have been observed to be several

degrees warmer than the air directly above or below them. The conclusion is that such

floors are warmed by radiation from the ceil- ing, the walls, and the contents of the room. From the observations herein described, it will be seen that the heat loss through a floor laid on the gromd or laid over a crawl space

is Hkely to be smaU compared to the total heat
2 Building Materials and Structures Reports

loss from the house. For this reason, the

temperature of the floor as it affects comfort

is, in most cases, as important as the heat loss considered as an economic factor. For determining the heat loss through several

types of floors, the general plan adopted for

the floor tests was to provide a heavily insulated structure above a specimen of each kind of

floor and to observe the amount of heat,, supplied in the form of electric energy, necessary

to maintain a temperature of 70° F within the

structure during cold v/eather. Although the

walls and ceiling of the structure were heavily

insulated, some heat loss through them was

inevitable. In order to correct the data for

this condition, tests were made during which

the floors themselves were so insulated that the

heat loss through the structure could be

measured.

Objectives of the project were to furnish

comparative data on floors of different types,

and, as far as practicable, to furnish data

whereby the performance of proposed floors could be predicted.

II. TEST EQUIPMENT

For the purpose of obtaining floor test data,

the structure shown in figure 1 was erected at the National Bureau of Standards. It provided a number of similar enclosures or compartments in which floors of different types

could be simultaneously tested under similar

conditions.

The structure was about 58 ft long and 12 ft wide and was divided lengthwise into 10 compartments ; the two end compartments, without

test floors, were used only as shields for the

other compartments in which eight different

types of test floors were installed. The structure, located with its long dimension east and

west, was built of wood, and its walls and ceiling- were insulated with 3% in. of rock wool to minimize heat exchanges everywhere except

through the floors imder test. There were no windows in the structure and only one door in one of the end compartments. For access to the compartments, manholes about 4 ft square were provided through the walls. The manholes were closed during tests and the closures

insulated.

Each test compartment was built to accom- modate a floor about 6- by 12-ft, with the 6-ft edges on the exposed sides of the structure. This arrangement provided about the same

ratio of exposed edge to floor area as exists in a

one-story house 25 ft sq.

As a' precaution,* an air space was provided

between adjacent concrete floors to minimize

the exchange of heat between them. This was

accomplished by means of the arrangements

shown in figiu'e 2. The concrete of two adjacent floors was held apart during construction

by a wood dam composed of two walls or faces

of 1-in. plank, separated by wood battens.

The dam between adjacent slab floors laid on

the ground extended down about 2 ft into the

ground, as shown in figure 2, A. The dam

between adjacent slab floors laid over crawl

spaces extended to the cap sill, as shown in

figure 2, B. The dams remained in place during the tests. The arrangement of wood floor 5

is shown in figure 2, C. The temperature difference between floors was slight during tests, and this fact and the

above precaution were considered sufficient ground for ignoring heat exchanges between

floors. The compartments were heated electrically,

and the amount of energy required to heat each

compartment was measured by means of a watthour meter. The heaters consisted of cast- iron radiators with immersion electric resistors

of the hairpin type screwed into their bottom

connections. The radiators used were of the

conventional free-standing, tubular type, consisting of eleven 26-in. 3-tube sections making an

over-all length of 29)^ in. Each radiator contained sufficient water to cover the heating

element. The heaters were controlled automatically by thermostats located in their

respective compartments. In each compartment, the thermostat was located in the middle

of the east wall, 30 in. above the floor.. The

thermostats were of the type commonly used for domestic heating devices, with bimetallic sensitive elements and metal contacts. Each

thermostat controlled its respective heater

through a relay with a mercoid contact. Alternating current of 110 volts was used for both the controlling and the heating circuits. During some of the tests, the radiators used

to heat the compartments were enclosed in

plywood jackets, with reflective inside surfaces, so that they functioned substantially as topoutlet convectors. This had no measurable

effect on the heat loss from any of the compartments nor on the floor-surface temperatures ex- cept near the radiators. The results of the

tests with the jackets on the radiators were

therefore averaged with the results of the other

tests and not treated separately.

A form of the NichoUs heat-flow meter was

used for observation of heat losses through the
Heat Losses from Slab Floors 3

SOUTH ELEVATION

U

—©-

'

1 1

1 1 r{ p(D-[-(D- -®—

1 1

'

3-4" , 8@6'-0" e'-8" 58-0"

N

I - O

FLOOf? AND FOUNDATION PLAN

4 ConcreteTor Papers

/ "Fiber Board

4 Concrete- y/ Tor Paper-.

jf 5 Gravel —8"Cone Block

FLOOR Z

5" Gravel-

"^Cinders

FLOOR 3

liaaaDllaaan'inpaDI

4 ConcreteTar Pod er~^

\4 Clay Tile- ^^B 5 Gravel FLOOR 4

^Double Wood Flooring

W I i i ^ ^2"" 6" Joists FLOOR 5

-•4 Concrete mmI ' I NalHng Strips- ^^fM 8" Cone Block J

FLOOR 6

4 ConcreteI Fiber Board-^

FLOOR 8
4 Building Materials and Structures Reports

hin Plank—

|

I

"8 Gypsum Board —Loose Fill Insulation

r

Concrete

Ah

I

I ^Gravel

^ -Air Space

A-SLAB FLOOR ON GROUND

mm

'8 Gypsum Board —Loose Fill

' Insulation

Concrete

Air Space

'I-in Insulating

Board

S-in Cinder

Cone Block

B-SLAB FLOOR OVER CRAWL SPACE

mmm

-Double Wood Flooring

XT-2x6 Joists

-2x10 Sill

C-WOOD FLOOR

Figure 2

structure above the test floors. This heat-flow

meter consisted of a panel of 1-in. insulating

board, approximately 6 by 8 ft, with thermocouples on both surfaces. The surfaces of the

panel were divided into areas approximately

2 ft sq, and a thermocouple was located at the

center of each square. The thermocouples were

so connected that the electromotive force

between those on the two sides indicated the

temperature difference between the two sides

and hence the heat flow through the panel. One

of these heat-flow panels was installed on furring
Reat Losses from Slab Floors

I

70

60

50

40

50

Note; Figures O.5. 1.0. 4.0,8.0 and 13.0 Denote Dep fh Below Ground Surface in Fe e f. J I \ I I

I I JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY

Figure 3

strips on each of the two exposed sides of the

eight inside compartments in the structure. The method of using the panels is described

in section III. Temperatures in the compartments, on the

floors, and under the floors, were measured with

a copper-constantan thermocouple system and

a suitable potentiometer.

The temperatures underground at various

levels beneath the surface, down to 13 ft, were

also measured by means of a thermocouple

system. For this purpose, a hole of the desired

depth was made in the ground about 50 ft from

the test structure by means of a mechanical

post-hole digger. The thermocouples and their

wires, enclosed in a rubber tube, were lowered

into the hole and the earth was replaced around

them. Thermojunctions were thus provided at about 1-ft intervals down to 13 ft below the

surface as noted on the figures. The tube fitted the wires snugly, protecting the wires and the

thermocouples from dampness. Because the

tube waU was thin, and the temperatm-e changes

slow, it was considered imlikely that the rubber

would cause significant error in the temperature

measurements. The results of the observations

made on earth temperatures are shown in

figures 3 and 4. Four of the floors tested were constructed

of concrete, slab type, laid on the ground,

arranged and insulated in various ways.

The other four floors were laid over crawl

spaces—of these, one was wood, conventional in

construction; the rest were concrete. The

details of construction for these floors are shown

in figure 1 . Nailing strips were provided on the

under side of the concrete laid over crawl spaces,

for floors 6, 7, and 8, as shown on the drawing.

The strips, placed on the forms before pouring

the concrete, were attached by nails that had

been previously driven through them and bent,

and which remained in the concrete. Only the

strips under floor 8 were put to use. They

supported the insulating material.

The floor-test structure had a pitched roof over one part, as shown in figure 1, and a flat roof over the other. It was thus designed to determine the heat loss through ventilated

pitched and flat roofs. However, inasmuch as the subject of heat loss through roofs is not

a part of this report, and as the roofs and

ceilings were not changed during the floor tests,

it is presumed that the tare observations will

compensate for any difference between roofs

and ceilings as well as for any other differences

in construction of the compartments.

The ceilings of the test structure consisted

of gypsum board supported by 2- by 6-in. joists

rimning crosswise of the buHding. The ceilings,

like the side waUs, were insulated with 3% sn, of rock wool.
6 Building Materials and Structures Reports

2 4 6 d 10 12 14 16 18 20 22 24 26 28 30

DAYS OF MONTH

Figure 4
Heat Losses from Slab Floors 7

III. PROCEDURE AND OBSERVATIONS

For any compartment at a steady state of

operation the total heat supplied escaped in

two ways, partly through the floor and partly

through the walls and roof of the structiu-e. Therefore the structure heat loss plus the floor heat loss equaled the heat supplied, or, what is more convenient for present purposes since it was desired to determine floor heat loss, the

floor heat loss equaled the heat supplied minus

the structure heat loss. The amount of heat supplied was determined

from the watthour-meter readings, and special

tests were conducted to determine the structure heat loss. The structure heat loss was termed the tare; to determine the tare, the floor in each compartment was covered with 8 in. of sawdust

insulation and the compartment maintained at approximately 70° F during 3 days. The

power input, observed by means of watthour

meters, was equal to the total heat loss. Some

heat escaped through the floor despite the in- sulation on it, and, to correct for this, the heat

loss through the sawdust was estimated by means of the measured temperature difference

thi'ough it from air above the sawdust to the

floor surface below the sawdust in conjunction

with conductivity and conductance factors from

the ASHVE "Guide." The observed tare then

equaled heat input minus the computed heat

loss through the floor insulation. • The observed

tare was then corrected for the efi^ect of that

portion of the side walls covered with sawdust

during the tare determinations, but which was

not covered during the floor tests. These operations yielded two factors of

importance in connection with each compartment: One was the tare, or structure heat loss, for a specific indoor temperature and a specific

outdoor weather condition; the other was the

electromotive force (emf) developed by the

thermocouples on the heat-flow panels for the

existing heat loss. The problem then was to compute the tare, corresponding to another

weather condition, from available data. For

this purpose, it was assumed that the tare was

proportional to the temperatm-e difference

through the heat-flow panels, and that this

temperature difference was proportional to the

emf developed between the thermocouples on

the two sides of a panel.

From this,

To Eo

or

- rp jp Tq

J

— "-Ji] 630063°—15 2

when

Ta=tare existing during floor test, watts,

To = tare observed dming preliminary

test, increased by 4 percent to correct for the efl'ect of sawdust

insulation against a portion of

the side walls during the tare determinations, watts,

£'a=emf developed by heat-flow panel,

thermocouples, during floor test, microvolts,

^o=emf observed during tare determinations, microvolts.

Of these factors, Tq and Eq were known for each

compartment by means of the preliminary

tests described above. The value of E^ for

any compartment was close to the average

for all the compartments, so the average E^ was

used in computing a factor, K, as follows:

Since the average emf developed by the

heat-flow panels was 1,598 microvolts dm-ing

the tare-determination tests, the value of K

for each compartment was computed by the

formula

1598

The tare for each compartment was computed during the floor tests by the formula

T,=KEa.

The data and derived tare factors for each

com.partment are given in table 1.

Table 1.—Tare ' determinations

Loss Energy through

Floor input Average floor Observed Factor number during power insulation tare 2 108 hr input and

partitions

whr w w w WlllV

1 15,088 139.7 14.9 124.8 0. 0811

2 16, 826 155.8 14.7 141.

.0917

3 14, 051 1.30. 1 9.5 120.6 .0784

4 20, 239 187.4 23.4 164.0 .1066

5 16. 805 1516 23.3 132. 3 .0860

6 16, 362 151.5 25. 1 126.4 .0822

7 15, 757 145.9 26.2 119.7 .0778

8 11,524 106.7 13.9 92.8 .0603

1 Tare is defined as the heat loss from a compartment except that through the floor. It was determined for each compartment by insulating the floor with 8 in. of sawdust.

2 Ohserred tare is power input minus calculated heat loss through the

insulated floor and partitions between compartments.

3 K\s tare in watts per microvolt of over-all average emf between ther- mocouples on the two sides of the heat-flow panels. K is corrected for that portion of the walls covered by sawdust during the tare observations but not covered during the floor tests.

« Over-all average of panel emf during tare observations was 1,598 mv.
8 Building Materials and Structures Reports

Table 2.Floor heat loss

Floor numberEnergy

input

Average power

input

Tare' Net Net

After completion of the observations of tare, an edge imbedded in such a wall, or an edge on

the sawdust was removed and the tests of the the outside of such a wall in contact with the

floors commenced. The compartments were ground, as in the case of a wall resting on the

maintained at approximately 70° F at the floor near the edge,

thermostat location continuously from Novem- The heat loss of a floor laid on the ground is ber 1 to May 23. Observations of several not proportional to the temperature difference

days' duration were made a number of times. between the air inside and the air outside of the

Inclusion in this report of results obtained dur- house at any given instant. The floor heat

ing all the observation periods was considered loss appears to be dependent upon the temperaunnecessary, but those obtained diiring the ture of the ground at some region beneath the

first observation period are shown in table 2 surface, and this, in turn, depends upon the

to illustrate the type of data gathered. average temperature of the air above the ground

and the amount of heat received by the ground

from the sun and the amount of heat lost from

[Observation period No. 1, from 8:00 a. m. January' 27 to 8:00 a. m. it by radiation or otherwise during some

January 31] period prior to the observation.

For each of the floors, 1, 2, 3, and 4, the

Floor eat oss observed heat loss was divided by the length

Pgj. of the exposed- edge, as defined above, and the

foot of result entered in the tables as "heat loss per foot

%dge^** of exposed edge." From this, the following

three heat-loss factors were derived:

Btu/hr 1. The heat loss in Btu per hom* per linear

It 25 foot of exposed edge was divided by the number

nil of degree-days estimated to have occurred

during the month preceding the observation, to yield factor .

- 2. The heat loss in Btu per hour per linear

foot of exposed edge was divided by the average

> Tare is defined as the heat loss from a compartment except that , . j j* i. through the floor. It was determined for each compartment by insu- temperature dinerence Observed durmg each

lating the floor with 8 in. of sawdust. observation period between the air inside the

1. Slab Floors Laid on the Ground ^^^.^^^J^^ T^^Y ''''^f^^' ^"/'^^"^ ^^''^?^

3. ihe heat loss m Btu per hour per linear

Results of the tests indicated that heat loss foot of exposed edge was divided by the average

through a slab floor laid on the ground, when difference observed during each observation

the floor and the ground outside the house are period between the temperature of the air inside at substantially the same elevation, is more the structure and the temperature of the ground

nearly proportional to the length of the "ex- 1 ft below the surface, at a distance of 35 ft from

posed edge" of the floor than to the area of the the structure, to yield factor F3.

floor. "Exposed edge" here means an edge of Derivation of these factors is shown in tables

the floor next to an exposed wall of the house, 3, 4, and 5.

12

34

5

6

7,8

whr

25, 190

25, 344

20, 966

28, 944

27, 466

36, 144

33, 187

262.4

264.0

218.4

301.5

286.1 376.5

345.7

281.1

Factor K

(from

table

1)

wlia

0. 0811 .0917

.0784

. 1006 .0860

.0822

.0778

.0603

142.5 161.2

137.8

187.4 151.2

144.5 136.8 106.0

119.9

102.8 80.6

114.

134.9 232.0 208.9

175.1

Btu/hr

409

351. 275 389

460 792

713 598

Table 3.Determination of the factor Fi

[^1 = Floor heat loss in Btu per hour per linear foot of exposed edge and for 1 degree-day occurring during month preceding observation]

Slab floors laid on the ground

Degree-days during month before test Number..

No. 1: Hourly heat loss Btu per ft of exposed edge.. -Fi=heat loss Btu per hr, per ft. and per degree-day .. No. 2: - Hourly heat loss Btu per ft of exposed edge..

ii'i=heat loss ..Bin per hr, per ft, and per degree-day.. No. 3: Hourly heat loss ._ Btu per ft of exposed edge.. i^i=heat loss Btu per hr, per ft, and per degree-day.. No. 4: Hourly heat loss __ Btu per ft of exposed edge.. Ji'i=heat loss Btu per hr, per ft, and per degree-day..

Observation period

34.0

0.035

29.3

0. 030

22.9

0. 023

32.4

0. 033

947

32.9 0.035

28.2

0.030

21.7

0. 023

.31.3

0. 033

917

34.5

0. 038

30.1 0.033

21.8

0. 024

.30.3 0.033

906

30.3

0.033

26.3 0.029

21.0

0. 023

26.7 0.029

882

31.2

0.035

25.3 0.029

19.8

0. 022

29.8 0.034

Mean

0.036

.030

.023

.'632"

Maxi- mum

deviation

Percent

8.5

10.0

9.3
Heat Losses from Slab Floors 9

Table 4.—Determination of the factor F2

[Ji'2=Floor heat loss in Btu per hour per linear foot of exposed edge and for 1 degree Fahrenheit difference in average air temperature between the inside and outside of structure occurring during observation period]

Slab floors laid on the ground

Observation period Mean Maxi- mum

deviation

No. 1: Hourly heat loss Btu per ft of exposed edge.. Temperature difference, inside to outside- __ .avg deg F.. f2=heat loss Btu per hr, per ft, and per deg F.. No. 2: Hourly heat loss - Btu per ft of exposed edge.. Temperature difference, inside to outside avg deg F..

i?'2=heat loss - ...Btu per hr, per ft, and per deg F.. No. 3: Hourly heat loss Btu per ft of exposed edge.. Temperature difference, inside to outside avg deg F.. J'2=heat loss _ Btu per hr, per ft, and per deg F.. No. 4: Hourly heat loss Btu per ft of exposed edge.. Temperature difference, inside to outside ,. avg deg F..

ii'2=heat loss Btu per hr, per ft, and per deg F..

34.0

39.

0.87

29.3 38.9

0. 75

22.9 38.3

0.60

32.4

39.4

0. 82

32.9

40.9 0.80

28.2 41.0

0.69

21.7 39.5

0. 55

31.3 41.4

0. 76

34. 5 42.7

0. 81

30. 1 43.0

0. 70

21.8

42. 1 0. 52

30.3 43.2

0.70

30.3 39.2

0. 77

26.3

39,

0.67

21.0 38.6

0.54

26.7 38.2

0. 70

31.2

38.9 0.80

25.3 39.0

0. 65

19.8

38.

0. 52

29.8

39. 5

0. 75

0. 81

.55

.75

Percent

9.0

9.3

Table 5.

Determination of the factor F3

[f'3=Floor heat loss in Btu per hour per linear foot of exposed edge and for 1 degree Fahrenheit difference in temperature between the air above the floor and the ground 1 ft below the surface and 35 ft from the structure]

Slab floors laid on the ground

Observation period Mean

^3 Maxi- mum

deviation

No. 1: Hourly heat loss _ Btu per ft of exposed edge.. Temperature difference, inside to ground deg F..

ii'3=heat loss Btu per hr, per ft, and per deg F.. No. 2: Hourly heat loss _ Btu per ft of exposed edge.. Temperature difference, inside to ground deg F.. f3=heat loss _ Btu per hr, per ft, and per deg F.. No. 3: Hourly heat loss _ Btu per ft of exposed edge.^ Temperature difference, inside to ground _ deg F..

i<'3=heat loss.. Btu per hr, per ft. and per deg F.. No. 4: Hourly heat loss ..Btu per ft of exposed edge. _ Temperature difference, inside to ground _ ..deg F..

ii'3=heat loss Btu per hr, per ft, and per deg F..

34.0

30.6

1.11

29.3

30. 5

0. 96

22.9

29.9

0. 77

32.4

31.1

1.04

32.9

32.6 L 01

28.2

32.7

0. 86

21.7

31.3

0. 69

31.3

3.3.3 0.94

34.5

32.8

1.05

30.

33.0

0. 91

21.8

32. 5 0.67

30.3 33.8

0.90

30.3 31.9

0. 95

26.3 31.9

0. 82

21.0 31.6

0. 66

26.7 32.5 0.82

31.2

33.2

0.94

25.3

33.3

0. 76

19.8 32.4

0. 61

29.8 33.9 0.88

Percent

1. 01 9.9

0. 86 a. 6

13.2

.92 13.0

Heat losses estimated by means of may

differ from those estimated by means of F^ for two reasons: First, that the number of degreedays occm-ring during the month preceding each

observation period was estimated from data in

the ASHVE "Guide" by weighting the degreedays given for Washington, D. C, with respect

to the time of the month when each observation

period occurred. The degree-day data on which

Fi are based do not coincide, therefore, with

what would be obtained if the temperature data

obtained at the site were used in determining

the degree-days. Second, that the commonly,

accepted degree-day system is based on an

outside temperature of 65° F, whereas F2 is based on an inside temperature of 70° F for

the structure.

2. Floors Laid Over Crawl Spaces

The results of the test of the floors laid over

crawl spaces are given in table 6.
10

I Building Materials and Strmtures Reports

Table 6.

Determination of the factor U for floors laid over crawl spaces

[17= Heat loss in Btu per hour for each square foot and for 1 degree Fahrenheit difference in temperature between the air 30 in. above the floor and the

air in the crawl space 15 in. below the floor]

Floors laid over crawl spaces

Observation period Mean U

Maxi- mum

deviation

Crawl space ventilated. No. 5: Hourly heat loss _ Btu per Temperature difierence, inside air to crawl space-.. (leg F.. U'=heat loss Btu per hr, per sq ft, and per deg F.. No. 6; Hourly heat loss Btu per sgft-- Temperature difference, inside air to crawl space deg F.. U"=heat loss _ Btu per hr, per sg ft, and per deg F-. No. 7: Hourly heat loss. Btu per sg ft.. Temperature difference, inside air to crawl space deg F.. U'=heat loss Btu per hr, per sgft, and per deg F.. No. 8: Hourly heat loss. Btu per sgft.. Temperature difference, inside air to crawl space.. deg F.. I7=heat loss. _ Btu per hr, per sq ft, and per deg F..

Yes

7. 46 30.4

.25

12. 84

29.8

.44

'11.56 "29.0 K 40

9. 69

32. 5 .30

No

4. 95 21.4

.23

8.04

17.6 0.47

'7. 54

' 17.5

«.43

7.19

23.2

.31

No

5.02 20.2

.25

8. 00

16.3

.49 »7.12

"17.1

".42

6. 69

21.6

.31

No

4.65

19.1 .24

7.06

15.9

.44

be. 06

b 17.0 b.36

6. 35 20.3

.31

Yes

7. 61 32.6

.23

13. 07 30.0 .44

t>10. 26

'•32.0 .32

8. 99

33.7

.27

Percent

0. 24

.46

" .42

b.34

.30

6.5

"4.7 '5.8

10.0

» Bare floor.

^ Carpeted floor. Each of the crawl spaces was provided with

ports for ventilation with areas of 1 sq ft for each

15 lin ft of wall in accordance with Federal

Housing Administration recommendations.^ As

indicated in table 6, some tests were made with

the ports open, others with the ports closed, to show the effect of ventilation.

When the ports are open and there is wind,

it is a safe presumption that the air in the crawl

space approaches the outdoor air in temperature. For estimating heat losses through floors laid over ventilated crawl spaces, it is therefore

recommended that the same temperature be

assumed for the crawl space as for the outside.

With no ventilation, the crawl-space temperature will be somewhere between the inside

and the outside temperature and will be lower

for an insulated floor and for a greater ratio

of exposed foundation wall to floor. The U factor for the floors laid over the crawl

spaces was computed from data contained in

the "Guide," and the computed and observed

values are given in table 7 for comparison.

The computed U values are based on the

difference in temperature of the air near the

upper and lower surfaces of the floors, whereas

the observed U values are based on the temperature difference of the air 30 in. above the

floors and 15 in. below. Since the air temperature differences are larger in the first case, the agreement between observed and computed

U values is better than that indicated in table

7, at least for floors 5, 6, and 7. The consider1 FHA Minimum Requirements for Rental Housing Projects, submitted under title VI, section 608, National Housing Act, May 26, 1942, and FHA Minimum Requirements for New Dwellings (issued separately for each State).

able excess of the observed over the computed

value of U for floor 8 is probably due to edge

loss, since this floor was insulated underneath,

which should result in a large ratio of edge loss to total loss.

Table 7.

Comparison of observed and computed values

of U for floors laid over crawl spaces

[ U =Btu per hour for each square foot and for 1 degree Fahrenheit difference

in temperature between air over the floor and air in the crawl spaces] U value

Floor number Difference Observed" Computed'' Numerical Percentage

5 0.24 0. 27 -0. 03 -13

6 .46 .50 -. 04 -9

7..._ .34 .38 -.04 -12

8.._ .30 .17 13 +43

" Observed conductance indicated by results of tests.

I" Conductance indicated by computations based on handbook data. A mathematical expression for the heat Joss from concrete floors laid over crawl spaces

shoifld, if precision is necessary, take into ac- count both the loss to the crawl space and the

loss through the edge. The crawl-space temperature depends upon the outdoor and indoor

temperature, upon the ratio of side-wall areas

to floor areas and upon the conductances of

the side walls. The loss through the edge depends upon a number of factors also. The

complexity of computing precise estimates of

heat losses through floors laid over crawl spaces

makes it doubtful that builders will consider

attempts to make them worthwhile.
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Heat Losses from Slah Floors 19

It is believed that the observed factors

shown in table 6 will be found suitable for estimating heat losses in small houses thi'ough

floors of the types tested because the test structure was purposely designed to have about

the same ratio of exposed wall area to floor area as would exist in a one-story house 25 ft sq.

3. Tempehature Distribution

The average temperature distribution observed on the surfaces of the floors are shown

in figures 5 to- 12, inclusive. The average for

all observations and the average differences in

temperature between the floors at the center of

the room and the air 30 in. above the center

are given in table 8,

Table 8.

Temperature distribution, on floors

[Test conditions: Air temperature at center of room 30 in. above the

floor 70° F; ground temperature at 1-ft level 38.2° F]

Floors

Observations

Floor surface, distance from wall

Difference in temperature between

12 in. 30 in. 66 in. Air andfloor surface

Floor

surface

at 66 in. and at 12

in. from

side wall

SLAB FLOORS LAID ON THE GROUND

No. 1 No. 2_._ - _.. No. 3 -

No. 4

°F

60.1 60.4

62.0

60.0

°F

63.1 63.5

63.9 64.0

"F

65.2

65.7

65.7 65.8

"F

4.8

4.3 4.3 4.2

°F

6.1 5.3

3.7

6.8 FLOORS LAID OVER CRAWL SPACES

No. 5Open

Closed No. 6: Open

Closed - No. 7: OP-{earpet-ed--

Clo=e<i{^rpeted'"'" No. 8: Open..

Closed ..

60.9 62.6

55.0

60.1

59.3 52.7

59.6

58.8

59.7

62.1

61.0

62.9

56.8

61.7

61.0 53.2 61.3

59.6

63.5

65.3

62.4 64.5

67.4

62.4

61.8

63.2 62.0

60.6

64.2

66.

7.6

5.5

12.6 7.6

8.2

16.8 8.0

9.4

5.8

3.9

1. 5 1.9

2.4 2.3

2.5 0.5

2.4

1.8

4.5

4.0

The data show that the temperature gradients across the floors were smaller and, therefore, in general, conditions were better in this respect for floors laid over crawl spaces than for those laid on the ground. On the other hand,

the difference in temperature between the floor and the air above it was less and, therefore, in

general, conditions were better in this respect

for the floors laid on the ground than for those

laid over crawl spaces. Of the bare floors, wood floor 5 had the least

lateral temperature gradient. Of the floors laid over crawl spaces, insulated concrete

floor 8 and wood floor 5 had temperatures

closer to that of the air above them than the

other floors. The thermocouples on floor 7 were under the

rug, so that the readings made with the rug in

place are useful in indicating the horizontal

temperature gradient, but the dift'erence shown

between floor-surface temperature and air temperature 30 in. above the floor is not comparable

with the others recorded because in all other

cases the floors were bare.

4. Condensation on the Test Floors

It is known that condensation on concrete

floors or on surfaces adjacent to them can be a

source of difSculty, especially in summer. In

order to determine to what extent condensation

would occur on the concrete floors, the test structure was gently ventilated with outside

air under summer conditions. For one part of

the test period all floors were left bare; during

another part, some were covered with rugs. Although no condensation was visible, the rugs

gained in weight. This fact may indicate that

slightly worse atmospheric conditions would

have resulted in visible condensation and even- tuaUy would have caused the rugs to deteriorate.

Sufficient data to generalize are not available,

but it may be necessary to remove rugs or other

insulating bodies from concrete floors during

the summer in climates with a relative humidity

similar to that of Washington, D. C.

The amount of condensation will, of course, be increased by cooking or wasliing operations,

which liberate water vapor within a house.

IV. SUMMARY AND CONCLUSIONS

Information gathered during these tests indicates that, as far as warmth or heat loss is concerned, a concrete floor may as well be

placed on the ground as to be laid over an

unheated crawl space. This conclusion does

not apply to a floor laid over a closed crawl

space containing heating pipes or ducts. Such

a floor would undoubtedly be warmer in winter

and therefore more comfortable than a concrete floor laid on the ground or a concrete

floor laid over an unheated space. Insulation at the edge was found to lower the

heat loss from a floor. An arrangement such

as that shown for floor 3, or one similar in
20 Building Materials and /Structures Reports

principal, for insulating slab floors laid on the

ground is probably practicable in many cases. Installation of an insulating barrier at the

edge of a floor laid above a crawl space complicates the support problem, and the expense

may make its use inadvisable. A wood floor requires no special insulating treatment at the

edge.

The data indicate that insulation at the

edge of the floor is much more important for

floors laid on the ground, so far as warmth in

winter is concerned, than insulation mider the

center of the floor. Water may be prevented

from entering the floor structure from underneath by using crushed stone, cinders, or gravel,

in a depth of a few inches, and a layer of tar paper or other material impervious to water. Such a layer of insulating material between the

floor and the mass of earth beneath may also

permit the floor temperature to follow the

changes in temperature of the air above it more

closely. This would lessen the probability

of condensation on the floor surface in summer,

since, if the floor can be sufficiently warmed by

the air at the beginning of a period of warm

weather, condensation on the floor will not

occur because the temperature will be above

the dew point at aU times.

The tests described in this report were made

with special reference to small houses, but there

appears to be no reason why the conclusions

are not applicable to large structures as well. For estimating design heat losses from slab

floors on the ground, factors are suggested for use in three formulas, as foUows:

Qin which

-LF.DD

--LF2{Tu— Tos)

--LF,{Tu-T,),

(?=heat loss from floor, Btu per hour;

i=length of edge of floor adjacent to

" exposed waU of building, feet; Z)D= number of degree-days occurring in

month preceding instant for which

estimate is made;

Tjs=temperature maintained within

building, degrees Fahrenheit;

T<,s= average outside temperatm-e during

a week preceding instant for which estimate is made;

jPi=heat loss factor, Btu per hour for each foot of exposed edge and for each degree-day occurring during

the month preceding the instant

for which the estimate is made;

i''2=heat loss factor, Btu per hour for

each foot of exposed edge and

for each degree Fahrenheit

average difference in air temperatiu-e inside and outside the building during a week preceding the

instant for which the estimate is made;

jP3=heat loss factor, Btu per hour for each foot of exposed edge and for

each degree Fahrenheit difference

in temperature between the air above the floor and the ground

1 ft below the surface, at a dis- tance of 35 ft from the structure, at the instant for which the

estimate is made.

Of the three factors, Fi, F^, and Fz, it is believed that F^, would yield the best estimate

of floor heat loss. However, since groundtemperature data for many localities are not

available, the use of Fz may, in some instances,

be impracticable.

For general purposes, factor F2 is probably

the most adaptable because of the possibility

of estimating with reasonable accuracy the

average temperature during the coldest week

occmring in a locality. This factor will

probably yield more accurate results than Fx because so many houses are maintained at other temperatures than 65° F, on which

Fx is based.

Factors for the slab floors tested are given

in tables 3, 4, and 5. The data are probably

sufficiently accurate basis for many estimating

purposes because the floor heat loss is likely to be small compared to other losses. However, the data are incomplete in that they do

not cover the cases of frozen ground and of

snow-blanketed groimd. To supply data, it would be necessary to repeat the tests in a

colder climate.

No reason is apparent why the data are not

applicable for regions where the average out- door temperature does not remain continuously

below freezing for more than a day or so, ex- cept that snow, which is an insulator, may

decrease the floor heat loss. The data indicate that insulating the floor at the edge is beneficial both in saving heat

and in reducing lateral temperature gradients

across the floor. The data on floors laid over crawl spaces

indicate that the factors contained in handbooks are suitable for estimating heat losses
Real Losses from Slab Floors 21

through such floors, except in the case of a

floor which is heavily insulated on the underside. In this case, the edge loss increases

largely in comparison to the total loss through

the floor, and this may result in an underestimate unless it is taken into consideration. The

number of factors involved indicate that heat

losses through floors laid over crawl spaces

should be computed on the basis of an esti- mated crawl-space temperature. For a continuously ventilated crawl space, the temperature should be assumed to be the same as the

outdoor temperature.

The drawings and graphs for this report were prepared by E. J. Schell. Washington, November 9, 1944.

o

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. _ 10^ BMS33 Plastic Calking Materials.-. 10^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 10^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ 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 10^ BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ 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, Jnc 10^ 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 15f5 BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 10^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS45 Air Infiltration Through Windows 15^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions for Walls,

Floors, and Roofs Sponsored by The Globe-Wernicke Co 10j5 BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions,

and Floors Sponsored by American Houses, Inc 10^ BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co lOfi BMS49 Metallic Roofing for Low-Cost House Construction 10^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

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

Sponsored by the Munlock Engineering Co 10f5 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 10^ BMS56 A Survey of Humidities in Residences 10^ BMS57 Roofing in the United States—Results of a Questionnaire 10^ BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings : 10^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 15fi BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association 10(i BMS63 Moisture Condensation in Building Walls 10^ BMS64 Solar Heating of Various Surfaces 10^ BMS65 Methods of Estimating Loads in Plumbing Systems lOi

BMS66 Plumbing Manual 20(4 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 of Floor Coverings for Use in Low-Cost Housing: Part 3 15^ BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10^ BMS70 Asphalt-Prepared RoU Roofings and Shingles 156 BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20^

BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 10^ 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 15^5 BMS75 Survey of Roofing Materials in the North Central States 15^ BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 15^ BMS77 Properties and Performance of Fiber Tile Boards ' 10^ BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-WaU

Constructions 200 BMS79 Water-Distributing Systems for Buildings 15(J BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 isjs

[List continued on cover page iv]

font of print.
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS81 Field Inspectors* Check List for Building Construction (cloth cover, 5 x 7% inches) 20^ BMS82 Water Permeability of Walls Built of Masonry Units 20^ BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 10^ BMS84 Survey of Roofing Materials in the South Central States 16^ BMS85 Dimensional Changes of Floor Coverings with Changes in Relative Humidity and

Temperature 10^ BMS86 Structural, Heai^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 10^ BMS88 Recommended Building Code Requirements for New Dwelling Construction with Special

Reference to War Housing 20^ 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 Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15^5 BMS91 A Glossary of Housing Terms . 15^ BMS92 Fire-Resistance ClassMcations of Building Constructions 25^ B MS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure 10^ BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" WaUs 10^ BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry WaUs isjs BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 10^ B MS97 Experimental Dry-Wall Construction With Fiber Insulating Board 10^ BMS98 Physical Properties of TeiTazzo Aggregates 150 BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels"

for Walls, Floors, and Roofs 15^ BMSlOO Relative Slipperiness of Floor and Deck Surfaces 10^ BMS101 Strength and Resistance to Corrosion of Ties for Cavity Walls lOfi BMS102 Painting Steel ^ 100 BMS103 Measurements of Heat Losses From Slab Floors 100