S. DEPARTMENT COMMERCE..."^Cinders FLOOR3 liaaaDllaaan'inpaDI 4Concrete-TarPoder~^...

$: S. DEPARTMENT COMMERCE..."^Cinders FLOOR3 liaaaDllaaan'inpaDI 4Concrete-TarPoder~^ \4ClayTile-^^B5Gravel FLOOR4 W^DoubleWoodFlooring I i i ^ ^2""6"Joists FLOOR5-•4Concrete mm-I'NalHngStrips-^^fM8"ConeBlock$
IPNational 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" Con-

structions for V/alls, Partitions, Floors, and Roofs 10^.

BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Spon-sored by the H. H. Robertson Co 10j5

BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Construc-tions for Walls and Partitions 10j5

BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and RoofsSponsored 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 bythe 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 Spon-sored 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 theNational 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 BrickManufacturers Association of New York, Inc 10^

BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile Cavity-Wall 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 ConstructionSponsored by the Nelson Cement Stone Co., Inc lOji

BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by theBender Body Co 10^

BMS28 Backflow Prevention in Over-Rim Water Supplies 10^BMS29 Survey of Roofing Materials in the Northeastern States 100BMS30 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 Spon-sored by The Insulite Co 16 j5

[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 STRUCTURESREPORT 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 con-

struction. 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

d

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

CONTENTSPage

Foreword nI. 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 weretested 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 continu-

ously heated; that the edge loss for a wood floor laid

over a crawl space is small ; and that the edge loss for aninsulated concrete floor laid over a crawl space wasconsiderable.

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 com-promise between the cost and the performanceof building elements. Therefore, information

on the heat-transfer properties of floors should

be helpful to designers, especially in the low-

cost housing field. Insofar as heat transfer is

concerned, the desirable characteristics of afloor are (1) low heat loss, considered as aneconomic 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 doesnot depend solely upon temperature; with the

same surface temperature, materials of highthermal conductivity and of high heat capacityper unit volume feel colder to the touch thanothers. For example, a concrete floor feels

colder to the touch than a wood floor at thesame 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 heatedbasements or over other heated spaces, thoselaid over unheated spaces, and those laid onthe ground.

In most houses having heating devices in

the basement, the heat loss through the floor

is practically negligible because the basementis warmed by radiation and convection fromthe heating device and from the pipes andducts. Very often the same condition is trueof floors laid over closed crawl spaces contain-ing heating pipes and ducts. In many cases

there is an actual gain of heat in the house fromthe basement through the floor. This acci-

dental effect probably accounts for the satis-

factory performance of some heating systemsthat would not otherwise provide uniform heatin houses. In view of these facts, further con-sideration will not be given in this paper to

floors laid over heated spaces.

The temperature at a given point or givenregion of a floor ob\'iously depends upon therate at which heat is gained or lost at that pointor region. If the walls are poorly insulated,

the floors will be cold near the exposed walls

because a cold draft of air descends along thesurface of such waUs.

Floors gain and lose heat by radiation, con-vection, and conduction, and the radiant gainis 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 suchfloors 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 spaceis 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,, sup-

plied 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 wasinevitable. In order to correct the data for

this condition, tests were made during whichthe floors themselves were so insulated that the

heat loss through the structure could bemeasured.

Objectives of the project were to furnish

comparative data on floors of different types,

and, as far as practicable, to furnish datawhereby 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 pro-

vided a number of similar enclosures or com-partments in which floors of different typescould be simultaneously tested under similar

conditions.

The structure was about 58 ft long and 12 ft

wide and was divided lengthwise into 10 com-partments ; the two end compartments, withouttest floors, were used only as shields for the

other compartments in which eight different

types of test floors were installed. The struc-

ture, located with its long dimension east andwest, was built of wood, and its walls and ceiling-

were insulated with 3% in. of rock wool to

minimize heat exchanges everywhere exceptthrough the floors imder test. There were nowindows in the structure and only one door in

one of the end compartments. For access to

the compartments, manholes about 4 ft squarewere provided through the walls. The man-holes 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 sameratio of exposed edge to floor area as exists in aone-story house 25 ft sq.

As a' precaution,* an air space was providedbetween adjacent concrete floors to minimizethe exchange of heat between them. This wasaccomplished by means of the arrangementsshown in figiu'e 2. The concrete of two ad-jacent floors was held apart during constructionby a wood dam composed of two walls or facesof 1-in. plank, separated by wood battens.The dam between adjacent slab floors laid onthe ground extended down about 2 ft into theground, as shown in figure 2, A. The dambetween adjacent slab floors laid over crawlspaces extended to the cap sill, as shown infigure 2, B. The dams remained in place dur-ing the tests. The arrangement of wood floor 5is shown in figure 2, C.

The temperature difference between floors

was slight during tests, and this fact and theabove precaution were considered sufficient

ground for ignoring heat exchanges betweenfloors.

The compartments were heated electrically,

and the amount of energy required to heat eachcompartment was measured by means of awatthour meter. The heaters consisted of cast-

iron radiators with immersion electric resistors

of the hairpin type screwed into their bottomconnections. The radiators used were of theconventional free-standing, tubular type, con-sisting of eleven 26-in. 3-tube sections making anover-all length of 29)^ in. Each radiator con-tained sufficient water to cover the heatingelement. The heaters were controlled auto-matically by thermostats located in their

respective compartments. In each compart-ment, the thermostat was located in the middleof the east wall, 30 in. above the floor.. Thethermostats were of the type commonly used for

domestic heating devices, with bimetallic sen-

sitive elements and metal contacts. Eachthermostat controlled its respective heaterthrough 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 usedto heat the compartments were enclosed in

plywood jackets, with reflective inside surfaces,

so that they functioned substantially as top-

outlet convectors. This had no measurableeffect on the heat loss from any of the compart-ments nor on the floor-surface temperatures ex-

cept near the radiators. The results of the

tests with the jackets on the radiators weretherefore averaged with the results of the othertests and not treated separately.

A form of the NichoUs heat-flow meter wasused 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"

NI

- O

FLO Of? AND FOUNDATION PLAN

4 Concrete-

Tor Papers

/ "Fiber Board4 Concrete-

y/ Tor Paper-.

jf 5 Gravel

—8"Cone Block

FLOOR Z

5" Gravel-"^Cinders

FLOOR 3

liaaaDllaaan'inpaDI

4 Concrete-Tar Pod er~^

\4 Clay Tile-

^^B 5 Gravel

FLOOR 4

^Double Wood Flooring

W I i i^

^2"" 6" Joists

FLOOR 5

-•4 Concrete

mm-I ' I NalHng Strips-

^^fM 8"Cone Block

J

FLOOR 6

4 Concrete-

I Fiber Board-^

FLOOR 8


hin Plank—

|

I

"8 Gypsum Board—Loose Fill

Insulation

rConcrete

Ah

I

V

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 FLOORFigure 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 thermo-couples on both surfaces. The surfaces of the

panel were divided into areas approximately2 ft sq, and a thermocouple was located at the

center of each square. The thermocouples wereso 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. Oneof these heat-flow panels was installed on furring

Reat Losses from Slab Floors

I

70

60

50

40

50Note; 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

II

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

Figure 3

strips on each of the two exposed sides of theeight inside compartments in the structure.

The method of using the panels is describedin section III.

Temperatures in the compartments, on thefloors, and under the floors, were measured witha copper-constantan thermocouple system anda suitable potentiometer.The temperatures underground at various

levels beneath the surface, down to 13 ft, werealso measured by means of a thermocouplesystem. For this purpose, a hole of the desired

depth was made in the ground about 50 ft fromthe test structure by means of a mechanicalpost-hole digger. The thermocouples and their

wires, enclosed in a rubber tube, were loweredinto the hole and the earth was replaced aroundthem. Thermojunctions were thus provided at

about 1-ft intervals down to 13 ft below thesurface as noted on the figures. The tube fitted

the wires snugly, protecting the wires and thethermocouples from dampness. Because thetube waU was thin, and the temperatm-e changesslow, it was considered imlikely that the rubberwould cause significant error in the temperaturemeasurements. The results of the observationsmade on earth temperatures are shown in

figures 3 and 4.

Four of the floors tested were constructedof concrete, slab type, laid on the ground,arranged and insulated in various ways.

The other four floors were laid over crawlspaces—of these, one was wood, conventional in

construction; the rest were concrete. Thedetails of construction for these floors are shownin figure 1 . Nailing strips were provided on theunder 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 pouringthe concrete, were attached by nails that hadbeen previously driven through them and bent,

and which remained in the concrete. Only thestrips under floor 8 were put to use. Theysupported 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 nota part of this report, and as the roofs andceilings 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.


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

DAYS OF MONTHFigure 4


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 minusthe structure heat loss.

The amount of heat supplied was determinedfrom 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 com-partment was covered with 8 in. of sawdustinsulation and the compartment maintained at

approximately 70° F during 3 days. Thepower input, observed by means of watthourmeters, was equal to the total heat loss. Someheat escaped through the floor despite the in-

sulation on it, and, to correct for this, the heatloss through the sawdust was estimated bymeans of the measured temperature difference

thi'ough it from air above the sawdust to thefloor surface below the sawdust in conjunctionwith conductivity and conductance factors fromthe ASHVE "Guide." The observed tare thenequaled heat input minus the computed heatloss through the floor insulation. • The observedtare was then corrected for the efi^ect of thatportion of the side walls covered with sawdustduring the tare determinations, but which wasnot covered during the floor tests.

These operations yielded two factors of

importance in connection with each compart-ment: One was the tare, or structure heat loss,

for a specific indoor temperature and a specific

outdoor weather condition; the other was theelectromotive force (emf) developed by thethermocouples on the heat-flow panels for theexisting heat loss. The problem then was to

compute the tare, corresponding to anotherweather condition, from available data. Forthis purpose, it was assumed that the tare wasproportional to the temperatm-e difference

through the heat-flow panels, and that this

temperature difference was proportional to the

emf developed between the thermocouples onthe two sides of a panel.

From this,

To Eoor

- rp jpTq

J-

a

—"-Ji]

630063°—15 2

whenTa=tare existing during floor test, watts,

To= tare observed dming preliminarytest, increased by 4 percent to

correct for the efl'ect of sawdustinsulation 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 deter-

minations, microvolts.

Of these factors, Tq and Eq were known for eachcompartment by means of the preliminarytests described above. The value of E^ for

any compartment was close to the averagefor all the compartments, so the average E^ wasused in computing a factor, K, as follows:

Since the average emf developed by theheat-flow panels was 1,598 microvolts dm-ingthe tare-determination tests, the value of Kfor each compartment was computed by the

formula

1598

The tare for each compartment was com-puted 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

LossEnergy through

Floor input Average floor Observed Factor

number during power insulation tare 2

108 hr input andparti-tions

whr w w w WlllV

1 15,088 139.7 14.9 124.8 0. 0811

2 16, 826 155.8 14.7 141.

1

.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 insu-

lating 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 observa-

tions but not covered during the floor tests.

« Over-all average of panel emf during tare observations was 1,598 mv.


Table 2.

—

Floor heat loss

Floornumber

Energyinput

Aver-age

powerinput

Tare'

Net Net

After completion of the observations of tare, an edge imbedded in such a wall, or an edge onthe 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 themaintained 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 heating all the observation periods was considered loss appears to be dependent upon the tempera-unnecessary, 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 groundand the amount of heat received by the groundfrom 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 someJanuary 31] period prior to the observation.

For each of the floors, 1, 2, 3, and 4, theFloor 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 occurredduring 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 eachlating 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 averagethrough a slab floor laid on the ground, when difference observed during each observationthe 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 groundnearly proportional to the length of the "ex- 1 ft below the surface, at a distance of 35 ft fromposed 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.

1

23

456

7,

8

whr25, 19025, 34420, 96628, 94427, 46636, 144

33, 187

262.4264.0218.4301.5286.1376.5345.7281.1

FactorK

(fromtable

1)

wlia0. 0811.0917.0784. 1006.0860.0822.0778.0603

142.5161.2137.8187.4151.2144.5136.8106.0

119.9102.880.6

114.

1

134.9232.0208.9175.1

Btu/hr409351.

275389460792713598

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

34.00.035

29.30. 030

22.90. 023

32.40. 033

947

32.90.035

28.20.030

21.70. 023

.31.3

0. 033

917

34.50. 038

30.10.033

21.80. 024

.30.3

0.033

906

30.30.033

26.30.029

21.00. 023

26.70.029

882

31.20.035

25.30.029

19.80. 022

29.80.034

Mean

0.036

.030

.023

.'632"

Maxi-mum

deviation

Percent

8.5

10.0

9.3

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 insideand outside of structure occurring during observation period]


Observation periodMean Maxi-

mumdeviation

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:


Temperature difference, inside to outside avg deg F..J'2=heat loss _ Btu per hr, per ft, and per deg F..

No. 4:


Temperature difference, inside to outside ,. avg deg F..ii'2=heat loss Btu per hr, per ft, and per deg F..

34.039.

1

0.87

29.338.90. 75

22.938.30.60

32.439.40. 82

32.940.90.80

28.241.00.69

21.739.50. 55

31.341.40. 76

34. 5

42.70. 81

30. 1

43.00. 70

21.842. 1

0. 52

30.343.20.70

30.339.20. 77

26.339,

1

0.67

21.038.60.54

26.738.20. 70

31.238.90.80

25.339.00. 65

19.838.

1

0. 52

29.839. 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]


Observation periodMean^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..

34.030.61.11

29.330. 5

0. 96

22.929.90. 77

32.431.11.04

32.932.6L 01

28.232.70. 86

21.731.30. 69

31.33.3.3

0.94

34.532.81.05

30.

1

33.00. 91

21.832. 5

0.67

30.333.80.90

30.331.90. 95

26.331.90. 82

21.031.60. 66

26.732.50.82

31.233.20.94

25.333.30. 76

19.832.40. 61

29.833.90.88

Percent

1. 01 9.9

0. 86 a. 6

13.2

.92 13.0

Heat losses estimated by means of maydiffer from those estimated by means of F^ for

two reasons: First, that the number of degree-

days occm-ring during the month preceding eachobservation period was estimated from data in

the ASHVE "Guide" by weighting the degree-

days given for Washington, D. C, with respect

to the time of the month when each observationperiod occurred. The degree-day data on whichFi are based do not coincide, therefore, withwhat would be obtained if the temperature data

obtained at the site were used in determiningthe degree-days. Second, that the commonly,accepted degree-day system is based on anoutside 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 overcrawl 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 theair in the crawl space 15 in. below the floor]

Floors laid over crawl spaces

Observation periodMeanU

Maxi-mumdevia-tion

Crawl space ventilated.No. 5:

Hourly heat loss _ Btu perTemperature 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. 4630.4.25

12. 8429.8.44

'11.56"29.0K 40

9. 6932. 5

.30

No

4. 9521.4.23

8.0417.60.47

'7. 54' 17.5«.43

7.1923.2.31

No

5.0220.2.25

8. 0016.3.49

»7.12"17.1".42

6. 6921.6.31

No

4.6519.1

.24

7.0615.9.44

be. 06b 17.0b.36

6. 3520.3.31

Yes

7. 61

32.6.23

13. 0730.0.44

t>10. 26'•32.0

.32

8. 9933.7.27

Percent

0. 24

.46

" .42b.34

.30

6.5

"4.7'5.8

10.0

» Bare floor.

^ Carpeted floor.

Each of the crawl spaces was provided withports for ventilation with areas of 1 sq ft for each15 lin ft of wall in accordance with FederalHousing Administration recommendations.^ Asindicated in table 6, some tests were made withthe 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 tempera-ture. For estimating heat losses through floors

laid over ventilated crawl spaces, it is therefore

recommended that the same temperature beassumed for the crawl space as for the outside.

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

and the outside temperature and will be lowerfor an insulated floor and for a greater ratio

of exposed foundation wall to floor.

The U factor for the floors laid over the crawlspaces was computed from data contained in

the "Guide," and the computed and observedvalues are given in table 7 for comparison.The computed U values are based on the

difference in temperature of the air near theupper and lower surfaces of the floors, whereasthe observed U values are based on the tem-perature difference of the air 30 in. above thefloors and 15 in. below. Since the air temper-ature differences are larger in the first case,

the agreement between observed and computedU values is better than that indicated in table

7, at least for floors 5, 6, and 7. The consider-

1 FHA Minimum Requirements for Rental Housing Projects, submit-ted under title VI, section 608, National Housing Act, May 26, 1942, andFHA Minimum Requirements for New Dwellings (issued separately for

each State).

able excess of the observed over the computedvalue of U for floor 8 is probably due to edgeloss, 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=B tu per hour for each square foot and for 1 degree Fahrenheit differencein 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 -136 .46 .50 -. 04 -97..._ .34 .38 -.04 -128.._ .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 tem-perature depends upon the outdoor and indoortemperature, upon the ratio of side-wall areas

to floor areas and upon the conductances of

the side walls. The loss through the edge de-

pends upon a number of factors also. Thecomplexity 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 aboutthe 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 ob-

served on the surfaces of the floors are shownin 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 centerare given in table 8,

Table 8.

—

Temperature distribution, on floors

[Test conditions: Air temperature at center of room 30 in. above thefloor 70° F; ground temperature at 1-ft level 38.2° F]

Floors

Observations

Floor surface, distancefrom wall

—

Difference in

temperaturebetween

—

12 in. 30 in. 66 in.

Air andfloor

surface

Floorsurfaceat 66 in.

and at 12in. fromside wall

SLAB FLOORS LAID ON THE GROUND

No. 1

No. 2_._ - _..

No. 3 -No. 4

°F60.160.462.060.0

°F63.163.563.964.0

"F65.265.765.765.8

"F4.84.34.34.2

°F6.15.33.76.8

FLOORS LAID OVER CRAWL SPACES

No. 5

OpenClosed

No. 6:

OpenClosed -

No. 7:

OP-{earpet-ed--

Clo=e<i{^rpeted'"'"

No. 8:

Open..Closed ..

60.962.6

55.060.1

59.352.759.658.8

59.762.1

61.062.9

56.861.7

61.053.261.359.6

63.565.3

62.464.5

67.462.4

61.863.262.060.6

64.266.

1

7.65.5

12.67.6

8.216.88.09.4

5.83.9

1. 5

1.9

2.42.3

2.50.52.41.8

4.54.0

The data show that the temperature gra-dients across the floors were smaller and, there-fore, in general, conditions were better in this

respect for floors laid over crawl spaces than forthose 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 concretefloor 8 and wood floor 5 had temperaturescloser to that of the air above them than theother floors.

The thermocouples on floor 7 were under therug, so that the readings made with the rug in

place are useful in indicating the horizontaltemperature gradient, but the dift'erence shownbetween floor-surface temperature and air tem-perature 30 in. above the floor is not comparablewith the others recorded because in all othercases the floors were bare.

4. Condensation on the Test Floors

It is known that condensation on concretefloors or on surfaces adjacent to them can be asource of difSculty, especially in summer. Inorder to determine to what extent condensationwould occur on the concrete floors, the test

structure was gently ventilated with outsideair under summer conditions. For one part of

the test period all floors were left bare; duringanother part, some were covered with rugs.Although no condensation was visible, the rugsgained in weight. This fact may indicate thatslightly worse atmospheric conditions wouldhave 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 otherinsulating bodies from concrete floors duringthe summer in climates with a relative humiditysimilar 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 testsindicates that, as far as warmth or heat loss is

concerned, a concrete floor may as well beplaced on the ground as to be laid over anunheated crawl space. This conclusion doesnot apply to a floor laid over a closed crawlspace containing heating pipes or ducts. Sucha floor would undoubtedly be warmer in winterand therefore more comfortable than a con-crete floor laid on the ground or a concretefloor laid over an unheated space.

Insulation at the edge was found to lower theheat loss from a floor. An arrangement suchas 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 com-plicates 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 under-

neath 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 moreclosely. This would lessen the probability

of condensation on the floor surface in summer,since, if the floor can be sufficiently warmed bythe air at the beginning of a period of warmweather, condensation on the floor will notoccur because the temperature will be abovethe dew point at aU times.

The tests described in this report were madewith 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:

Q-

in 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 whichestimate is made;

Tjs=temperature maintained withinbuilding, degrees Fahrenheit;

T<,s= average outside temperatm-e duringa 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 duringthe month preceding the instantfor which the estimate is made;

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

each foot of exposed edge andfor each degree Fahrenheitaverage difference in air temper-atiu-e inside and outside the build-

ing during a week preceding theinstant 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 ground1 ft below the surface, at a dis-

tance of 35 ft from the structure,

at the instant for which theestimate is made.

Of the three factors, Fi, F^, and Fz, it is

believed that F^, would yield the best estimateof floor heat loss. However, since ground-temperature data for many localities are notavailable, the use of Fz may, in some instances,

be impracticable.

For general purposes, factor F2 is probablythe most adaptable because of the possibility

of estimating with reasonable accuracy theaverage temperature during the coldest weekoccmring in a locality. This factor will

probably yield more accurate results than Fxbecause so many houses are maintained at

other temperatures than 65° F, on whichFx is based.

Factors for the slab floors tested are given

in tables 3, 4, and 5. The data are probablysufficiently accurate basis for many estimating

purposes because the floor heat loss is likely

to be small compared to other losses. How-ever, the data are incomplete in that they donot cover the cases of frozen ground and of

snow-blanketed groimd. To supply data, it

would be necessary to repeat the tests in acolder climate.

No reason is apparent why the data are notapplicable for regions where the average out-

door temperature does not remain continuouslybelow freezing for more than a day or so, ex-

cept that snow, which is an insulator, maydecrease the floor heat loss.

The data indicate that insulating the floor

at the edge is beneficial both in saving heatand in reducing lateral temperature gradientsacross the floor.

The data on floors laid over crawl spacesindicate that the factors contained in hand-books are suitable for estimating heat losses

Real Losses from Slab Floors 21

through such floors, except in the case of afloor which is heavily insulated on the under-side. In this case, the edge loss increases

largely in comparison to the total loss throughthe floor, and this may result in an underesti-

mate unless it is taken into consideration. Thenumber of factors involved indicate that heatlosses through floors laid over crawl spacesshould be computed on the basis of an esti-

mated crawl-space temperature. For a con-

tinuously ventilated crawl space, the tempera-ture should be assumed to be the same as theoutdoor temperature.

The drawings and graphs for this reportwere prepared by E. J. Schell.

Washington, November 9, 1944.

o


[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 Wis-

consin 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 ConstructionsSponsored 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 lOiBMS66 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 156BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20^BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Con-

struction 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 Sheet-

Steel Constructions for Walls, Partitions, and Roofs Sponsored by the TennesseeCoal, 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 200BMS79 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.


[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 Subcom-

mittee on Specifications of the Central Housing Committee on Research, Design,and Construction 10^

BMS88 Recommended Building Code Requirements for New Dwelling Construction with SpecialReference to War Housing 20^

BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) PrefabricatedWood-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^BMS93 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^BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board 10^BMS98 Physical Properties of TeiTazzo Aggregates 150BMS99 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^BMS 101 Strength and Resistance to Corrosion of Ties for Cavity Walls lOfi

BMS102 Painting Steel ^ 100

BMS103 Measurements of Heat Losses From Slab Floors 100

S. DEPARTMENT COMMERCE..."^Cinders FLOOR3 liaaaDllaaan'inpaDI 4Concrete-TarPoder~^...

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