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Report on a study of wall surface condensation in prairie houses
REPORT ON A S T U D Y O F WALL SURFACE
CONDENSATION IN PRAIRIE HOUSES
i
NATIONAL RESEARCH COUNCIL O F CANADA
DIVISION OF BUILDING RESEARCH
(Prepared for the Central Mortgage and Housing Corporation)
b y
G.O.P. Handegord
I
Division o f Building Research
1
(Prairie Regional Station)
DBR Report Ottawa,
R16 1 October 1949.
(Preliminary c o p y circulated for comment)
The following report summarizes the results of an investigation carried out by the Division of Building Research of the National Research Council for Central Mortgage and Housing Corporation as a part of the co- operative work of these two organizations,
The winter of 1947-48 proved to be an unusually severe one in the Prairie region of Canada. As the winter approached its end, the VJinnipeg 3egional Office of Central Mortgage and Housing Corporation received a numher of
complaints with regard to condensation appearing on the inside walls of houses for which the Corporation was res- ponsible.
The complaints indicated a situation which appeared to be so serious that it should be investigated immediately before the conditions complained of had dis- appeared with a change in the weather. Accordingly, Mr. Handegord was asked to leave his regular work in developing the Prairie Regional Station af the Division of Building Research and to make visits to houses in areas from which complaints had been received with a view to discovering causes of the condensation.
This report summarizes Mr, Handegordls findings. As was expected, the problem proved to be of major propor- tions, pointing the way to a number of associate investi-
gations which
D.B.R.
hope to follow up during the comingwinter.
This report is a record of the initial studies made of this problem in actual houses occupied for use. It is believed that the information which it contains will be of interest to those concerned with the problem of
condensation. At the same time it paves the way for future studies which it automatically suggests.
Since the report mentions commercial products by their trade names quite freely, it is to be noted that the report is an entirely private document, the contents of which are to be regarded as of a confidential character.
Robert F. Legget, Director,
Division of Building Research, October lst, 1949,
TABLE
OF CONTENTSPage
Introduction
..'...
1Summary
. . 0 . . . 0 0 0 . . .
1The Problem
. . . 0 . . . 0
2 General Analysis of Conditions Causing Condensation. . . O .
3 Psychrometric principles governing condensation...
3Condensation on vs
.
condensation in walls...
5. . .
Wall surface temperatures 5 Humidities to be expected. . . O . . . . O .
6 The effect of ambient air temperature on surface tempera- ture 8 Vertical air temperature gradientsO . . .
11The fluctuation of air temperatures with time
...
11The effect of the proximity of objects to the wall
...
11Conclusions . . O . . . O . . . . O O . . . O . . . 12
Experimental Investigation of Corporation Houses
. . . O . .
14Houses investigated . . . O . . . O . O . . . O . . O 14 Instrumentation of houses . . . O . . . O . . . O . O . O . O O O . O . . . . 14
Horizontal surface temperature measurements oo o o o oo o o oo o 1 5 Horizontal heatometer measurements
. . . o . O . . .
17Discussion of results of horizontal surface temperature and heatometer measurements o o o o oo o o o on o o o o oo o o 20 Comparison of wall surface temperatures c o o a o o o o oo o o o o oo 22 Vertical air and surface temperature gradients
. . .
25Vertical heatometer measurements . . . O . . O . O O O . . . . O . . . O . O O 25 Discussion of results of vertical heatometer measure- ments
....
29 General discussion of the experimental results . o . . . o . 29INTRODUCTION
This investigation, requested by Central Mortgage and Housing Corporation, called for a determination of the causes of condensation on the surface of walls of basementless houses insulated with Type 1 Alfolo Since no complaints had been received of condensation of the
same nature, occurring on similar walls insulated with two inch rock wool batts, the Alfol insulation appeared to be at fault,
After a preliminary survey, experimental investigations were conducted in four houses with readings taken of air and wall surface temperatures, inside humidities, and of rates of heat transfer, For various reasons the adequacy of the experimental data obtained was very much limited by the conditions under which the tests were con-
ducted. The conclusions, therefore, which can be drawn from the results of these tests alone are very limited in scope,
The overall problem is now known to be exceedingly complex, It involves several widely different and variable factors embracing
much more than,the properties of the insulating material, For this
reason the report has been expanded beyond the limited scope of the test results to provide the necessary background, This background material is presented in the section entitled ''General Analysis of Conditions causing Surface Condensation", while the discussion of test results is included in the final section entitled "Experimental
Investigation of Corporation house^'^, The summary has been placed
at the beginning of the report for the convenience of those who do not wish to study $he background material in detail,
The appearance of surface condensation is attributable to two possible conditions,
1. Increase in moisture content of the space,
2. Decrease in temperature of the wall surface.
While it is not possible to rule out completely, in any given case, the possibility that the humidity in Alfol insulated houses may be higher than in rock wool insulated houses, sufficient evidence is presented to show that the surface temperatures on Alfol walls are sufficiently lower than on rock wool walls to explain the occurrence of condensation in the majority of cases in questiono
All inside surface temperatures over the lower portions of
exterior walls tended to be low in the houses in question, regardless of the insulation used, for the following reasons:
l o There were no basements and the crawl spaces were cold,
2, Floors were uninsulated,
3. The stove heating employed led to large variations in air
temperature from floor to ceiling and from room to room, as well as to variations with time,
The klfol insulated houses undoubtedly had lower wall surface temperatures attributable to the following:
1. The lower overall insulating value led to lo we^ average
inside surface temperatures,
2, The lower overall insulating value led to forcing of stoves
which in turn produced lower temperatures near the floor for the same average comfort temperature
3. The g e n e ~ a l form of the insulation was such as to produce localized cold areas in the vicinity of studs, plates, fire stops, girts, and on exposed heads of nails driven into cold studs,
Type 1 Alfol, having a single foil curtain forming two air spaces, is considered to be inadequate insulation for houses in the Prairie .area,
Limited tests on Type 2 Alfol, having two foil curtains forming
three air spaces, together with results of tests made at the
University of Saskatchewan indicate that, while the overall insulating value approaches that provided by two inches of rock wool, the surface
temperature variations are more extreme than with Type b Alfol, when
it is used in low-cost dry-wall construction- Such variations may be 1
expected to lead to t h e ~ m a l precipitation of dust, causing black marks
on surface finishes on all cold areas, Where condensation is imminent
i
these cold areas may also lead to condensation of moisture, The i
insulating value, and therefore, the average surface temperature, is 1
higher with Type 2 Alfol, However, the surface temperature differences
produced are greater so that the actual surface temperatures on the
colder areas may be as low or lower than those produced by Type 1
Alfol, It does not follow that the absence of complaints from houses
insulated with Type 2 Alfol indicates its superiority over Type 1 so
far as condensation is concerned, since all the corporation houses in
which it has been used have basements and furnaces, It is likely that
Type 1 under these conditions would have given no trouble from con- densation although the fuel consumption would have been higher,
There is no doubt that both Types 1 and 2 Alfol in their present
form have the inherent weakness that they produce substantial
variations in inside supface temperatures, When Alfol insulation is used in houses in which the wall surface temperatures are already low, this weakness may be sufficient to lower them still further to a point below the critical at which condensation will o c c u ~ ,
The weaknesses in the present forms of Alfol are related to its
construction and installation features and'are not inherent in
reflective type insulations as such, It is quite possible that certain forms of batt and blanket insulations may exhibit similar weaknesses,
The Problem
The request from C . M , H , C , for assistance in the form of an
investigation of certain rental houses resulted mainly from complaints received from tenants of basementless houses insulated with Alfol
high fuel consumption and particu1,arly of noticeable frost accumu- lation on the baseboard and interior surface of outside walls,
This frost a@cumulation h.ad also beer^ experienced in houses with
basements, i-nsulated with Alfol Type 2 when first occupied but had
disappeared with time,
A preliminary survey was made early in February of several of the houses involved in Saskatoon and the nature of the difficul- ties was determined at first hand, The severity of the surface condensation problems involved in the houses visited is illustrated
in Figures 1 and 2, showing heavy frosting on and above the base-
board, The frost pattern extends higher above the floor at studs and frosting over nail heads is particularly noticeable, As far as could be determined the case illustrated here was typical,
The frost formation as observed in the houses insulated with Type 1 Alfol insulation had not been experienced in houses of
similar construction insulated with two inch mineral wool batts, The initial problem was, therefore, the determination of the
extent to which .the characteristics of Alfol insulation not common
to rock wooX. contributed to the formation of surface condensation,
The general problem was, however, found to be of a very complex nature involving additional factors aside from those
directly contributed by the properties' of the insulation, In view of these factors it was considered advisable that the report
include a general analysis of the conditions likely to influence surface condensation,
GENERAL ANALYSIS OF CONDITIONS CAUSING SURFACE CONDENSATION
Surface condensation will occur only under certain combined conditions of air moisture content and temperature, It can be produced on any surface which is at a lower temperature than the adjacent air either by increasing the moisture content of the air or by lowering the temperature of the surface.
Psychrometric Principles .- Governing Condensation
At any given temperature a definite amount of water is required to saturate a given weight of air, The amount of water vapour required for saturation increases markedly as the temperature is increased.
The amount of water vapour in an air vapour mixture is
conveniently designated by the ratio of' water vapour to air, that is pounds of water vapour per pound of dry air, which is called Specific Humidityo The d e g ~ e e of saturation of this air vapour mixture is expressed in terms of Relative Humidity, which is the ratio in percent of the weight of water vapour present to the weight required for saturation at that temperature,
If any partially saturated air vapour mixture be cooled, its
specific humidity will remain constant, However, on lowering the
temperature, the ca.pacity for holding water vapour is reduced so that the ratio of water vapour present to the water vapour required for saturation is increased, That is, the relative humidity is increased.
If this same air vapour mixture be cooled still further until the actual amount of water vapour present which has remained un- changed is exactly enough to saturate the air, the relative humidity will have reached 100% and the temperature at which this occurs is said to be the dewpofnt temperature, Any further lowering of the temperature will result in precipitation of moisture as condensation,
since at this temperature the original amount of water vapour cannot be held in the air,
For example, an air vapour mixture at 70 deg, F o and 3% saturation will have the following propsrtiesr
1, Relative Humidity
=
3@2, Specific Humidity
=
0,00475 lbs,water vapour/lb, dry air3, Dewpoint Temperature
=
37,6 deg,F,If this mixture is cooled the Relative Humidity will increase,
reaching 100% when the temperature has been lowered to 37,6 deg, F , ,
which is the dewpoint temperature of the original mixture, Further coolfng t o 30 degc, F o will result in the precipitation of 0,00130 lbs,
of water, The Specific Humidity will be reduced to 0,00345 lbs,
water vapour/lb, dry air with the Relative Humidity remainfng at 10% since the mixture is still saturated with the reduced amount of water vapour at the new low temperature.
Condensat ion On vs , Condensation In Walls
The discussion outlined above is basic to the condensation phenomenon in its various forms, It is necessary, however to differentiate between surface condensation and condensation which occurs inside walls, attics, and crawl spaces, Both types are commonly encountered in houses but it is surface condensation
occurring on surfaces exposed to inside air that is involved here, Wall Surface Temperatures
The air inside a house is in contact with the colder surfaces of outside walls and windows in winter and it is these areas which con- stitute the danger spots for surface condensation, Heat is continually
being transferred from the air inside the roo^ through the wall to the
outside, and resistance to this flow of heat is offered by the walb and the air itself, The major resistance offered by the air is that
of the air film present in the vicinity of the walb surface and con-
sequently, for heat flow to occur through this film a temperature drop must exist across it, The magnitude of this temperature drop will be determined by the rate of air circulation over the wall surface and by the relative thermal resistance of the wall itself, The actual surface temperature to be expected will be dependent on these factors and the inside and outside air temperature existingo
Figure 3 has been prepared to illustrate the effect of the thermal resistance of the wall on inside surface temperatures by assuming still air conditions to exist inside the house, and a
wind of 15 m,p.h, outside, Temperature g ~ a d i e n t s have been plotted for a double window and t h ~ e e different f ~ a m e walls for an inside
air temperature of SO dego F , and an outside air temperature of
minus 40 deg, F , These gradfents have been calculated in accor-
dance with the standard resistance concept of heat transfer and are
listed in Table
I.
Windows, by virtue of their lower thermal resistance, will
exhibit lower surface temperatures for the same air tempe~ature and
film conditions than will normal frame walls For this reason,
condensation would be expected to take place on these areas
initially, In the example shown, the ambient air in the poom is
assumed to be at 70 d e g , F o g while in the vicinity of the surface
this air'is cooled to 31 deg, F o Assuming the moisture content
of the afr in the room at 70 deg,
F u ,
to be the same as that nearthe surface, the maximum dewpoint temperature that can exist
without condensation will be 31 deg, F, This would require that the
air near the surface at 31 deg<, F, have a ~ e l a t f v e humidity of 10%
while the afr in the room at 70 deg, F, containing the same amount
of moisture will have a relative humidity of 22%-
Humidities To Be Expected
In order that condensation occur on colder window surfaces the moisture content of the air in the room must be above that
corresponding to a dewpoint temperature equal to that of the window surface. Relative humidities in houses in winter have usually been
very low in the past, due mainly to the high rates of a f ~ leakage
which carried off moisture and to the high rates of vapour transfer
directly through walls which have ocourred, Due t~ these conditions
no particular difficulty with condensation was experienced, Houses are now often more tightly constructed so that air leakage is reduced and vapoup b a r r i e ~ s preventing Dhe passage of water vapour through the walls are now used in order to protect the
insulation f ~ o m condensation, As a result, higher humidities exist
in these more recently constructed houses, Several other reasons may contribute to this tendency for higher humidities fn the Corpora- tion houses studied:
l o The houses are smaller than normal for the same sources
of moisture
2, Tenants are generally families with small children,
involving additional sources of moisture from bathing, sterilizing, etc,
3. Washing and drying of clothes is done in the Living
space rather than in the basement
4. Outside ventilation through windows is held to a
minimum for warmbh with lower fuel consumption,
These higher humidities are desirable for living but would be expected to result in some condensation on cold window surfaces in most houses,
C a l c u l a t e d Temperature G r a d i e n t s Through Windows and Walls I n s i d e Temperature +70°F. O u t s i d e Temperature - 4 0 O ~ ~ Double W i n d o v Thermal $ of T o t a l Temperature Component R e s i s t a n c e R e s i s t a n c e D i f f e r e n c e Temperature O u t s i d e A i r F i l m 0 0 2 0 1 1 , O 1 2 , 0 -40 1/81q Glass 0, 02 1 , O 1 , O -28
A i ? ? Space 0 0 9 1 52,O 57,O -27
118" G l a s s 0 0 0 2
l o o
l o o
-530 I n s i d e A l p Film-
0,61 35,O-
39, Q: +3P 1 0 7 6 10000 11060 8 '70 Frame Wall f f ~ f t '-
N g t x n s u l a t i o n .+ O u t s i d e F i l m 0.17 5,O 5 0 5 -40 Asbestos S h i n g l e s 0 0 1 7 5,O 5 , s -34,5S h e a t h i n g & Paper 1 0 1 6 35,O 3 8 , O -29 0 A i r Space O091 28,O 3 1 , O 9 g o o
P l a s t e r b o a r d 0 0 2 7 8 , O g o o +4000 I n s i d e Film 0 0 6 1 1 9 o 0 2 l O O 849,O
3,29 1m
lip
+7000Frame Wall "Bn
-
One i n c h R,W, n s u l a t i o nO u t s i d e Film 0 0 1 7 2 - 0 2,O Asbestos S h i n g l e s 0 0 1 7 2 0 0 2 , 0
S h e a t h i n g & Paper 1 0 1 6 17,O 19,O
Air Space 0 0 9 1 13,o 14,O
One inch Rock Wool 3,?0 53,o 59,O P l a s t e r Board O027 4,O 4,O I n s f d a Film
-
0 0 6 1 Q O O 1 0 o O6,99 1 0 0 0 0 l l O o O
Frame Wall "C"
-
Two i n c h e s R.W. I n s u l a t i o n Outside Fflm 0,17Asbestos Shingles 0,17 S h e a t h i n g & Paper 1 0 1 6
A i r Space 0 , 9 1
Two i n c h e s Rock Wool 7,40 r l a s t e r b o a r d 0 0 2 7 I n s i d e Film 0 0 6 1
Condensation on windows is generally accepted in modern houses
since little damage or inconvenience results,
In
order that conden-sation occur on wall surfaces however, the temperature of such surfaces must be as low as that of the window if uniform moisture content is assumed throughout the air in the house,
While it would be unwise to ignore the possibility that large variations in moisture content of the air may exist throughout a house, there are several considerations which tend to eliminate this possibi- lity from the present discussion. First, vapour diffuses relatively readily throughout a space, as evidenced by the absorption into the air of steam from a kettle. More important, however, is the factor of air circulation by convection, which is relatively very extensive in houses being heated by convection, so that there is little reason to suspect that any large concentrations of water vapour can be consistently maintained at any point in a room of a house, Finally, the fact that
condensation occurred with one type of insulation and not with another leads to the conclusion that the cause of condensation was one associa- ted with variations in surface temperature and not with possible
variations in moisture content of the air.
The Effect of Ambient Air Temperature on Surface Temperature
If the window temperature is below the dewpoint temperature of the air, the windows will act as dehumidifying surfaces, controlling the
moisture content of the air to a value corresponding to this temperature, Under these conditions condensation would not appear on wall surfaces unless the temperature of these surfaces was equal to or lower than that of the windows,
On the basis of the values shown in Figure 3 wall surface tempera-
tures would not be expected to be as low as those of window surfaces
when exposed to the same inside air temperature, However, air temperatures are not uniform throughout the house, for while air temperatures may be
kept at 70 degu
F o
at the breathing level in a room, lower air tempera-tures may be expected near the floor, Adjacent air temperatures will have a marked effect on surface temperatures and it will be necessary
to consider this effect i n more detail,
Calculated inside surface temperatures for the three walls in Figure 3 are plotted in Figure 4 for various inside air temperatures
and an outside temperature of minus 40 deg, F o assuming constant air
film conditions, Under the conditions assumed, the inside air tempera-
ture near the floor would have to be lowered to 47,2 deg, F o for Wall
A
in order that its surface be the same temperature (31 deg,
F.)
as thewindow exposed to 70 deg, F o air, For Wall
B
this air temperature would have to be 37,6 dego I?, and for Wall C 35,3 deg, F,Under these theoretical considerations, severe air temperature gradients vertically would be necessary to reduce wall surface tern- peratures near the floor to cause condensation, The severity of these gradients is dependent on the general construction features of the house and the type of heating system being used, space heaters being particularly at fault in this'regard,
Vertical Air Temperature Gradients
To determine the air temperatures existing in the basementless houses in question three recording thermo hygrographs were installed
in each of two houses in Saskatoon for a one week period, Two of
these recorders were placed in different locations in the house during the period, the third recorder remaining at the three foot
level in the living room of the house for the entire week, The values
indicated by these instruments have been plotted in Figures 5 and 60
Figure 5 illustrates the conditions occurring in a single storey
basementless house insulated with Type 1 Alfol and having a semi-
automatic 091 fired space heater, Figure 6 illustrates the conditions
existing in a similar house insulated with two inch rock wool batts and having a hand fired coal space heater, The results do not serve
to indicate a comparison of insulation properties but show the extreme
air temperature gradients produced by space heaters in basementless
houses and are therefore included here,
In this regard, it may be seen from Figures 5 and 6 that even
with outside temperatures above zero, differences in air temperature
between the three foot level and the floor are of the order of 15 to
20 deg, F o In the living room of the house, essentially the most
adequately heated room, In Figure 6 for outside temperatures ranging ten to thirty degrees below zero, the air temperatures at the floor level in bedrooms not directly heated were from 15 to 28 degrees
below the air temperature at the three foot level in the living room, These differences are greater in Figure 5 due to the opening of
windows during the night, Only the window in the N O W , bedroom was
opened, however, and this practice resulted in an air temperature at floor level in the SOW, bedroom at times 40 deg, F , below that at the three foot level in the living room,
The Fluctuation of Air Temperatures with Time
The lower surface temperature conditions produced by these severe air temperature gradients are made worse by the general
lowering of air temperatures in the house, The use of a coal fired space heater, as in Figure 6, results in wide fluctuations in
temperature, with air temperatures at the three foot level in the
lfvfng room falling to 50 deg,
F o
at times, Less severe fluctuationsin the ease of Figulae 5 are due to the use of a semi-automatic oil fired heater,
The Effect of the Proximity of Objects to the Wall
In addition to the factors mentioned, the proximity of furniture
and other objects contributes to the lowering of wall surface tempera-
tures at the critical area near the floor, The most severe frost formation observed in the houses studied was located behind chester- fields, card tables, and clothing which were placed directly against
or in close proximity to the wall,
In
some cases these objects wereso placed in an effort to reduce the frost accumulation while their use actually made the conditions worse.
Fu~nfture or other articles placed against outside walls will reduce the natural air circulation over the wall surface, increasing the air film resistance, The object itself will offer some resistance to heat flow, and the net effect will be the addition of insulation on the inside of the wall, resulting in a lower surface temperature of the wall itself with the air in the room still free to contact this colder wall surface,
This condition is illustrated in Figure 7, showing the effect of
placing a sheet of plywood against the a a l l surface to form an one
inch still air space between the plywood and the wall surface, The
reduction in wall surface temperature so produced is greatly influenced
by the original thermal resistance of the wall, ranging from 25 deg,
F,
for the uninsulated wall to 13 deg, F, for the wall insulated with two
inches of mineral wool, While the assumption of a stfll air space represents an extreme condition, the general effect of the proximity of objects to the wall is clearly indicated,
The more severe conditions produced by the placement of these
objects against the wall is not to be considered as a contributing factor in the basic problem, however, the existence of such conditions may be considered as an important factor in promoting complaints from tenants ,
Conclusions
Under the uniform air temperature and humidity conditions normally assumed to exist in modern houses, surface condensation would be
expected to occur only on the windows, and not on the surface of outside walls,
These uniform conditions do not exist and while variation in air moisture content throughout the house is likely, the variation in air temperature produced by the type of heating system employed is con- sidered to have a more direct bearing on the problem,
Due to the extperne variations in air temperature from floor to ceiling existing in the houses studied, the possibility of wall supface temperatures near floor level approaching those of the window surface 1s evident, and condensation would be possible on these areas provfded some additional factors served to lower these temperatures stfll further,
Since condensation did occur, in fact, on wall surfaces in houses insulated with Type 1 Alfol and not on similar houses insulated with two
inch mineral wool batts, certain properties of Type 1 Alfol insulation
would appear to provide the necessary further lowering of the tempera- t u ~ e ,
The investigation of the relative properties of these insulations constitutes the main subject of experimental observation in this report,
EXPERIIVIEl!!TAL INVESTIGATION OF CORPORATION ROUSES
Houses Investigated
-
-
Following the prelimfnary survey it was decided to concentrate on the experimental study of only two similar houses in Saskatoon, This decision was made for the reason that with the limited time and equfp- ment available and with the difficulties anticipated in such an investi- gation, more information could be obtained from several observations on a few houses than from relatively few observations on a great many
houses, This program was later expanded to include a less extensive study of two houses in Prince Albert to obtain additional information on
Alfol Type 2 insulation,
The houses investigated were as follows:
House No, 1
-
Sfngle storey type H-6 basementless houselocated at 1010 7th Street East in Saskatoon,
-
Wall construction-
asbestos shingles, buildingpaper, wood sheathing, 2"
x
4 " studding, Alfoltype 1 insulation, plasterboard,
-
Heating system-
oil burning space heater withpropeller type circulating fan, Coal range in kitchen,
House No, 2
-
Single storey type H-5 basementless houselocated at 915 8th Street, Saskatoon,
-
Wall construction - same as House No, 1, butwith two inch pock wool batts insulation,
-
Heating system-
coal burning space h e ~ . t e r ~ Coal range In kitchen,House No, 3
-
Single storey type H - 6 basementleas house located at 339 12th S t ~ e e t , Prince Albert,-
Wall construction-
same as House No, I,,-
Heating system-
coal burning space heaterYHouse No, 4
-
Single storey type A-1 house with full basement,located at 1012 4th Street East, Prince Albert,
-
Wall construction-
similar to House N o , 1 butwith Alfob Type 2 insulation,
-
Heating system-
coal fired gravity warm air,Instrumentatfon of Houses
Temperatu~e Measurements
Supface temperatures in the houses studfed were measu~ed with
30 B & S Gauge copper-constantan thermocouples fastened to the wall surface with masking tape, Adjacent air temperatures were measured wfth identical thermocouples unshielded from radiation effects, A
Rubfcon flYofnter%itett portable potentiometer was used for all
measurements except those in House No, 1, where a portable Cambridge
potentiometer was employed, which was subsequently found to be con- siderably less accurate,
Heat Flow Measurements
Heat flow measurements were made with an instrument known as a
"~eatometer", manufactured by Gier and Dslnkle, Oakland, California, The instrument used consisted of three laminated, four inch square
sheets of bakelfte totalling approximately 3/64 inches thick, the center sheet supporting 240 pairs of differential thsrpmocouples connected in series, The electromotive force generated by this
thermpile is a measure of the temperature drop across the thin bakelite sheet and by suftable calibration indicates the pate of heat flow
through the meter in b.t,u, per square foot per hour, m e heatometers
were secured to the wall with masking tape and the sane potentiometer was used for the heatometer readings as was employed for temperature measurement.
Heatometer and supface temperature measurements obtained for House No, 1 were found to be inconsistent in themselves and with measurements in similar houses, These inconsistencies could be
attributed to faulty installation of the insulation
or
to
the useof inaccurate instruments, Examination of the insulation being impossible, these results have, for the most part, been omitted from the report, The recorded inside air temperatures obtained in
this house have, however, been included in Figure 3.
The investigation of Houses Nos, 3 and 4 was made when the outside air temperatures were well above zero and the lack of sub- sequent colder weather prevented observations under more extreme conditions, The results obtained, therefore, are not representative of conditions likely for surface condensation,
The general experimental procedure employed in this investi- gation was patterned after that used in tests on Alfol Type 2
insulation at the University of Saskatchewan, These tests on Alfol
Type 2 indicated the probable faults in thfs type of insulation
to be associated with the discontinuities introduced by framing members in the wall and the structure of the insulation, Alfol
Type 1, being of the same general f o m as Type 2, was thought likely to exhfbit similar properties and that these properties could result
Sn lower temperatures in the vicinity of studs and other "through"
framing members than would normally be expected under the general assumption of uniform heat flow,
The experimental study involved, therefore, tbe measurement of heat flow pnd surface temperature gradients in the vicinity of studs and other framing members, These results have generally been reported
on a relative basis in view of the variation in the conditions of
different tests,
Horizontal Surface Temperature Measurements
The results of inside surface temperature measurements across
stud spaces in Houses 2, 3 and 4, ape shown in Table 2. These surface
temperatures were measured at different wall locations in the houses at heights above the floor where the influence of horizontal framing members was thought to be at a m i n i m ,
The average differences in temperature between any one point and that at the center of the stud space have been calculated in Table 2. These values do not give a true comparison between the Alfol Types and rock wool batts, since the former were obtained for an inside to outside
air temperature difference of 40 deg, F o while those for rock wool are
for a difference of 64 deg, F o
It will be necessary to correct these values to the same basis for comparison, It will be assumed that the difference in surface tempera- ture between two points will vary directly with the inside to outside air temperature difference, This assuniption has already been used in
correcting the data for House No, 2 in Table 2 as indicated, and is used
in bringing subsequent data to a comparsble basis, The data of Table 2
using the rock wool values corrected to 40 deg, temperature difference
has been plotted in Figure 8.
The curves in Figure 8 show that greater differences in surface
temperature between points over the center of the stud space and over the studs are experienced with walls insulated with Alfol Type 2 than
with those insulated with Alfol Type 1 or two inch rock wool batts,
These differences are slightly greater for walls insulated with Type 1 Alfol than those insulated with two inch rock wool batts,
These results are supported to some extent by additional surface temperature measurements taken in conjunction with heatometer measure- ments, These surface temperatures were measured at the previous loca- tions only over the center of the stud and stud space, The values
obtained are listed in Table 3 as differences in temperature between
the center of the stud and stud space, For compa~ison, these values
have been expressed as a percentage of the overall inside to outside
tempe~ature difference,
On the basis of the percentages given in Table 3, at an overall
air temperature of 40 deg, F , , the wall surface over the stud would be
103 deg, F, below that at the center of the stud space for walls
insulated with two inch rock wool batts; 2,O deg, F, for those
insulated with Alfol Type 1, and 4,1 deg, F o for those insulated with
Alfol Type 2, These calcuiated results are in fairly close agreement
with those of Figure 8 except for the values shown for Alfol Type 2 ,
A probable reason for this discrepancy #ill be discussed later,
Horizontal Heatometer Measurements
The variations in surface temperature across a stud space as
shown in Figure 8 and Table 3 would indicate similar variations in
heat flow, To further investigate this phenomenon, two four by four inch Heatometers were applied to the inside surface of the wall, one at the center of the stud space and the other centrally located over one adjacent stud at approximately the same locations as were used for the surface temperature measurements, The values obtained are given in Table 4 as b , t , u . per hour per square foot flowing into the surface of the wall at the Heatometer location,
T a b l e Noo 3
D i f f e r e n c e i n Temperature of S u r f a c e o v e r S t u d and S t u d Space a t Mid Height a s a P e r c e n t a g e of O v e r a l l Temperature D i f f e r e n c e
Ins i de Average
Temperature a t t o O u t s i d e of Corner of S t u d Space A i r temp, R a t i o R a t i o ~ o u s e on Minus Temp. a t s t u d ~ i f f e r e n c e
-
d d No, P l a n I n s u l a t i o n d D D D,,
x 1 0 0 2 A 2" RockwooH 2 , 3 8 0 0 4 2,86 2 A"
n 2 , 3 8 0 0 4 2,86 2 B " tt 2.4 8 0 0 4 2.98 Average 3 , 3 2 A"
tt 1.8 53,6 3 " 3 6 2 B tt 2.6 56,6 4.60 ~- 3B
~ l f o l Type 1 2.1 37,7 5.57 3 F tt 1 1 , 4 3 8 , 3 3.65 3 C t? tt 1 2.1 4 1 0 5 5.56 3 D I t 1 2.2 43,2 5 , 1 0 3 E tt tt 1 2 , 0 4 2 , 1 4,75 Average 5,O 3 A n 1 3,o 3 g 0 2 7,65 3 B 1 ? 1 1 o 7 3709 4 , 4 8 3 F I t It 1 2.4 43,2 5 , 5 5 3 C rt tr 1 1 e 6 43,O 3.72 3D
I t 1 1 , 4 43,4 3.22 3 E ?t 1t 1 2,4 4 2 , l 5 , 7 0-
-.-- 4 A A l f o l Type 2 5 , 2 37,9 1 3 , v 4 B 11 tt tt 4,l 39,7 1 0 , 3 4 C I t I t tt 4 , 7 3 9 , l 1200 4 D I? I t I t 4,6 4 1 , l 1 1 , 2 Average 1 0 , 3 4 E n 11 tt 3 0 9 3 7 , s 10,4 4 F tt tt n 2 ,1 41,4 5 , 0 8 4 G I t n I? 4 , l 4 2 , l 9 , 7 5The ratio of heat flow into tko area over the stud to heat flow into the center of the stud space has been calculated for the various walls and the average value of this ratio for each wall is given in Table 4. These results support in a qualitative manner the previous surface temperature differences, indicating an increased effect of studs on the horizontal heat flow pattern in Alfol insulated walls as compared to similar walls insulated with two inch mineral wool batts,
Discussion of Results of Horizontal Surface Temperature and Heatometer Measurements
The reason for the more extreme variations in surface tempera- ture horizontally with walls insulated with Alfol is suggested by an examination of the structure of the insulation, illustrated i.n
Figure g o
In the first instance, the full effectiveness of the insulation is not obtained across the entire width of the stud space, decreasing from its full value at approximately one inch from the stud to that of a single air space with one reflective side.at the edge of the stud, This not only reduces the insulating value in the vicinity of the stud but leaves two sides of the stud exposed to the cold air in the outer air space.
The studs in Alfol insulated walls therefore not only transfer heat by conduction normal to the wall but also transfer heat by
convection to the air in the outer air space, the stud acting as a fin heat transfer surface.
Two inch rock wool batt insulation on the other hand, provides constant insulation protection across the entire width of the stud space and only a portion of the stud loses heat by convection to the outer air space,
For the same insulating value at the center of the stud space, which is approximately the case with Alfol Type 2 and two inch rock wool batts, greater differences in surface temperature between stud and stud space would be expected with the Alfol type insulatfon, The lower insulating value of Alfol Type 1 at the center of the stud
space, and the resulting higher air temperature of the outer air space would reduce the heat flow and surface temperature differences across the stud space below those produced by Alfol Type 2, but by reason of the convective heat loss these gradients would be more severe than for walls insulated with two inch wool batts,
On the basis of this discussion it would appear that the con- structional features of Alfol insulation are the cause of more
severe temperature differences across the surface over a stud space as compared to those resulting from the use of two inch rock wool batts, A comparison of actual surface temperature gradients pro- duced by these i n s u l a t i o ~ n e c e s s a r y , however, to illustrate their relative performance in regard to the possibility of surface condensation,
Comparison of Wall Surface Temperatures
A comparison of the actual surface tempekatures as measured is impossible in view of the different conditfons under which the measure- ments were made, However, an analysis can be made to show the approxi- mate surface temperatures to be expected for the three walls in question,
Tests conducted at the University of Saskatchewan on two four by four foot huts have shown the thermal resistance of a wall insulated with Alfol Type 2 to be approximately the same at the center of the stud space as that for walls insulated with two inch rock wool batts, It should be mentioned, however, that the overall thermal resistance of
Alfol Type 2 wall was found to be only eighty-five percent of that
for the rock wool wall due to the increased heat loss through the studs
of the former,
In
this immediate discussion, however, only a con-sideration of the relative thermal resistance at the center of the stud space is necessary,
According to the A . S , H , V , E , Guide for 1946 the thermal resfs-
tance of three afr spaces separated by two foil curtains is given
as 7.69 deg. ~,/btu.hr.ft~, and that for two such air spaces as
4.35 dego~,/btuohr,ft20, for a temperature difference of 40 deg, F o
Employing the resistance values for the remaining components of the wall as given in the Guide, the overall thermal resistance of a wall
consisting of asbestos shingles, fir sheathing and paper, 3 518 inch
air space and plasterboard with Alfol Type 1 insulation would be
6.73 deg, ~./btu,hr,ft2, and with Alfol Type 2, 10007 deg, ~,/btu,hr,ft~. Using these values, the surface temperature to be expected at
the center of the stud space for an inside temperature of 70 deg,
F,
and
an
outside temperature of 30 deg F o assuming an inside air filmresistance of 0.61 deg. ~./btu,hr,ft~, may be calculated as follows:-
1) Wall with two inch rock wool batts
Surface temperature 70
-
(40 x 0,61)=
6706 deg,F o
13
om
2) Wall with Type 1 Alfol
Surface temperature a 70
-
(40 x 0,61)6,73 " 66,4 degc.
F,
3) Wall with Type 2 Alfol
Surface temperature 70
-
(40 x 0061)=
67,6 deg, F,1 m
These values of surface temperature have been used in replotting
the curves of Figure 8 in Figure 10 to show actual temperature gradients
that may be expected in walls incorporating the three types of insula- tfon,
The air temperature conditfons assumed in Figure 10 are definitely not those under which surface condensation is likely, The same general
procedure as used above may be used to replot the results in Figure 8
for more extreme conditions, but the effect of air temperature difference on the surface temperature kradient must also be considered,
It will be assumed as was done previously that horizontal differences in surface temperature will be directly proportional to overall afr temperature dffference, It is generally accepted,
however, that overall air temperature difference and mean temperature affect the thermal resistance of reflective insulations to a more serious degree than for bulk or batt type insulations, This fact is illustrated by the published resistance values for reflective fnsula- tion being much higher for summer than for winter conditions, The lack of complete data as to this variation at temperature differences and mean temperatures experienced in this pegion makes ft rather
difficult to take this variation into consideration, and in view of the approximate nature of this discussion these effects wfll be assumed negligible,
On the assumption that horizontal differences in temperature are
proportional to overall air temperature difference, Figure 11 has been
plotted for an outside air temperature of minus 30 deg, F,, and an
inside air temperature of 50 deg, F o These values have been chosen as
being representative of those occurring near floor level in the basement-
less houses studied on the basis of Figures 3 and 4.
The surface temperatures at the center of the stud space are calculated as follows:-
1) Wall insulated with two inch rock wool
batts
Surface temperature = 50
-
(80x
0,611,
45,1 deg4*,
lrn
2) Wall insulated with Type 1 Alfol
Surface temperature = 50
-
(80x
0.61),
4 Z Q 7 deg., F o6,"n 31 Wall Insulated wfth T m e 2 Alfol
Surface temper;iture SO (80 x 0,61)
,
45,l dego F,1m
Differences in surface temperature between points over the stud and over the center of the stud space obtained from tests at the
University of Saskatchewan for an overall air temperature difference of 80 deg, F , are fn fair agreement with those shown in Figure 11 for two inch rock wool batts, but are considerably less t,han those calcu-
lated for Alfol Type 2, being of the order of 7 to 9 dego F, These
latter values are in agreement with the reau1t.s in Table 3 , A possible
explanatfon would be the fact that the surface temperature gradient measurements shown in Figure 8 (used as a basis for Figure 11) were taken at a time when the outside air temperature was rising, Under these conditions the studs would increase in temperature at a lower rate than the remainder of the wall due to their higher heat capacity and consequently lower surface temperatures would exist over the stud than under steady state conditions, The surface temperatures for
Alfol Type 2 walls, used as a basis for Table 3, were taken some time
later when the transient heat flow effects would be reduced
Transient heat flow conditions no doubt existed in all the walls studied and hence an analysfs of the results obtained under these con-
ditions on a steady state basfs, as has been done, it is not strictby correct, Even under steady state conditions the assumption of surface temperature differences being proportional to inside to outside air temperature difference is questionable, An analysis of the actual
phenomena would be exceedingly difficult, however, in view of the limited experimental data available and the simplified analysis as presented is considered sufficient to warrant the following conclusions,
1) The constructional features of Alfol insulation produce a
greater difference in surface temperature between points over the center of the stud space and over the stud than are experienced with similar walls insulated with two inch rock wool batts,
2) Under identical air temperature and film conditions, walls
insulated with Alfol Type 1 or 2 will exhibit lower inside surface
temperatures than similar walls insulated with two inch rock wool batts,
3) Under identical air temperature and film conditions, walls
insulatedawith Alfol Type 2 may exhibit lower surface temperatures in
the vicinity of studs than similar walls insulated with Alfol Type 1 insulatf on,
Vertical Air and Surface Tem~erature Gradients
The reduction in surface temperature in the vicinity of studs produced by Alfol insulation indicates that a similar condition could exist in the vicinity of horizontal framing members since standard practice requires that the expanded Alfol blanket be flattened over these members,
Vertical surface temperature and adjacent air temperature
measurements were taken in all the houses investigated in an effort to
obtain some indication as to the effects produced by horizontal framing
members,
In
view of the lfmited number of measurements taken and ofthe variation in conditions no quantitative comparisons can be made,
-
The results obtained in Houses 3\and 4 have been plotted inFigure 12 to indicate the effect of firestops located at the four foot level in walls insulated with Alfol insulation, It is of interest to compare the general shape of these curves with those of Figure 13 obtained for House No, 2 under a much lower outside air temperature, Vertical Heatometer Measurements
Heatometer measurements of heat flow into the center of the stud space and into the area over the stud at distances of six inches, one foot and four feet above the floor indicated more clearly the heat flow pattern existing at the lower part of the wall in the basementless
houses,
These heatometer readings have been reduced to a parent overall
onductivity ("Un values) by dividing the value of btu/kroft2 by the
verall air temperature difference in an effort to compensate for the vertical variations in inside air temperature, The resultant values have been expressed as a ratio to that at mid height of the wall for the
center of the stud space based on the results of Table 4 and are listed
Table 5
Ratio of Apparent "U" Value to that for the Center of the Stud Space at Mid Height of the Wall
Incorporating the results shown in Table 4
Mid Height 1 Fto Above Floor 6 Inso Above Floor
Dver Over Dver
House Stud Over Stud Over Stud Over
No. Space Stud Space Stud Space Stud Remarks
2 1 1.14 1.11 0,79 1,39 1.42 2" Rock Wool 1 1.14 0,89 0.67 1.55 1,26 Batts Average 1 1,14 1.00 0.73 1047 1.34 No Basement - 3 1 1061 0062 1.61 1.64 2.36 1, 1,61 0.85 1,39 1-70 3,49 Alfol Type 1 A v e r a g e 1 1061 0.74 1.50 1,67 2,93 No Basement
The results listed in Table 5 for the baseaentless houses indi- cate an increased amount of heat flowing into the wall at the six inch level as compared to that at mid height of the wall for houses insulated with both Alfol Type 1 and two inch mineral wool batts,
This increase, however, is more severe in the case of the Alfol Type 1 insulated wall where almost three times the arnount of heat flows into the area over the stud six inches from the floor as flows into the center of the stud space at mid height,
Discussion of Results of Vertical Heatometer Measurements
The construction features of the basementless houses in question at this critical area are illustrated in Figure 14, showing a vertical section through the lower part of each wall, It may be seen from this Figure that the lower plate of the wall is likely to be cold regardless of the type of insulation used, due to the lack of insulation protec- tion separating it from the cold outside air or cold air in the crawl space, In the case of Alfol insulated walls, the entire upper surface of the plate is in contact with the cold air in the outer air space of the wall while only a portion of this surface is exposed in two inch rock wool batt insulated walls, As a further contributing feature, the intersection of studs with the lower plate creates an area where
the Alfol blanket is "pinched offN in two directions,
In
this area,therefore; the increase in heat flow produced by the construction of klfol insulation at the stud is superimposed on a similar condition
produced at the plate, and a most critical area results,
There is some reason to suspect, although it has not been proven, that the free air spaces in Alfol insulation will contribute still
further toward increasing the gradient in temperature from bottom to top, thus tending to lower still further the temperature at the lower part of the wall,
General Discussion of the Experimental Results
On the basis of the experimental results and the preceding
discussions it is concluded that surface temperatures of walls insulated
with Alfol Types 1 and 2 will be lower near studs and plates than for
walls insulated with two inch rock wool batts, In walls insulated with
Alfol Type 2 the lowering of surface temperature in these areas is
primarily a result of the structural features of the insulation since the insulating value at the center of the stud space is about equal to that of two inches of rock wool, In the case of Alfol Type 1 insulation these lower temperatures are the result not only of the structural
features but also of the lower overall thermal resistance,
The thermal resistance of a wall insulated with Alfol Type 1 at
the center of the stud space is 67% of that of a similar wall insulated
with two inch mineral wool batts on the basis of the calculations on Page 22 but the variation in heat flow across the stud space is more severe, For this reason the overall thermal resistance of walls insu-
similar walls insulated with two inch rock wool batts. While the lower overall resistance of Alfol Type 1 and its structural features are directly related to the surface temperatures produced, the former will also contribute to the lowering of surface temperatures by in-
creasing the heat loss from the house, and hence, requiring greater output from the heating system, Tests by the U.S, Bureau of Standards
(Ref, B.M.S. Report Noo BMS 114) have shown that the air temperature
gradients from floor to ceiling and room to room are increased with increased heater output in houses heated by space heaters, and in view of the previous discussion, these conditions would result in a further lowering of wall surface temperatures near floor level,
It has previously been mentioned on Page 22 that due to the
severe variations in heat flow existing in walls insulated with Alfol
Type 2, the overall thermal resistance is approximately 85% of that
for similar walls insulated with two inch rock wool batts,
Insofar as air temperature gradients are concerned, this lower value would not be too serious but the severe variations in heat flow and surface temperatures mentioned could conceivably produce localized
surface temperatures as low or lower than would exist if Alfol Type 1
insulation were used. It is possible, therefore, that the use of Alfol
Type 2 insulation in basementless houses such as those studied would
have resulted in surface condensation similar to that resulting from the use of Alfol Type 1,
The relative overall thermal resistance of Alfol insulation has been considered primarily in regard to surface condensation but this resistance will also determine, to a large extent, the general comfort conditions and fuel consumption resulting in a house, If it is
assumed that the minimum insulation required in the prairie region is equivalent to that afforded by two inch rock wool batts, Alfol Type 2 would almost meet the requirements while Alfol Type 1 would be considered inadequate,
Conclusions
The general conclusions of this report are included in the Summary
on Page 1, These conclusions are necessarily very restricted in view of
the limited experimental results obtained and of the variable con-
ditions under which the measurements had to be made,
In
fact, the mostdefinite conclusion that may be made is that the normally accepted
concepts of heat flow through building walls based on uniform conditions and simple straight line heat flow are entirely inadequate, and that a great deal of experimental research is necessary for a complete under- standing of the phenomena involved,
Recommendations
Surface condensation as observed in the Corporation houses insu- lated with Alfol Type 1 could conceivably be eliminated by lowering the humidity of the air inside the house, This practice would,
however, result in lower comfort conditions inside the house both from lower humidities and increased ventilation requirements,
The alternative, and recommended remedial measure would be the addition of insulation to increase the inside surface temperature of exterior walls, Fill insulation could be blown or poured into the exterior air space in the walls insulated with Alfol Type 1 and while it might only be required in the lower portion of the wall, the filling of the entire height would serve to improve the comfort conditions and to lower fie1 consumption.
The behaviour of the Alfol insulation under this fill insulation should first be studied to determine to what degree the Alfol will collapse and the effect of its presence on the future settlement of the fill insulation, The surface temperatures in the critical region will be raised, however, even if settlement does occur.
Adequate vapour protection of the fill insulation should be afforded by the Alfol blanket so that no additional protective measures will be required in this regard.
