US 2855869 A
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Description (OCR text may contain errors)
Oct. 14, 1958 c. G. MUNTERS ETAL 2,355,369
v RQOFS 0F BUILDINGS- Filed Nov. 28, 1952 2 Sheets-Sheet 1 Tlil.
1 TI ORNE w INVENTORS BY M Oct. 14, 1958 c. e. MUNTERS EI'AI 2,855,869
ROOFS OF BUILDINGS Filed Nov. 28, 1952 I 2 Sheets-Sheet 2 T .L E JE.
asvmzgw ATTORNEY 2,855,869 I ROOFS F BUILDINGS Carl Georg Munters, Stocksund, andErling Berner,
Goteborg, Sweden Application November 28, 1952, Serial No. 322,884
4 Claims. 7 (Cl. 108-6) This application is a continuation in-part relating back to our co-pending application Serial No. 720,578 filed December 26, 1946, now abandoned. 1 I
Our invention relates to building roofs of the kind comprising a layer of heat insulating material over which there is an outer rain and weather-proof layer which may, for example, be sheet metal, asphalt, tar or the like the latter materials being possibly combined with impregnated building paper or felt, a common characteristic of all of which materials is that they are substantially proof against diffusion of water vapor through the roof to the outside atmosphere as well as being proof against leakage of water from the exterior through the roof.
While the provision of a continuous outer covering of water-proof andsubstantially diffusion-proof material accor'nplishes the purpose of preventing moisture from reaching the insulation from the exterior of the roof, such a layer paradoxically result in roof constructions of the kind hitherto employed, and particularly in what is generally regarded as flat roof constructions, in accumulation of moisture in the insulating layer of the roof to an extent such that not only may the insulating quality thereof be seriously impaired, but also to the extent such that the insulation may ultimately-be seriously damaged in other respects by corrosion or decomposition,
The accumulation of moisturein insulated wall and roof structures has previously been recognized as a phenomenon which in many instances occurs and it has previously been suggested that removal of moisture from I such insulated structures may be accomplished by circulation of a moisture-removing medium such as air through the insulated structure.
Such prior proposals have, however, not provided a practical solution for the removal of moisture from roofs of the kind with which the present invention is particularly concerned, largely because of lack of appreciation heretofore of the very large quantities of moisture that maybe diffused into flat roofs of the character under consideration in vapor'form and condensed therein, unless additional and highly essential features of roof construction are combined with ventilation for the purpose of removing such moisture as may be diffused intothe roof I structure in spite of all practical precautions taken to minimize or eliminate such diffusion.
The general object of the present invention is, therefore, to improve upon prior constructions by the pro vision of novel insulating roof structures, particularly for flat roof buildings such as factory buildings and other commercialstructures, which roofs combine with means for minimizing the diffusion of water vapor into the insulation of the roof to a relatively small value, ventilating means for removing from the insulation such moisture as area in desired condition by natural draft creating means of practical dimensions, or, in the case of verylarge structures or unusual circumstances, by power operated draft creating means only a fraction of the size than would otherwise be required.
Other and more detailed objects of the invention and of the ensuing portion of this specification, taken in conjunction with the accompanying darwings and diagrams forming a part hereof, in which:
Fig. 1 is a diagram illustrative of water vapor conditions in an insulated roof structure; I Fig. 2 is a perspective view, partly in section, of a roof construction embodying the invention; 7
Fig. 3 is a fragmentary section on enlarged scale take on the line 33 of Fig. 2;
Fig. 4 is a fragmentary section taken on the line 4- ofFigZ;
Fig. 5 is a view similar to Fig. 2 showing another form of construction embodying the invention;
Fig. 6 is a cross-section on enlarged scale taken onthe line 6-6 of Fig. 5; e
Fig. 7 is a view similar to Fig. 6 showing another. form of construction embodying the invention;
Fig. 8 is a perspective view on enlarged scaleof a detail of the structure shown in Fig. 7; and
Fig. 9 is a view similar to Fig. 8 showing still anothe form of construction embodying the invention.
In the accompanying drawings, Fig. 1 is a diagram of which the abscissa indicates the cross section through a roof composed of a layer A of insulating materialand a rain and diffusion-proof outer coating or layer B. The
ordinate represents water vapor pressure and the curve C illustrates saturated water vapor pressure for an assumed temperature drop though the roof in the direction from the interior of the building to the external atmosphere The air of the interior of the building from which mois'-' ture'is diffused into the insulation has a moisture content, for example as represented by the point D, which is much below the corresponding point on the saturated water vapor pressure curve C, that is to say, in the portionof the insulated layer A adjacent to the interior of the build ing the air is not saturated by water vapor. 'Now, if the.
impervious outer coating B were not provided, the vapor pressure in the insulating layer A would follow the curve B. This curve extends below the curve C, and may touch or intersect curve C in the portion of the insulating layer adjacent to the external air. densation of moisture may take placeonly in this limited region and thus to a'limited extent.
of the insulating layer A. If tha't'is done the vapor pressure then falls to the point H at the inside face of the insulating layer and will then, as shown by the curve I, remain at all times below the curve C.
The'weather-proof external layer B, which is substantially diflusion-proof as well if the roof is to be satisfac tory, results however in the vapor pressure followingthe curve K, which meets the saturation curve C close to the inner surface of the insulation. The layer B forms a barrier to thediffusion of the water vapor, so that practically may be diffused thereinto, at a rate operative to maintain the insulation in a stabilized substantially dry state. By
combining such diffusion;'resis ting and ventilating means it is possible, as will hereinafter more fully appear, to
maintain even very flat roofs ofjcomparatively large this layer only lowers thev vapor pressure at the inner face;
no fall in vapor pressure takes place within the insulating layer. The difference invapor pressure between the imaginary portion K of curve K and that of the correspond ing portion of the saturation curve C is large and would,
under the assumed conditions, result in very substantial condensation of moisture-withinthe insulation. Further,
As aresult of this, con-' Improvement may be obtained by providing a barrier layer G'on the inside 3: of the insulating layer to the point H, the vapor pressure curve from that point following the line L which is substantially parallel to the abscissa, like line K and also intersects the saturation curve C in the inner portion of the insulating layer.
However, if an internal diffusion barrier which is highly resistant to the diffusion of water vapor is provided, together with ventilation of the insulation, in accordance with the principles of the present invention, then, even with a substantially diffusion-proof external layerB', the vapor pressure curve can be maintained along a line, such as that indicated by curve M, well below the value resulting, in the condensation of moisture within the ins'ula'tion;
If the external temperature rises, or the roof is sub-' jected to sun radiation, any moisture enclosed in the insulation evaporates so as to cause a pressure on the coverstood from the above that the conditions in' roof structures l are different from those in walls, for example, which are not moistened by rain or snow in the same manner as the roof,. and which therefore do not require as weatherproof an external coating layer.
As previously noted, the invention contemplates the provision of roof construction in which diffusion of moisture into the insulation is minimized, and to this end the invention contemplates the provision on the inner face of the roof, and inside the" insulation, of a layer of material which is made as nearly continuous as practical constuction permits and which is of a material highly resistant to diffusion of moisture in vapor form therethroughand which provides what may conveniently be termed for the purposes of this specification, a diffusion barrier.
By the provision of such a diffusion barrier the amount of moisture that can be diffused in vapor form into the insulation and condensed therein, because of the inability of moisture to diffuse through the outer layer of the roof to the external atmosphere, is reduced to an amount representing a very much smaller fraction of the moisture that-otherwise would be diffused and condensed than has heretofore been recognized. One of the reasons why this hasnot heretofore been fully recognized and appreciated is the fact that the relation between the diffusion constants or factors of various materials available for building construction purposes and the enormous difference in the effect due to the differences in the values of these constants have not previously been fully understood.
This has apparently been particularly due to the fact that different materials which are generally water-repellent, such as concrete, wood, brick and materials of that kind, have been considered reasonable proof against passage of moisture therethrough, whereas in fact they are, so far as diffusion of moisture in vapor form therethrough, relatively porous and capable of permitting moisture to be diffused through relatively thick masses of the material at quite a rapid rate.
In contrast with this class of materials, there are certain other materials which, in addition to being waterrepellent, are also very highly resistant to the diffusion of moisture through even very thin layers.
Sheet metal of" course is resistant to diffusion of moisture therethrough, and for that reason insulated, panels in which the insulation is hermetically sealed between inher andouter layers of metal do not present any problem due to moisture accumulated through diffusion.
However, roof constructions consisting of hermetically sea-led panels are not practically feasible for roof construction for economic as welL as many other praetic'al To illustrate the difference in the physical properties between different materials, insofar as their ability to provide a diffusion barrier is involved, the following tabulation gives the diffusion factors, as established by the best information presently known to us, of a number of different common building materials, and also the diffusion factor for still air.
The diffusion constant d as given in the following table, is expressed is terms of grammes of water vapor diffusing per square meter, per hour, through material 1 centimeter inthick ness, under the influence of a vapor pressure difference of'l millimeter of mercury.
Material: d Still air 8 to 10 Porous concrete 3 to 6 Pine (parallel with the directions of fibres) 3 to 6 Mineral wool 3 to 6 B'ricksl to 3 Porousfibre board 1' to'3 Pressed mineral wool l t'o Plywood 0. 5'to 1 Plaster 0.546 1 Concrete 0L5 tol Pine (perpendicular to the directions of fibres) 0.05 to 0.1 Hard fibre board 0L05to 01l Rubber of various kinds 0.0001 to 0.001 Asphalt 0.00005 to 0.0003 Wax 0.0000l In addition to the materials shown in the above table, there are certain other materials available in sheet form which might be thought suitable for the purpose of providing an inner layer or lining for the insulating layer of a roof of the kind under consideration to prevent substantial diffusion of water vapor into the insulation. Among such materials are various papers and the like and certain of the synthetic materials available in sheet form. Actually, however, it is the case that such materials are generally of little value as diffusion barriers, as is shown by the following tabulation of the diffusion factors for some such materials, the values of'the factors being comparable to those given in the preceding table, but for thicknesses ofthe' material indicated in the following table rather than for thicknesses of one centimetre thickness of the material.
From the foregoing schedules it is at once apparent that of the many different and commonly available materials only a very few are useful from the standpoint of providing an e'flicient diffusion barrier; It is also evident that the dilference between these materials and the" others is of very great magnitude.
Of the materials listed which have desirable a factors, wax has the weaknesss that in some instances the heat required to be withstood is above the softening or. melting point of most waxes, and while from the standpoint of physical properties rubber is a better material, its' cost is a deterrent factor.
From all standpoints, asphaltic material is probably most advantageous of the commonly available materials, its d factor being such that it can provide a highly effective diffusion barrier if applied only as a very thin layer. Thus for plain a'sphaltic coating, for example one cold and two hot applications which would have an ag gregate thickness of only approximately 3.040 mm, the d factor will be of the order of 0001. Suchcoatings with comparable: d factors may also be combined with paper or felt impregnated with the asphalt. Also, metalfoil'of aluminum or like material, so thin as to be not wholly impervious to diffusion of vapor therethrough, as for example 0.09-0.10 millimeters thick, when glued in place with asphaltic or artificial resinous material such as cellulosic derivative exhibits a d factor of only 0.001 or even less.
Thus, the provision of an effective diffusion barrier is not limited to a single material or construction but as of the present state of the materials art, asphaltic materials appear to be most advantageous when all factors inclusive of cost and installation are considered.
The extent to which the presence or absence of an effective dilfusion barrier affects quantitatively the amount of vapor condensate accumulating per unit of time in an insulated roof of the kind under consideration, under like conditions, is vividly illustrated by consideration of the following empirical formula, which has been found quite sufiiciently accurate for all practical commercial purposes, even though certain theoretical factors of negligible magnitude are omitted for the sake of simplification.
The formula, which is here stated for roofs having different layers of different materials, which layers may be of different number in diflerent specific case; is
a 2 n cl tz is in which V=amount of dilfused vapor, in grammes per square meter per hour.
P =water vapor pressure in millimeters of mercury at inner face of roof.
P =water vapor pressure in millimeters of mercury at outer face of roof.
t t etc., thickness in centimeters of the several layers.
d d g, etc.,=the diffusion factors of the materials of the several layers expressed as previously noted.
For the purpose of utilizing the above formula to illustrate the magnitude of the influence of a suitable vapor barrier on the quantity of vapor diffused into an insulated roof it is only necessary to apply it to two simple examples of roof construction of quite common nature, consisting of an insulating layer of porous concrete 12 centimeters thick laid on a supporting solid concrete decking 12 centimeters thick, in both cases the roof having a weather and diffusion proof outer covering, and in one case an internal difiusion barrier of 0.3 centimeter of asphalt being laid between the insulating layer of porous concrete and the supporting concrete decking while in the second case no diffusion barrier (other than the 12 centimeters of solid concrete, heretofore believed to be a sufficient barrier) is provided.
Applying the formula, and employing the highest a' values given in the first table above for the respective materials; for the first case,
and for the second case, P,--P., P,-P,,
application of the above formula, using the lowest if value for the plaster, shows that diffusion of vapor into the insulation will be more than fifty times greater without the diffusion barrier than with it.
Even with the provision of a diffusion barrier of the nature contemplated by the present invention, there will be sufficient diffusion of vapor into insulation so that its removal is required if the efiiciency of the insulation is to be maintained. However, when a diffusion barrier of the kind contemplated is provided the rate of diffusion is quantitatively so reduced per unit time that removal of the diffused moisture from the insulation continuously at a rate sufficient to maintain the insulation in substantially dry state may be eifected by continuous ventilation of the insulation through the medium of air channels which are in dilfusion relation with the insulating material and through which flow or circulation of air may be maintained by relatively small, simple and practical natural draft creating means, even in the case of roofs of the kind under consideration and hereinafter generally referred to as fiat roofs. By the term flat roofs we do not mean to restrict ourselves to roofs which are exactly horizontal but intend to use the term to cover both horizontal and substantially or generally horizontal roofs of the kind characterizing commercial and factory buildings, as contrasted with the relatively steeply pitched roofs generally characteristic of dwellings and other gabled structures.
We accordingly contemplate in accordance with the present invention not only the provision of roof construction including a highly efiicient vapor diffusion barrier, but also a roof construction in which vapor which does diffuse into the insulation is removed by ventilating air circulated through suitable ventilating channels in diffusion relation with the insulating material.
The specific ways in which the principles of the invention may be carried into effect may be varied considerably and will in most instances be dictated to a material extent by the specific character of the roof construction which it is desired to employ.
By way of example but without limitation several different specific forms of roof construction suitable for carrying the invention into efiect are illustrated in Figs. 2 to 10 hereof, which are now to be described.
Referring now more particularly to Figs. 2 to 4 inclusive, the roof therein illustrated comprises a generally fiat structure the support for which is provided by the roof girders or beams 10 having only a very slight pitch and spaced at appropriate intervals, only a pair of such beams being shown in Figs. 2 and 4.
Beams 10 support the roof which in the present case is indicated as being made up of a number of units or slabs 12 of porous or so-called cellular concrete, which material has relatively high heat insulating value and which also has sufficient structural strength to form a roof decking when supported by beams spaced at reasonable intervals. The units 12 provide the insulating layer and over this is laid a weather-proof outer layer or covering 14 which may be of any well-known form suitable forv the purpose and which is ordinarily comprised of one or more coatings of asphaltic or equivalent bituminous material which may or may not be used in conjunction with building paper or roofing felt impregnated with such material. 1 v .In order for the roof to be satisfactorily rain-proof the outer layer is made as continuous as practical conditions permit, so that it constitutes not only a watertight but'also a substantially diffusion-proof covering for the roof. I r The insulating layer provided by the units 12 is further covered on its inner surface by a diffusion barrier 15, which is made as continuous and unbroken as circumstances permit and which may comprise an asphaltic coating or a layer of other material which is characterized by 'very high resistance to diffusion of water vapor therezgscagseo through, as for example, some of the other materials-and constructions herei-nbefore mentioned which are char-- acterized by diffusion factors a of very low value;.
The roof structure is provided with a multiplicity of channels 16 extending in diffusion relation or connection with the insulating material, these channels in the embo'dim'ent illustrated, being located at the: outer face of the insulating layer and advantageously being bridged by channel bars 18 providing suitable support for the portionsof" the outer layer 14,.overlyingthe channels.
As shown the channels 16 extend in parallel spaced: relation to each' other from the caves of the roof, where they communicate with the external atmosphere, to the ridge where they communicate with a common channel or header 20, such channel being'fornied in any suitable manner as, for example, by means of the-hood strip 22 and the bridging strip 23" connecting. confronting portions of the insulating material onopposite sides of the ridge. Channel 2% communicates with a: chimney or stack 2"4'- providing theoutlet for the air circulating system, the inlets of which should be confined to the inlets of the several ventilating channels 16:
Assuming winter conditions to be prevailingg so that the. ambient external atmosphere is at lowertemperature than that within the building; the temperature of the air in the channel 16 is slightlyhigher than that of'theopenair, and the stack 24 provides anair column the" temperature of which is also higher than that of the outside air; A difi'erential' pressure is thus setup, creating a natural draft in directions of how indicated by the arrows in Fig. 2. Due to this natural thermal flow, at'r'no'spheric and consequently relatively cold dryair enters the ventilating channels 16' at the eaves. This air, due
among other things to rise in temperature, is capable of and absorbs moisture from the insulating material with which the channels are in diffusing relation; The air from channels 16 discharges to the collecting or header channel 20 and tlows to the stack 241 in this as in other embodiments hereinafter described the spacing of the channels 16 from each other is suchas to enable the air flowing through the channels to have diffused thereto and to entrain and carry away the moisture condensed in the insulating layer as a result of diffusion of water vapor thereinto from the interior of the building.
A different kind of roof construction is illustrated in Figs. 5 and 6, these figures showing a very flat form of roof construction in which a continuous decking of solid concrete 26 is laid upon the supporting roof beams 10,
this decking in turn having laid therein an insulating layer 12 which may for example" be of a suitable form of cork, the latter being overlaid by the outer weatherproof and substantially ditfusi'on proof' coating or layer 14 as previously described. In this construction the internal diffusion barrier 15 for preventing diffusion of relatively large quantities of Water vapor into the insulating layer is located between the solid concrete decking 2.6 and the insulating layer 12. Obviously such a barrier may readily be applied in continuous form by applying fluid bitumen to the upper face'ofthe concrete decking 26 before the layer of cork or other insulating material is laid upon the decking In this embodiment the ventilating channels 16' are formed in the inner rather than the outer face of the insulating material. At their inlet ends they communicate with the ambient atmosphere and at' their outlet ends" connect'with a collecting or header channel 20 formed between the spaced apart portions of the insulating layer 12".
In this form of construction the air in the-ventilating channels receives more heat from the interior of the building than is the case when the ventilating channels. are a-tior adjacent to the external: surface of. the roof. As a result of this; higher air velocity through the channels may be developed due to thermal head. and if desired IOY this can beenhanced byffurthe'r' absorption of heat from the interior of: the building through an exit. stack 28, a portion of which 28a is made. in. the form of a U-bend extending from channel 20. into. the. interior of the buildingf to absorb heat: lhfil'fifLOIl'h The expedient of the use oh an additional heat absorbing conduitsuch as 2811: is not essential, and Whether or not such expedient is resorted to, it is desirable to provide: heat insulation such asis indicated: as 30 for the externally exposed wall of the channel 20 as well as heatinsulation 28b for the externally exposed portion of the stack 28, in order to avoid possible chilling. of. the warmed air delivered from the channels 16, during its passage through channel 20 and stack 28, fo a; temperature below the: dew point thereof and consequent condensation of moisture from such air before it is discharged to the ambient atmosphere.
In connection with theembodimentof construction just described it is to be: noted that the relatively small quantity of moisture which it isnecessary to remove from the insulating layer in order to maintain itin stabilized relatively dry condition, makes it possible for the ventilating channels tobe placed on the inner or warm side of the insulating layer without resulting in an uneconomically great loss of heat from the interior of the building to the ventilating air. This in turn enables the relatively small quantity of ventilating air to be heated through a relatively greater temperature range than if the ventilating channels were on the exterior face of the insulation and this greater temperature increase in. turn aids in creating a greater temperature or thermal head, so that either a greater velocity of air flow through relatively small. channels can be secured with a chimney or stack of given height, or, for channels having the same flow resistance, the desired velocity of flow can be obtained with a stack of. lesser height.
As previously noted, many other specific forms of construction. may be employed within the scope of the invention, and. by way of. example thereis shown in Figs. 7 and 8 a further embodiment of construction in which the units 12' forming the insulating layer are provided with tubular metallic reinforcing members 32 located in the lower portions of the units for reinforcing the insulationand enabling single units of the latter to bridge the gap between supportihg' beams spaced more widely than otherwise would be possible. In such construction the members 32 constitute the ventilating channelsand are provided with' amultiplicity of slotlike openings 34whi'ch pl ace the interiors .ofthe members indiflfusion relation with the surrounding insulation. The openings 3'4 may be coveredW-it-h suitable material which is substantially non-resistant to: diffusion of water vapor therethrough. inorder toen'sure' against the channels formed by the members 32 beii1g' filled or partially filledby debris material. I I
Fig: 9 is illustrative of an embodiment in which the insulating layer, with its inner diifusion barrier 15, has laid thereon a plane layer 36 and' a corrugated layer 38 of material which is substantially non-resistant to diffusion of moisture. Over thecor-rugated layer 38 there is laid a layer 40 or cement, mortar or the like, and upon the latter, after'it has set, there is laid the outer weather-proof layer or covering 143 this arrangement the ventilating passages 42- are formed between the plane and corrugated layers 36: and 38 respectively. The construction just described is adapted to provide greater load-carrying capacity than would otherwise be available, while at the same time affording. all of the requisite features foravoi'ding. accumulation of moisture within the insulating layer. 7
As will be observed from all of the structural modifications above described, the header or collecting channels 20; are. made. of larger cross sectionalarea than the ventilating channels 16 which deliver to them, and the entire ventilating system should be. laid out soas to provide the minimum practical amount of resistance to air flow, so that the necessary ventilation can be efiected with the minimum in the way of special draft creating means. We have found from experience that when channel systems are properly distributed and with the channels having appropriate areas, that for flat or substantially flat roof panels up to approximately 15 meters in width, sufiicient draft to provide the required ventilation, provided the roof is equipped with the eflicient diffusion-barrier contemplated by the invention, can be created by the provision of a thermal draft creating column or stack of approximately 2 meters height. It will be evident from the foregoing that the specific nature of the roof construction and also the specific form and arrangement of the ventilating and header channels, as well as the specific means for creating the required circulation of ventilating air, may be subject to wide variation without departing from the principles of the present invention, the scope of which is accordingly to be considered as embracing all forms of structure falling within the scope of the appended claims.
What is claimed is:
l. A roof structure comprising a substantially continuous layer of insulating material, an external finishing layer of weatherproof material supported by said insulating material, a substantially continuous internal layer of material providing a diffusion barrier resistant to diffusion of water vapor therethrough on the inner face of said insulating material, a multiplicity of channels extending between said internal and external layers and in diffusion connection with said insulating material, header means comprising one or more collecting conduits with which said channels communicate, said collecting conduits having a substantially greater cross sectional area than said channels, said channels also communicating with a source of relatively dry air, said roof structure having insufficient slope to create substantial flow of air through said channels and header means due to natural draft, and draft creating means connected with said header means for creating flow of said relatively dry air therethrough to absorb and remove moisture from said insulating material.
2. A structure as defined in claim 1 in which said multiplicity of channels is formed in said continuous layer of insulating material.
3. In a building, a roof comprising a supporting structure, a substantially continuous layer of insulating material supported by and located externally of said supporting structure, an external finishing layer of weatherproof material supported by said insulating material, means comprising an asphaltic material providing a substantially continuous internal layer forming a diffusion barrier highly resistant to diffusion of water vapor therethrough interposed between said insulating material and the interior of the building, a multiplicity of channels extending between said internal and external layers and in diffusion connection with said insulating material, header means comprising one or more collecting conduits with which said channels communicate, said collecting conduits having a substantially greater cross sectional area than said channels, said channels also communicating with a source of relatively dry air, said roof structure having insufiicient slope to create substantial flow of air through said channels and header means due to natural draft, and draft creating means connected with said header means for creating flow of said relatively dry air therethrough to absorb and remove moisture from said insulating material.
4. A roof as defined in claim 3 in which said multiplicity of channels is formed in said continuous layer of insulating material.
References Cited in the file of this patent UNITED STATES PATENTS 1,931,066 Eckcrt Oct. 17, 1933 2,192,458 Swenson Mar. 5, 1940 2,318,820 Voigt May 11, 1943