Patent Publication Number: US-8966843-B2

Title: Wall for separating the inside of a building from the outside

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a wall for separating the inside of a building from the outside, to a building sheath, and to a building having such a wall, as well as to a method for the construction of a building. 
     2. Description of the Related Art 
     If there is a difference in the content of water vapor or in temperature between the outside and the inside, then there is an effort to balance out this lack of equilibrium, in that a corresponding water vapor stream or heat stream occurs. In order for no damage to the building construction to occur, the wall must be designed in such a way, among other things, that no relative humidity occurs that brings about mold formation and/or the condensation of water. 
     In climate zones in which the water vapor stream over the course of the year always comes from the same direction, as is predominantly the case in western Europe, for example, the wall structure is configured in such a way, in order to avoid the aforementioned problems, that the moisture can leave the wall in the direction of the vapor diffusion stream more easily than it can penetrate into the wall from the direction of the vapor diffusion stream. 
     However, there are also climate zones in which the water vapor stream can come from both directions, i.e. from the inside and from the outside, over the course of the year. This is typically the case in those climate zones where a rainy season occurs, and thus very high humidity combined with warm temperatures prevails over an extended period of time. If it is then cooler and/or drier indoors, for example on the basis of air conditioning, then the water vapor stream is directed from the outside to the inside. During the cooler season, in contrast, the indoor spaces are generally warmer and more humid than the outdoors, so that a water vapor stream in the opposite direction occurs. Such climate conditions, with a water vapor stream in both directions, which are found in Japan, New Zealand, and other countries, for example, promote condensation and mold formation, particularly if the indoor spaces are air conditioned. 
     One possibility for avoiding damage to the building construction in the case of such climate conditions consists in structuring both sides of the wall to be vapor-tight, and thus to completely prevent a vapor diffusion stream through the wall. However, this configuration has the disadvantage that it is extremely susceptible to mechanical damage, and thus can easily lose its effectiveness as the result of damage to the vapor-tight planes. Often, such a configuration is therefore not used, and it is accepted that there can be problems with regard to condensation and mold formation. 
     BRIEF SUMMARY OF THE INVENTION 
     It is a task of the present invention to indicate a damage-resistant wall for separating the inside of a building from the outside, which wall is particularly suitable for climatic conditions in which a water vapor stream occurs from the inside to the outside as well as from the outside to the inside. 
     This task is accomplished by means of a wall in accordance with claim  1  or  15 . The further claims indicate preferred embodiments of the wall according to the invention, a building sheath, and a building having such a wall, as well as a method for the construction of a building. 
     The wall according to the invention has the advantage, among other things, that the climate conditions that occur do not lead to mold formation or condensation of water, because of its special configuration. 
     Further characteristics and their advantages are evident from the following description and figures of exemplary embodiments, where 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  show a first and a second exemplary embodiment of a wall according to the invention, in an exploded view, and 
         FIG. 2  shows a graphic representation in which values for the heat transfer coefficient (U-value) and the water vapor diffusion resistance (SD-value) for the wall according to the invention, as well as for various known buildings, are indicated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the following construction physics parameters and terms are referred to:
         heat transfer coefficient (also called U-value):   The U-value indicates the heat stream that flows through 1 m 2  of a building component, perpendicular to the surface, in the stationary state, if a temperature difference of 1 Kelvin prevails between the air that lies against it on both sides. The U-value is indicated in watts per square meter and per Kelvin [W/(m 2 ·K)]. (For determining the heat transfer coefficient, see also the corresponding standard: EN ISO 6946 “Building Components and Building Elements—Thermal Resistance and Thermal Transmittance—Calculation Method”.)   Water vapor diffusion resistance (also called SD-value):   The SD-value is related to the water vapor conductivity (amount of water that passes through a cross-sectional area of 1 m 2  per hour, if a water vapor pressure gradient of 1 Pa prevails along the diffusion distance of 1 m). The SD-value is indicated by SD=μ·d, where μ is the ratio of the water vapor conductivity of the air relative to the water vapor conductivity of a building component, and d is the layer thickness of the building component. The dimension of the SD-value is meters of equivalent air layer thickness [m]. (For determining the water vapor diffusion resistance, see also the corresponding standard: ISO 12572:2001 “Hygrothermal performance of building materials and products—Determination of water vapour transmission properties”.)   Moisture storage capacity (also called FK-value hereinafter):   The moisture storage capacity can be stated in kilograms per square meter [kg/m 2 ] and corresponds to the amount of water vapor that can be absorbed by one square meter of a building component, in kilograms. The moisture storage capacity is determined by way of the difference in the mass that the building component demonstrates in the state of equilibrium at a specific temperature T1 and a specific relative humidity phi, and the mass that the building component has in a specific starting state. This starting state is either the dry state of the building component or the state that the building component has when it is in the state of equilibrium, at a specific starting temperature T0 and a specific starting relative humidity phi0. The dry state is achieved in that the building component is heated to 100 degrees Celsius, so that the moisture evaporates completely. (For determining the moisture storage capacity, see also the corresponding standard: ISO 12571 “Hygrothermal performance of building materials and products—Determination of hygroscopic sorption properties”.) Hereinafter, the following FK-values are used:
           “FK-value 0/80”: Is the FK-value that results from the weight difference of the material being considered between the completely dry state and the regulated state at T1=20 degrees Celsius and phi=80%.   “FK-value 0/85”: Is the FK-value that results from the weight difference of the material being considered between the completely dry state and the regulated state at T1=35 degrees Celsius and phi=85%.   “FK-value 20/80”: Is the FK-value that results from the weight difference of the material being considered between the regulated starting state at T0=20 degrees Celsius and phi 0 =20% and the regulated state at T1=20 degrees Celsius and phi 0 =80%.   
           Thermal mass:   The thermal mass can be indicated in kilojoules per cubic meter and per Kelvin [kJ/(m 3 ·K)], and corresponds to the specific heat capacity multiplied by the density.   Moisture buffering:   A moisture-buffering material has the property of being able to store liquids and/or vapor, particularly water, and later, i.e. with a time delay, to release it again in gaseous form. The processes relevant in storage particularly relate to physorption (storage by means of a physical process, e.g. accumulation of molecules on surface and/or in pores) and chemisorption (storage by means of a chemical process).       

     The wall (also called “outer wall” hereinafter) separates the inside of a building from the outside and serves as a bearing wall construction of the building. It comprises multiple layers, where a central, statically bearing layer is lined on both sides with additional layers. 
       FIGS. 1   a  and  1   b  show two exemplary embodiments of an outer wall according to the invention. The exemplary embodiment indicated as  1   a  in  FIG. 1   a  has the following layers, seen in the sequence from the outside (indicated with “OUT” in  FIG. 1   a ) in the direction toward the inside (indicated with “IN” in  FIG. 1   a ):
         an exterior finish  8 ,   an outer layer  9 ,   a bearing layer  10 ,   an inner layer  11 , and   an interior finish  12 .       

     Depending on the design of the outer wall, a film can be provided between the layers  9  and  10 , as an additional layer, as a wind and air seal. 
     The exterior finish  8  is designed as a façade finish that is not water-vapor-tight, and accordingly has a regulating effect on the water vapor diffusion stream. The finish  8  is treated in such a way that mold and fungus formation is prevented. This happens, for example, in conventional manner, by means of providing suitable chemical substances. However, biocide-free finishes are also known, which regulate heat and moisture in such a manner that the formation of surface condensation is prevented, and thus no growth of algae or fungus takes place. Such finishes are commercially available under the name AQUA PURA®, for example. 
     The exemplary embodiment indicated in  FIG. 1   b  as  1   b  is designed for a ventilated, suspended construction, and is therefore provided with a suspended façade on the finished building, in place of the exterior finish  8  (not shown in  FIG. 1   b ). For the remainder, the outer wall according to exemplary embodiment  1   b  has the layers  9  to  12 . 
     The bearing layer  10  forms the statically active element of the outer wall and is made from wood, for example. Particularly stable wooden elements are known, for example, under the name Lignotrend®. In these elements, wooden boards are glued to one another crosswise. 
     In the present exemplary embodiment, the bearing layer  10  is configured as a continuous plane that acts to inhibit water vapor, because of its water vapor diffusion resistance. By means of a suitable design of the further layers  9 ,  11  and—if present—the layers  8 ,  12 , however, a critical moisture level in front of the water-vapor-inhibiting plane can be prevented, and in total, an outer wall having a low SD-value can be made available. Entry of moisture into the wall is therefore permitted to a certain degree. This method of functioning, by preventing possibly critical moisture amounts in front of one or more water-vapor-inhibiting planes, is also possible with embodiments other than the one shown in  FIGS. 1   a  and  1   b.    
     The outer layer  9  is disposed on the outside of the bearing layer  10 . On the one hand, the outer layer  9  is heat-insulating, and thus serves to reduce the transmission heat losses. On the other hand, it acts as a moisture buffer, i.e. it is sorption-active, so that it is able to absorb moisture and release it again. The outer layer  9  is designed in such a manner that it absorbs moisture that penetrates from the outside to the inside, in such a manner that moisture accumulation and condensation on the bearing layer  10  is prevented. 
     Suitable materials as insulation for the outer layer  9 , which demonstrates not only a heat-insulating function but also a moisture-regulating function, are, among others, those on an organic basis such as wood fibers, cellulose, etc. Known products are wood fiber insulations of PAVATEX® and products sold under the name ISOFLOC®. 
     It is also possible to use materials on a mineral basis, e.g. porous stones, as insulation. 
     The outer layer  9  can also be structured from multiple planes having different compositions, for example in the form of a wood fiber panel known under the name DIFFUTHERM®. It is also possible that the outer layer  9  has a graduated structure, in that one or more water-vapor-inhibiting planes (e.g. films, coatings, adhesive planes, etc.) are used in order to optimize the absorption in the insulation. Constructions structured in such a graduated manner are available as wood fiber panels under the name PAVADENTRO®, for example. 
     The inner layer  11  is disposed on the inside of the bearing layer  10  and forms the inner covering. The inner layer  11 , like the outer layer  9 , acts as a moisture buffer and is therefore active for absorption. The inner layer  11  is designed in such a that it can store the amount of moisture that occurs in the interior if the building sheath is designed to be wind-tight, and in this way, moisture accumulation and condensation on the bearing layer  10  are prevented. 
     Materials on a mineral basis, such as clay, gypsum, etc., and on an organic basis, such as wood, are suitable, among others, as materials for the inner layer  11 . For example, the layer  11  is configured as a wood, clay, or gypsum panel, or as a composite of such panels. 
     Typically, the inner layer  11  is designed for short-term storage, while the outer layer  9  acts for long-term storage. The time interval during which moisture can be absorbed in the outer layer  9  and released again is therefore longer than in the case of the inner layer  11 . In this way, short-term moisture peaks in the interior can be absorbed by means of the inner layer  11 , on the one hand, and the slower moisture changes on the exterior can be absorbed in effective manner, on the other hand, by means of the outer layer  9 . 
     In the exemplary embodiments shown in  FIGS. 1   a  and  1   b , the outer wall furthermore has a layer in the form of an interior finish  12 . This is configured in usual manner. Depending on the design of the interior space, the interior finish  12  can also be left out and/or replaced with a different layer, e.g. a wallpaper. 
     In the exemplary embodiments shown in  FIGS. 1   a  and  1   b , the two layers  9  and  11  act as moisture-buffering planes that are matched with the bearing layer  10  concretely used. In the finished construction, the water vapor is absorbed, on its path through the outer wall—whether from the outside or from the inside—ahead of the layer  10 , in an amount that prevents a critical level of the water vapor from being reached ahead of the layer  10 . The sorption-active composition of the outer wall allows releasing the absorbed water vapor again during other seasons, from the wall into the interior or the exterior. In this way, it can be avoided over multiple years that water accumulates in the outer wall. In the case of a suitable design, the performance capacity of the wall also does not decrease over the years. 
     In total, the outer wall acts by means of dampening and delaying temperature variations, by means of thermal mass and thermal inertia, as well as by means of storing moisture by means of materials capable of absorption. In this way, variations in the moisture and moisture peaks are reduced, so that moisture concentrations that would be harmful for the construction can be prevented. 
     The selection of the composition of the layers as well as the precise dimensioning of the individual layers, particularly the layer thickness, are performed, for example, by means of a suitable simulation program. This program allows calculating the behavior of the outer wall with regard to moisture and temperature (“hygrothermic behavior”) on the basis of predetermined starting variables and the known physical equations. These physical equations relate, among other things, to heat and moisture transport, to the moisture absorption velocity, the moisture release velocity, and the sorption capacity. 
     Starting variables are, among others, local climate data (e.g. measured values regarding temperature and humidity, which were reached locally over the course of the year), data regarding the planned construction materials (e.g. heat conductivity, water vapor conductivity, etc., which the materials used demonstrate), and data that define the precise purpose of use and the desired concept of the building (e.g. type of desired façade such as exterior finish or suspended façade, planned use and design of the interior space, and the moisture load, size of the building, etc., that result from this). 
     The outer wall is then designed in such a manner, using the simulation calculations, that not too much moisture can collect on the inside of the wall, or that no relative humidity can occur that would lead to mold and condensation (also called “moisture avoidance condition” hereinafter). For example, it is demanded as a moisture avoidance condition that the moisture concentration in the bearing layer  10  does not reach the maximum of 100%, and that the moisture concentration in the layers  9  to  11 , and preferably also in the layers  8  and  12 , does not go above 80% over a specific period of time (e.g. two weeks and more). Of course, the latter condition can also be selected to be different, for example also in such a way that specific requirements with regard to permissible moisture are established for the individual layers. 
     In general, the possible starting variables have a broad spectrum. In particular, the local climate conditions and the user needs can vary greatly. Because of the layer-by-layer construction of the outer wall, a type of modular system is created, which allows adapting the outer wall to a broad spectrum of starting variables, in such a manner that the moisture avoidance condition is also met. 
     The outer wall is coordinated, with regard to water vapor transfer resistance, storage capacity, and insulating effect, in such a manner that condensation and mold are avoided. The outer wall has a range of effect defined by the SD-, FK-, and U-values, which lie in the following ranges, in terms of value:
         The SD-value (water vapor diffusion resistance) amounts to at most 20 meters, preferably at most 15 meters, and particularly preferably at most 10 meters. Preferably, the SD-value amounts to at least 2 meters and/or at least 3 meters. The SD-values indicated relate, of course, to the resistance of the intact surface. Possible joins or other leaks are not taken into consideration.   The “FK-value 0/85” amounts to at least 1 kg/m 2 , preferably at least 2 kg/m 2 . Typically, the “FK-value 0/85” amounts to at most 20 kg/m 2  and/or at most 15 kg/m 2  and/or at most 12 kg/m 2 .   The “FK-value 0/80” amounts to at least 2 kg/m 2 , preferably at least 3 kg/m 2 , and particularly preferably at least 4 kg/m 2 .   The “FK-value 20/80” amounts to at least 2.0 kg/m 2 , preferably at least 2.5 kg/m 2 , and particularly preferably at least 3.0 kg/m 2 .   The U-value (heat transfer coefficient) amounts to at most 1.5 W/(m 2 ·K), preferably at most 1 W/(m 2 ·K), and particularly preferably at most 0.7 W/(m 2 ·K). Preferably, the U-value amounts to at least 0.1 W/(m 2 ·K) and/or at least 0.15 W/(m 2 ·K) and/or at least 0.19 W/(m 2 ·K).   As is evident from  FIG. 2 , the SD- and U-values of the outer wall lie in the left lower range, which is indicated with 20. (The rectangle shown with a broken line in the range 20 indicates the preferred value range.) For a comparison, further ranges 21-24 are shown in  FIG. 2 , which indicate typical SD- and U-values for known buildings in Japan.       

     The outer layer  9  and/or the inner layer  11  comprise a moisture-buffering material that has a thermal mass that is typically greater than 100 kJ/(m 3 ·K), preferably greater than 200 kJ/(m 3 ·K), and particularly preferably greater than 300 kJ/(m 3 ·K). 
     Each layer  8 - 12  can be structured in form of a homogeneous or heterogeneous layer. Furthermore, the individual layers  8 - 12  can be configured in a self-contained manner or they can also be configured such that adjacent layers engage with each other and/or overlap. When seen in the cross-section, the individual layer  8 - 12  can have a layer thickness which is substantially constant or variable. 
     To form a building sheath, additional building components such as floor and ceiling/roof have to be provided in addition to the outer walls. These building components can be structured in multiple layers in a similar way as the outer wall and be designed in such a manner that the building sheath, as a whole, has U-, SD- and FK-values such as those indicated above in connection with the outer wall.