Measurements

Introduction

Depending on the task, the renovation objective and the scope of measures, it may be necessary to determine properties of the building materials in the existing wall structure as a prerequisite for selecting an internal insulation system. Measurements are required if the building as a whole cannot be classified as uncritical (showing no cracks, indication of presence of salt or indication of moisture related damage) (See ‘Assessment of state of the building envelope’). This is also the case if the assessment described in ‘Collection of information about the building and surroundings’ not sufficient to regard the external wall and adjoining building elements (esp. wooden beams supporting suspended floors) as sufficiently robust to let the external wall be internally insulated.

Such an evaluation might require measurements either on-site or in a laboratory (Figure 4–40), although it might be possible to use simpler aids to obtain some basic values. Measurements cost from approx EUR 2.000 for simple, basic parameters to EUR 9-10.000 for an extensive investigation. Measurements needed to perform a simulation using DELPHIN on a specific building material cost approx EUR 5-6.000.

Many damages in buildings are caused by moisture, e.g. by leakages at the roof, at the facade or in the ground area (Figure 4–41). The moisture load causes existing salts in the building material/component to dissolve and to be transported in the direction of the drying area. The hygroscopic properties of many salts can cause water accumulation, which are often accompanied by an extensive increase of the volume. Thus, even after the construction has dried, damage is unavoidable if the cause and extent of the damage is not clear. Therefore, moisture measurements on walls to determine the moisture content and distribution and knowledge of the salt content are necessary prerequisites to consider further measures, especially in the case of planned renovation.

The most important parameters are:

1)      Water vapour permeability (µ-value)

Knowledge of this value is important, for example, for structures at risk of driving rain, to be able to assess the vaporous drying potential through the existing structure and, on this basis, to shortlist or exclude certain insulation systems for internal insulation. The value can only be determined by means of a laboratory measurement.

2)      Water absorption capacity (w or AW) of the facade material

It is always necessary to determine the water absorption capacity of the façade material if it is not possible to ensure that the façade is sufficiently resistant to driving rain.

Option 1: Laboratory measurement of capillary water absorption
Option 2: In-situ tests, e.g. Karsten's test tube, test plate according to Franke, or Water Absorption measuring instrument (WAM)

3)      Thermal resistance (R) or U-value

This value results from the type of materials used, the material thicknesses and their thermal conductivity. There are different ways of determining or estimating these values.

Option 1: Laboratory measurement of thermal conductivity
Option 2: In-situ testing
Option 3: Use of characteristic values from databases

RIBuild deliverable D3.2 (RIBuild Deliverable D3.2, 2019) presents the hygrothermal performance of a number of internally insulated case study buildings, either RIBuild-cases or published monitoring projects. And it gives a description of material testing methodologies that can be done on-site with a minimum destruction of the buildings (Section 4.3.1 in deliverable D3.2). Laboratory testing methodologies are described in (RIBuild Deliverable D2.1, 2018).

Building material properties can be differentiated into storage and transport characteristics. The heat storage capacity is a simple characteristic value which is described by the mass-related storage capacity (specific heat storage capacity) and the bulk density. The thermal conductivity results from the conductivity of the material itself and, if it is a porous building material, from the conductivity of the material enclosed in the pore space (water or air). The water present in the pore space is mapped via the moisture storage function.

The moisture transport property of a building material is in turn subdivided into the transport function for vapour and for liquid water. Both components, as well as the thermal conductivity, depend on the water content of the brick, i.e. on its storage properties. This storage property is measured in the form of the equilibrium moisture content (sorption isotherm) for specific values of relative humidity.

On-site measurements

Moisture penetration through existing structures is not always visible. If, for example, the outer surface of the external wall has dried after a period of sunny weather, it may be difficult to determine whether the wall core has become moist. On the other hand, in unused, cold basement rooms in summer, surface condensation may be visible, which does not necessarily indicate moisture penetration from outside, but can be summer condensation. On-site measurements (if possible in combination with sampling) can be used to make sufficiently accurate statements. The scale of on-site measurement activities depend on:

• available time

• non-destructive vs destructive method

• cost

• derivable material properties

• measuring accuracy (high, medium, low)

• measurement prerequisites/flexibility

Fundamental different types of methods are used for measurement of moisture properties and heat transport.

On-site moisture measurements

In practice, there are many on-site moisture measurement methods with different requirements and accuracies. A distinction is made between indirect (or non-destructive) and direct (or destructive) methods as presented in Figure 4–42.

Indirect or non-destructive measurement methods

There is a multitude of indirect or non-destuctive measurement methods (electrical, optical, thermometric, hygrometric, acoustic...), many of which are not relevant or usable for construction practice. Only the most common procedures in the construction industry will be dealt with here; the electrical procedures, listed in Table 4‑22.

Table 4‑22. Overview of indirect moisture measurement methods

Capacitive measurement

This method allows non-destructive moisture measurements in near-surface areas, up to approx. 2-4 cm depth of material depending on the building material density (Figure 4–43). It is well suited for comparative measurement to detect differences between wet and dry areas in mineral building materials and wood, but is considered unsuitable for qualified humidity measurements. It is suitable as a pre-tester for destructive measurement methods (Laboratory measurements).

The capacitive humidity measurement is based on the functional principle of a capacitor. The procedure exploits the different dielectric constants of dry, non-conductive substances (about 2-10) and water (about 80). Depending on the dielectric constant, the capacitance of the capacitor changes. The higher the humidity, the higher the electrical conductivity and at the same time the increase in the dielectric constant of the substance to be measured. The complex relative dielectric constant is a material-specific quantity. One factor to be considered is the raw density of the test product. With increasing density, the display value increases with dry and moist material.

The measuring field is formed between the active probe on the upper side of the device and the material to be evaluated. The change in the electric field due to material and moisture is recorded in the meter, converted to digital (output, for example, as a digit unit or also as a conversion in % by weight). The measurement is a relative measurement. The difference between the dry and the wet building material is displayed. Dissolved salts can turn the building material into an electrolytic conductor, resulting in higher capacitance values.

Resistance humidity measurement

The resistance measurement method can be used to measure the moisture content at the material surface, but also in deeper component layers. However, drilling is required to allow longer electrodes to be inserted. It is well suited for wood based materials (see Figure 4–44).

In this method, the electrical resistance is measured as a function of the electrical conductivity between two electrodes that are hit, rammed or drilled into the material. In dry building materials the resistance is very high, as they conduct the power poorly. Thus, a low reading is displayed on the meter. As the moisture content of the material increases, so does the conductivity, as water contained in the material conducts the current well. This displays a higher reading. The displayed measurement results can be converted into moisture percentages taking into account different building materials.

Falsifications of the measurement results are possible due to unequal moisture distribution and inhomogeneity in the material, to other conductive materials in the wall (e.g. cables or wires), salts in the building material, surface treatment, or poor contact of the electrodes to the material. However, such incorrect measurements can be corrected somewhat by performing several measurements.

Figure 4–44: Examples of a resistance moisture meter (Source: left: testo.com, right: www.gann.de)

Microwave moisture measurement

With this method, moisture measurement can be carried out from near the surface to a penetration depth of 800 mm, through the use of different measuring heads (see Figure 4–45). The method is well suited for the usual building materials. Non-destructive, systematic, multi-layer raster moisture measurements can be carried out and graphically displayed as both areal and depth-resolved moisture distributions. Thus, a distinction in near-surface moisture and moisture in the core of components is possible. Moisture damage can be clearly classified and multi-dimensionally characterized with the area-based grid moisture measurements, since different patterns of moisture distribution are produced depending on the type of moisture damage. In particular, damage from rising damp and leaks can be easily identified with volume measurements (at various depths). Material-specific calibration curves of various building materials are integrated in the sensors.

The measuring principle is the radar reflection method. The waves are reflected as they pass through the material and detected by a meter. The method belongs to the dielectric measurement methods, i.e. the measurement is based on the determination of the permittivity of a medium to be examined. Since the dielectric constant of water is significantly higher than for dry building materials, the measured value of building materials increases significantly with the moisture content.

Figure 4–45: Example of a microwave moisture analyzer with different measuring heads (Source: hf-sensor.de)

The influence of ionic conductivity on the measurement results is low in high frequency engineering, i.e., saline independent measurements can be made. The measuring accuracy depends on various disturbing factors such as thickness, density and grain size of the material to be examined.

Non-destructive measurement of capillary water absorption

Introduction

One of the most important criteria for the planning and dimensioning of internal insulation measures is the assessment of the driving rain load and the local driving rain protection of the individual facades of the building.

By installing internal insulation, the existing wall becomes colder and wetter, as the heat transport from the room side and through the wall, is reduced due to the insulation layer.

For a general assessment of the condition of the façade, a visual inspection should be supplemented by information on maintenance measures carried out during the use of the building. For a rough overview, ideally a first on-site inspection takes place directly after a rain event to visually record the capillary water absorption of the façade and, above all, to clearly identify and document damage to the splash water area and the roof drainage system.

However, for the on-site measurements of the capillary water absorption of the façade, which serve as an important criterion for classifying the driving rain protection of the façade, the following weather conditions are required: 

• The temperatures are above 5°C for a long time.

• There has been no rain event for several days, i.e. the facade must be dry. A measurement in the late afternoon hours is ideal here, since then a falsification of the measured values can be excluded also by any existing impact of nocturnal surface condensate on the facade.

In the following, some on-site non-destructive measurement methods are presented, starting with the most simple, fast and inaccurate (wetting the façade), gradually becoming more precise and time consuming, with the water absorption measuring device (WAM) as the most advanced. All methods are suitable for brick masonry, however it must be ensured that a sufficient number of measurements (on all sides of the facade, at different heights) are carried out to achieve representative results. The smaller the suction surface, the more measurements are necessary. The accuracy of the measurements increases with the size of the test surface or with the complexity of the investigations.

Wetting the facade

An easy way to get the first impression of water absorptivity of building materials is to simply wet the facade with water. With a squirt bottle one can generally determine whether the facade is strongly absorbent or rather water-repellent and whether there are serious differences in the different façade orientations and heights or in certain areas. On this basis, the location of inspection points can be determined for the measurement of capillary water absorption.

Karsten's test tube

The Karsten water penetration test tube is a simple proven method for the on-site measurement of capillary water uptake of building materials and components. For exposed brickwork facades, this method is suitable as a coarse estimation. The test is very simple. The water penetration tester is applied to the test surface with a contact material (putty) (Figure 4–46). After pouring a specified amount of water into the test tube, the absorbed amounts of water and the associated penetration times are read off and documented at specific time intervals.

Due to the small cross-sectional dimensions of the tube and the strong edge influence, however, only very limited statements are possible, especially in brick-faced facades with joints. The correct determination of the water absorption coefficient in the laboratory requires a one-dimensional transport, but this cannot be achieved with the Karsten test tube. In addition, in this in-situ measurement method, the water is brought through the water column in the tube with a hydrostatic pressure on the facade, thus resulting in increased values. Further measurement errors can result from the strength and shape of the putty.

More detailed information about Karsten’s tube method can be found in RIBuild deliverable D2.1, Section 5.3.5 (RIBuild Deliverable D2.1, 2018).

Test plate according to Franke

The design of this measurement setup is a further development of the Karsten test tube. The measuring principle is the same. Again, the test plate is applied with a putty to the test area (Figure 4–47). The quantities of water absorbed and the associated penetration times are likewise read off and documented at specific time intervals to obtain a water absorption coefficient by evaluating the measurement curve. Due to the larger wetting area with a rectangular structure in the size dimension of a normal format brick plus the horizontal joint and vertical joint (25 x 8.3 cm), the entire system can be recorded here as a combination of brick and joint share.

Also in this method, a multidimensional liquid transport takes place. Due to the larger test area, the edge effects are less influential here than with the Karsten test tube. This allows more accurate statements about the capillary water absorption of the entire system as an average of brick and joints. Also in this in-situ measurement method, the water is brought to the facade with a hydrostatic pressure, resulting in increased values. Further measurement errors can be due to the strength and shape of the putty, as with the test tube.

Water absorption measuring instrument (WAM)

A new and more elaborate process is the measurement with the water meter WAM 100 B according to (Stelzmann, 2013) using a wetting area of ​​30 cm x 40 cm. This makes it possible to measure an integral water absorption over several stone and joint layers for brick-faced facades (Figure 4–48). Here, the façade area is pressurized with a superficial water film, which is produced with a constant and closed water cycle. The measuring principle is based gravimetrically on the determination of the mass differences. Depending on how absorbent a surface is, the water is absorbed by the facade or flows back into the circulation. This allows a more accurate non-destructive measurement of capillary water absorption on the facade.

Especially after the implementation of measures for the production of impact protection (for example, subsequent hydrophobing), the effectiveness of the measure in the combination of brick and joint layers can be checked well (Stelzmann, Berg, Möller, & Grunewald, 2016) (Stelzmann, 2013).

Figure 4–48: Water absorption measuring device WAM 100 B, construction and measuring principle [Source: hf-sensor.de]

More detailed information about the water absorption measuring device can be found in RIBuild deliverable D2.1, Section 5.3.6 (RIBuild Deliverable D2.1, 2018).

Direct measurement methods

Direct measurement methods are destructive measurement methods in which material samples have to be taken. This means that new samples must be taken for any subsequent measurement.

CM method (calcium carbide method)

In this method, which is a chemical method, only small material samples (5 g – 20 g) are taken, wet weighed, carefully crushed and mixed with calcium carbide in a pressure vessel with steel balls and a glass ampoule.

The amount of acetylene gas produced, which is determined by measuring the increase in pressure using a manometer (Figure 4–49), is a measure of the water content of the sample with reference to the sample mass. This procedure is applied directly on the spot, but requires some experience.

The accuracy of this method is low compared to the Darr weighing method (approx. ±3%). Nevertheless, it is frequently used in building practice, as it allows the moisture content for the investigated building materials to be determined quickly on-site at individual measuring points.

On-site heat flow measurements

Thermal resistance R or thermal transmittance of a building element U-value

The most important thermal characteristic value in this context is the thermal conductivity or, derived from this, the thermal resistance R or thermal transmittance of a building element U-value. An approximate U-value of the specific existing structure can be obtained by non-destructive on-site measurements.

This is done by means of heat flow measurements. Since these values are determined transiently and are always subject to the fluctuations of the boundary influences on-site, the results can also only be used as orientation guidance. Measurements should preferably be taken on a day when the outside temperature remains approximately constant for at least 24 hours to maintain a stable and appropriate indoor temperature. In addition, the temperature difference between the inside and outside should be as constant as possible, at least 15 K. The construction to be measured must not be exposed to direct sunlight, as this would falsify the measured values. Thus cold winter days or cloudy days are well suited for the measurements. The measured values must be recorded over a sufficiently long period of time to determine a stable mean value. A thermographic image taken beforehand can be used to determine representative points for the U-value measurement. Thermography is described in the following section.

ISO 9869 (ISO 9869, 2014) provides a guide about heat flow meter measurements for the determination of U-values. The heat flow through a wall depends on the thermal conductivity of the individual layers, the area and the temperature difference between the two sides of the component (inside and outside). With a heat flow meter sensor directly applied to the hot side of the wall surface, the density of heat flow rate is quantitatively measured (see Figure 4–50). If air temperatures are detected on the room side and on the outside, the U-value or heat transfer resistance can be calculated from this. In this case, the same boundary conditions and a sufficiently long measuring time must be observed. The same boundary conditions and a sufficiently long measuring time must be observed as for temperature measurement.

The larger the U-value of a component, the smaller the influence of measurement errors. This means that these measurements can give a good indication for uninsulated constructions, while the influence of measurement errors is more significant for insulated constructions.

Thermography

Thermography is a non-destructive measurement method that can be used to identify local heat loss (thermal bridges, air leaks, gaps in the construction) (see Figure 4–51). Although it is not possible to measure the  moisture content on building components, the method is well suited for leakage location. A higher moisture content increase the heat transfer within the component and lead to a temperature reduction at the component surface. Thus a temperature difference between dry and humid areas is recognizable. However, the results must be interpreted correctly, as the procedure does not discern between temperature change due to moisture and due to a thermal bridge.

The method is to be seen as a supplementary method for recording the actual condition and analysing damage and represents a snapshot of the surface temperature distribution on components.

Care must be taken to ensure that the temperature differences between inside and outside are as large as possible (heated building on a cold winter day). Environmental influences such as wind, rain and solar radiation can lead to a warming or cooling of the building envelope and thus falsify the heat flow-induced temperatures at the component surface. Therefore, it should preferably be carried out in the early morning or late evening hours in calm and dry weather.

Figure 4–51: Example of thermography images from Willers-Bau (Germany): Thermographic images on the upper floor (left) and on an outer door (right)

Laboratory measurements

Laboratory measurements offer significantly higher measurement accuracy than on-site tests. In addition, some characteristic values, such as equilibrium moisture content (sorption isotherms) or water vapour permeability (expressed as a μ-value) can be determined exclusively by laboratory measurements. These laboratory measurements require samples to be taken, e.g. in the form of core drillings or stone samples. Finding possible tapping points in the existing structure is sometimes a challenge and must be done very carefully. The number and size of the samples to be taken vary depending on the measurement method.

Laboratory measurements of moisture

Darr weighing method (gravimetric method)

In this classical, destructive method for determining the moisture content of materials, the mass difference between moist and dried material samples is determined in the laboratory. This is a very accurate method (up to ±0.5%). Material samples are taken on-site from the existing structure, weighed moist, packed airtight, brought to the laboratory and dried in a drying cabinet until the mass remains constant (drying temperature usually 105°C for mineral building materials). The dry material is then weighed again. The mass difference between moist and dried material samples represents the water content.

This method is calibration-free and can be used to calibrate other measurement methods. It is used when precise humidity values are required.

When taking drilling samples, the drilling time must be kept as short as possible to avoid excessive heating of the sample, as this can cause water to escape from the sample. In addition, it is more advantageous to take larger samples instead of drill cores with small diameters or, if possible, to take whole stones without significant heat exposure.   

Salinity measurements

Salinity measurements are made to determine the salt content or salt composition. Material samples are taken on-site, either as a drill core, or as drill dust.

In accordance with WTA Leaflet 4-5-99 (WTA 4-5, 1999), a classification of salts is given, from which the required order of magnitude of measures can be deduced. For simple conclusions about the total salt content, the determined highest content of salt ions, independent of whether chloride, nitrate or sulphate, and the evaluation shown in Table 4‑23 is decisive according to (WTA 4-5-99).

Table 4‑23: Assessment of the damage-causing effect of different salt ions in masonry bodies (data in M-%) (WTA 4-5, 1999)

Water vapour diffusion resistance

At low relative humidity of up to approx. 30%, moisture is transported in a building material exclusively by water vapour diffusion (vapour transport). This diffusivity can be measured with the aid of the so-called "dry cup method". At higher air humidities of up to about 95 %, vapour and liquid water transport occur simultaneously. This combined transport is measured by the wet cup method and the extraction of the vapour component.

The water vapour diffusion resistance provides a measure of how much water vapour is transported through a porous material in the presence of a vapour pressure gradient. The building material characteristic value is the µ-value (water vapour diffusion resistance factor). This indicates the factor by which the building material in question impedes water vapour transport in comparison with air.

When considering to apply internal insulation, it is crucial to know the drying potential of the wall construction to the exterior as only limited transport to the indoor can take place, depending on the characterisics of the insulation system.

More detailed information about water vapour diffusion resistance method can be found in (RIBuild Deliverable D2.1, 2018), Sections 5.1.5 and 5.2.2.

Water absorption capacity and water absorption coefficient

In historic wall constructions, the choice of suitable materials was partly used to prevent the wall from absorbing too much water. This applies mainly to basement walls or plinth areas where dense sandstones, granite, diabase or basalt were used. Diabase, for example, has a water absorption capacity of less than one percent by volume. The water absorption capacity of a material depends on how large the pore volume is, on the one hand, and on which pore structure is accessible to water, on the other. Therefore, the water absorption capacity of a building material can at most reach the value of the total pore volume, but is usually lower.

In contrast to these materials often used for the lower part of external walls (including basements), other natural stones (sandstone, travertine, tuff, etc.) have a porosity of up to 30% and are correspondingly more absorbent. They are therefore not used for components which are exposed to liquid water for a longer period of time.

The water absorption capacity of building materials is meaningful for the foundation or basement construction, as these can be exposed to groundwater.

When liquid water (e.g. driving rain) acts for a short time, a building material absorbs considerably less water. This short-term water absorption capacity of a relatively dry starting material can differ greatly from the maximum possible water absorption. It is therefore recorded as a separate characteristic value (water absorption coefficient) and is an important criterion for external wall materials. The corresponding water absorption test indicates how much the water absorption of a building material slows down over time. It is therefore expressed as water mass per square metre of contact area (between building material and liquid water) and per root second. The higher the water absorption coefficient, the faster the material can absorb liquid water.

The water absorption coefficient for a material exposed to the weather provides a decisive parameter for the dimensioning of an internal insulation measure, since the damage potential depends strongly on the rainwater input.

To obtain an exact statement on the capillary water absorption of facade materials and in the case of obvious or emerging necessity for further investigations and measures to reduce the capillary water absorption, it is often necessary to take material samples and have them examined in the laboratory, especially for brick facade without plastering.

In the case of plastered facades, the water absorption coefficient for the facade can be sufficiently fulfilled with a suitable facade coat applied to the intact facade as part of the renovation, so that in this case the water absorption coefficient does not necessarily have to be determined in the laboratory.

More detailed information about water absorbtion coefficient test method can be found in (RIBuild Deliverable D2.1, 2018), Section 5.1.6 and 5.2.3.

Equilibrium moisture content

The equilibrium moisture content (or practical moisture content) is the moisture content in a building material after prolonged storage in a room with constant relative humidity and temperature. The equilibrium moisture content is typically measured in the laboratory for several levels of ambient moisture. A constant moisture level is created with the help of saturated salt solutions. The choice of salt determines the moisture level in the measuring vessel (e.g. 75.4% for saturated saline solution). If all measured equilibrium humidities are applied over the ambient humidities applied, the so-called sorption isotherm is obtained.

The equilibrium moisture content at a certain relative humidity thus represents a single characteristic value from the moisture storage curve of a material. From the equilibrium moisture content and the porosity of a building material, for example, it can be concluded how high its practical thermal conductivity is. For bricks it can be assumed that an increase in moisture content of one percent by mass produces an increase in thermal conductivity of 10%. Since the practical moisture content of a brick lies between 0.5 (vertically perforated brick) and 1.5 % by volume (other bricks), a tolerance of 5 (vertically perforated brick) to 15% (solid brick) is therefore required for the thermal conductivity of the dry building material. If the brick is completely moistened, the characteristic value increases accordingly.

More detailed information about equilibrium moisture content test method can be found in (RIBuild Deliverable D2.1, 2018), section 5.1.8 and 5.2.4.

Moisture storage function

Depending on the measurement method used, moisture storage is divided into a hygroscopic and a suphygroscopic portion. The moisture storage function is made up from sorption isotherms and pressure plate measurements.

More detailed information about moisture storage function test method can be found in (RIBuild Deliverable D2.1, 2018), Section 5.1.9 and 5.2.5.

Saturated moisture content

The saturation moisture is the moisture content that results after storage in water until saturation of all pores. For this purpose, the dry sample is weighed and reweighed after storage in water.

Saturation of samples is also used when determining the porosity, described in (RIBuild Deliverable D2.1, 2018), Section 5.1.2.

Degree of moisture penetration

The degree of moisture penetration describes the ratio of moisture content to maximum water absorption in building materials. The degree of moisture penetration is determined indirectly by measuring the moisture content and the maximum water absorption, both as mass percentages. The degree of moisture penetration allows evaluation of moist building materials. On this basis, the degree of moisture penetration of a material can be indicated after a moisture measurement.

Other methods for determination of material parameters are presented in (RIBuild Deliverable D2.1, 2018), Section 5.3.

Laboratory measurements of U-value/heat

Bulk density

The bulk density describes the density of a porous building material based on the gross volume (including pores). It also serves to determine the heat storage capacity. Conclusions on other characteristic values, such as thermal conductivity, can also be drawn conditionally from the bulk density.

More detailed information about bulk density test method can be found in (RIBuild Deliverable D2.1, 2018), Section 5.1.1 and 5.2.1.

Porosity

Porosity is the ratio of the pore volume to the total volume of a building material.

In general, a decreasing porosity is associated with a lower thermal insulation capacity (higher thermal conductivity) and higher storage capacity (higher bulk density) of the building material. However, when comparing different types of building materials, this conclusion is not always correct.

In addition to the porosity itself, it is also decisive which pore structure is present. Pores that are accessible to water contribute to a high water absorption capacity while other pores are inaccessible to water in liquid form. No pores are inaccessible to water vapour although it takes time to get acces to them. In addition, the composition of the solid matrix is also important. The derivation of further building material properties such as liquid water and steam conductivity is therefore only possible to a limited extent even with this basic characteristic value.

More detailed information about porosity test method you can find in (RIBuild Deliverable D2.1, 2018), Section 5.1.2 and 5.2.1.

Thermal conductivity

Thermal conductivity can be specified both as dry thermal conductivity and in the form of thermal conductivity with a standardised equilibrium moisture content. The thermal conductivity thus depends on the water content of the porous building material and increases with it. The lower the thermal conductivity and layer thickness of a building material, the lower the heat losses through the outer wall. Thermal insulation materials have characteristic values of less than 0.10 W/mK, porous natural and brick stones have values of around 0.50 to 2.50 W/mK.

More detailed information about thermal conductivity test method can be found in (RIBuild Deliverable D2.1, 2018), Section 5.1.4 and 5.3.1.

Specific heat capacity

The heat capacity represents the ability of a building material to retain thermal energy. The specific heat capacity indicates how much heat energy per kg of building material and degree Kelvin temperature difference can be stored and is given in J/(kgK). It is between 800 and 1000 J/kgK for standard building materials and between 800 and 900 J/kgK for brickwork. Wood-based materials have higher values of approx. 1500 J/kgK. For the actual storage capacity, however, the density is decisive. Wood and wood-based materials have a density that is about one third of that of solid building materials. Thus bricks and natural stones are still clearly better heat accumulators despite the lower specific characteristic value of the heat storage capacity in comparison to wood.

More detailed information about specific heat capacity test method can be found in (RIBuild Deliverable D2.1, 2018), Section 5.1.3 and 5.3.1.

Alternatives to determining the characteristics of the existing structure

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