Building Physics Fundamentals
Content:
1. UV Stability
2. Driving Rain Exposure
3. Temperature Differences
4. Sound Insulation
5. Movements from the Building
and Window Construction
6. Air Permeability
7. Indoor Air Humidity and Ventilation
8. Fire Behavior
9. Environmental Compatibility
10. Thermal Insulation
11. Material Compatibility
1. UV Stability
This is defined by the short-wave radiation in sunlight, invisible to the human eye, which is described as UV (ultraviolet) rays.
This radiation not only damages human skin but also the sealing materials used on the exterior of buildings.
These influences and their effects are consistently subjects of controversial discussions.
Especially because there are various measurement methods to simulate these influences in time-lapse.
Test methods, for example, from the paint industry or other surface coatings, proved to be
less representative.
Due to economic constraints, sealing products that are not weather-resistant are still being used.
These usually lead to the failure of the sealing system within a very short time.
2. Driving Rain Exposure
Exterior building joints are subject to natural stress from driving rain. In this process,
raindrops are pressed against exterior wall components by wind pressure (up to 600 Pa, corresponding to approx. 12 Beaufort) or as a result of air currents. The penetration of this moisture must be prevented, either constructively or by using suitable sealing products.
Another moisture load is created by absorbent or capillary-forming joints in the building connection.
Due to capillary action (narrow joint), water is drawn into the building structure without the effect of wind pressure.
In the external area of the building envelope, it is necessary to:
1. ensure defined drainage of moisture from the structure.
2. prevent uncontrolled water ingress into the structure.
3. limit the moisture content of sensitive materials.
4. ensure defined moisture removal from the structure.
Window frame materials
ε in mm/m
Hard PVC (white) 1.6 Hard PVC (colored) and PMMA colored extruded 2.4 Thermally insulated aluminum composite profile (light) 1.3 Thermally insulated aluminum composite profile (dark) 1.2
3. Temperature Differences
Thermally induced movements occur in practically every joint. In the case of wood frame material, however, thermal movements are so small compared to moisture-induced movements that they can be neglected.
For dark-colored facade components made of aluminum or plastic, surface temperatures of over 80 °C occur on the south side. This results in changes in length of up to 3 mm per linear meter, depending on the material composition. Therefore, the temperature changes of the profiles occurring in the installed state, caused by the outdoor climate, are decisive. These movements must be absorbed by the sealing materials used.
Taking into account research results on the actually occurring length movements, the following temperature-related changes must be assumed in the connection joint:
4. Sound Insulation
The so-called keyhole effect is of particular importance in this context. Small openings or hairline cracks
can negatively affect sound insulation values in the connection area. A reduction in the sound level by 10 dB
is perceived by the human ear as a halving of the volume.
An unfilled joint has a sound insulation value of 15 dB. A mineral wool rope achieves approx. 35 dB,
the same value is achieved by a joint filled with sealant. A compressed sealing tape achieves sound insulation values
greater than 42 dB.
For the requirements for sound insulation of windows, there are two sets of regulations that contain the recognized rules
of technology. In addition to the legally introduced DIN 4109 "Sound insulation in building construction", the VDI guideline 2719 "Sound insulation in building construction and its additional facilities" is also very frequently used.
5. Movements from the building and the window construction
An expansion joint, movement joint, or dilatation joint is a
joint used to interrupt components to prevent stress cracks.
These cracks arise from different expansion properties of the
materials used (thermal expansion, expansion due to moisture absorption) or load-induced changes in length (so-called creep). For the formation of possible stress cracks, see also dilatation. The joint avoids the resulting forces ("restraints") that can lead to damage to components.
Areas of application
- Bridges: Formation of transition constructions to avoid
restraint stresses, especially due to thermal expansion
- Parquet or laminate flooring: Prevention of stresses, especially due to
moisture expansion (mostly humidity, but also condensation)
water). This prevents the wood or laminate from breaking or
lifting in places.
- Floor coverings such as floor tiles: the edge of the floor of a
room against the wall is generally designed as an expansion joint.
- Facing masonry
If warm, moisture-saturated indoor air can penetrate the building connection joint, it will encounter cold building components there. The moisture from the indoor air will then condense on their surface due to the lower surface temperature of the building component. This effect can also be observed with a drinking vessel filled with chilled beverages.
The diagram below shows how a so-called "Blower Door Test" works. In this test, a negative pressure of 50 Pa is created via a building or room opening using a fan. This locates possible leakage points.
Principle of measuring air permeability. With windows and doors closed, the fan speed is increased until a building pressure difference of, for example, 50 Pa is established. The volume flow read is referred to as the volume flow of air permeability.
7. Indoor air humidity and ventilation
If, as mentioned in Chapter 6, the component temperature drops and the ambient air is no longer able to absorb the accumulating moisture, condensation occurs. A temperature of 12.6 ºC has proven to be critical here. Using special software, the surface temperatures in a building connection are determined and connected to form a line, the so-called isotherm profile.
In the past, people commonly spoke of the 12 ºC isotherm. More precise scientific investigations have now led to the aforementioned 12.6 ºC. In popular science, the 13 ºC isotherm has been agreed upon.
8. Fire Behavior
According to the requirements of the state building codes, the building materials used, and thus also the materials used for the connection design, must at least comply with building material class B 2 according to DIN 4102 or the corresponding class E according to EN 13501-1.
9. Environmental Compatibility
In recent times, there has been a general shift towards environmentally friendly products in both civil engineering and building construction. The use of, for example, products containing solvents has declined significantly. They are only used in areas where they cannot be replaced.
Similarly, products whose process is based on a chemical function are used to a lesser extent. Pre-compressed sealing tapes have an advantage here because their application is based on physical processes.
Furthermore, sealing products contribute significantly to positively influencing the indoor climate, thereby substantially improving the energy efficiency of a building. This contributes to further reducing global environmental impact.
10. Thermal Insulation
When sealing windows and external doors, thermal insulation is a building physics property whose consideration is also bindingly required by the legislator through legally introduced regulations and ordinances.
In this context, the Energy Saving Ordinance (EnEV) and DIN 4108 "Thermal insulation and energy saving in buildings" are of particular importance.
Thermal insulation in new construction
In newly constructed buildings, a construction method with as few thermal bridges as possible should be chosen.
This essentially consists of three requirements in the window connection:
- Seamless connection of insulating elements
- The sealing materials should have the highest possible thermal resistance.
- The construction should be chosen so that a maximum possible amount of sealing or insulating elements can be accommodated.
Thermal insulation in existing buildings
In general, the same standards apply to renovations as to new construction. However, these are very rarely achievable in practice, as one is dependent on the existing conditions.
Therefore, cover strips equipped with sealing tapes are very often used. Such solutions are certainly not optimal in terms of thermal insulation, but in many cases, they represent the only solution.
11. Material Compatibility
In many cases, the sealing of joints represents a link between different materials. This can involve paints, treated wood constructions, various plasters, or even residues of existing sealing products.
For the sealing product to permanently fulfill its requirements, no harmful interactions may occur. These can be chemical, physical, or optical impairments, which are generally to be avoided. To ensure this, compatibility tests must be carried out.
As a rule, pre-compressed sealing tapes have an advantage here, as only physical expansion takes place.
Depending on the installation position of the window, the following materials can lead to impairments of the sealing products:
- the paint system of the facade or window
- impregnation systems of a wooden construction
- old sealing materials
- release agents from the production of window profiles
- natural pests
12. Construction Site Assembly
Here, the dimensions for sizing with sealants are shown.
The significantly wider joint widths can be clearly seen from the table.
12. Construction Site Assembly
To ensure that as few errors as possible occur when dimensioning pre-compressed sealing tapes, the table below was designed by ift Rosenheim. In comparison of Table 1 to Table 2, it quickly becomes clear that when using sealing tapes, the joint can be chosen narrower than with pasty sealants. This is a clear economic advantage of sealing tapes.
Joint Sealing of Exterior Wall Components
The problem of sealing is probably as old as humanity's desire to
influence its environment to its advantage and benefit. Even in the animal kingdom, activities with the purpose of sealing can be observed. For example: bees use a wax (propolis) specially produced by themselves for this purpose to seal their beehive against drafts and rain.
Some birds also seal their brood cavities against external influences, using natural aids such as salivated earth, debris, and plant parts. There is no significant difference between the aforementioned natural seals and the sealing of external joints, neither in terms of the task nor the desired effect. In both cited cases, the aim is to protect an area from weather influences. Essentially from wind, moisture, and heat losses.
