Building Physics Fundamentals
Content:
2. Driving Rain Exposure
3. Temperature Differences
4. Sound Insulation
5. Movements from the Building Structure
and Window Construction
6. Air Permeability
7. Indoor Air Humidity and Ventilation
8. Fire Behavior
9. Environmental Compatibility
10. Thermal Insulation
11. Building Material Compatibility
1. UV Stability
This is defined by the invisible portion of short-wave radiation in sunlight, 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 repeatedly the subject 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 in a very short time.
2. Driving Rain Exposure
Exterior building component joints are subject to natural exposure to driving rain. Here, raindrops are pressed against external wall components by wind pressure (up to 600 Pa, corresponding to approx. 12 Beaufort) or due to 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 joints in the building connection.
Due to capillary action (narrow joint), water is drawn into the building structure without the influence of wind pressure.
In the external area of the building envelope, the following must be ensured:
1. Defined drainage of moisture from the construction.
2. Prevention of uncontrolled water ingress into the construction.
3. Limitation of the moisture content of sensitive materials.
4. Defined removal of moisture from the construction.
| Window profile materials
|
ε in mm/m
|
| Rigid PVC (white) | 1.6 |
| Rigid 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 almost 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.
In dark-colored facade components made of aluminum or plastic, surface temperatures of over 80 °C occur on the south side. This results in length changes of up to 3 mm per linear meter, depending on the material composition. Therefore, the temperature changes of the profiles in the installed state, caused by the outdoor climate, are decisive. These movements must be accommodated by the sealing materials used.
Taking into account research results on the actual length movements that occur, the following temperature-related changes in the connection joint should be applied:
4. Sound Insulation
In this context, the so-called keyhole effect is of particular importance. Small openings or hairline cracks in the connection area can negatively affect sound insulation values. 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 braid 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 DIN 4109 "Sound insulation in building construction", which has been introduced by the building supervisory authorities, VDI Guideline 2719 "Sound insulation in building construction and its auxiliary equipment" is also very often used.
5. Movements from the Building Structure and Window Construction
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 accumulated moisture, condensation occurs. A temperature of 12.6 °C has proven to be critical here. Using special software, the surface temperatures in a building connection are determined and connected to a line, the so-called isotherm curve.
In the past, people commonly spoke of the 12 °C isotherm. More precise scientific investigations have now led to the aforementioned 12.6 °C. Popular science has agreed on the 13 °C isotherm.
8. Fire Behavior
According to the requirements of the state building codes, building materials used, and thus also the materials used for connection formation, 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 structural and civil engineering. The use of, for example, products containing solvents has decreased significantly. They are only still used in areas where they cannot be replaced.
Products whose process is based on a chemical function are also used to a lesser extent. Pre-compressed sealing tapes have an advantage here, as their application is determined by the course of physical processes.
Furthermore, sealing products contribute significantly to positively influencing the indoor climate, thereby significantly improving the energy efficiency of a building. This helps to further reduce global environmental pollution.
10. Thermal Insulation
When sealing windows and external doors, thermal insulation is a building physics property whose consideration is also legally required by the legislator through building 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 that is as free of thermal bridges as possible should be chosen.
This is essentially composed of three requirements in the window connection:
- Seamless connection of insulation 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. Building Material Compatibility
In many cases, the sealing of joints acts as a link between different materials. This can involve paints, treated wood structures, various plasters, or even residues of existing sealing products.
For the sealing product to permanently fulfill its requirements, no harmful interactions may occur. This can involve chemical, physical, or optical impairments, which must generally be avoided. To ensure this, compatibility tests must be carried out.
As a rule, pre-compressed sealing tapes have an advantage here, as only a physical expansion occurs.
Depending on the installation position of the window, the materials listed below can lead to impairments of the sealing products:
- the paint system of the facade or window
- impregnation systems of a wooden structure
- old sealing materials
- release agents from the production of window profiles
- natural pests
12. On-Site Installation
Here, the dimensions for sizing with sealants are shown.
The significantly wider joint widths can be clearly seen from the table.
12. On-Site Installation
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 for its own advantage and benefit. Even in the animal kingdom, activities for the purpose of sealing can be observed. For example: Bees use wax (propolis), specially produced by themselves for this purpose, to seal their beehive against drafts and rain.
Some birds also seal their nesting cavities against external influences, using natural aids such as saliva-covered earth, gravel residues, and plant parts. There is no significant difference between the aforementioned natural seals and the sealing of external joints, neither in the task nor in the desired effect. In both cited cases, the aim is to protect an area from weather influences, primarily from wind, moisture, and heat loss.