Wall renovation with ventilated façades
The ventilated façade is a system that consists of cladding material fastened to a load-bearing frame fixed onto the wall of a building so that the protective-decorative cladding and the wall are separated by an air gap.
The ventilated air gap is a barrier of air open to exterior air that is located between the cladding and the wind insulation. A layer of thermal insulation can also be installed for additional heat retention. In such a case, the air gap should be placed between the cladding and the thermal insulation. It is this air gap that gives ventilated façades a high-performance edge.
The ventilated façade system consists of the following components:
- Fastening and fixing elements;
- A frame;
- A layer of thermal insulation;
- A layer of wind insulation;
- External cladding, typically fastened with rivets or screws.
The cladding elements and the thermal insulation layer are fixed to a wood or metal frame. The latter can be made of aluminium, galvanised steel or stainless steel profiles. What elements are used and how they are assembled depends on various factors, such as wall type, building height, wind loads and cladding material.
Aluminium frames, which consist of aluminium steel profiles, are typically the structure of choice due to their great resistance to corrosion, simple assembly, light weight and price.
There is no need to even out or straighten exterior walls when installing a ventilated façade. Any unevenness is compensated by the frame system to which the exterior cladding is attached.
Atmospheric stress is one of the most important factors in the disintegration of external walls. Atmospheric stressors are typically classified as natural processes (rain, snow, sleet, wind, cold, heat) or complex chemical and biological processes caused by air pollution. Sulphur dioxide and nitrogen oxide are the main air pollutants that affect buildings. These pollutants react with water, oxygen and various oxidants to form acid rain. Such acids settle on external walls and corrode them.
The Lithuanian climate is much harsher towards external building structures than the climate conditions in Central Europe. More attention should be paid to the impact of freeze-thaw cycles, especially if they are accompanied by higher levels of moisture.
When carrying out thermal insulation work for buildings, the movement of heat, moisture and air must be taken into account.
Moisture has a great influence on the thermal conductivity of various materials. The thermal conductivity coefficient of water is about 20 times greater than that of air, and the thermal conductivity of ice is 4 times greater than that of water. If a material gets wet, moisture enters its pores and pushes the air out. This means that the thermal conductivity of the material increases.
When a structure is not ventilated and the layer of thermal insulation is pressed against the outer layer of cladding, water can enter the layer of insulation in one of two ways. During the heating season, the water vapours that pass through structures at low temperatures begin to condense within the material or on the surface of the structural layer behind the thermal insulation. Affected by wind pressure and capillary action, rainwater can also leak through exterior cladding and dampen layers of thermal insulation. Water absorption depends both on the capillary properties of the cladding material and the quantity and size of the cracks within it. Once a uniform film of water forms on the surface of a wall, the wind pushes the water into these cracks and the gaps of various structural joints.
Thus it is important to ensure the water tightness of external structures when renovating a building and seeking to prevent heat loss. Ensuring adequate interior ventilation is also essential because poor ventilation leads to increased levels of moisture. This, in turn, leads to greater levels of condensation, greater risk of mould infestation and poorer air quality. However, increasing circulation with forced ventilation also increases heat loss and this can only be rectified by using a recuperator.
Renovation designs must be drawn up with a special focus on the prevention of condensation in the layer of thermal insulation due to air movement from the outside in. Damp thermal insulation has poorer thermal conductivity than dry insulation. Moisture levels can be reduced by using materials that are permeable to water vapours in the construction of a building's external insulation system.
Regulations applicable in Lithuania demand that walls are designed and constructed only using thermal insulation elements for ventilated façades that have European Technical Assessments (ETA) and/or CE marking. STR 2.01.11:2012.
Panel characteristics are governed by the LST EN 12467 standard.
Taking into account the materials they are made of, all the elements used in the construction of ventilated façades must be resistant to corrosion, moisture, mould and UV light or they must undergo appropriate protective treatment before use. The resistance of system elements to the mentioned stressors should be evaluated with tests based on the standard requirements for each product type. The frame, fastening elements and the metal elements of the cladding material must be selected so that the conditions for electrochemical corrosion are not created. The cold tolerance of cladding elements must be no lower than that indicated by integrated product standards and no lower than 100 freeze-thaw cycles. STR 2.01.11:2012