The insulation of components in contact with the ground on their outside is called perimeter insulation, it is always outside the waterproofing of a building.
Particularly high demands are placed on perimeter insulation under floor slabs, as it is directly adjacent to the ground and has to bear part of the building's weight when used as load-bearing insulation. It is also exposed to moisture and chemical influences. Therefore, perimeter insulation is pressure-resistant, rot-resistant, and does not absorb moisture (or only to a small extent).
Due to increased requirements for thermal insulation due to the Energy Saving Ordinance, floor slabs are increasingly insulated underneath, even though constructions without external perimeter insulation under floor slabs are still permitted according to DIN 4108 Supplement 2. However, a closed thermal envelope cannot be created with insulating boards inserted in the inner floor structure alone, so that a thermal bridge is inevitably created at the transition between the foundation and the outer wall:
Whether
basement buildings or buildings without basements, the perimeter insulation under floor slabs ensures a closed thermal envelope and thus a structurally flawless Detailed design:
Approval as load-bearing thermal insulation: Not all perimeter insulation also has approvals for use under foundation panels. The decision as to which product may be installed must be agreed with the structural engineer responsible for the construction project and the manufacturer's specifications or building authority approvals.
Frost resistance: When constructing a building, a frost-proof foundation must be ensured in accordance with DIN EN 1997-1, otherwise the floor slab can freeze and as a result serious damage to the building (e.g. ground breakage). In the case of a building with a basement, frost protection is provided solely by the depth below the ground surface. In the area of excavations or cellar exits, on the other hand, there is also a risk of frost damage. Everywhere, precautions must be taken to protect the floor slab from freezing.
To avoid frost damage, the following options are available according to DIN EN 1997-1, point 6.4 (2):
1. The soil is not sensitive to frost: e.g. due to a substructure made of frost-proof gravel:
2. frost-free foundation: foundation depth below the frost line or formation of insulated frost aprons:
3. Frost is eliminated by insulation: Manufacturing a frost screen:
Thermal conductivity: The rated thermal conductivity value (λ value) is specified by the manufacturers. When planning and calculating, however, it must be taken into account that the λ value of most insulation materials must be reduced if damming or pressing water is to be expected. A multi-layer installation of panel-shaped insulating materials also leads to a negative change in the λ value. Precise information about the exact values can be found in the respective manufacturer's specifications and the DIBT's building authority approvals.
Cleanliness layer at XPS: Perimeter insulation made of XPS must always be laid on level ground, usually on a cleanliness layer. Currently, there is no applicable standard that requires a cleanliness layer made of lean concrete. If this is dispensed with by placing the insulation boards on a layer of sand or trickle, the greater inaccuracy of the subsoil must be taken into account when covering the concrete reinforcement of the floor slab, i.e. it must also be agreed with the structural engineer.
Cleanliness layer for foam glass panels: According to the manufacturer's instructions, these must always be laid on a cleanliness layer of approx. 10 cm thick underlay concrete. The individual foam glass panels are then glued to the cleanliness layer over the entire surface and completely with hot bitumen in the casting process.
Foam glass gravel substrate: Before installing the insulating fills, a geotextile should be applied to the natural soil. A cleanliness layer or a capillary-breaking layer is not necessary. Foam glass gravel is particularly economically sensible to use where soil has to be replaced, as the insulating fill also serves as a load-bearing and capillary-breaking base course.
Covering: A layer of PE film is applied to all the perimeter insulation mentioned above as a covering and sliding layer before concreting the floor slab.
XPS (extruded polystyrene) construction method: The panels are laid at the edge of the cleanliness layer or the flat and compacted substrate. When laying the slabs, cross joints must be avoided at all costs. If accumulating water or pressing water is to be expected, the lateral edges of the thermal insulation layer must be protected from water penetration by suitable measures (e.g. by filling with an adhesive or suitable sealants).
XPS insulation can also be installed in several layers in the area of non-accumulating leachate and soil moisture (note the manufacturer's data sheet!). In the case of pressing or damming water, it must be laid in a single layer. If the XPS panels are arranged in several layers, the superimposed panels must be laid offset from each other so that there are no continuous joints. Various manufacturers offer system components made of perimeter insulation materials that function simultaneously as edge formwork of the floor slab and perimeter insulation of the floor slab overhang, so that significant time savings can be achieved during execution.
Foam glass gravel: Insulation fills such as foam glass gravel are placed on the excavation pit floor, which is covered with geotextile, and distributed. Compaction is carried out by means of a roller or plate vibrator to the required layer thickness. In contrast to panel-shaped insulation materials, the substrate does not have to be levelled. The subgrade will be created with the insulating fill.
Foam glass panels: the approx. 10 cm thick underlay concrete made of unreinforced lean concrete is placed on the bottom of the excavation pit and levelled off to create a clean and even work surface. A bituminous primer is applied to this with a roller or sprayer. After drying, the foam glass panels are glued to the underlay concrete over the entire surface using the so-called pouring process with hot bitumen. The joints are also filled with hot bitumen, so that no water can penetrate the insulation layer and lead to damage or reduction of the insulation effect. A so-called top swab is created on the finished insulation layer of foam glass panels by pouring hot bitumen on the insulation boards and spreading it with a rubber scraper.
Note: DIN 4108-1 (Thermal insulation in building construction; Sizes and units) has been withdrawn and replaced by DIN EN ISO 7345
DIN 4108 Supplement 2, Thermal insulation and energy saving in buildings - Thermal bridges - Planning and execution examples
DIN 4108-2, Thermal insulation and energy saving in buildings - Part 2: Minimum requirements for thermal insulation
DIN 4108-10, Thermal insulation and energy saving in buildings - Part 10: Application-related requirements for thermal insulation products - Factory-made thermal insulation products
DIN EN 13164, Thermal insulation products for buildings — Factory-made products as extruded polystyrene foam (XPS) — Specification
DIN EN 13167, Thermal insulation products for buildings — Factory-made products made of foamed glass (CG) — Specification
DIN EN ISO 7345, Thermal insulation - Physical quantities and definitions
DIN EN ISO 13793, Thermal insulation, building foundations, protection against frost uplift
EnEV - Energy Saving Ordinance for Buildings, Ordinance on Energy-Saving Thermal Insulation and Energy-Saving System Technology for Buildings
Leaflet on thermal insulation of components in contact with the ground from the Polystyrene Extruder Foam Associationdimagb.de - Information for building owners Source: bauwion
