Perimeter insulation - the efficient external insulation for the basement

Perimeter insulation can be applied to new buildings as well as to old buildings. It includes the external insulation of the cellar walls and in new houses also the bottom plate. From a building physics point of view, it is considered to be the most efficient method for basement insulation, but is more complex than an interior insulation due to the required earthworks.

With regard to the energy efficiency of a house, efficient cellar insulation is often hardly in focus. For new buildings, the question does not arise to what extent cellar insulation is necessary - the Energy Saving Ordinance (EnEV) 2014 prescribes the complete insulation of the entire house. In old buildings, however, the focus of many builders is primarily on the insulation of the roof and the facade insulation. About an uninsulated basement, however, about ten percent of the heat energy lost, also can the lack of thermal insulation in the long run lead to moisture damage to the building fabric of the house.

Table 1: m2 costs for perimeter insulation and other forms of cellar insulation

DämmungsartCost per m2 (EUR)
Perimeter insulation (excluding earthworks)40 – 60
Earthwork for perimeter insulation20 – 30
Interior insulation of the basement walls80
Insulation of the basement ceiling from below15 – 25
Insulation of the basement ceiling by floor insulation on the ground floor70 -160
Basement floor insulation70 – 160

Perimeter insulation - the most efficient form of cellar insulation

The most efficient form of cellar insulation is the perimeter insulation, ie the insulation of the basement walls from the outside. In new buildings, the floor slab from the outside / below is also mitigated by a perimeter insulation - an internal insulation of the basement floor can therefore be dispensed with. Whether an additional insulation of the basement ceiling is necessary, depends on the extent to which the perimeter insulation of the outer walls is made.

Efficiency through high efficiency and replacement of other insulation measures

At first glance, a perimeter insulation is also more expensive than other forms of cellar insulation due to the additional effort required for earthworks. It can prove to be much more economical if it makes other forms of basement insulation unnecessary. In addition - in comparison to an interior insulation of the cellar walls - the optimization of the thermal insulation and the moisture balance of the house. Properly executed perimeter insulation also makes a significant contribution to the long-term protection of the building fabric.

Tips & Tricks

A Perimeterdämmung should not be made in-house or at least not without the advice and supervision of a specialist tradesman. Perimeter insulation requires comprehensive preparation and planning with regard to the load characteristics of the insulation layer, the selection of the optimum insulation material and flawless construction - corrections are later difficult to achieve.

Different variants of perimeter insulation

Structurally, a perimeter insulation is the thermal insulation of earth-contacting components on the outside of buildings. It is made on the outside of a basement outer wall integrated in the reach and - in new buildings - below the floor slab of the building. Subsequent perimeter insulation of the floor slab during renovations is not possible. A perimeter insulation can be done in different variants:

Base insulation up to 30 cm below ground level

The simplest form of perimeter insulation is a superficial pedestal insulation made to a depth of 30 cm below the ground level. Their advantage is a comparatively low effort for soil excavation. If necessary, earthworks and the application of the insulating layer itself can be done. However, the construction supervision by a specialist company is also recommended here. A complete external insulation of the basement walls is not associated with this Dämmmaßnahme. For a sustainable improvement of the energy efficiency of the house and the quality of living on the ground floor, an additional basement ceiling insulation is usually necessary.

Base insulation up to 80 cm below ground level (up to frost depth)

Alternatively, a base insulation can also be pulled to the depth of frost - about 80 cm below the ground level. The excavation takes place in the form of a trench about one and a half meters deep. The same applies to this type of perimeter insulation as to a superficial base insulation: complete insulation of the basement walls is also not achieved hereby. Also in this insulation measure a basement ceiling insulation is also recommended.

Complete perimeter insulation up to the foundation

With complete perimeter insulation, the base of the building is insulated to the foundation. The result is a complete external insulation of the basement walls. An additional basement ceiling insulation is no longer necessary. However, there is room for this form of perimeter insulation, which is not always given due to neighborhood conditions: the excavation takes place over the entire basement depth, at a basement height of two meters creates a at least two and a half feet wide ditch.

Execution of a perimeter insulation

To perform perimeter insulation, the following steps are required:

  • Excavation of the soil: In new buildings, the soil is removed over the entire basement area, in old buildings renovation the ditch is dug along the foundations of the building.
  • Preparation of the masonry: Subsequent insulation of the perimeter in the context of renovations requires the preparation of the exterior walls. The wall is cleaned, cracks are filled. Optionally, a moisture renovation of the outer walls is necessary before the implementation of the insulation.
  • Wall drying: Before the start of insulation work, the wall must dry out completely. A Perimeterdämmung in the context of an energetic renovation is also made for this reason only in the warm season
  • Mortar: A mortar is distributed between masonry and foundation.
  • Bitumen painting: The wall is provided with a bitumen primer and an insulating coating - usually a so-called bitumen thick coating. If necessary, the wall is plastered before painting.
  • Barrier layer: Several layers of glued blocking plates or plastic sheets are applied to the moisture-insulated masonry.
  • Installation of the insulation boards: Subsequently, the insulation boards are laid. They are fastened by gluing, in special cases additional dowels are necessary. Perimeter insulation panels for the basement wall insulation must have a fixed contact area at the foot point so that slippage is prevented during the subsequent compaction of the substrate. They are pushed close together in the bandage. The bonding must be made over the entire surface, so that no running behind with water can take place. For example, solvent-free cold bituminous adhesives are used as adhesives.
  • Cleaning layer: The application of a vapor-permeable plaster on the insulating layer is optional.
  • Backfilling: The perimeter insulation is covered about two weeks after installation - so the trench is filled up again. In front of the pedestal, a barrier-free drainage of rainwater must be made possible, as otherwise building damage can occur - errors in this part of the construction work also apply from the point of view of building law as a defect.

Perimeter insulation of the floor slab

The perimeter insulation under a load-bearing floor slab is made with single or multi-layer insulation boards. Their laying is usually done on a clean layer of lean concrete or on a stripped and highly compacted gravel sand layer. Important for such a board insulation is an absolutely level substrate to ensure the full-surface resting of the plates. On the insulating layer is a protective layer, which may for example consist of a polyethylene film and is intended to prevent cement or Betonnasen can penetrate the composite of the insulating layer.

Edge formwork - as a separate component or part of the insulation

In modern systems often no separate edge formwork for the concreting of the base plate must be made, but this consists directly from the insulation material. An advantage of this method is that it remains verifiable whether there is a seamless connection of the perimeter insulations of the base plate and the outer walls.

Insulating materials for perimeter insulation

Perimeter insulation must be able to handle complex loads, including:

  • earth pressure
  • soil moisture
  • Traffic loads: Traffic loads result from building statics. The entire payload of the building rests on the perimeter insulation of the floor slab.
  • Sicker-congestion and groundwater
  • Changing effects of frost and dew.

Robust insulating materials are an absolute must

For a Perimeterdämmung therefore particularly robust insulation materials are required. Natural insulating materials are not suitable for perimeter insulation. For the insulation of the floor slab, mainly XPS as well as foam glass / foam glass insulation panels are used. For perimeter insulations of the basement walls, EPS / Styrofoam is also an option. Foam glass also optimizes the fire protection properties of the building. All three materials are pressure-resistant, moisture-resistant and have a high insulation capacity. PUR / PIR insulation boards are not suitable for this form of external insulation.

Table 2: Insulation materials for perimeter insulation

insulationThermal conductivity (W / mK)Minimum insulation thickness (cm)Cost / m2 (EUR)
XPS0,035 – 0,0451418 – 30
EPS / Styrofoam0,035 – 0,045145 – 20
0,04 – 0,051610 – 20

Moisture restoration before insulation

A complete perimeter insulation prevents any moisture exchange between basement wall and soil. On the one hand this prevents moisture damage in the walls - however, moisture produced in the basement rooms can not be removed, so that regular and thorough ventilation of such insulated basements is necessary. Before the start of insulation work, the basement walls must dry, in remediation projects may need to be a moisture remediation:

  • Moisture condensation: Condensation moisture as a reason for damp basement walls is unproblematic here, as it is usually prevented by the insulation itself and with regular ventilation also does not return.
  • Defective basement waterproofing: In front of a Perimeterdämmung the basement waterproofing is basically renewed.
  • Rising Moisture: Rising moisture can occur if the horizontal moisture barrier in the masonry is no longer intact. The simplest method of remediation is to drill holes horizontally over the entire wall surface, into which a liquid resin is then pressed. For other methods, the wall is sawn or prized to incorporate a new moisture barrier.

EnEV specifications for perimeter insulation

The EnEV 2014 prescribes for the insulation of the living area and the attic, that at least a heat transfer coefficient (U-value) of 0.24 W / (m²K) is achieved, for the thermal insulation of basements, this benchmark is 0.30 W / (m²K ). Insulation measures that go beyond these minimum requirements can be supported by a KfW loan or a KfW construction subsidy. Prerequisites for the funding are the application before the start of insulation work and a professional energy assessment.

Tips & Tricks

Insulation materials for perimeter insulation require robust materials that cope with high pressure loads, moisture and pressure. In practice, mainly EPS / Styrofoam, XPS and foam glass / foam glass are used. Perimeter insulation of the floor slab is made almost exclusively with XPS or foam glass.

Video Board: Installing Rigid Foam insulation at slabs and foundations