Basement ceiling insulation - energy efficiency in the lower part of the house

A basement ceiling insulation can be done as an insulated Dämmmaßnahme in the basement area or as part of a complete basement insulation. It is done from the basement side or from the ground floor. If the insulation work is possible on the basement side, the basement ceiling insulation is a rather favorable method to improve the energy efficiency of a building.

About an uninsulated cellar is about ten percent of the heat energy lost. Especially on the ground floor, the lack of thermal insulation in the basement area can lead to noticeable restrictions on the quality of living - cold feet and, in the worst case, rising damp from below should be the order of the day. In addition, there is a high energy consumption and correspondingly high costs. Already the insulation of the basement ceiling effectively prevents the house from cooling down. It leads to a noticeably higher floor temperature on the ground floor and a better energy and moisture balance of the house.

Table 1: Costs of basement ceiling insulation and other types of basement insulation

DämmungsartCost per m2 (EUR)
Basement ceiling insulation from the basement side15 – 25
Basement ceiling insulation on the ground floor70 – 160
Perimeter insulation (external insulation of basement walls)40 - 60 (+ earthworks)
Interior insulation of the basement walls80
Insulation of the basement floor70 – 160

Is a basement ceiling insulation sufficient for good thermal insulation?

Even the insulation of the basement ceiling leads to a noticeably higher floor level on the ground floor and to a better energy balance of the house. As an insulated Dämmmaßnahme for an unheated, used only as a storage and storage room basement, it is sufficient and then a very economical form of thermal insulation. A basement ceiling insulation allows reliable lower thermal insulation of the living area and provides sufficient protection against rising damp.

No influence on the moisture balance of the cellar

In contrast, basement ceiling insulation in itself has no influence on the moisture balance of the cellar. Moist walls in the basement area arise in two different ways: Firstly, on the walls of an unused cellar quickly condensed humidity on the walls, which can lead to moisture damage and mold growth, on the other pulls moisture from the surrounding soil in the basement walls. For cellars with high humidity a complete basement insulation is therefore definitely recommended to protect the building fabric of the house in the basement area sustainably.

Complete basement insulation - always necessary for intensively used cellars

In a cellar that is heated, used as a hobby and commercial space or temporarily inhabited, a complete basement insulation (walls, ceiling, floor) is necessary. The insulation of the basement walls can be done from the outside as so-called Perimeterdämmung or as interior wall insulation.

Tips & Tricks

A basement ceiling insulation improves the energy efficiency and the quality of living on the ground floor of the house. For a non-intensively used cellar, it is sufficient for the heat insulation of the living area. In this case, an additional insulation of the upper 50 cm of the outer wall should be done to reduce the risk of thermal bridges.

General information about basement ceiling insulation

An insulated basement ceiling insulation is the equivalent to the thermal insulation of the top floor ceiling in the roof area. For efficient thermal insulation of the living area should be made - if no further expansion of the roof structure and the basement are planned - both insulation. The insulation of the basement ceiling can be done on the basement side or by a floor insulation on the ground floor.

Drying and professional preparation of the cellar ceiling

Before the start of insulation work, the basement ceiling must be completely dry. If moisture has collected in the ceiling area, the further procedure depends on the degree of moisture penetration. Extensive ventilation may be sufficient for low degrees of humidity; more intensive drying is possible by heating the cellar and, if necessary, by using a built-in dryer or an infrared heater. To prepare the ceiling for the insulation also includes the removal of dirt, paint residues and plaster. It is optimal if the substrate on the side on which the Kellerdeckendämmung is to be made, as flat as possible.

Basement ceiling insulation - from below or as floor insulation on the ground floor?

The easiest way is if the insulation of the basement ceiling can be done from below. Too low ceiling heights, strongly curved ceilings or numerous cables and pipelines on the basement ceiling often present obstacles here. By choosing the right method, however, a basement ceiling insulation is often possible. A floor insulation on the ground floor can be an alternative for more complicated room and construction conditions, but compared to a cellar-side insulation, however, significantly more expensive and expensive. In addition, the insulation of the basement ceiling from the ground offers, if in any case a complete floor renovation should take place, which in this case also contributes to the efficiency of this Dämmmethode.

Procedure for thermal insulation on the basement side

There are different methods for a basement insulation of the basement ceiling. If the substrate is level and the ceiling height is sufficient, the simplest method is to apply insulation boards to the basement ceiling. For vaulted cellars and basement ceilings with piping and cables, a substructure is possible. Alternatively, a cellar-side insulation can also be done as a blow-in insulation or in the so-called spray-on process.

Slab insulation of the basement ceiling

A slab insulation is the simplest method for basement ceiling insulation. The insulation boards are glued or pegged from below with the ceiling. Which method of attachment is chosen depends on the nature of the substrate and the respective insulating material. Bondings can be made with classic construction adhesives. Mineral wool (stone and glass wool) or plastics (EPS / Styrofoam, PUR / PIR) are usually used as insulating material for this form of basement ceiling insulation. In addition, composite construction materials such as EPS / Styropor and Rigips combi panels can also be used. Natural insulating materials such as wood fiber or hemp are also available in sheet form, but play only a minor role because of the usually required higher insulation thicknesses and cost reasons for basement ceiling insulation.

Problems with piping and cables

Problems with piping and cables in a panel insulation can be solved by so-called insulation strips. These are mounted as spacers on the ceiling and the insulation boards then glued to it. An additional insulating effect can be achieved by plug insulation with fiber insulating materials, which fill the cavities between basement ceiling and cables / cables.

Slab insulation with substructure

More complex is the insulation of a basement vault, which has no smooth surface. Substructures can be a good and equally uncomplicated solution here. They are pegged to the basement ceiling and then filled with insulation mats. Due to their good insulation performance and the low price, mats and fleeces made from mineral wool are the ideal insulation material. Finally, the construction will be cladded with Rigips or OSB panels.

Insulation systems for vaulted cellars

Some manufacturers - Rockwool, among others - offer special insulation systems for the insulation of vaulted ceilings, optional custom-made versions are possible.

Blow-in insulation in cavities or with wooden frame substructure

If the basement ceiling has a sufficiently large cavity, a blow-in insulation can be made. The insulating material is injected with a packer through a hose into the cavity while compressed at the same time, the injection can be made from the basement side or from the ground floor. This method for basement ceiling insulation is particularly efficient and inexpensive, but carries a high risk of thermal bridges. If a blow-in insulation is provided, but no cavity is present, this is not sufficient for the insulation or too many thermal bridges exist, a wooden frame base can form the basis for this form of basement ceiling insulation. As an insulating material cellulose flakes are most commonly used, other suitable materials include fiber insulation, rock wool or EPS / polystyrene granules.

Spray-on method

In the spray-on process, a mixture of water and cellulose flakes is sprayed onto the basement ceiling, pipes and cables can be included here. After solidification of the mixture is optionally the cladding of this insulation layer. For basement ceiling insulation, which is then plastered, a binder is added to the insulating material - corresponding mixtures are offered in the building materials trade. In this method for the basement ceiling insulation, a review of the insulation thickness is necessary before completion of construction.

Basement ceiling insulation on the ground floor

For a basement ceiling insulation from the ground floor, the entire floor must be renewed. Above the basement ceiling, a vapor barrier in the form of a watertight film is placed on top of which insulation boards - such as polystyrene (EPS / polystyrene, at higher loads also XPS), hemp or cork and the floor covering are laid. Due to the higher floor construction, it may also be necessary to adapt doors and stair landings. A thinner screed may help to avoid such modifications.

Table 2: Selected insulation materials for the basement ceiling insulation

insulationThermal conductivity (W / mK)Minimum insulation thickness (cm)Cost / m2 (EUR)
glass wool0,032 – 0,0401410 – 20
rock wool0,035 – 0,0401410 – 20
EPS / Styrofoam0,035 – 0,045145 – 20
PUR / PIR0,02 – 0,0251010 – 20
cellulose0,04 – 0,0451610 – 20
hemp0,04 – 0,04515/1610 – 30
cork0,04 – 0,051815 – 40

Basement ceiling insulation and insulation thicknesses

In practice, basement ceiling insulation often raises questions about insulation thickness. A basement insulation inevitably reduces the ceiling height, which can be problematic in low basements, especially when using substructures. When renovating it is important that the basement ceiling insulation as possible no modifications of the door and window connections are necessary. A particularly high-performance insulation material such as PUR / PIR enables a noticeable reduction in insulation thickness compared to other materials - with a very good price-performance ratio.

EnEV specifications for the basement ceiling insulation

The Energy Saving Ordinance (EnEV) 2014 stipulates that the thermal insulation of residential buildings must have at least a heat transfer coefficient (U-value) of 0.24 W / (m²K). If this value is undershot, public funding of the insulation measure is possible through a KfW construction subsidy or a low-interest KfW loan. Prerequisite for the promotion are each the application for funding before the start of the construction project and the opinion of a professional energy consultant.

Tips & Tricks

Basement ceiling insulation - especially a simple slab insulation - can be made well as an own contribution. Nevertheless, a professional advice with regard to possible insulating materials and the optimal insulation method is recommended in advance. Blow-in insulations always belong in the hands of a specialist tradesman.

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