Inside insulation is an alternative or supplement to retrofitting outside insulation and/or core insulation. Whilst in these systems the supporting masonry lies on the warm side of the insulation, which means it is usually physically uncritical, the potential or risk of condensation should always be taken into account. There are usually two decisive reasons for using inside insulation and improving the thermal protection:
- The above-mentioned other possibilities for the arrangement of insulating layers are not possible or inadequate. For instance, in the case of older buildings that are used and heated, where it is neither permitted, desired or economically viable to change the façade view, inside insulation is often the only way to reduce the transmission heat loss.
- Entire buildings or individual rooms are only used and heated occasionally. This applies e.g. for meeting rooms, ball rooms or sport and hobby rooms. Inside insulation offers decisive energy-saving benefits here. Fast, effective heating is possible because the solid external walls do not need to be heated due to the insulation applied on the inside.
Architects and engineers that were trained before or in the 1990s, often associate inside insulation with constructional damage. The were taught that dew can form in constructions with inside insulation by means of comparative calculations of walls with outside and inside insulation using the Glaser procedure. The solution then was: Careful planning and conscientious installation of inside insulation only in combination with interior vapour proof barriers and retarders.
However, part connections and openings, and also deformations (e.g. beam ends of wooden joist ceilings) represent a problem that is difficult to solve. The positive effect of preventing water vapour diffusing into the inside of the part and therefore condensation through films and/or vapour inhibitors is offset with a reduction of the drying potential for e.g. for moisture penetrating from outside. The summer process of drying moisture toward the inside of construction exposed to driving rain is obstructed by part layers with a high vapour diffusion resistance which can lead to a build up of moisture in the wall cross-section.
In contrast to system structures with vapour proof barriers or inhibitors, the properties of capillary-active inside insulation systems allow longer-term drying, even of previously damaged parts due to the retention of the drying potential. The creation of condensation is accepted because the capillary activity ensures fast and large-scale return of the moisture throughout the entire year. During the past decade, the group of capillary-active insulating materials has proven the most ‘application-safe’ for inside insulation.
The multi-dimensional calculation programs that have been available for some years and are now extremely well calibrated and are used to simulate the thermal and hygric behaviour of façade constructions prove this impressively.
Vapour barrier and inhibiting systems
These classic construction types and the functioning e of inside insulation have been available in two basic variants for decades.
- Systems in which a facing shell is installed on the room side in front of the insulating layer on a corresponding sub-construction.
This type of construction is often offered as a ‘DIY’ solution. However the avoidance of damage can only be guaranteed if fitted correctly and if the operability of the vapour proof barrier or inhibitor is ensured. Steps must be taken to prevent moisture entering the construction by means of convection as this creates large quantities of condensation. Steps must be taken to ensure that no air can circulate between the insulation and existing wall. The airtightness is usually achieved by means of a separate layer e.g. PE-film, vapour inhibiting paper etc. Here, a careful and permanently tight installation, in particular near the connections, is important.
- · Board systems that are directly adhered to the existing wall.
These kinds of boards are offered as composite boards, usually comprising insulation material, possibly a vapour barrier or inhibitor, and an installation layer, or as single-layer boards in which the insulating material itself assumes the vapour-inhibiting function, e.g. cellular glass. Here, too, steps must be taken to avoid moisture penetrating the construction by means of convection. Firstly, this can be achieved by positioning the boards carefully in a point-bead method or by means of full-surface cementing. Secondly, the airtightness can be achieved by applying a filler across the slab joints and/or applying a render across the entire surface.
The preferred system can be selected based on the quality of the existing wall. If the wall is even and strong, directly adhered composite boards are recommended, otherwise facing shells are usually the most inexpensive alternative.
Note:In principle, moisture penetration into the construction from outside must be minimised for vapour reducing or inhibiting inside insulation by means of functional driving rain protection. Most of the absorbed moisture is transported toward the inside wall surface especially in the cold winter months, because of a lack of drying potential for drying outwards e.g. low temperatures and the lower energy input because of the inside insulation. There is a risk of frost damage and mould infestation.
- Systems in which a facing shell is installed on the room side in front of the insulating layer on a corresponding sub-construction.
The so-called ‘capillary-active inside insulation systems’ were developed in the 1990s to bypass inherent system problems connected to certain vapour barriers or inhibitors. Pioneers were calcium silicate building materials that are still used as inside insulation today, outside their classic range of use in high-temperature areas. Today, there is an extensive range that includes a variety of materials and material combinations.
Capillary-active inside insulation work without inner vapour proof barriers or inhibitors. Therefore, in the cold season water vapour diffuses into the construction. At the point at which the dew point is reached, usually on the ‘outside’ of the inside insulation, parts of the water vapour condenses and condensation is created. Compared to water that penetrates from the façade side, there is a higher tolerance because, in contrast to vapour barrier systems, there is a higher drying potential toward the inside. Despite this, steps should also be taken to ensure functional driving rain protection to minimise the risk of frost damage, in particular on the outside of the brickwork.
The capillary-active inside insulation solves both described moisture problems - formation of condensation and outside moisture penetration - by increased fluid transport toward the room and accelerated evaporation. This helps avoid high local levels of moisture and limits the overall moisture in the construction.
Capillary-active inside insulation is a multifunctional system that combines various hygrothermal material properties. The coordinated interaction of moisture buffering, vapour and fluid water transport within the materials and/or between the system components is decisive for the operability and the ‘performance’ of the inside insulation. For this reason individual system components may not be replaced without consulting the manufacturers first.
Information about system selection
- Subsurface quality
As capillary-active systems require full-surface adhesion, the subsurface must be even to guarantee full connection of the system. In the case of composite boards with point-bead adhesion, a certain amount of unevenness is allowed, however convection security must be ensured. There are no special requirements with respect to the evenness of the surface with respect to facing shells.
- Surface material
Gypsum renders usually need to be removed before applying capillary-active systems and composite boards. The reason for this is the lack of moisture resistance of the gypsum-building materials and the incompatibility between cement and gypsum-based materials, which can lead to the creation of blowing minerals if there is any moisture. Some manufacturers approve the application of their breathable and capillary-open systems on gypsum-based surfaces, if the driving rain security of the façade is guaranteed. Please note that the planner should ensure this throughout his relevant guarantee period.
Brittle and salt-saturated renders, in particular lime renders, should also be removed.
Facing shells tend to be uncritical because they can bear themselves. If there are gypsum renders below the system, there is a risk of mould infestation, if the driving rain is not adequately guaranteed.
- Vapour reducing or vapour inhibiting inside insulations may only be fitted if the moisture penetration into the construction from the outside is adequately minimised by functional driving rain protection. Capillary-active systems are more tolerant here, but still require appropriate driving rain protection. In this case, a hygrothermal simulation is advisable.
- Use in wet rooms
In principle, all systems also function in wet rooms. Capillary-active systems require phases of relaxation, i.e. periods in which the absorbed moisture can be discharged again into the room air. Vapour barrier systems should be used in rooms that do not provide these drying times, e.g. swimming pools or similar. It should also be noted that a flow covering is also a vapour proof barrier and counters the ‘functional principle’ of a capillary-active system.
- Inside insulation of exposed timber-frame façades
Due to the unavoidable cracks between the in-fill and the wood, exposed timber-frame façades must be treated carefully. When the façade is exposed to rain, the named cracks can lead to high water absorption, in particular on the side of the building exposed to driving rain. The water quantities absorbed here can exceed the dew quantities created many times over due to the capillary-active inside insulation. To ensure that the penetrated water can dry again, energy needs to be input into the construction. It is therefore recommended limiting the insulation value of additionally installed inside insulation. The corresponding recommendation is defined in the WTA information sheet 8-5-00/D Formwork repair according to WTA V:Inside insulation systems. “The additional inside heat insulation should not exceed a value of D Ri = 0.8 m²K/W.” In the case of cladded framework, e.g. with board formwork, tiles or render, this recommendation does not apply because no or a only every small amount of moisture can penetrate into the construction when the framework is cladded.
- Subsurface quality
Requirements with regard to the processing
We can only provide general advice here due to the large amount of different systems. It is always recommended following the processing instructions of the system suppliers (manufacturer information).
- Security against back-flow (convection)
When installing inside insulation, always take steps to avoid convection. In the case of capillary-active systems, full-surface cementing is stipulated - smaller hollow spaces created during installation that are unconnected to each other or the room air are uncritical so that there is no risk of convection. In the case of systems with a facing shell and also for composite boards, steps must be taken to prevent room air penetrating the construction. This is achieved by adhering the composite board in a point-bead method and/or by attaching and adhering the vapour barrier or inhibitor carefully, in particular to adjacent parts and openings. Ensure that the airtightness level during the usage phase is not damaged or does not become fatigued.
- Installation of sockets, light switches, etc.
Sockets for holding switches or power sockets may not represent a weakness with respect to the insulation nor the airtightness. Therefore, they usually require rear insulation. Also, vapour-tight and/or vapour-inhibiting versions should be selected for non-capillary-active systems. Steps must be taken to prevent any back-flowing behind the facing shell. If old cables are kept, it is recommended removing the old socket, expanding the holes and applying an insulation strip.
- Relocation of heating and hot water lines
It is always recommended relocating the heating and hot water lines to the ‘warm side’ of the insulation, i.e. on the room side to prevent energy losses and/or in worst cases, freezing.
- Surface design
Uniform recommendations cannot be provided due to the functional variety of the available systems. As a general trend, the surface design of capillary-active systems places higher requirements on the physical properties of the decorative system closure than tighter systems. Requirements relating to the respective system-specific physical requirements are formulated by the system supplier. Whilst there are usually reliable indicators for renders, fillers ad coatings, the availability of this kind of information for wall cladding and their adhesives is usually limited.
- Mechanical attachment of inside insulation
In contrast to thermal insulation systems, there are no general regulations for the mechanical attachment of inside insulation. For system-specific requirements, in particular for constructions subject to dynamic loads (e.g. framework), please see the corresponding recommendations in the information provided by the respective manufacturer.
- Flank insulation and insulation of heat bridges
Calculations of the minimum hygienic thermal insulation are required in some cases to determine the respective necessary insulation depths and thicknesses. It is usually possible to install flank insulation to integrated parts, like ceiling or dividing walls, using system-specific solutions, e.g. insulation wedges.
- Integration of the beam ends for wooden joist ceiling
If possible, storey ceilings should be insulated completely. To this end the beams are exposed. To prevent convection near the respective beam end, cracks within the beam where the inside insulation is to be connected should be chiselled out. In the case of capillary-active systems, the beam in this area needs to be surrounded with a collar of suitable compression tape; where vapour-inhibiting or blocking systems are used, the corresponding layer needs to be tied to the beam with a suitable adhesive tape. Then the selected system is processed. If possible, a cavity should be available for the beam end itself.
It is recommended using boron cartridges in the beam end as additional preventive protection, in particular for construction parts at risk from moisture usually connected with moisture input via the façade. The pressed salt cartridges create a depot of inorganic boric acid to prevent wood-destroying fungi and insects. It is applied in a borehole procedure. One or two boron cartridges (see information sheet ‘Special procedures for handling danger points’ by the DGfH) are used for each beam end. In rare, particularly critical cases, it may be necessary to temper the timber beam ends.
- Security against back-flow (convection)
Inside insulation of parts that have contact with the ground
Moisture-saturated walls that have contact with the ground can be restored successfully by subsequent interior water proofing in combination with inside water proofing. Even if the currently valid version of the ENEV (2009) does not contain explicit and mandatory U-value requirements for the interior water proofing, the requirements for the hygienic minimum thermal protection need to be met at least in the case of heated cellar rooms. This usually means that an insulating layer needs to be installed, which makes the issue of where installation is required obsolete, and compliance with the requirements of the EnEV mandatory.
Ordinance on thermal insulation (WSchV) / German energy conservat
German energy saving efforts began in 1977 with the ordinance on thermal insulation (WSchV) that was aimed at saving energy in buildings.
Taking economic viability into account, the objective of the law is to ensure that all buildings are almost climate-neutral by the year 2050.
German energy conservation act (EnEV)
The EnEV is a summary of the ordinance on thermal insulation and the heating systems ordinance. It is an intelligent solution aimed at reducing the energy requirements (heat requirements and heat generation) of buildings. The EnEV refers to engineering standards and implements European legal specifications.
- Building with normal inside temperatures. (Buildings that are heated to an inside temperature of 19°C and higher, and annually more than four months.)
- Building with low inside temperatures. (Buildings that are heated to an inside temperature of more than 12°C and less than 19°C, and annually more than four months.)
- Work buildings used for keeping animals
- Work buildings, large and open for longer periods
- Underground buildings
- Under-glass systems and cultural rooms for breeding, propagation and the sale of plants
- Air domes, tents and others. Building that are designed to be put up and dismantled repeatedly
Requirements acc. to EnEV
Buildings with normal inside temperatures are formulated using the annual primary energy needs and the transmission heat loss.
The transmission heat loss HT describes those heat losses through the building envelope (walls, windows, roof, lower building section etc.).
Fxi = Temperature correction factors acc. to table
Ui = Heat transition coefficient in [W/(m²K)]
Ai = Surfaces of the individual parts in [m²] for which the heat transition coefficient U and the temperature correction factor are constant
∆UWB = Heat bridge transmittance in [W/(m²*K)]. This takes heat losses as a result of heat bridges into account. In a simplified procedure, this is set to 0.05 W/(m²*K)
A = heat transferring enclosing surface in [m²]
The transmission heat loss HT of an element of the building envelope depends on the heat transition coefficient (U-value) of the associated part and its surface.
Company declaration about compliance with the EnEV requirements
In the case of constructional measures connected to energetic restoration of external construction components of a building, for instance windows or façades and/or external walls, the EnEV 2009 prescribes that the companies need to document their work and issue a private document, a so-called a company declaration. This aims to ensure that the requirements of § 26a EnEV 2009 and the minimum technical requirements are met. There are corresponding forms online.
Over the past 100 years, the emissions of greenhouse gases, both from private households and also industrial operations, has increased significantly. This has led to an increase in the surface temperature of the earth of around 0.6 °C, which is causing natural disasters of previously unknown severity. Across the globe, scientific, business and political circles are working on saving the earth as a habitat. The Kyoto protocol is a first political step toward reducing greenhouse gas emissions.
The most important natural greenhouse gases include
- Water vapour (H₂O)
- Carbon dioxide (CO₂)
- Methane (CH₄) and
- Nitrous oxide (N₂O)
In addition, artificially produced gases, like hydrochlorofluorocarbons (HCFC) and fully fluorinated and partly fluorinated hydrocarbons (CFC, HFC) also have a climate-relevant impact.
The global CO₂ emissions now total approx. 25 billion tonnes annually.
The CO₂ emissions per capita in the USA are approx. 20 tonnes annually, in Germany approx. 14 tonnes annually and in most development countries 0.5 - 3 tonnes annually.
Measures to reduce emissions
There is a new ordinance on thermal insulation that came into effect for new buildings and important modifications in January 1995. The goal of this ordinance is to reduce the energy consumption and the connected CO₂ emissions by 30 percent.
Heat transition coefficient (U-value) / heat transmission coeff
Heat transition coefficient
The heat transition coefficient states the heat flow in watts that crosses a structural component per m² and 1 Kelvin temperature difference.
U = Heat transition coefficient in [W/(m²K)]
RT = Thermal resistance in [(m²K)/W]
Rsi = Heat transfer resistance inside in [(m²K)/W]
Rse = Heat transfer resistance outside in [(m²K)/W]
Ri = Heat transmission resistance of the individual part layers in [(m²K)/W]
R = d/λ with d= Density of the part layer in [m] and λ = Calculated value of the thermal conductivity in [W/(m²*K)]
Overall heat transfer coefficient (R si and R se)
Heat transfer coefficient
The transport of heat from a part surface into the air and vice versa is called heat transfer.
- Rsi (inside) in [(m²*K)/W]
- Rsi (outside) in [(m²*K)/W]
The DIN V 4108-4 is used to calculate and/or determine the heat transfer coefficients.
The following table values apply for even surfaces, if there is no special information about the underlying conditions:
(the DIN EN ISO 6946 apply for uneven surfaces and special underlying conditions)
Direction of the heat flux
Upwards Horizontal Downwards 0,10 0,13 0,17 ↑ → ↓ 0,04 0,04 0,04
Overall heat transfer coefficient (R T)
Overall heat transfer coefficient
The thermal resistance RT of an even part made of thermally homogeneous layers comprises the heat transfer resistance R and the heat transmission resistances Rsi and Rse.
RT= Rsi + d/Lambda + Rse in [m²K/W]
The following applies for several part layers:
RT= Rsi + Total Ri + Rse in [m²K/W]
Total Ri = Total of the heat transmission resistances of the part layers [m²*K/W]
U-value calculation [iQ-Lator]
The iQ-Lator is not only used to calculate U-values of one-dimensional surrounding constructions (external walls, also with contact with the ground, and roofs), it is also possible to carry out a hygrothermal assessment. This program can be used to generate various designs and the heat, and also provides estimates relating to the moisture transport by the construction. According to definition or modification of the construction or the climate condition, the fast calculation algorithm provides results that allow a realistic assessment of the construction.
iQ-Lator - principles
The calculation scheme upon which the iQ-Later program is based is described and derived in detail in the following program: Nicolai, A., The generalised COND algorithm for the hygrothermal assessment of constructions, construction physics, WILEY-VCH publishing house, 2012, 34, 24-31.
The brief introduction here describes the principle of the procedure.