Vejledning 3 - Isoleringssystemer / Isoleringssystemer
Insulation systems available for internal insulation
Products used for internal insulation can be divided into two main categories:
Insulation system – pre-fabricated product containing layers of materials, e.g. insulation material, vapour barrier, finishing material etc. to be used for insulation of building envelope
Insulation materials – stand-alone materials used for insulation of building envelope.
Two decisive material properties of internal insulation layers are thermal resistance and vapour diffusion resistance. Neglecting the thickness of a particular chosen insulation layer, thermal conductivity (λ) and vapour diffusion resistance factor (μ) can be identified as very basic hygrothermal properties of insulation materials. A multitude of other material properties and functions is relevant for hygrothermal simulations and partially simulation model depending. Their explanation and identification requires an increased expenditure and will therefore be topic.
The overview of applicability of internal insulation materials or systems is presented here:
In accordance to the basic properties and following WTA 6-4 and DIN 4108-3, existing product range can be distinguished into three systems:
Condensate-preventing insulation systems
Condensate-limiting insulation systems
Condensate-tolerating insulation systems
Detailed information about insulation materials and material systems products and producers is available in Appendix 1 of this report.
Condensate-preventing insulation systems
Condensate preventing systems disable vapour transfer from the room side into the construction by a vapour barrier. According to WTA 6-4 and DIN 4108-3, vapour barriers are sealing layers with a vapour diffusion equivalent air layer thickness sd (product of μ and layer thickness) of min. 1500 m. The barrier can be a separate layer at the room side of the construction or alternatively be part of the insulation layer itself. Depending on the system only a minor or none interaction between the construction (maybe inner cladding) and the room climate can be expected. Typical application fields are buildings with high inner moisture loads, i.e. water vapour pressures like indoor swimming pool. Temperature, dew point, vapour saturation pressure and vapour pressure profiles for this system is seen in Figure 2.5.
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Figure 2.5. a) Temperature profile (black line) and dew point profile (blue line), b) vapour pressure profile (black line) with vapour saturation pressure (blue), for a massive wall (2) with condensate preventing internal insulation system including vapour tight insulation material (1) (diagrams generated with https://www.u-wert.net/)
Condensate-preventing systems performance is normally independent on the room climate and prevents moisture accumulation in the construction due to vapour transfer from inside to outside. It is very sensitive to high moisture loads from outside, e.g. wind-driven rain, and other additional loads, e.g. convective moisture input through leakages, because there is no drying potential towards room side. An intact coating for the reduction of the wind-driven rain input and a precise workmanship (esp. sealing around openings and junctions) are therefore essential for the functioning of these constructions. Furthermore, standard surface requirements ensuring hygienic minimum standards (no mould growth, no surface condensation) and comfort requirements (no strong radiant asymmetry resp. limited differences between construction surface and indoor operative temperature) are to be ensured.
Examples for condensate-preventing systems are vapour tight insulation materials (e.g. foam glass, extruded polystyrene, polyurethane), and systems including metal sealing foils (e.g. aluminium foils). Vacuum insulation panels (VIP) can be regarded as a special case of vapour tight insulation materials. The work by Baetens et al. (2010) give a review of VIP.
Condensate-limiting insulation systems
Condensate- limiting insulation systems include, according to DIN 4108-3, a vapour brake with an sd- value of min. 0.5 m and max. 1500 m. Vapour control layer should reduce the vapour input from the room side into the construction and has to be combined with a sufficient wind-driven rain protection. The wide range of vapour resistances implies a great diversity of constructive solutions and potential problems. In any case constructions with potential condensate must fulfil three criteria beside standard surface requirements. These are no long-time accumulation of condensate within the construction, sufficient drying-out of interstitial condensate during the drying period (summer) and uncritical moisture loads of the particular material (e.g. wood). Temperature, dew point, vapour saturation pressure and vapour pressure profiles for this system see Figure 2.6.
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Figure 2.6. a) Temperature profile (black line) and dew point profile (blue line), b) vapour pressure profile (black line) with vapour saturation pressure (blue), for a massive wall (3) with condensate limiting insulation system including vapour open insulation material (2) in combination with a vapour barrier (1) (diagrams generated with https://www.u-wert.net/)
To fulfil the requirements for condensate-limiting insulation system, the physical characteristics of vapour brake and insulation material should be such, that during the heating season vapour resistance should be sufficiently high to avoid interstitial condensation, while during the offheating season vapour resistance should be sufficiently low to allow drying out of the building structures. Therefore Kunzel (1999) proposed a vapour barrier with variable vapour resistance values depending on the humidity, a so-called smart vapour retarder. A smart vapour barrier having variable values of vapour resistance depending on the humidity, was proposed (Kunzel 1999), (Christensen & Bunch-Nielsen, 2005). Damage due to planning of these insulation systems might occur if boundary conditions, e.g. influence of precipitation, are underestimated or material properties, e.g. performance moistureadaptive vapour brakes, are misjudged. The complex and non-linear interaction of materials due to their properties (heat and moisture transfer and storage processes as well as boundary conditions) requires a sound evaluation of these constructions. Use of HAMT simulation tools is recommended.
Moreover the precise installation and exploitation of these systems is crucial, since the research by Slanina and Silorova (2009) performed wet-cup tests of vapour retarders and the results showed that the performance is significantly reduced in the case the vapour barrier has some small, artificially made damages.
Harrestrup et al. (2015), Morelli et al. (2010) and Morelli et al. (2012) report on a historic building built in 1896 and located in Copenhagen, Denmark, where internal insulation solutions was part of in-situ retrofitting measures, including also replacement of windows and ventilation system. One façade of this building was insulated from outside using mineral wool (with thermal conductivity of 0.039 W/(m K)) and remaining facades from inside using an aerogel/mineral wool mix (with thermal conductivity 0.019 W/(mK)) and thermoset modified resin insulation ((with thermal conductivity of 0.02 W/(mK)). The achieved energy saving was 47 % and specific energy consumption reached 82 kWh/(m2 year). From this energy saving around 40 % was achieved by insulation, around 40 % by replacement of windows and remaining by mechanical ventilation with heat recovery. At some spots the buildings had potential problems because of a high humidity level, especially the façade not receiving sunlight. A solution was presented where the insulation is stopped 200 mm above the floor, showing no risk of moisture problems, but the specific energy consumption increased by 3 kWh/(m2 year).
Examples for condensate-limiting insulation systems range from vapour open insulation material with vapour barrier mineral wool based systems (mineral wool with PE-foil or SVR), EPS or PUR based systems, wood or textile fibre based systems, or glass foam granulated systems to insulation systems made of composite boards with vapour controlling sealing.
Condensate-tolerating insulation systems
Condensate-tolerating insulation systems consist of capillary active insulation material and glue mortar. The only vapour resistance in these insulation systems is given by the material itself, therefore they show very small vapour transfer resistances (sd value < 0.5 m, according to DIN 4108-3). The main advantage of the application of condensate-tolerating systems is that they are not dependent on the precise workmanship and additional climate or human behaviour factors, e.g. wind-driven rain or temporary raised usage loads. This is because drying-out of these systems is not hindered, neither inwards nor outwards. Since the diffusion of moisture occurs freely in these systems, the material is porous and acts as a sponge, which means that the insulation material is not moisture-sensitive and is able to absorb and distribute water in its pores. As the material is diffusion open, water vapour penetrates into the wall and condensates in the wall near the surface of original historic wall, e.g. brick or stone. At some point inwards diffusion stops and equilibrium situation due to capillary forces is established. In order for the moisture to diffuse evenly an air gap must be avoided as this will hinder diffusion processes and condensation can occur. As drying periods for these systems are necessary to avoid moisture accumulation and associated risks (e.g. frost damage), they cannot be applied for buildings with permanently high usage or high loads of outdoor moisture, see Figure 2.7.
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Figure 2.7. a) Temperature profile (black line) and dew point profile (blue line), b) vapour pressure profile (black line) with vapour saturation pressure (blue), for a massive wall (2) with a condensate tolerating insulation system (1) (diagrams generated with https://www.u-wert.net/)
Examples of these systems are absorptive insulation boards with an additional cladding at the indoor side (e.g. vapour-open internal plaster) and absorptive insulation plastering. As capillary active materials in these insulation system wood fibre board, calcium silicate or aerated concrete are often used. Recent products also contain multiple materials in one insulation board. For example, wood fibre with mineral functional layer, PUR with calcium silicate or calcium silicate with PUR, pyrogenic silica or VIP.
An internal insulation system with calcium silicate was first presented in 1995. Further research of such systems focused on obtaining the same hydrothermal properties of glue mortar and insulation material, and at the same time providing the glue mortar with higher thermal conductivity than the insulation material (Scheffler and Grunewald, 2003). Haupl and Fechner (2003) proposed a methodology to describe moisture storage and moisture transport in the insulation material. As case study calcium silicate (capillary active insulation material) was modelled. Calcium silicate was selected as it is used often as internal insulation in historic buildings. Insulation systems containing calcium silicate are not cheap, therefore research on hydrophilic mineral wool is ongoing (Pavlik et al., 2005; Pavlik and Cerny, 2008; Pavlik and Cerny, 2010).
Complex retrofitting strategy was analysed by Ascione et al. (2015) for heritage building located in Italy. The authors found that most economically viable energy efficiency measures included replacement of windows, application of internal insulation and insulation roof slab. As the internal insulation material thermal insulating plaster (with thermal conductivity of 0.058 W/(mK) and thickness of 0.05 m) was selected. For the roof insulation expanded polystyrene panels of 100 mm thickness was chosen. Toman et al. (2009) studied thermal performance of an internally insulated historical brick building located in Prague, Czech Republic which has been used for 4 year after the renovation. The applied strategy for internal insulation was to use two types of hydrophilic mineral wool insulation boards. Each of these boards has different bulk density and was tightly put together. The “hard” board of 0.03 mm was used. This layer was used for moisture transport. The “soft” board of 0.005 m was fixed to the brick wall. The water vapour retarder on lime-cement basis was put on the brick wall. Surface finishing was done using plaster. The water condensation was not observed during the 4 years period.
Standard surface requirements ensuring hygienic minimum standards and comfort requirements have to be provided as for the other systems, too. For absorptive systems, greater differences between estimated and real thermal resistance might be a consequence of higher moisture contents, since the thermal conductivity linearly reduces when the moisture content in the insulation material increases (Haupl et al., 1995). Despite this, absorptive materials show an increased tolerance against critical surface conditions because temporary surface condensate can be distributed and the usually high pH-value (board systems) limits the risk of mould growth strongly.