The building is a half-timbered construction with visible oak beams and compartments filled with bricks and loam. In 1995, in addition to the insulation work, the owner also completed the necessary structural repairs (timber repairs, extension of the compartments and new filling of the compartments). New windows were installed and the house’s heating system was connected to the community’s own heat generation system. Various constructions were insulated with interior and/or exterior insulation. This encompassed four wall structures: the North-East and North-West facades were insulated with an interior insulation layer with an average thickness of 12cm. A further construction with a vapour retardant membrane (sd-value 2.3m) was also installed in the North-East façade, in the ground floor bathroom. All other interior installation measures were carried out in the same fashion as the first installation i.e. without a vapour retardant membrane and just using building paper as a vapour-proofing layer.
The aim of the ZHD-Project was to gain knowledge of the moisture-related behaviour of half-timbered constructions at the interface to the insulation material and to determine whether the principle advantages of vapour-permeable constructions using isofloc cellulose insulation could be proven in practice. The measurement results were used to evaluate the suitability of this type of insulation material in insulating the interior of half-timbered constructions.
The insulation of half-timbered buildings using cellulose insulation
The Kaufungen community is one of the largest communities in Germany. The organisational form is similar to a kibbutz. About 80 people live and work on a consensual basis in 13 different areas such as crafts, social work or agriculture. The conversion and energy-efficient renovation of an 18th and 19th century two-storey, residential, half-timbered house took place in 1995. The building measures were supervised by the former ‘Centre for Building Conservation and Preservation of Old Crafts’ (Zentrum für Denkmal und Handwerkspflege (ZHD)), Propstei Johannisburg Fulda, Germany. This project was documented and the results evaluated in a ZHD project report within the framework of a model project “System determination – Thermal protection” (original title: Systemfindung Wärmeschutz) sponsored by the German Federal Environmental Foundation (DBU-Deutsche Bundesstiftung Umwelt). In the year 2000, the project was awarded the 2nd prize in the Hessen State competition for energy-efficient building renovations. The cellulose insulation installed was supplied by the manufacturer - isofloc.
| The republication of the original German language article was approved by SBM VERLAG GmbH, Magazin Baustoff Partner, December 2005 edition, Internet-Link: www.sbm-verlag.de (Please note: This is an unauthorised translation of the original German language article.) |
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| Cellulose insulation from isofloc |
Measurements confirm the functionality
Twenty-eight moisture sensors were installed throughout the whole building. The main focus was the monitoring of the contact-surface between the timbers and the interior insulation, as this was the area where the greatest problems were expected when using such a thick interior insulation layer. Between August 1995 and October 1997, the timber moisture levels were recorded. The interior insulation on the weather-side of the house, with its visible half-timbering, was subject to special scrutiny. The isofloc insulation was installed using the spray-on method. This involves adding water to the insulation and moistening the substrate against which it is to be installed. This moistening promotes adhesion and cohesion (papier-mâché effect). The water added led to an initial increase in the moisture level of the timbers that subsequently took a long time to dry out and reach its equilibrium moisture level. This was exacerbated by the fact that the interior cladding had to be installed very quickly.
This effect was further intensified by the presence of additional moisture which resulted from the renovation of the compartments. The cellulose insulation can also be applied blown-in at layer thicknesses of 8cm or greater. The timber-moisture levels reached their initial level after a period of nine months. The slight increase from November 1996 was caused by the build up of condensation but was limited to a small percentage of the mass. By the beginning of the first summer after the completion of the work in the autumn of 1995, all moisture values had fallen to a level of under 20 M.-%. Variations in the summer months are probably due to the effects of driving rain. No measurements were taken in the years from 1998 to 2000. In July 2003 and September 2005, the isofloc applications technician Jürgen Küllmer determined the timber-moisture levels using the remaining available sensors. All values lay within the optimal range. No moisture build-up effects were evident. The values tended to lie under the measurement results recorded in comparable periods from the first two years. The internal sd-values in the constructions without a vapour retardant membrane lay slightly below the value recommended for interior insulation in half-timbered constructions of 0.5 to 2m. In the wintertime periods of thawing, this led to a slightly higher timber-moisture level compared to the variant with a vapour membrane but in the case of the North facing façade, where the effects of driving rain greatly exceeded the extra moisture caused by the effects of diffusion in the winter, it provided a greater potential for the moisture to diffuse into the building and so support the drying process. In addition, the fact that the cellulose insulation is able to reduce the amount of condensation in winter by raising the moisture balance level and also to absorb water from the exterior, this reduced the negative effects upon the compartments and the timber beams. This is confirmed by the authors of the ZHD-report in their overall evaluation. They did however state the requirement for the further monitoring of a certain number of the measurement sensors. These measurements took place in 2003 and 2005 and confirmed the long-term functionality and suitability of insulating the interior of a half-timbered construction (with visible timbers) using isofloc cellulose insulation – even with a thickness of up to 13cm. This is a further proof of the advantages of vapour-permeable (open-diffusion) construction methods using moisture-adaptive building materials.
| The republication of the original German language article was approved by SBM VERLAG GmbH, Magazin Baustoff Partner, December 2005 edition, Internet-Link: www.sbm-verlag.de (Please note: This is an unauthorised translation of the original German language article.) |
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Saving CO2
How thick should the insulating layer be?
As basic rule is: As thick as possible! This has less to do with the fact that we want to sell as much insulation as possible (naturally we are in business to sell insulation :-) ), but rather with the fact that over the years the recommendations for the optimum insulation thickness are continually being revised. This is because of
- the ever increasing price of energy
- and the associated rise in running costs for tenants
Therefore, such statements as “10cm are absolutely fine” are completely insufficient.
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