Full-scale Studies of Improving Energy Performance by Renovating Historic Swedish Timber Buildings with Hemp-lime

Abstract

With an increased focus on reducing greenhouse gas emissions, energy saving is of great importance in all sectors of society. EU directives set targets for member states to reduce energy use in buildings. Energy saving in historic buildings requires special measures, balancing energy-saving renovations against the preservation of heritage values. Traditional constructions are open to vapor diffusion and generally work differently from modern constructions. Modern materials in traditional constructions sometimes damages the original material as they are usually diffusion-tight. The aim of this study was to investigate whether hemp-lime could be used as an insulation material to improve the energy efficiency of historic timber building envelopes with a rendered façade in Sweden. The objective was to determine the actual energy savings for space heating. An additional objective was to determine the actual thermal transmittance and to study thermal buffering through in-situ measurements in a full-scale wall renovated with hemp-lime. Two full-scale wall sections were constructed at the Energy and Building Design laboratory at Lund University: A traditional post-and-plank wall with a lime render (80 mm), and a post-and-plank wall with a hemp-lime render (90 mm). Energy use for space heating was monitored continuously over a period of one year. The wall with a hemp-lime render required 33% less energy for space heating than the traditional post-and-plank wall with a lime render. This was accomplished without changing the framework, appearance or material in the render and without drastically changing the hygric properties of the façade. From the gathered data, the thermal transmittance (U-values) for both walls was calculated using two different methods, one based on material properties and the other based on energy use data. For both walls, thermal transmittance based on actual energy use data during the heating period was lower than what was expected from their material properties. This indicates that more material properties than thermal conductivity and material thickness need to be taken into account when performing energy use calculations. With hemp-lime, a renovation can be accomplished without damaging the timber structure and wooden slats, and it can be done with local traditional materials and building methods with no difference in appearance to a traditional lime render. This allows for heritage values to be preserved, while also allowing the building to comply with modern standards and with increased thermal comfort and reduced energy use.

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“…By adding hemp to the lime render and slightly increasing the thickness of the render, a significant improvement in the energy efficiency of the buildings was achieved. The proposed solutions not only preserve the historic form of the buildings, but are almost entirely in line with traditional construction techniques [16].…”

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“…Thanks to their thermal performance, the hemp composites have been positively considered for the building refurbishment or restoration [60]. Some papers discuss the energetic performance of historic buildings after the application of hemp-lime compared with gypsum lime [61]. For instance, Agliata et al [62], using a case study "Palazzo Jadicicco", found that the overall energy performance of the building increased by around 20% with a one-level improvement of the building energy class, from E to D. Besides, if it is a good result, it should underline that the decrease in thermal transmittance was not sufficient to fulfill the regulatory requirements, in Italy.…”

A Technical Assessment of Comfort Performance of Hanok Using Comparative Field Surveys between Experts and Users

“…Traditional houses have a distinctive shape with features that depend on the climate, culture, environment, and the location of the country in which they are built. Strandberg-de Bruijn, Donarelli, and Balksten have conducted research for the preservation and development of traditional architecture in the region, through the case of historic Swedish timber buildings, the most historic single-family houses in Sweden [11]. Their concept is quite impressive, and the main issue suggests that it will be necessary to improve the architectural performance of historical buildings with materials suitable for the architectural framework, while preserving its characteristic elements.…”