In traditionally ventilated pitched roof construction, energy lost by ventilation can account for up to 25% of the total heat lost through the roof. The latest designed non-ventilated systems will substantially reduce heat loss in the building. With this in mind roofing manufacturer, Chesterfelt has commissioned a special report unique to Chesterbreathe membranes in the UK, to measure the Hygrothermal performance (the measurement of humidity and temperature conditions in the roof assembly) of non-ventilated cold roofs, using the Chesterbreathe Active and Chesterbreathe Rapid underlays. The successful test results have provided Chesterfelt with a valuable additional accreditation to complement their recent BBA approval for the products. The research was carried out by the Fraunhofer Institute for Building Physics in Germany who have developed their own computerised programme, WUFI to accurately calculate and record the results. The Fraunhofer Institute conducts specialised building research programmes including sound insulation, moisture control, weathering protection, preservation of building structures and energy reduction projects. The Holzkirchen Test Site with its outdoor testing site which is exposed to extreme climate condition (700 metres above sea level) offers the possibility of investigating building structure, elements and materials. The profiles of temperature and relative humidity in the roof assemblies were calculated over a period of two years. Critical locations at the surface of the roof underlay membrane were investigated and engineering assessments made. Calculations were carried out on both the North and South side of the roof structures with weather data from specific locations, Holzkirchen (Bavarian Alps), Oban and Aviemore (Scotland), Kilcaldy (Scottish Highlands) and London (England) all located at measured heights above sea level. The compilation of moisture behaviour of the whole roof systems was analysed. It was concluded that the most vulnerable areas that could create harmful condensation build up, were areas of prolonged freezing temperatures coupled with high levels of relative humidity and the building location in respect of height above sea level, in these extreme cases the use of a full combined system using Chesterbreathe breathable membranes and vapour control layer would be recommended, this would regulate potential condensation build up. For most areas of the UK however the climate is not this severe and the use of a vapour control layer may not be necessary. More information relating to the Fraunhofer Institute can be found by visiting http://www.ibp.fhg.de/ Photo Caption (1) Aerial Shot of Fraunhofer Institute Photo Caption (2) Chesterbreathe |
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