Attic Conversion – Hygrothermal Assessment of Historical Roof Truss

Abstract

In the City of Prague centre, an investor had the intention to convert the unused attic space of a historical palace into office and exhibition floor. It was necessary to design such a solution that would not worsen the humidity conditions and would not jeopardize the original Renaissance roof truss. The requirements of the heritage protection agency and the architect predetermined the use of very efficient thermal insulation above the rafters. The paper introduces and assesses several design solutions for: (1) new roofing layers and (2) the critical detail near the eaves, including variants with active heating elements. The assessment was based on results of 2D steady-state hygrothermal modelling using two criteria: (1) the interior surface temperature under winter design boundary conditions and (2) the relative humidity in the area of the timber elements under average January boundary conditions. The results showed hygrothermal implications of different design measures and helped to identify acceptable solutions for further project phases.