Benefits of Investigating the Thermal Component for Moisture Safety in Ventilated Attics

Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceeding

Abstract

Cold ventilated attics often have mould problems in Sweden. This is valid both for old and sometimes newly built attics. Increased insulation on the attic floor is assumed to increase the problem. To investigate this, numerical 1D models like WUFI or WUFI+ are typically used. These models give results but the physical processes are not so transparent for the user due to the complex numerical techniques involved and takes a long time to simulate. The problem is mainly related to the temperature in the attic, the ventilation rate and possible of leaks from the living space. All exposed surfaces in the attic will buffer moisture variations. But if this buffering is neglected and the leakage is treated as a constant the moisture content in the attic is only dependent on the ventilation with outside air and the assumed leakage. This would make a pure thermal investigation meaningful. An analytical model for the thermal problem was developed that took into account radiation between the interior surfaces and the different boundary conditions at the outside and inside surfaces. Using this model a parameter study of exterior roofing insulation was done using a moisture transport model that only took into account convection exchange. The results were compared with WUFI Pro and WUFI+ simulations which included the moisture exchange between air and internal surfaces. The comparison showed that the pure thermal model gave, as expected, larger variations in relative humidity, but that the results were qualitatively very similar. This indicates that analytical solutions of thermal problems can be used as a base in qualitative investigations of certain combined heat and moisture problems.

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Subject classification (UKÄ) – MANDATORY

  • Building Technologies
Original languageEnglish
Title of host publication12th Nordic Symposium on Building Physics (NSB 2020)
Volume172
Publication statusPublished - 2020
Publication categoryResearch
Peer-reviewedYes
Event12th Nordic Symposium on Building Physics, NSB 2020 - Tallinn, Estonia
Duration: 2020 Sep 62020 Sep 9

Publication series

NameE3S Web of Conferences
PublisherEDP Sciences
ISSN (Print)2555-0403

Conference

Conference12th Nordic Symposium on Building Physics, NSB 2020
CountryEstonia
CityTallinn
Period2020/09/062020/09/09