Moisture Risk Analysis for Three Construction Variants of a Wooden Inverted Flat Roof

Agnieszka Sadłowska-Sałęga,Krzysztof Wąs

doi:10.3390/en14237898

Abstract

The paper presents an analysis of the hygrothermal performance of an inverted flat roof with a CLT (cross-laminated timber) structure in a building that meets the requirements of Passive House Standard (PHS) with regards to the potential risk of moisture. The calculations were made in the WUFI®Plus and WUFI®Bio software. The following variants were taken into account: three structure configurations, three different external climates and different scenarios of microclimate control and air change rate. The results of the calculations show that, especially in cooler climates, there is an actual moisture risk in the structure despite the excellent thermal insulation. The structure of the inverted flat roof, due to the use of a tight membrane on the outer side, allows for the partition to discharge the excess moisture only to the inside of the building. Ensuring the comfort of users may require periodic humidification of internal air, which translates directly into an increase in moisture content of the structure. The performed analysis clearly showed that there are no universal solutions. It is important to point out that for the proper performance of inverted wooden roofs, it is crucial to analyse moisture, not only thermal and energy parameters.

Highlights

Wood and wood-based materials are becoming an ecological alternative to materials commonly used in the construction of buildings [1]
The aim of the presented study is an analysis of the hygrothermal performance of an atypical inverted flat roof with a cross-laminated timber (CLT) structure in a building that meets the requirements of Passive House Standard (PHS) with regards to the potential risk of moisture
The concept of using prefabrication in as many building elements as possible. This applied to the flat roof, the structure of which was designed in a wooden frame system filled with insulation and closed on both sides with CLT panels

Summary

Introduction

Wood and wood-based materials are becoming an ecological alternative to materials commonly used in the construction of buildings (such as concrete, steel or ceramics) [1]. Investors and designers appreciate naturalness, ease of processing and the so-called low carbon footprint (CFP) of wood [2]. The lifecycle of a wooden house yields 20 tons of CO2-eq emissions compared to 72 tons for the typical house [3]. Wooden houses consume about 45% of the fossil fuels used in the typical house [3] during their lifecycle. For the European building sector, an achievable potential for net carbon storage can reach about 46 million tonnes CO2-eq per year in 2030 [1]. Wooden structures are used in single-family housing and in multiapartment, office and public buildings (i.e., schools, swimming pools). It is possible to create various types of partitions: walls, floors, ceilings and roofs

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Conclusion