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HYGrothermal performance in exterior walls

Project description

Project Background

In recent years, the requirements for energy efficiency in buildings in Denmark have increased. The increased demands regarding energy efficiency and the need for adding insulation to existing buildings result in extra challenges when it comes to protecting buildings from humidity and mold issues. The challenges are not only present in older buildings but can also be found in new buildings. This could be due to e.g., the increased demands regarding insulation thickness which can lead to longer drying time for materials when a building is erected or renovated. 

This project will investigate original buildings and buildings that have been renovated. The results of the investigations will provide significant knowledge to civil engineers, architects and constructors about the standards and design that are needed for designing a durable building envelope. We wish to be able to provide third-party guidance for operators in the construction industry and to building owners in connection with their building processes.

The goal of this project is to provide guidelines for how to build long-lasting and sustainable building envelopes now and in the future which will not suffer from humidity and mold problems.

Project purpose

  • Generate new data on actual durability of various types of exterior wall constructions
  • Identify best practices for ensuring a long lifespan for exterior wall constructions
  • Evaluate the risk of damage from humidity and mold due to climate changes

Project description

There are many ways to build highly efficient and durable exterior wall constructions. Unfortunately, there are also ways the construction design can result in problems caused by humidity. In Denmark, it is recommended that the warm side of the insulation is made airtight and diffusion tight, and when you use heavy exterior wall constructions, then a heavy back wall will ensure this.

If you instead build conventional exterior walls constructions of light materials (such as walls with a wooden framework between the insulation) then it is recommended to use a vapour barrier on the warm side of the insulation layer. However, experiences from several studies show that in some types of light exterior wall constructions, such as new buildings built with natural materials (such as wood and clay) it is possible to omit the vapour barrier without experiencing problems caused by humidity while improving the indoor air quality.

In this project we will examine the hygroscopic capacity of building materials (the capacity of absorbing and releasing humidity of the materials) in particular, the interior layer, and we will examine the role this layer plays, in order to determine when a vapour barrier is necessary and when it can be omitted. We will also examine to which degree protection from rain and choice of material matter when we want to ensure durable constructions for the climate-to-come. Furthermore, we will study if well-planned management of rainwater plays a role in the durability of the building envelope which is the outer layer of a building providing cover and insulation from the outdoors.

Target groups

The primary target groups of this project are researchers and advisors, such as civil engineers, architects and constructors who are responsible for the quality of the building envelope.

Secondary target groups are building owners and operators in the construction industry who are looking for third-party guidance when they seek to build long-lasting and sustainable exterior wall constructions.


The aim of the project is to gather new knowledge about different types of exterior wall constructions to be able to compare these and identify best practice and risk factors for ensuring durable and damp-proof constructions. This new knowledge will contribute to an improved construction design and prolonged durability of buildings and service life of the exterior wall constructions thus reducing the environmental impact.

In this project we will measure humidity and temperature conditions in exterior wall constructions as well as conduct tests for mold in a minimum of 60 buildings in Denmark; these will be our case studies. Additionally, we will conduct airtightness tests in selected case studies.  The case studies are selected to represent the most common types of buildings in Denmark. Our point of departure will be the classification of building types according to the TABULA classification (Institut Wohnen und Umwelt GmbH 2016), and we will supplement with buildings with light exterior wall constructions using alternative materials such as bio-based materials.

We will investigate buildings in different regions of Denmark, as well in Greenland and Canada.

By measuring buildings in their original form as well as buildings that have undergone renovation, we will be able to identify best practices, which will help support productive renovations of buildings in Denmark.

Furthermore, we will examine the effects that climate change and the future climate could have on the durability of buildings. For this, we will apply data from measurements of buildings in Southern Germany or Belgium, and we will use these for benchmarking. By comparing the climate in Southern Germany/Belgium with climate measurements in Denmark, our research will indicate the type of climate impact Danish buildings will be exposed to in the future.

In this project we can gather important data on the actual hygrothermal capacity (capacity for absorbing and releasing moisture), durability and the presence of mold in the selected exterior wall constructions. Based on measurement data of relative humidity and temperature conditions in relevant measurement points in various exterior wall constructions, we will calculate the risk of mold growth based on the mold growth index. However, when using merely estimated data for calculating mold development based on the mold index, the results are prone to many uncertainties. By combining relative humidity and temperature measurements in existing buildings with visual inspection and testing for mold we can gather important data which can be used not only for evaluating the quality of the constructions but also for validating mold growth models. In addition, we will simulate relative humidity and temperature conditions by using future climate data for selected exterior wall constructions, and also calculate the risk of mold development based on the simulations.

TABULA is a European project in which residential property is classified according to age and building types in Denmark and in the other EU countries. In TABULA all in all 7 building typologies which are representative for detached houses in Denmark are defined (1. half-timbering, 2. (Solid) Brick, 3. Brick cavity wall, 4. Exterior Brick-Interior Concrete (hybrid), 5. Exterior Brick-Interior light structure (hybrid), 6. Light exterior wall with sheathing cladding, 7. Light exterior wall with lightweight concrete).


The aim of the project is to provide new knowledge about best practice for building durable buildings with moisture proof constructions. At the same time, an increased durability will also contribute to reduce the environmental impact of the construction industry. Moreover, by identifying risk factors for mold it will become easier to avoid damage from moisture and the health issues that often follow. One of the goals of the project is to identify best practices to ensure long service life of buildings. It is our expectation that we - after the data analysis - will be able to answer the following questions:

  • Which types of exterior wall constructions demonstrate robustness, also in future climate scenarios. Is the answer depending on hygrothermal capacity of the building materials, thickness of the insulation, presence of ventilation behind the cladding, the climate, or other factors?
  • When is better to build walls with a vapour barrier in light (and hybride) exterior wall construction or during renovation, when is better to avoid it and when is it not of importance?
  • Besides the vapour barrier in light exterior wall constructions, which other factors are important to control to avoid water damage and prolong the service life of buildings?

We will make all information available for the public in such a way that researchers and all others who are interested in this topic will have access to the data. At the same time, this project makes it possible to enhance mold growth models in future projects, as the current models display significant inconsistencies.




Faculty of Engineering Department of Technology and Innovation University of Southern Denmark

  • Campusvej 55
  • Odense M - DK-5230
  • Phone: +45 6550 7450

Last Updated 14.12.2022