1 Introduction

Moisture is usually the primary cause of damage to Danish buildings. Typical minor of brief exposure to moisture (e.g., from rain on a wooden fence or washing a wooden floor) will not usually cause problems. However, if extensive moisture exposure occurs in inaccessible places, this will cause water damage. Similarly, sustained moisture exposure above a threshold leads to damage, possibly in the form of deformed components, mould growth on surfaces, or deterioration of organic materials (resulting from decay and dry rot). Moisture is a direct or contributing cause to the deterioration of materials due to corrosion, shrinkage, bulking, frost bursts, and efflorescence. Moisture may also cause odour nuisances and adverse health problems. Finally, excessive moisture content in building materials will reduce their insulating properties.

Moisture problems in building constructions and materials can largely be avoided if the constructions are built in such a way that anticipates their exposure to moisture loads deriving from precipitation, relative air humidity, user behaviour, etc. Problems caused by actual water damage such as burst pipes are often not entirely avoidable, but the extent of the damage can normally be reduced if effective action is taken quickly and the area is effectively dried out until the moisture has disappeared.

These Guidelines address the mechanisms which dictate the moisture content of buildings and building parts. They address the precautionary steps to take to avoid moisture damage.

The first part of the Guidelines includes a review of moisture theory with basic information on air humidity, the equilibrium moisture content (EMC) of materials, and moisture transport in air and building materials. In the chapter on moisture sources, we introduce the concept of humidity exposure classes (Fugtbelastningsklasser), which replaces the former indoor-climate classes (Rumklimaklasser). This concept is used when assessing whether a given structure is damp-proof. Finally, critical moisture content (introduced by BR08) is briefly mentioned. Note that this field has not yet been fully developed.

In the second part of the Guidelines, the most common types of building materials are reviewed. These chapters show examples of how buildings and building parts can be designed to meet the requirements stipulated in the Building Regulations. The examples are based on practical experience as well as the calculation methods mentioned earlier in the Guidelines. These sections on parts of buildings can be read and applied independently of the more theoretical chapters.

Furthermore, the final part of the Guidelines contains a chapter on building surveys with a specific focus on moisture investigations and moisture measurements.

The annexes include tables of information that is useful when integrating moisture control into building design. They also contain a glossary explaining the specialist terms used.

Critical moisture issues, moisture measurements, a historical account of moisture issues, documentation of moisture control, and an assessment of mould growth are subjects which are still under development. We recommend remaining updated on the latest developments by regularly visiting www.sbi.dk/fugt.

Structures in wet rooms are outside the scope of this publication. Instead, please consult the guidelines issued by By og Byg Anvisning 200 Vådrum (Wet Rooms) (published in 2001).

When re-insulating small buildings, SBi Guidelines 240 provides information to facilitate the assessment of risks associated with moisture control (Efterisolering af småhuse – byggetekniske løsninger (Re-Insulating Small Buildings – Constructional Solutions) (Møller, 2012a)). The Guidelines contain examples of how to re-insulate roofs, exterior walls, basements, and ground floor slabs with special focus paid to robustness and moisture performance. Moisture conditions when re-insulating high-rise flats are discussed in SBi Guidelines 221, Efterisolering af etageboliger (Re-Insulating High-Rise Flats) (Munch-Andersen, 2008).

Moisture problems in buildings have been recognised for many years. In the context of the Danish Building Research Institution, the issue has been addressed since the publication of SBi Guidelines no. 7, Fugt og isolering (Moisture and Insulation) in 1951, and the now discontinued 2nd edition in 1957. These Guidelines house examples of how to ensure correct moisture performance in contemporary constructions. Here, mention had already been made to moisture barriers, capillary breaks, ventilation of crawl spaces and roofs, and required heights for roof flashings. However, these guides did not  focus on mould growth and only made passing mentions to the appearance of ugly discolorations due to thermal bridging.

In the 1970s, the Danish Building Research Institute published a series of booklets on humidity, addressing humidity theory as well as individual building parts Fugt i luft (Moisture in Air) (1973), Fugt i byggematerialer (Moisture in Building Materials) (1973), Fugt og kondensation (Moisture and Condensation) (1973), Fugt og kældre (Moisture and Basements) (1973), Fugt og krybekældre (Moisture and Crawl Spaces) (1973), Fugt og terrændæk (Moisture and Ground Floor Slabs) (1974), Fugt og ydervægge (Moisture and Exterior Walls) (1974), and Fugt og tage (Moisture and Roofs) (1974). During this period, crawl spaces were considered a very sound damp-proofing solution and ground floor slabs were, as a rule, built with the insulation placed on top of the moisture barrier. Attention was also given to the design of joints, and two-stage rainscreen sealant systems were recommended. In the case of basements, exterior basement insulation was discussed. However, these only recommended modest insulation thicknesses. As for roofs, great emphasis was placed on visualising how to install vapour barriers that would protect roof constructions against humidification resulting from both diffusion and convection.

SBi Guidelines 139, Bygningers fugtisolering (Structural Moisture Insulation), from 1984 replaced the humidity booklets and, beyond gathering the subject matter into a single cohesive publication, the examples were updated with increased insulation thicknesses in response to rigorous energy requirements. Furthermore, the theoretical content was extended and a self-contained section on windows was added. Due to the call for increased insulation thickness, the position of moisture barriers in ground floor slabs was changed, so that at least some of the insulation material was placed underneath the moisture barrier to avoid condensation on its upper surface. Both exterior and interior re-insulation of basements was also addressed. In the case of roofs, readers were urged not to install the formerly ubiquitous roof vent cowls in flat roofs. Inverted roofs and roofs with exterior re-insulation were also discussed.

SBi Guidelines 178, Bygningers fugtisolering (Structural Moisture Insulation) from 1993 replaced SBi Guidelines 139. SBi Guidelines 178 was further updated and the subject matter was extended. The chapter on basements was extended with a separate section on renovation of damp basements. Warm crawl spaces were endorsed (i.e., crawl spaces with insulated walls and bottom decks) and the re-insulation of cold crawl spaces was detailed. Interior re-insulation near exterior walls was discouraged unless the wall was completely waterproof. In the chapter on roofs, indoor-climate classes were introduced for the purpose of grouping buildings according to their expected humidity exposure. Moisture-adaptive vapour barriers in roof constructions were also mentioned.

In addition to booklets and guidelines on moisture and humidity, a number of reports and articles have appeared over the years on the investigation of humidity issues in various constructions (e.g., Komponenter til udvendig facadeisolering (Components for Exterior Facade Insulation) (1984); Bygningsrenovering kombineret med efterisolering (Building Renovation Combined with Re-Insulation) (1985); and other SBi Guidelines such as SBi Guidelines 71, Ydervæggen som klimaskærm (Exterior Walls as Weather Screen) (1971), SBi-anvisning 72, Terrændæk (Ground Floor Slab) (1972); and SBi Guidelines 189, Småhuse(Small Houses) (1999) (2nd edition) (SBi 189 listed examples designed with special focus on moisture control)). These publications supplement the actual guidelines on humidity, adding new knowledge and practical examples relating to the construction of various building parts.