Prevalence and extent of moisture damage in Finnish housing

Moisture damaged homes are a significant problem in Finland, with implications for occupant health, the economy, and building structures. Understanding the prevalence of moisture damage in buildings with different construction methodologies and structures will help inform ways to manage this damage now and in the future. We analyse pre-sale condition inspection data from 14,996 Finnish detached and semidetached houses, surveyed between 2016-2019, examining the presence and prevalence of moisture and mould damage within risk structures. Confirmed or moisture damage was found in 15% of inspected houses, with around 4% having damage in multiple locations. House age was the greatest risk factor for damage, while log external walls, fibreboard roofs, and no mechanical or gravitational ventilation system were also significant.


Introduction
Indoor moisture damage and mould is a major issue in Finland and subject to significant public and political interest, despite its prevalence in the Finnish building stock being relatively low compared to elsewhere in Europe [1].While definitions of moisture damage and indoor mould are inconsistent, studies have estimated moisture damage to occur in 52% of Finnish homes [2], with 80% showing signs or present of past moisture damage [3].Exposure to indoor moisture and mould can lead to various physical health concerns in occupants, such as asthma and respiratory symptoms, and the associated stress can contribute to poor mental health [4].Symptoms from exposure are estimated to cost around €23-953 million euros annually in Finland due to healthcare costs and productivity loss [5], while repairs cost around €1.2-1.6 billion annually [6].Due to these political, health, and economic impacts, there has been considerable research and attention into moisture damage and indoor air quality issues in Finnish buildings.
Finland has a cold climate, with low wintertime indoor relative humidity and relatively well insulated structures.The dominant moisture problems come from roof and pipe leaks, diffusing humidity from the soil and interstitial condensation of moist air as it diffuses outdoors.This means that moisture problems are usually hidden within the structure of buildings [2], levels of surface condensation and visible moisture of mould are low, and building occupants may not be aware of damage until they smell mould or exhibit symptoms of exposure [7].The presence of structures at particular risk of moisture and mould damage may vary across different building types depending on construction methodologies.The aim of this study is to understand the prevalence of these hidden moisture damages in housing and how these damages can vary across housing types and construction methods using a large dataset of surveyed houses.

Methods
This paper describes the analysis of a database of moisture condition inspections conducted on 14,996 Finnish detached and semidetached houses between 2016-2019 by Raksystems Oy.The inspections are conducted according to technical guide KH-90-00394 [8], and is a organoleptic inspection for signs of visual moisture damage and microbial growth.It includes an inspection for damages on surfaces, as well as the limited inspection of risk structures within the building fabric through small structural openings if there is suspected damage and homeowners give permission.Housing inspection data was linked to regional wind-driven rain classification by municipality [9].The odds ratio for confirmed damage within a risk structure was then calculated for different housing characteristics using logistic regression in R both for individual building characteristics and adjusting for the age of construction.

Results and Discussion
At least one confirmed moisture damage was found in 15% of surveyed homes.Commonly damaged structures include foundation walls (5.5% of homes), ventilated wooden ground floors (3.5%) and false plinths (2.6%).House age was the greatest risk factor for confirmed damage in a risk structure, with an odds of damage of 1.48 (1.45 -1.51) for each decade since construction.Other risk factors are shown in Table 1 as crude estimates and adjusted for age.The risk of one or more confirmed moisture damage was greater, for example, in homes constructed in-place, those with ventilated wooden ground floors, houses with old log walls, flat or double-ridged roofs, and gravity or natural ventilation.Adjusting for housing age substantially reduced the damage odds of all factors, with flat and double-ridged roofs no longer showing an increased risk.The risk of confirmed damage was higher in areas with the most driving rain, and in homes with smaller floor areas.Around 4% of dwellings had confirmed damage in multiple locations, with age also the greatest risk factor for multiple damages.Results indicate that older buildings are at significantly greater risk of moisture damage than newer buildings.This is -in part -due to the presence of different risk structures that were common in buildings constructed during different eras.Adjusting for age reduced the significance of other risk factors, and in the case of roofs removed it entirely.The difference in moisture damage by housing age may also be attributed to older buildings having been exposed to environmental moisture for a longer period, inadequate maintenance over time, and improvements in construction methods.That the risk of moisture damage was higher in areas with the greatest amount of driving rain confirms that precipitation is an important contributor to moisture damage, likely due to increased exposure and slower drying.Future increases in wind-driven rain predicted due to climate change in Finland [10] may pose a risk to certain buildings in the housing stock as well as certain geographic locations.
Our study has various limitations.It excludes apartments and row houses, and represents only a segment of the Finnish housing stock.As the survey is undertaken as part of a sales transaction, rental or supported housing is underrepresented in the analysis.This paper has described only the occurrence of confirmed moisture damage, but the survey also notes 'more inspection required' where damage may be possible but cannot be confirmed, either because the surveyor has examined the risk structure but is not confident it is undamaged, or because the risk structure cannot be accessed.We also exclude records of moisture damage in bathrooms, which is commonly recorded when bathrooms are past their technical lifespan.Therefore, these numbers represent a likely underestimate of the true damage in the detached and semidetached housing stock.
Despite these limitations, the analysed dataset represents a very large number of houses that are broadly representative of the detached and semidetached housing stock in Finland and has both moisture inspection results and multiple housing characteristics.Future research will link the outcomes of this analysis with health data for the housing occupants, enabling the further study on how the presence and degree of moisture damage may impact upon occupant health outcomes.

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Corresponding author.Jonathon.taylor@tuni.fi The Author(s).This is an open access article distributed under the terms of the Creative Commons Attribution Licence (CC-BY) 4.0 https://creativecommons.org/licenses/by/4.0,which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.DOI: 10.14293/ICMB230014 2nd International Conference on Moisture in Buildings (ICMB23), online, 3-4 July 2023

Table 1 .
Odds of damage with housing characteristics (and comparator group).