Carbon footprint calculations for roof repair: moisture damage causes a significant environmental impact

The construction industry is a significant contributor to carbon dioxide emissions. The carbon dioxide emissions from moisture damage repairs were assessed for three different roof areas of varying sizes. The calculations show that moisture damage and its repairs cause significant amounts of carbon dioxide emissions. For this reason, considering the risks of moisture damage and taking preventive measures should be an essential part of environmentally friendly construction and building maintenance.

The construction industry accounts for a significant portion of global carbon dioxide emissions. According to estimates, construction and building maintenance contribute to nearly 40% of the world’s energy-related carbon dioxide emissions (IEA)​​ (UNEP – UN Environment Programme). For this reason, both the construction industry and lawmakers have taken steps to reduce the carbon footprint of construction (IEA).

According to Andenæs, Kvande, and Bohne (2020), the prevalence of construction defects and moisture damage due to various causes is underestimated in the assessments of buildings’ carbon footprints. Andenæs, Kvande, and Bohne (2020) argue that underestimating the risks of moisture damage in carbon dioxide emission calculations leads to a one-sided view of environmentally friendly construction and that the actual carbon dioxide emissions related to buildings will be much higher.

This article assesses the impact of roof moisture damage on carbon dioxide emissions for three hypothetical roof areas of different sizes (100, 200, and 1,000 m²) on a bitumen-covered roof with a total area of 2,000 m². Emissions occur when roof areas need to be replaced. The calculations show that the carbon footprint of moisture damage and repairs is significant. For example, the emissions from repairing a 1,000 m² roof area are equivalent to over five around-the-world trips by car. The results highlight that recognizing the risks of moisture damage and implementing preventive measures and products should be an essential part of environmentally friendly construction and building maintenance.

How the total emissions of roof moisture damage were calculated

Ramboll Finland Oy performed the calculations on behalf of VILPE Oy. The results were calculated for three different sizes of flat roof repair areas: 100, 200, and 1,000 m². The repair involves demolishing the old structure, installing the new structure, and the materials used. The roof structures used included bitumen roofing, grooved thermal insulation, vapor barrier, and TT slab. The assessment was conducted using the OneClickLCA software, and the emission data for the materials were based on the conservative values from the Finnish emission database CO2data.fi. It is assumed that the repair does not change the replacement interval of building products during the building’s lifecycle. The repair measures also do not affect the building’s operational energy consumption.

The calculations considered the following carbon dioxide emission sources:

  • Manufacturing of building products. In repair construction, the manufacturing phase of the products includes the building parts that are involved in the repair area, i.e., the parts of the building and site that are being repaired. In this case, it is assumed that the repair extends up to the top surface of the roof slab.
  • Transportation to the worksite. The impact of transportation on the carbon footprint was assessed for each product using the default transportation distances provided by the calculation software.
  • Worksite activities. As part of worksite activities, the material surplus and waste generated at the worksite were estimated based on the default values of the calculation tool. The emissions from the energy consumption at the worksite were not considered due to the lack of reliable baseline data.
  • Roof demolition and disposal of construction materials. The end-of-life phase in this context refers to the demolition of the old roofing structure and the handling of demolition waste, which is carried out before the repair. The transportation during the end-of-life phase was estimated using assumed transportation types and distances, utilizing unit emission data from the construction emission database. The emissions from waste management and final disposal were based on the unit emissions values of the waste management and final disposal processes in the emission database by material type.

Significant carbon footprint of moisture damage repairs

The carbon footprints of roof repairs are presented as the total climate impact of the repairs (in kilograms of carbon dioxide equivalent, kgCO2e) (see Table 1). Roof leak repairs result in significant emissions. The scale of the results can be understood by comparing them to car emissions. A 100 m² repair produces 5,332.4 kg CO2e, equivalent to driving approximately 21,300 kilometres in a car, roughly halfway around the Earth. A 200 m² repair produces 10,664.8 kg CO2e, which is equivalent to driving about 42,600 kilometres in a car, more than the Earth’s circumference. A 1,000 m² repair produces 53,324 kg CO2e, comparable to driving around 213,300 kilometres in a car, which is more than five trips around the world.

Table 1: Carbon footprint by lifecycle phase for different sizes of roof repairs (kgCO2e)

Since the calculation method used expresses the unit in carbon dioxide equivalent per heated net square meter of the building and per year of the building’s lifecycle (50 years), the results are also presented in this unit (see Table 2). The heated net area of the building has been specified as 2,000 m². In other words, in the most extensive repair, it could involve, for example, a two-story building with a floor area of 1,000 m² per floor, where the entire roof is replaced. Replacement would mean an annual additional load of 0.53 kgCO2e/m² on the building’s carbon footprint. This additional load is significant for the building’s actual carbon footprint, and if the emissions caused by roof repairs were considered in the planning phase, it would mean that emissions should be reduced or otherwise compensated in the project to reach the desired limit value. The scale of the results can be understood, for example, by comparing them to the carbon footprint limit set by the City of Helsinki for new residential buildings. This limit is 16.0 kgCO2e/m²/a.

Table 2: Carbon footprint by lifecycle phase for different sizes of roof repairs (kgCO2e/m²/a). Building area 2,000 m² and lifespan 50 years.

Moisture damage prevention is an important part of low-carbon construction and maintenance

The results indicate that a moisture damage event on a roof area of 100 m² or larger results in significant carbon dioxide emissions, with the largest impact coming from product manufacturing. Considering the high risks of moisture damage and the substantial emissions generated from repairs, preventive measures and products for moisture damage should be an essential part of environmentally friendly construction practices and building maintenance.

VILPE Sense is a system developed by VILPE Oy for the prevention of moisture damage. VILPE Sense monitors the condition of structures in real-time and alerts users to elevated moisture levels. With VILPE Sense, it is possible to address moisture issues at an early stage, preventing minor moisture problems from developing into large, costly, and environmentally damaging issues. The VILPE Sense product family includes a leak detector, which can detect leaks even on larger roofs. Moisture damage can also occur when structures do not ventilate sufficiently for various reasons. The VILPE Sense humidity control system is designed to prevent moisture damage caused by environmental conditions. The system responds to excessive moisture in structures and enhances ventilation as needed. The VILPE Sense humidity control system is suitable for both roofs and subfloors in all types of buildings.

Glossary:

  • Carbon footprint refers to the total amount of greenhouse gas emissions directly and indirectly caused by a specific product, service, organization, or activity. It is usually measured in carbon dioxide equivalents (CO2e), allowing for the comparison of the impacts of different greenhouse gases.
  • Carbon handprint describes actions or innovations that reduce greenhouse gas emissions or sequester carbon from the atmosphere. This can be related to the use of renewable energy, improving material efficiency, carbon sequestration in forests, or products that act as carbon sinks. The concept of a carbon handprint emphasizes positive impacts on the climate; in other words, how much greenhouse gas emissions can be avoided or removed due to a specific activity or product.
  • OneClickLCA software allows for lifecycle assessments (LCA) and environmental product declarations (EPD) in the construction and manufacturing sectors. Users can calculate the environmental impacts of construction projects and manufacturing processes. OneClickLCA is used in over 170 countries.
  • The Finnish emission database, CO2data.fi, provides information on the climate impacts of building products and services in Finland. The service is provided by the Finnish Environment Institute (SYKE) and is open and free for all users. The database includes information on the carbon footprint and handprint of building products, material efficiency, and recyclability. This helps standardize the calculation of greenhouse gas emissions throughout the building lifecycle and facilitates the planning of low-carbon construction.

The article is based on a calculation report by Ramboll Oy, which is available in full upon request. Please contact sales@vilpe.com.