Attic Retrofit Strategies in Sweden: Design Parameter Interactions and Trade-offs in Thermal Comfort, Energy, and Daylight

Abstract

The renovation and adaptive reuse of existing buildings is increasingly recognised as a strategy to address both housing shortage and climate targets in Europe. In Sweden, there is a large potential in converting cold attic spaces in mid-twentieth-century multi-family buildings which offers increased housing capacity without new construction. However, attic retrofits involve complex interactions between energy demand, thermal comfort, daylight availability, while overheating becomes an increasing concern under future climate conditions.
This study investigates how retrofit design parameters influence the energy performance, thermal comfort, and daylight availability of residential attic spaces in Sweden. A simulation-based parametric approach was applied in IDA ICE to evaluate the effects of glazing configuration and orientation on heating energy demand, daylight provision, and thermal comfort, as well as the effects of shading strategies and natural ventilation controls on overheating risk. Daylight performance was assessed according to EN 17037, while thermal comfort and overheating risk were evaluated using the adaptive comfort model according to EN 16798-1. The analysis was conducted on a representative Swedish attic apartment under present climate conditions, while future climate conditions (2050, SSP2-4.5 scenario) were assessed specifically in relation to overheating risk. Both typical and advanced renovation contexts were considered, corresponding to different envelope structures.
The results show that glazing-related parameters have the strongest influence on performance, although their impact varies across the evaluated aspects. Roof windows were the main drivers of daylight availability and thermal comfort, with increased number of roof window improving daylight provision while also increasing overheating risk. In contrast, façade windows had a stronger influence on heating energy demand. Compared to the typical renovation context, the advanced renovation context reduced heating energy demand while increasing overheating and slightly reducing daylight availability. The effectiveness of the control strategies varied depending on window type: shading was more effective for roof windows, while natural ventilation was more effective for façade windows. The combined application of both strategies resulted in the lowest overheating levels. Under future climate conditions, overheating increased across all analysed cases, and shading strategies used alone were less effective. Natural ventilation therefore played a greater role in maintaining acceptable indoor temperatures, while the combined application of smart shading and smart natural ventilation controls resulted in the best thermal performance.
Overall, the study contributes to the understanding of multi-performance attic retrofit design by balancing daylight provision, thermal comfort, and energy performance, while highlighting the increasing role of shading and natural ventilation control strategies in maintaining acceptable indoor conditions, especially under future climate scenarios.

Popular Abstract

As cities continue to grow and housing shortages become more severe, finding new homes without constructing entirely new buildings is becoming increasingly important. One promising solution in Sweden is the conversion of unused attic spaces in older apartment buildings into apartments. These attic retrofits can create new housing while making use of already existing building, reducing both construction waste and environmental impact.
But turning an attic into a comfortable home is not as simple as adding walls and windows. Attics behave very differently from regular apartments because they sit directly beneath the roof and are heavily exposed to sunlight and outdoor weather conditions. This creates a difficult balancing act. Large windows can fill a space with daylight and make it feel bright and attractive, but they can also trap heat indoors and increase the risk of overheating.
Why is overheating becoming such an important issue, especially in a country like Sweden? As climate change leads to warmer temperatures and more frequent heat waves, buildings that were once designed mainly to keep heat inside during winter may begin to struggle during summer instead. Spaces such as attics are especially vulnerable because they receive large amounts of solar heat throughout the day.
This thesis explored how different attic retrofit design choices affect three important aspects of indoor performance: energy use, thermal comfort, and daylight availability. Using advanced building performance simulations, different combinations of roof windows, façade windows, shading systems, and natural ventilation strategies were tested under both current and future climate conditions in Sweden.
The results showed that windows play a major role in attic performance. Roof windows were especially effective at bringing daylight into the space, but they also increased overheating because they receive high levels of direct sunlight. Façade windows, on the other hand, had a stronger influence on heating energy demand, because they contribute higher losses than gains.
The study also explored ways to reduce overheating without relying on air conditioning. Two important passive strategies were shading and natural ventilation. Shading helps by blocking excess solar heat before it enters the building, while natural ventilation removes heat that has already built up indoors by bringing in cooler outdoor air.
The findings showed that automated “smart” control systems performed much better than manual controls. In this study, smart controls automatically adjusted shading devices and opened or closed windows depending on indoor temperature and weather conditions, while manual controls relied on occupants making these adjustments themselves. In particular, natural ventilation proved highly effective at maintaining comfortable indoor temperatures. The best overall performance was achieved when automated shading and automated natural ventilation were combined.
Future climate conditions were also examined using a 2050 climate scenario. The results showed that overheating is expected to become a much greater challenge in the future, even in Sweden’s relatively cold climate. Strategies relying only on shading became less effective, while natural ventilation became increasingly important for keeping indoor spaces comfortable.
Overall, the study highlights that attic retrofits require a careful balance between daylight, thermal comfort, and energy performance. Improving one aspect can negatively affect another, meaning that design decisions cannot be considered separately. The findings emphasise the importance of climate-responsive and integrated retrofit strategies for creating comfortable and resilient homes in the future.

• author: Ilkyaz, Pelin and Georgiou, Anna Nektaria
• supervisor: Niko Gentile
• organization: Division of Energy and Building Design
• course: AEBM01 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Attics, Renovation, Energy Efficiency, Adaptive Comfort Model, Daylighting, Parametric Study
• language: English
• id: 9230525
• date added to LUP: 2026-06-05 11:06:10
• date last changed: 2026-06-05 11:06:10