Session: 03-01: Advances in Indoor Environment Technologies and Solutions

Paper Number: 155263

155263 - Enhancing Hygrothermal Performance of Building Envelopes in Cold Climates 

Abstract: 

This study examines the hygrothermal performance of existing and retrofitted building envelopes, focusing on a school building in Minneapolis, where cold climatic conditions pose significant challenges to energy efficiency and structural integrity. The analysis includes key factors such as thermal bridging, surface condensation, and interstitial condensation, which directly influence the building's thermal comfort, energy consumption, and long-term durability.

Thermal bridging was a critical concern in the existing building, particularly at junctions like the roof-wall connection, balcony-slab intersection, and window frames. These areas exhibited significant heat loss, contributing to higher heating demands and localized cold spots that could potentially lead to condensation issues. The retrofitted design incorporated advanced insulation materials, improved detailing at junctions, and optimized construction techniques to mitigate thermal bridging. The retrofitting measures achieved a substantial reduction in linear thermal transmittance, minimizing energy losses and improving overall envelope performance.

Surface condensation was assessed under controlled indoor conditions, maintaining temperatures at 20°C and relative humidity at 50%. While no significant surface condensation was observed in the existing configuration, the potential for issues in extreme conditions underscored the importance of insulation and detailing. Interstitial condensation analysis revealed a more critical issue, as moisture accumulation within wall layers during winter could lead to structural damage, insulation degradation, and mold growth. In the existing envelope, the absence of adequate vapor barriers exacerbated this problem, allowing water vapor to condense within the construction layers.

To address interstitial condensation, the retrofit strategy introduced vapor control layers on the warmer side of the insulation. This intervention effectively reduced the vapor diffusion rate, maintaining moisture levels within safe limits across the wall assembly. Combined with added thermal insulation, the retrofitted envelope achieved significantly lower U-values, reducing energy demand while enhancing indoor thermal comfort. The measures ensured that all envelope components remained above the dew point under operational conditions, eliminating the risk of condensation-related damage.

The analysis also included a comparison of energy performance between the existing and improved cases. The retrofitted design demonstrated notable energy savings, primarily through reduced heating loads, achieved by addressing both thermal bridging and moisture management. The study emphasizes the critical role of integrating hygrothermal considerations into retrofitting practices, especially in cold climates. Strategies such as proper placement of insulation, inclusion of vapor barriers, and correction of thermal bridges not only improve energy efficiency but also extend the lifespan of the building by preventing structural degradation.

This research provides a comprehensive framework for evaluating and enhancing the hygrothermal performance of building envelopes, offering practical insights for sustainable retrofitting. The findings contribute to the growing body of knowledge on designing energy-efficient, durable, and comfortable educational facilities that meet modern sustainability standards while addressing the unique challenges posed by extreme climates.

Presenting Author: Boshra Akhozheya Texas A and M university

Presenting Author Biography: Boshra Akhozheya is a PhD student at Texas A&M University with a Master’s degree in Building Engineering and a Bachelor’s degree in Architectural Engineering. As a certified LEED AP professional, they bring five years of experience in sustainability consulting, with a focus on energy efficiency in buildings. Their research interests aim to advance sustainable practices and innovative envelope solutions in buildings to optimize energy use and support environmental goals.