Thermal Resistance and Condensation in the Light-frame Timber Wall Structures with Various Composition of Insulation Layers

Abstract

As energy costs increase, more people has become interested on energy efficiency and savings in residential buildings. The two main subjects related to energy in residential buildings are insulation and condensation. There are two approaches to prevent condensation; increasing air tightness and maintaining the temperature inside of the wall structure over the dew point, which is in turn related to insulation. Even though the Korean government has highlighted the importance of energy efficiency for residential housings, and in spite of the customers' demands, the timber construction industry is still using conventional light-frame construction without even trying to improve energy efficiency. In this study, various types and combinations of wall structures were tested under cold outdoor and warm indoor temperatures to analyse the temperature gradients and to determine the possible sites of condensation in the wall structures. In addition to the experimental tests, three theoretical models were developed and their estimations of temperature change through the wall structure were compared with the actual measurements to evaluate accuracy of the models. The results of the three models agree relatively well with the experimental values, indicating that they can be used to estimate temperature changes in wall structures. The theoretical analysis of different insulation layers' combinations show that condensation may occur within the mid-layer in the conventional light-frame wall structures for any combination of inner-, mid-, and outer-layers of insulation. Therefore, it can be concluded that the addition of an inner and outer insulation layer or increasing the thickness of insulation may not be adequate to prevent condensation in the wall structure without preventing penetration of warm moist air into the wall structure.

Fig. 1. Framing of wall specimen with 2 × 4 stud of 406 mm spacing.

Fig. 2. Wall specimen placed between two chambers simulating the exterior and interior temperature in winter.

Fig. 3. Temperature change through thickness for Type I wall specimen exposed to cold condition.

Fig. 4. Temperature change through thickness for Type II wall specimen exposed to cold condition.

Fig. 5. Temperature change through thickness for Type III wall specimen exposed to cold condition.

Fig. 6. Effect of increasing the thickness of the outerlayer insulation on the temperature change through thickness for Type III wall specimen exposed to cold condition.

Fig. 7. Effect of increasing the thickness of the innerlayer insulation on the temperature change through thickness for Type III wall specimen exposed to cold condition.

Table 1. Three types of wall specimen tested in this study

Table 2. Thermal resistances of various materials used in this study

Table 3. Thermal resistance and temperature change coefficient for three types of wall specimen

Table 4. Comparison between the actual temperature and the estimated temperature in Type I wall specimen

Table 5. Comparison between the actual temperature and the estimated temperature in Type II wall specimen

Table 6. Comparison between the actual temperature and the estimated temperature in Type II wall specimen