During sunny conditions, surface temperatures on masonry façades can rise to over 40°C above the ambient temperatures. Conventional wall designs minimize the benefits of this solar heat through the use of thermal insulation. However, air that is drawn from the outdoors, between the façade and sheathing, can be used to recover heat from the masonry. The system, which utilizes a dynamic buffer zone (DBZ), acts as a solar air collector. This system can provide an effective way to preheat ventilation air at little to no extra cost, while not compromising the architectural features of the masonry wall system. A numerical model was developed to predict the amount of heat recovery possible using a DBZ. The numerical model was verified by comparing results with a commercial computational fluid dynamics software package and by conducting laboratory experiments. Preliminary results indicate that the DBZ as a solar air collector can achieve as high as 33% daily solar efficiency and seasonal solar efficiencies of up to 27%. Since this system is low-cost, yet effective, it may offer designers an opportunity to build more sustainable masonry wall systems.

Built-in moisture in the insulation layer of a compact roof will generally dry out very slowly, compared to the drying rate in a ventilated roof construction. Intended or unintended leakages of outdoor air through the insulation layer may, however, speed up the drying rate. In this investigation, the drying potential of various configurations of compact wood frame roofs with a high level of built-in moisture has been investigated, through test house measurements and hygrothermal simulations. Compact wood frame roof elements has been wetted, and mold spores has been added to the elements. The hygrothermal conditions of the elements has been monitored through a period of 2 years, and the microbial conditions has also been registered. The possible drying effect of outdoor air leaking through the insulation layer from one side of the roof to the other has been investigated.

This article presents a numerical procedure for calculating heat flux through fibrous insulation. It deals primarily with the radiation component, and the interaction between the radiation and conduction. The program determines the temperature profile by an iterative method, and uses it to evaluate the conductivity of the air and the extinction coefficient of the fibrous material at locations through the material. The temperature dependence of the extinction coefficient accounts for the nongray nature of fibrous materials. The algorithm allows for the edge effect. The article deals primarily with steady state heat flow, and includes an example of nonsteady heat flow. A method to estimate the contribution of the fiber structure is included. The thermal properties of insulation are derived from the results of R-value tests in vacuum and in air at different mean temperatures.

This article demonstrates how monitoring of construction during a laboratory mock-up test was used to diagnose proneness to air leakage and to devise improved details. The curtain wall was built on a moveable, rigid frame that simulates the load-bearing structure. Construction details and components were identical to those used in actual buildings. The frame brings the curtain wall into contact with the test box, ensuring that the wall’s structural supports are not affected. Construction activities were monitored while the measurements included air flow rate versus air pressure difference across the wall, and horizontal deflections of wall mullions and beams. Locations of leakage points were detected using white smoke. The wall showed a density of air flow rate of 1.5 m³m^-2h^-1 at a pressure difference of ~300 Pa, barely meeting the requirements for EN 12152 classification level A2. Correlating leakage points with detected construction weaknesses led to remedial actions by the manufacturer. The tests were repeated, revealing an improved air-tightness (density of air flow rate less than 0.6 m³m^-2h^-1 at 350 Pa, and 0.8 m³m^-2h^-1 when extrapolated to 600 Pa), which meets the requirements for classification level E.

Full-scale laboratory measurements were taken and 2D simulations were performed to determine the moisture convection performance of the joint of an external wall and an attic floor. Both the measured and simulated results showed that the building fabric is locally sensitive to exfiltration airflow as moisture convection could cause a remarkable increase in the moisture accumulation rate on the inner surface of the sheathing. The results prove that in modern houses with balanced ventilation, where the positive pressure caused by the stack effect cannot be easily controlled, it is essential to control moisture convection by good airtightness and the use of assembly solutions with improved hygrothermal performance, such as the case with mineral wool sheathing that was tested. The simulated results showed that the use of a constant moisture excess value instead of the profile did not cause any inaccuracy in the moisture content. At the same time, the use of the constant outdoor temperature over a long time period did change the hygrothermal performance, which became significantly more critical when simulated with variable outdoor temperatures. The laboratory measurement and simulation results show that in a cold climate, for the assemblies being studied with mineral wool sheathing, leakage rates of 0.1–0.2 L/(s·m) at a 10 Pa pressure difference may be used as performance criteria for moisture convection in a two-storey house with dimensioning moisture excess 4 g/m³ and a cold outdoor climate. Previous studies on the leakage characteristics show that these leakage rates are easily achievable in practice with careful workmanship.

There are several biological processes causing aging and damage to buildings. This is partly due to natural aging of materials and excessive moisture. The demands on durability, energy balance, and health of houses are continually rising. For mold development, the minimum (critical) ambient humidity requirement is shown to be between RH 80% and 95% depending on other factors like ambient temperature, exposure time, and the type and surface conditions of building materials. For decay development, the critical humidity is above RH 95%. Mold typically affects the quality of the adjacent air space with volatile compounds and spores. The next stage of moisture-induced damage, the decay development, forms a serious risk for structural strength depending on moisture content, materials, temperature, and time. The worst decay damage cases in North Europe are found in the floors and lower parts of walls, where water accumulates due to different reasons. Modeling of mold growth and decay development based on humidity, temperature, exposure time, and material will give new tools for the evaluation of durability of different building materials and structures. The models make it possible to evaluate the risk and development of mold growth and to analyze the critical conditions needed for the start of biological growth. The model is also a tool to simulate the progress of mold and decay development under different conditions on the structure surfaces. This requires that the moisture capacity and moisture transport properties in the material and at the surface layer be taken into account in the simulations. In practice there are even more parameters affecting mold growth, e.g., thickness of the material layers combined with the local surface heat and mass transfer coefficients. Therefore, the outcome of the simulations and in situ observations of biological deterioration may not agree. In the present article, results on mold growth in different materials and wall assemblies will be shown and existing models on the risk of mold growth development will be evaluated. One of the results of a newly finished large Finnish research project ‘modeling of mold growth’ is an improved and extended mathematical model for mold growth. This model and more detailed research results will be published in other papers.

A probabilistic model of the thermal performance of a building envelope is proposed. The model predicts the probability density function of the heat loss over a specified period of time on the basis of the design parameters of the house, climatic characteristics of the site as well as the air change rate due to mechanical or natural ventilation. Reliability of the heat loss performance of the building envelope components exposed to various climatic conditions is analyzed, and the probability of excessive heat loss is quantified. Different design options are considered. They involve a dynamic wall strategy and various types of building ventilation.