William C. Brown

Monitoring of the building envelope of a heritage house: a case study

Abstract The paper describes the long-term monitoring of the hygrothermal performance of the building envelope of a heritage house located in Ottawa. The house, once the residence of two of Canadas Prime Ministers, now serves as a museum. To preserve the historical artifacts within the building, the specified temperature and relative humidity (RH) for the indoor air are 21°C and 35% to 50%, respectively. As the house must also be preserved, there was concern about the effect of the high indoor RH (moisture) on the durability of the building structure. The main objective of the monitoring was to assess the effect of the conditioned air on the building envelope. Selected wall sections and a window were continuously monitored from March 1995 to August 1996. The monitoring included indoor and outdoor conditions and the attic environment. Temperature, RH, surface wetting–drying cycles (from precipitation or condensation), and air-pressure differential were monitored. This paper describes the monitoring approach and results. The results indicated that the brick walls are unlikely to experience internal condensation problems as long as they are subjected to a negative air pressure difference. However, because the building is quite leaky, the negative pressure introduced too much cold dry air from the exterior. It caused localized cold spots with condensation and ice formation on interior of walls and ceiling. Negative air pressure differences are not a solution unless the leakage paths are reduced.

Performance of Pressure Equalized Rainscreen Walls under Cyclic Loading

WIND-INDUCED PRESSURE difference is one of the forces that contributes to rain penetration of walls. It can be attenuated by using the pressure equalized rainscreen (PER) approach to wall design. In such a wall an air space that is located mside the exterior cladding is vented to the outside so that the pressure on the inside of the cladding equalizes to the pressure on the outside. As pressure equalization is the key element of the process, it is important that the system be fast enough to respond to most changes in exterior pressure. In 1963, Garden introduced the concept of the &dquo;open rainscreen&dquo; to building designers. The significance of this work lies in the formulation of basic design guidelines. These have subsequently been modified on several occasions in order to address the complicated nature of the interaction between wind-driven rain and wall systems. Kilhp and Cheetham (1984) reviewed the process of rain penetration through walls. They also performed simplified experiments to measure the pressure drop in the cavity for various venting and leakage conditions. Field measurements on PER walls were undertaken by researchers at the Institute for Research in Construction of the National Research Council 3f Canada (IRC/NRCC). From June 1983 to October 1984, the Place Air

Barrier EIFS Clad Walls: Results from a Moisture Engineering Study

This paper presents the results of work performed to enhance understanding of water penetration and moisture characteristics of barrier Exterior Insulation Finish Systems (EIFS) clad walls. The investigation was prompted by recent failures of barrier EIFS clad walls on houses in the Wilmington, North Caro lina area. The objective was to determine the cause of the problem and gain a better understanding of water penetration and moisture transport in these systems. The study included a field investigation, laboratory experiments, and computer simulation. The experimental results indicate that barrier EIFS clad walls are prone to leak in areas around penetrations and allow water to enter into the wall cavity. A drainage cavity wall was also tested, and observed to perform well, managing water around penetrations and preventing leakage into the wall cavity. The computer simulation indicates that barrier EIFS clad walls in Wilmington have low moisture tolerance due to slow drying rates. In conclusion, barrier EIFS clad walls do not provide effective management of rain penetration. As such, in-service performance is unpredictable and unreliable. In con trast to barrier EIFS clad walls, walls using a drained cavity approach were shown to provide good control of rain penetration.

Long-Term Field Monitoring of an EIFS Clad Wall

A popular retrofit option is to install an exterior insulation and finish system EIFS to the walls of existing buildings. This study evaluates the thermal and moisture performance of such a system with a vented wall assembly. In addition to being a case study, this field monitoring was intended to verify computation methods of building envelope performance. The long-term monitoring was designed to be non-destructive so that the building envelope performance was not affected by the measurements that are made, and so that removal of sensors, for recalibration and re trieval at the end of the test period was easy. The field monitoring is planned for two years to capture a wide range of environmental conditions. This paper discusses the instrumentation used in the study and presents interim results of the thermal resis tance of the wall and surface moisture.

Water Management in Exterior Wall Claddings

This paper presents results of laboratory testing on the performance of wall claddings using direct-applied (DEFS) and exterior insulation finish systems (EIFS) that incorporate water management features into their design and construc tion. The work presented in this paper is a continuation of earlier work conducted by the Institute for Research in Construction (IRC) of the National Research Council, Canada (NRCC) and the United States Gypsum Company (USG) evaluating the water penetration and moisture performance of barrier EIFS clad walls (Brown et al., 1997). Direct-applied exterior finish systems (DEFS) are exterior wall claddings that use a water durable substrate, typically cement board, mechanically fastened to the wall framing over a sheathing membrane. A cementitious basecoat and textured acrylic synthetic stucco finish is then applied directly over the substrate. Insulation for the DEFS system is in the stud cavity. EIFS systems use a layer of foam insulation applied over the wall substrate, with basecoat and finish applied over the foam. The performance of three water managed wall cladding designs in protecting wood framed construction from water intrusion by wind-driven rain is described. Three different drainage systems were evaluated. Performance measures evaluated in cluded cladding airtightness, pressure equalization potential, and water drainage under wind-driven rain conditions. In each of the three systems, partial pressure equalization was observed, and any water that did breach the exterior skin was stopped at the sheathing membrane and directed down and out of the wall through the flashing and weep openings.

Building Envelope: Heat, Air and Moisture Interactions

HEAT, AIR AND moisture transport across a building envelope are inH se p arable phenomena. Each influences the others and is influenced by all the materials contained within the building envelope. Often we simplify the process of architectural design by relating control of each phenomenon to a particular material. The thermal insulation, for example, is perceived to control heat transfer and the air barrier to control air leakage. Likewise, the rain screen and the vapour barrier eliminate ingress of moisture to materials. However, these materials perform many different and interrelated functions, and frequently participate as one of several factors in overall system performance (see Table 1). For instance, while controlling air leakage, the air-barrier system may also provide effective moisture control. Similarly, by increasing temperature in the wall cavity, thermal insulating sheathing may also reduce the degree of condensation in the cavity. Thus the process of environmental control depends on strong interactions between heat, air and moisture transport. And to ensure that all aspects of the building envelop perform effectively, we must deal with heat, air and

Dynamic Evaluation of the Building Envelope for Wind and Wind-Driven Rain Performance

The building envelope should be designed to provide a comfortable indoor environment irrespective of changes in the weather. Therefore, to provide a functional and durable building envelope, the dynamic character of the driving forces must be recognized by the envelope designer. The dynamic performance of the building envelope can be evaluated in laboratories in which the design details and most of the dynamic properties of the driving forces are simulated. This paper dis cusses the dynamic processes and the need for dynamic evaluation of structural per formance under wind loading and of rain penetration performance under wind driven rain conditions. Three research facilities are examined for their approach to dynamic evaluation of structural performance and rain penetration performance. Ad ditional information on dynamic evaluation of the building envelope was gathered from standards and the literature. Based on this information, procedures for dynamic evaluation under wind loading and wind driven rain conditions are proposed.

Building Envelope and Environmental Control: Issues of System Integration

DESIGNING FOR ENVIRONMENTAL control compels professionals to address the building envelope system as a whole while recognizing that both the choice of materials and the design details affect the environmental performance of the building envelope system. Achieving the right harmony between materials, design and system performance depends on integrating two extremes in conceptual thinking: qualitative assessment based on experience in use and quantitative evaluation based on results of testing and analysis. This article, the last of three addressing environmental control through design of the building envelope, demonstrates how qualitative and quantitative thinking converge. Part 1 reviewed the impact of heat, air and moisture interactions on bmlding envelope design. Part 2 discussed the challenges involved in selecting thermal insulating materials. On the qualitative side of the environmental control picture is the knowledge of what makes a bmlding envelope function, plus a general understanding of how suitable the materials are for a given use. However, qualitative decisions can appear somewhat arbitrary, so attempts are made to support them with a quantitative analysis. Additional effort is directed at changing material standards so they are based less on the properties of the materials and more on field performance. Over the years, prominent building scientists such as Neil Hutcheon, Kirby Garden and Max Baker underlined the need for combining the science and the practice of construction. For instance, Max Baker stated in 1971 at

Noncombustible, Pressure-Equalized Rainscreen Technology to Reduce Leaking in Eifs

Leaking in wall assemblies has been shown to be reduced if the air pressure difference across the cladding can be reduced. The EIF system described has been tested to demonstrate that mineral wool insulation can be used to allow the air pressure difference across the exterior coating of the system to be equalized. The mineral wool is vented at the bottom of the panel. Channels are introduced into the insulation to facilitate the speed of pressurization. Testing has also shown the system to be durable.

Computer Controlled Thermophysical Test Facility — 2) Software

The Division of Building Research (NRC of Canada) has developed a mini-computer centered data acquisition and control system to run a test laboratory in which the thermophysical properties of materials are measured. At present the laboratory has five guarded hot plate apparatus and two heat flow meter apparatus with provision for connecting three more apparatus to the system. The laboratory runs on a 24-hour, 7-day basis and is unattended during non-working hours. The computer system is used to control the temperatures of the apparatus, to read, process and log the test results, and to monitor the operation of the equipment for alarm conditions. The system is designed to take corrective action in the event of an alarm condition being sensed.