Wall Assemblies Research Articles

Watertightness performance of face-sealed versus drained window-wall interfaces

Several research studies have identified window-wall interfaces as one of the major sources of water ingress through building envelopes. Window-wall interfaces can either be sealed by means of face-sealed or drained sealing systems. In general, it is assumed that drained window-wall interfaces show an improved rainwater resistance compared to face-sealed interfaces. However, only a limited number of studies can be found in literature evaluating the watertightness performance of both face-sealed and drained window-wall interfaces. The objective of this paper is to evaluate the performance of both face-sealed and drained sealing methods and to identify the primary factors affecting the water resistance of window-wall interfaces.Various combinations of exterior seal, drainage layer, air barrier, airtightness level, installation method and wall assemblies were assessed by means of 5 face-sealed test specimens and 9 drained specimens. Both static and cyclic tests were performed. It was found that both tests showed corresponding results with regard to the pressure threshold value for water ingress. The results in this study also indicated that the airtightness of the interfaces and the presence of a separate air barrier at the interior side of the interface affected the watertightness performance to a great extent. The findings showed that it is very difficult to obtain water resistant face-sealed window-wall interfaces, even in lab conditions. It is therefore recommended to always provide drainage possibilities behind the exterior seal or cladding.

Assessing the Moisture Load in a Vinyl-Clad Wall Assembly through Watertightness Tests

The moisture load in wall assemblies is typically considered as 1% of the Wind Driving Rain (WDR) load that is deposited on the surface of wall assemblies as specified in the ASHRAE-160 standard whereas this ratio has been shown to be inaccurate as compared to results derived from several watertightness tests. Accurate assessment of moisture loads arising from WDR can be obtained through the watertightness test during which different levels of WDR intensities and Driving Rain Wind Pressures (DRWPs) are applied to a test specimen and water that penetrates wall assembly can thus be quantified. Although many previous studies have included watertightness tests, only a few of these have attempted to correlate the moisture loads to WDR conditions as may occur in specific locations within a country. To improve the assessment of moisture loads for a vinyl-clad wall assembly, a wall test specimen was tested following a test protocol based on local climate data using National Research Council of Canada’s Dynamic Wind and Wall Testing Facility (DWTF). The use of this test protocol permitted quantifying the moisture load in the vinyl wall assembly when subjected to several different simulated WDR conditions. The moisture load was formulated as a function of the WDR intensity and DRWP which thereafter allowed evaluating the moisture load based on a given climate’s hourly rainfall intensity and wind velocity. Such work is particularly relevant considering that the intensity, duration and frequency of WDR events across Canada will in some regions increase due to the effects of climate change.

Assessing ventilation cavity design impact on the energy performance of rainscreen wall assemblies: A CFD study

The impact of the ventilation cavity design on the energy performance of the rainscreen wall assembly was numerically investigated in CFD. The ventilated cavity design parameters considered were the cladding material type (i.e. Fibre cement, brick, and metal cladding), the sheathing membrane emissivity coefficient (i.e. 0.1–0.9), the ventilated cavity height (i.e. 1H and 2H) and the air gap width (i.e. 13 mm–50 mm). The CFD model was validated with experimental data and a dynamic simulation for a typical hot day and cold day is performed for a timestep interval of 5 min. The heat flux through the wall assembly was compared amongst the design alternatives. For the range of parameters considered, the ventilated cavity construct with brick cladding, sheathing membrane emissivity of 0.1, one-storey ventilated cavity, and 13 mm air gap width minimized the heat loss for a typical cold day. However, ventilated cavity construct with brick cladding, sheathing membrane emissivity of 0.1, one-storey ventilated cavity, and 50 mm air gap width minimized the heat gain for a typical hot day.

A LCA-based Optimization Method of Green Ecological Building Envelopes: A Case Study in China

Climate change and resource depletion have led to the destruction of the environment, making it more urgent to address the irreversible environmental effects caused by construction industry. Life Cycle Assessment (LCA) is a systematic analytical method applied to evaluate buildings since 1990, covering every phase of buildings’ whole life cycle. However, the application and influence of LCA has been restricted due to the time-consuming procedures, the high cost of software, the hysteresis and limited samples in academic studies. This research takes a light-frame industrialized housing product as a prototype, collects a variety of common building envelope materials, evaluates the life cycle energy of 1344 possible wall assemblies by using C# language, and investigates the influences of different materials. The results show that construction energy accounts for 65.97% to 68.41% of life cycle energy, which is the largest part in the whole life span, much higher than the proportion of operation energy. Meanwhile, both life cycle energy and construction energy are strongly influenced by the outer layer materials of the building’s envelope, and the operation energy is closely related to the thermal insulation materials. In addition, this paper also shows a feasible methodology that could be adjusted to estimate various life cycle performance (including life cycle energy, life cycle carbon emissions, life cycle cost assessment, etc.) automatically in the architectural design stage and guide the buildings’ design more effectively.

Experimental validation of a hybrid fire testing framework based on dynamic relaxation

Fire testing of large-scale structural prototypes is costly and requires highly specialized facilities. For this reason, most of the research on the structural response to fire loading relies on cheaper single-component experiments. However, such experiments do not reproduce the internal force redistribution in a realistic assembly, which plays a pivotal role in determining the failure mode of every component. Hybrid fire testing overcomes this limitation by harnessing fire experiments and numerical simulations in a closed feedback loop. Specifically, the boundary conditions of the tested specimen are updated on-the-fly to match those of a numerically simulated subassembly. In order to test gypsum-plasterboard-based wall assemblies under realistic loading scenarios, the Danish Institute of Fire and Security Technology has recently implemented hybrid fire testing. This paper describes the developed hybrid testing setup and the results of a demonstrative experimental campaign.

Effect of vapor diffusion port on the hygrothermal performance of wood-frame walls

Vapor diffusion ports (VDPs) that are drilled in the exterior sheathing of wood-frame walls are commonly used in wood-frame buildings in the coastal region of British Columbia with the intention to improve the drying capacity of wood-frame exterior walls. This practice originated following the systematic building envelope failures due to rain penetration that occurred in this region around 1985–1995. A previous laboratory study found that VDPs provided substantial improvement in the drying rates of OSB sheathed walls, but not for plywood sheathed walls. A more recent laboratory test using wood-frame walls with higher insulation levels in compliance with the current energy code found that VDPs did not significantly improve the drying rates. To provide a more comprehensive evaluation of the effect of VDPs, hygrothermal simulations using WUFI 2D are carried out based on the recent tests. The WUFI 2D model is firstly validated with measurements from the recent tests and the validated model is then used for a parametric study to evaluate the effect of VDPs under three wetting scenarios using yearly weather data for Vancouver. It is found that VDPs have the ability to improve the rate of drying, which is directly related to the moisture content level of the wall assemblies, although the improvement is moderate even for high moisture levels. The contribution of VDPs to reducing mold growth risk is insignificant under a moderate moisture load and becomes considerable only under a sustained high level of moisture load, i.e., east orientation with an ongoing rain infiltration. Therefore, efforts should be made towards properly designing and constructing building envelope details instead of relying on VDPs as a mitigation measure to improve durability performance.

Environmental performance of miscanthus-lime lightweight concrete using life cycle assessment: Application in external wall assemblies

In the UK context, miscanthus is a potential alternative perennial crop for the development of bio-based building materials. This paper presents the environmental benefits of using miscanthus shives in lightweight blocks and their potential application in wall assemblies. A systemic life cycle assessment (LCA) is carried out for miscanthus-lime blocks, and the effects of binder type and binder content are discussed. The environmental performance-based analysis reveals that miscanthus blocks can capture 135 kg CO2eq/m3 for an assumed 100-years life period. The impact analysis using the University of Leiden, institute of environmental science (CML) baseline (v4.4) method shows that 75% of the greenhouse gas emissions are attributable to the production of mineral binders. A reduction of binder to aggregate ratio from 2.0 to 1.5 reduces greenhouse gas emissions by 32.9%. The use of 10 wt% mineral additions can potentially stabilise blocks while having little effect on their overall environmental impacts. The environmental profiles of wall systems incorporating miscanthus-lime blocks have been evaluated in this this study. Combining miscanthus blocks with fired clay bricks enables a potential low carbon retrofitting technique for the current stock of residential buildings in the UK. Timber-framed system filled with miscanthus blocks enables a carbon storage of ~97.3 kg CO2eq/m2, which presents a potential carbon offsetting strategy in new-build dwellings. Consideration should be given to the potential negative impacts related to agricultural activities for the production of miscanthus shives. The largest negative environmental impact was ozone layer depletion, where a relative difference of 12.8% was recorded between miscanthus timber-framed wall and a typical solid wall insulated with mineral wool. It appears that miscanthus-lime composites can substantially improve the environmental profile of wall assemblies and sustainability be applied in existing uninsulated masonry walls or incorporated in timber- framed new-build houses.

Quantification and prediction of the thermal performance of cold-formed steel wall assemblies

Steel elements installed at or in the building envelope are susceptible to forming thermal bridges, where heat and energy are transferred from the building interior to the exterior. Thermal bridges have a negative impact on overall embodied energy in the structure, which can be compounded over the service life of a building. Furthermore, poor thermal performance also results in condensation and occupant discomfort. This work specifically examines the thermal behavior of cold-formed steel wall assemblies. These assemblies are typically comprised of studs and tracks, sheathed in gypsum and weather-proofing sheathing. Walls are repetitively framed. While the performance and efficacy of insulating materials and potential mitigation strategies is known, prior works have not examined the impact of specific detailing inherent to these wall systems. To determine the influence of these engineering decisions, a large parametric study of wall assemblies was conducted via three-dimensional steady-state thermal analysis. The parametric study included steel thickness, stud depth, stud spacing, and was conducted across ASHRAE 90.1 climate zones. The contribution of isolated details and the sensitivity of overall thermal performance to these details is presented herein. Comparisons to relevant design codes are presented and predictive methods for determining thermal performance of assemblies are proposed.

Theoretical-experimental analysis of selected passive timber house wall

The advancing times and legislation require constant research of new progressive building envelope structures. Walls based on wooden material are perspective in this regard. These are capable of elimination the wall thickness while providing the required thermal resistance. The pavilion research of KPSU UNIZA laboratory includes this kind of wall structures intended for passive wooden houses. This paper deals with one of the researched wall assemblies in the annual operation. The measurements show that such a construction is suitable for near to zero energy buildings. It also points out that the correct design can eliminate thermal bridges in the area of the load-bearing wooden studs.

Determining the thermal resistance of a highly insulated wall containing vacuum insulation panels through experimental, calculation and numerical simulation methods

The purpose of this paper is to investigate the potential for calculation methods to determine the thermal resistance of a wall system containing vacuum insulation panels (VIPs) that has been experimentally characterised using a guarded hot box (GHB) apparatus. The VIPs used in the wall assembly have not been characterised separately to the wall assembly, and therefore exact knowledge of the thermal performance of the VIP including edge effect is not known. The calculations and simulations are completed using methods found in literature as well as manufacturer published values for the VIPs to determine the potential for calculation and simulation methods to predict the thermal resistance of the wall assembly without the exact characterisation of the VIP edge effect. The results demonstrate that disregarding the effect of VIP thermal bridges results in overestimating the thermal resistance of the wall assembly in all calculation and simulation methods, ranging from overestimates of 21% to 58%. Accounting for the VIP thermal bridges using the manufacturer advertised effective thermal conductivity of the VIPs resulted in three methods predicting the thermal resistance of the wall assembly within the uncertainty of the GHB results: the isothermal planes method, modified zone method and the 3D simulation. Of these methods only the 3D simulation can be considered a potential valid method for energy code compliance, as the isothermal planes method requires too drastic an assumption to be valid and the modified zone method requires extrapolating the zone factor beyond values which have been validated. The results of this work demonstrate that 3D simulations do show potential for use in lieu of guarded hot box testing for predicting the thermal resistance of wall assemblies containing both VIPs and steel studs. However, knowledge of the VIP effective thermal conductivity is imperative to achieve reasonable results.

Improving the Accuracy of a Hygrothermal Model for Wood-Frame Walls: A Cold-Climate Study

A one-dimensional transient hygrothermal model was used to simulate eight different wood-frame wall assemblies. Simulations were compared with measured results from a two-year field study exploring the effects of exterior insulation on wall moisture performance in a cold-climate. The field study documented the moisture content, temperature, and relative humidity measurements in wall assemblies using oriented strand board (OSB) sheathing. Simulations were performed using generic design input values as well as input values based on measurements or sensitivity analysis. Laboratory material property measurements informed the choice of material property values in the improved model for OSB, asphalt-coated kraft paper, and interior latex paint. Simulations using improved input values typically agreed with field measurements within measurement error. The most significant model improvements were all related to vapor permeance. The vinyl siding used an effective permeance much lower than typically recommended. However, both the extruded polystyrene insulation and the asphalt-coated kraft paper facing on the cavity fiberglass insulation had higher permeance than literature values.

Assessing the hygrothermal performance of typical lightweight steel-framed wall assemblies in hot-humid climate regions by monitoring and numerical analysis

Lightweight steel-framed (LSF) construction has attracted interest and gained popularity worldwide in recent years; however, due to a lack of knowledge, LSF construction suffers from premature failure related to moisture problems in hot-humid regions. To assess the risk of durability failure in developing LSF assemblies, four typical LSF wall assemblies fabricated with two kinds of construction methods were monitored for 10 months under real environmental conditions in the typical hot-humid city of Guangzhou. Wall assembly can become wet when the weather is wet or the indoor environment is air conditioned. Wall assemblies with a ventilatable cladding system (Wall C) are the least susceptible to wetness, followed by assemblies with a ventilatable cladding system and external extruded polystyrene (XPS) board (Wall A), assemblies with stucco cladding (Wall D) and assemblies with stucco cladding and external XPS board (Wall B). Wall A performs the best in terms of mold growth and corrosion risk, while Wall B and Wall D have the highest risks with regard to mold growth and corrosion, respectively. However, the LSF components could reduce the time of wetness (TOW) on the surface of the external sheeting (insulation) board. The external XPS board could significantly reduce the TOW in the structural cavity, while the stucco cladding system leads to a higher moisture risk. Special attention should be given to the sealing quality of the edges, especially at the bottom, and at the interface between the stucco cladding and external insulation, as these locations have the greatest risk of moisture problems.

Fire resistance of wood stud wall assemblies

SummaryThis paper presents the fire resistance results of seven full‐scale wall assemblies that were conducted at the National Research Council of Canada (NRC) jointly with the North American construction industry and other Canadian government departments. Parameters investigated for protected interior wall assemblies with a single‐row of wood studs included: insulation types and mid‐height blocking. Parameters investigated for protected interior wall assemblies with a double‐row of wood studs on a separate plate included: insulation types, wood studs spacing and mid‐height blocking. The impact of the investigated parameters on the fire resistance of wall assemblies is discussed. Results of the parameters studied showed that the installation of mid‐height blocking in wall assembly with a single‐row of wood stud and filling the wall cavities with cellulose insulation in wall assembly with a double‐row of wood studs improved the fire resistance by 10 to 15 minutes, respectively. However, the other parameters studied had improved the fire resistance slightly by up to 6 minutes.

Thermal resistance of multi-functional panels in cold-climate regions

In recent years, energy efficiency and sustainability have garnered widespread attention as buildings account for 30–40% of total primary energy use in North America and 24% of global greenhouse gas emissions. Owing to the cold climate in Canada, energy-efficient building practices have drawn significant interest among authorities and researchers who aim to develop sustainable means of improving energy efficiency. Among these means is the use of environmentally friendly building materials that also contribute to improving thermal resistance. This research investigates and evaluates the long-term thermal performance of innovative multi-functional panels (MFPs) in various wall assembly configurations for residential buildings under varying climatic conditions. The two types of MFPs under investigation combine two layers of wood sheathing with either wood fiber or extruded polystyrene (XPS) as an additional external layer to conventional light wood-frame wall assemblies in order to improve the overall energy efficiency of the conventional wall assemblies. For this purpose, two full-scale identical demonstration buildings (test houses) are built for in-situ testing—one located in the cold continental climate of Edmonton, Canada, and the other in the humid coastal climate of Vancouver, Canada. The two types of MFPs (with wood fiber or XPS) are added to conventional wall assemblies and placed on both north and south façades of each of the test houses. Sensors are installed on each wall assembly under controlled indoor climatic conditions to monitor temperature, moisture content, and heat flux at the inner, middle, and outer layers and at three different vertical levels for each wall assembly. The indoor climatic conditions are maintained by installing a floor heating system, an air conditioner, and a rotating fan for even air circulation. Also, each test house is equipped with a weather station to monitor solar radiation, precipitation, atmospheric pressure, outdoor temperature, and relative humidity, among other metrics such as dew point, wind direction, and wind speed. Results from this study demonstrate the effect of various weather conditions on the thermal performance of MFPs in comparison with conventional wall assemblies and future research will determine the long-term hygrothermal performance of the MFPs under investigation. The ongoing long-term study will provide a practical guideline for the use of wood fiber—an environmentally friendly and recyclable material—as a sustainable insulation material in the North American housing market.

Hygrothermal behaviour of emerging timber-based envelope technologies in Australia: A preliminary investigation on condensation and mould growth risk

This study uses dynamic hygrothermal simulations to assess the risk of failure of both timber-framed and mass-timber emerging external wall assemblies across Australian major cities, where most of the population lives. The transient analysis also investigates the sensitivity of the simulation outcomes with respect to the indoor climate input data. Results suggest that the mass-timber timber envelope performs overall better across the different scenarios of analysis compared to the timber-framed solution. However, the hygrothermal behaviour of the massive envelope solution consistently changes with the indoor climate model variation. This article highlights the importance of addressing condensation risk and moisture safety in timber envelopes from the early design stage. Input data and simulation scenarios must be carefully defined according to the specific case as they can highly impact the results’ outcome.

Moisture Redistribution in Full-Scale Wood-Frame Wall Assemblies: Measurements and Engineering Approximation

A counter-balanced mass measurement system was constructed to allow measurement of water loss from a full-scale wood-framed wall assembly. Water was injected onto a localized area of paper towel adjacent to the oriented strand board (OSB) wall sheathing. Moisture pins in the OSB and relative humidity/temperature sensors inside the insulated wall cavity monitored conditions as the wall dried out. The wetted OSB area’s moisture content dropped at a faster rate than the total mass of the wall, indicating moisture redistribution within the wall. A simple model was used to calculate overall moisture redistribution, which was characterized using a near-exponential decay function. This simplification of the inherently three-dimensional physics of moisture redistribution could be incorporated into the one-dimensional hygrothermal models often used in research and engineering practice.

Evaluating the impact of operating energy reduction measures on embodied energy

Annually, 48% of the global energy is used by buildings in their construction, operation, and maintenance, causing significant damage to the environment due to the resulting greenhouse gas emissions. During their life cycles, buildings use energy in the form of embodied energy (EE) and operating energy (OE). In a conventional building, EE accounts for 10–20% of a building’s life cycle energy (LCE), while OE accounts for 80–90%. As a result, the building sector has taken several measures to reduce OE in buildings. These OE reducing measures fail to account for the subsequent increase in EE and might cause an increase in the building’s overall LCE. A systematic review of the literature shows limited research that comprehensively evaluates the impact of design measures aimed at OE reduction on EE for different construction assemblies. In this study, we quantify and compare trade-offs on EE demand, caused by OE reduction measuresfor eight different building wall assemblies across four climatic zones within the United States. The EE and OE demands of the ASHRAE 90.1–2016 benchmark model and its variations were computed using Tally™ and Autodesk® Green Building Studio® (GBS), respectively. The results helped us determine the EE factor (EE spent per unit of OE savings) for different OE reduction measures. Although the calculated EE factors vary across different climatic zones and construction assemblies, these factors show significant EE costs for different OE reduction measures. This knowledge could help inform the design of evolutionary and deep/machine learning-based algorithms to assess and optimize building energy use.

Fire Resistance of Exterior Wall Assemblies for Housing and Small Buildings

This paper presents the fire resistance results of 6 full-scale exterior wall assemblies study conducted at the National Research Council of Canada jointly with the North American construction industry and other Canadian government departments. The parameters investigated include: cavity insulation types (rock, glass and cellulose fibre) in exterior wall assemblies with oriented strand board sheathing; cavity insulation types (glass fibre and cellulose fibre) in exterior wall assemblies with Type X gypsum glass mat sheathing; and assemblies with different screw spacing of standard 400 mm o.c. and non-standard 200 mm o.c. for attaching the Type X gypsum board on the fire-exposed side and glass mat sheathing board on unexposed side to wood studs using glass fibre insulation in wall cavity. The impact of the investigated parameters on the fire resistance of exterior wall assemblies is discussed. Also, Further research recommendations on design changes to enhance the fire resistance of exterior wall assemblies are proposed. Results of the parameters studied showed that the effect of insulation types on the fire resistance of exterior wall assemblies with OSB sheathing can be considered significant when gypsum board on the fire-exposed side is attached to wood studs with screws spaced at 406 mm o.c., however, the effect insulation types on fire resistance when the gypsum board on fire-exposed side and gypsum glass mat sheathing are attached to wood studs with screw spaced at 203 mm o.c. can be considered insignificant. Also, results showed the use of non-standard screw spacing at 203 mm o.c. for attaching the gypsum board on the fire-exposed side increased the fire resistance by 37% compared to screw spacing at 406 mm o.c. Therefore, the effect of screw spacing on the fire resistance of exterior wall is significant.

Thermal inertia as an integrative parameter for building performance

Traditionally, the energy efficiency properties of building envelope components are prescribed world-wide using the steady-state “U-value” where the insulation capabilities rely on the thermal conductivity of construction materials only. However, the heat flow through the building envelope is also restricted by the effect of other material properties combined in the form of the thermal inertia, a widely used parameter that can be controlled in the building environment through transient-state parameters such as the cyclic transmittance “u-value”. By controlling the thermal inertia of the building envelope components key aspects of the building performance such as the building thermal, energy efficiency and fire performance can be evaluated in a holistic manner so that balanced design solutions are obtained without detriment affecting each other. Herein, it is proposed a holistic assessment method that uses a numerical model to obtain the thermal inertia of building components from their thermal insulating parameters to ultimately predict reaction-to-fire performance. The method includes a complementary thermal test to achieve reliable and realistic assessments that enable the analysis of aspects like the effect of construction imperfections. Two wall assemblies were built first to illustrate the method including the thermal test and finally to verify the method by conducting reaction-to-fire tests.

Fire performance evaluation of cladding wall assemblies using the 16‐ft high parallel panel test method of ANSI/FM 4880

SummaryCladding assemblies are façade systems made of cladding panels such as aluminum composite materials (ACMs) and high‐pressure laminates (HPLs), and layers of continuous insulation (CI) and weather resistive barrier (WRB). Recent incidents of catastrophic fires involving cladding assemblies have warranted efforts to understand their fire hazards and develop engineering risk mitigation guidelines for existing constructions. This research provides a comprehensive fire performance evaluation of cladding assemblies exposed to realistic fire scenarios. Twelve cladding assemblies, with a combination of four types of claddings, four types of CIs, and two WRBs are selected. The tests are conducted using the 16‐ft (4.9 m) high parallel panel test (16‐ft PPT) method of ANSI/FM 4880 standard; the method imparts realistic >100 kW/m2 heat flux to the wall assemblies. The results show that the chemical heat release rate (HRR) based evaluation criterion used in the 16‐ft PPT provides an objective and robust assessment of fire performance. The wall assemblies comprising of thermoplastic‐core ACMs demonstrated accelerated flame spread within a matter of a few minutes, regardless of the combustibility of the CI used. At low heat flux exposures, unlike severe fire scenarios of the 16‐ft PPT, it is shown that the thermoplastic‐core ACMs appear to perform favorably. The fire‐retardant ACM and HPL assemblies reveal limited flame spread, regardless of whether the CI used in the assembly was charring combustible or noncombustible. Lastly, for the assemblies evaluated, the flammability of claddings exhibits greater influence on the overall performance of the wall system, while the CI and WRB affect the system performance in a secondary manner.