External Wall System Research Articles

Evaluation of exterior wall cavity fires using an intermediate scale test method

AbstractCavities form an integral part of many external wall systems (EWSs). Numerous external wall fires worldwide have been primarily due to combustible exterior cladding. However, the Grenfell Tower and Knowsley Heights fire incidents (in the UK) are examples where wall cavity materials have impacted fire spread. Wall cavity materials are typically regulated by small‐scale fire test methods which do not necessarily represent the actual fire conditions that can exist within wall cavities. This experimental study proposes an intermediate‐scale test (IST) protocol to examine cavity wall fire behaviour. This protocol is a modified version of the FM Global Cavity Fire Test method (within the FM 4411‐2020 series). The study examines a broad range of cavity materials including sarking, polyester insulation, phenolic foam, PIR, and EPS. A low‐intensity (6–8 kW) and high‐intensity (~80 kW) ignition sources were used to represent two types of cavity fire scenarios. These two fire sizes were shown to differentiate reaction to fire behaviour between these materials and explore the “tipping point” in resulting fire behaviour (which may lie between these two intensities). This proposed cavity fire test protocol provides a suitable “elevated fire risk assessment tool” for combustible cavity materials.

External Wall Systems in Passive House Standard: Material, Thermal and Environmental LCA Analysis

The construction sector, a significant consumer of energy, possesses the potential to realize substantial environmental and economic advantages through the adoption of innovative technologies and design approaches. Notably, the Passive House standard, exemplified by energy-efficient single-family homes, emerges as a prominent solution. This study analyzes five external wall systems across multiple stages: (i) a literature review and examination of external wall techniques within the passive standard, utilizing the Passive House Database; (ii) a material and technological assessment of three wood-based and two masonry constructions; (iii) an in-depth thermal performance analysis of selected external partitions; and (iv) a Life Cycle Assessment (LCA) of the external wall systems. Our findings indicate that among the single-family homes built to the passive standard, 50.94% utilized timber constructions, while 34.21% employed masonry. Thermal analysis revealed that the masonry wall, EW-M-01, exhibited superior thermal efficiency with a heat transfer coefficient (U-value) of 0.0889 W/m2K. Meanwhile, the wooden wall, EW-T-01, led its category with a U-value of 0.1000 W/m2K. The LCA highlighted that the wooden wall EW-T-02 presented the lowest integrated non-renewable energy demand (PENTR) at 425.70 MJ/kg and the most favorable Global Warming Potential (GWP), with a reduction of 55.51 kg CO2e. Conversely, the masonry wall EW-M-01 recorded the highest energy demand and CO2e emissions, at 780.96 MJ/kg and 90.59 kg CO2e, respectively. Water consumption was lowest for the EW-T-02 wooden wall (0.08 m3) and highest for the EW-M-02 masonry wall (0.19 m3). Conclusively, our analysis of passive house external walls demonstrates that wood-based systems offer superior performance in terms of materials, thermal efficiency, and LCA indicators, positioning them as the preferred option for sustainable passive construction.

Mould Growth Risks for a Clay Masonry Veneer External Wall System in a Temperate Climate

To reduce greenhouse gas emissions, nations have introduced energy efficiency regulations for new and existing buildings. This has been considered advantageous as more efficient building envelopes would reduce energy consumed to heat and cool home interiors to within accepted thermal comfort bandwidths. However, as these methods have been adopted, many nations have identified an unintended visible presence of surface and interstitial condensation and mould in new code-compliant buildings. In Australia, it has been estimated that up to 50% of Australian houses constructed in the last decade (2006–2016) have a presence of condensation and mould. Australia introduced its first condensation and mould-related building regulations for new homes in 2019. This paper reports on the hygrothermal and mould growth analysis of the most common low-rise residential external wall system, a timber-framed clay masonry veneer wall. A key component of this paper discusses the application of innovative methods in the Australian context. The external wall’s moisture accumulation and mould growth were simulated for a period of ten years using the transient hygrothermal simulation tool, WUFI® Pro, and the mould growth model, WUFI® VTT. This study identified significant risks for this typical external wall system when constructed in a temperate climate.

Hygrothermal Modelling of the Differences between Single versus Variable Relative Humidity Vapour Diffusion Resistivity Properties of Pliable Membranes

The study investigates through hygrothermal modelling the effect of different boundary conditions and varying measured vapour diffusion resistivity values on the hygrothermal performance of five pliable membranes. Previously, this research quantified the variable water vapour diffusion resistivity properties of five different pliable building membranes. The membranes were assessed under varying humidity conditions using the gravimetric wet and dry cup test method. The varying humidity conditions better represent the boundary conditions experienced by materials in the building envelope. The pliable membranes include two permeable, two impermeable, and one variable products, which are commonly used to provide air and vapour control layers in the construction of framed external wall systems. This article focusses on the transient hygrothermal modelling of each of these membranes as a component of a typical timber-framed, clay brick veneer external wall system. The simulations were completed for three different climate types, namely, hot and humid, temperate, and cool-temperate with snow, and with a northern and western orientation. The results from hygrothermal and bio-hygrothermal simulations highlighted different responses subject to climate type and orientation. These results show that there are significant differences in simulated moisture and mould growth risk between the results of pliable membranes with single vapour resistance factor value and pliable membranes with multipoint vapour resistance factor values.

Evaluation of thermal bridging mitigation techniques and impact of calculation methods for lightweight steel frame external wall systems

Thermal bridging is known to affect the thermal performance of lightweight steel-framed external walls. Various manual calculation methods have been developed to estimate this impact, including the parallel path, NZS 4214 and modified zone methods, with the NZS 4214 method recently adopted for non-residential buildings by the Australian National Construction Code 2019 via its explicit reference in AS/NZS 4859.2. These methods have been validated against different wall assemblies from those currently used in the Australian context, therefore this paper aims to examine the validity of thermal bridging calculation methods in this context and evaluate the impact of mitigation methods on the overall thermal performance. We developed a set of 34 realistic external cold-formed steel-framed wall configurations based on available market products and construction practices and compared the R-values from manual calculation methods with outputs from the 2D simulation THERM. Results have shown that the NZS 4214 method as recently adopted by the Australian National Construction Code 2019 for non-residential buildings has good applicability for wall assemblies with lower R-values (R = 1.8–2.3 m 2 K/W). However, it was shown to have larger differences for calculations of walls with higher R-values (R > 2.5 m 2 K/W). The isothermal planes method can produce various results for the same building assembly, depending on which planes are assumed to be isothermal. This study has demonstrated that superior accuracy may be obtained by varying the definition of such planes depending on the R-value of the assembly. When considering designs to mitigate thermal bridging effects and improve overall wall performances, outside frame insulation and high resistance claddings have been shown to provide the best results (decreasing variation in temperature across the surface by 75%). • R-values for suite of Australian cold formed steel wall configurations assessed. • NZS4214 calculation method shown to have good applicability for low R-values. • Isothermal plane boundary location for NZS4214 requires investigation. • External insulation and high resistance claddings provide thermal bridge mitigation.

Fire resistance of external light gauge steel framed walls clad with autoclaved aerated concrete panels

This paper presents an investigation into the fire resistance of external light gauge steel framed (LSF) walls clad with autoclaved aerated concrete (AAC) panels exposed to fire on the external side. Past research has been limited to the fire resistance of internal LSF walls clad with gypsum plasterboard on both sides. A series of experimental studies including thermal material property tests, a full-scale (3 m × 3 m) ambient capacity test of LSF wall and full-scale standard fire tests of non-load bearing and load bearing LSF walls were conducted to investigate the fire resistance of external LSF walls clad with AAC panels. Finally, a small-scale (1.2 m × 1.2 m) fire test of a wall made of AAC panels was also conducted to investigate the performance of joints between AAC panels. AAC panels with very low thermal conductivity performed exceptionally well by keeping the temperatures low for 160 min achieving a fire resistance level (FRL) of 204 min in load bearing conditions and 240 min in non-load bearing conditions. Hence, LSF walls clad with AAC panels can be used when higher FRLs are required. Experimental studies such as these on the whole system enable a good understanding of the overall fire performance of external wall systems in terms of structural adequacy and integrity instead of focusing only on the cladding.

The Application of Silica-Based Aerogel Board on the Fire Resistance and Thermal Insulation Performance Enhancement of Existing External Wall System Retrofit

Due to the need of good thermal performance, external wall insulation (EWI) is usually made of materials that are not fire resistant and sometimes flammable. That restricts its application to a particular circumstance such as limited building height. Hence, a material with good thermal insulation and fire resistance performance would allow EWI to be more widely applied. This paper introduces a novel material: a silica-based aerogel porous board, which differs itself from mainstream products available in the market because of its outstanding properties, such as low density, high surface area, low thermal conductivity and superhydrophobicity. Herein, its thermal insulation and fire-resistant performance were tested and compared with commercial products. The cone calorimeter analysis results indicated that the aerogel porous board could improve the fire resistance performance. Moreover, the evaluation of thermal insulation performance suggested that the application of an aerogel porous board on the external stone wall of existing buildings can decrease the U-value by 60%. Through the detailed insight into the case-study, it is quite clear that the carbon impact of building stock could be greatly reduced by means of a coherent set of building envelope retrofitting actions based on this innovative heat insulation material, without compromising the fire safety.

Energy Optimization and Environmental Impact of an Office Building at Biskra City, Algeria: Life Cycle Assessment, Applied to the Building Envelope in Hot and Dry Climate

This work assesses the environmental impact generated by an office building in arid region throughout its life cycle (cradle to grave), by means of a Life Cycle Assessment (LCA). This study focuses on a comparison of different external wall systems that are conventionally used in building. With recycled materials and thermal insulation system, it’s possible to reduce demand of energy consumption, evaluate their environmental indicators impacts, and also reduce them, throughout the building life cycle. In doing so, this work can contribute not only to control energy, long-term economic growth, but also to address pressing social issues, and mainly environmental impacts. We use an environmental analysis with a thermal dynamic simulation, to test the hypothesis on a data base of hot and dry climate of Biskra city. The last part consists of a technical approach, indicating the economy is the use of ecological and recycled materials. The results of this study show that the exterior insulation system, obtained the best environmental scores, being 30% less than the interior insulation system and 50% less than the distributed insulation system. Also, recycled materials save energy in their manufacture, and building energy consumption for its use and have a reduced building impact on the environment throughout its life cycle (cradle to grave). This work shows how LCA application is not only feasible, but recommended because it is a decision support tool in the search for sustainability and make use of recycled materials.

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

The presence of an air-space within a building envelope is known to have a varying contribution to the overall thermal performance of the wall assembly due to the combined effect of convection and radiation in the air cavity. In particular, the thermal resistance of a ventilated air-space can vary significantly depending on multiple environmental and thermo-physical parameters. Although the thermal resistance of enclosed air-spaces in the building structures has been thoroughly investigated in the literature, it has not been defined for a ventilated cavity. This paper aims to introduce the plausible definitions of the thermal resistance of a vertical ventilated air-space behind external cladding systems. Both theoretical and applied formulations are provided and compared. The energy balance method is used to model the steady-state heat transfer through two types of traditional external wall systems (i.e., brick and vinyl siding) in summer and winter conditions. A range of air exchange rates in the cavity is examined, and the effect of the presence of reflective insulation in the air-space on the thermal resistance of the air gap is analyzed. The results show that the presence of a ventilated cavity in the wall assembly can influence the thermal performance of the building envelope. In particular, the effective thermal resistance of a ventilated air-space behind a brick cladding wall could be between 0.17 and 1.85 times the thermal resistance of the cladding in the range of air change rate in the cavity from 0 to 100 1/h. The effective thermal resistance of the ventilated air gap behind vinyl siding could reach up to 9 times the thermal resistance of the cladding.

The valuation of high-risk residential buildings and the role of EWS1

In response to the tragic fire at Grenfell Tower in June 2017, the UK Government proposed regulatory reform with the purpose of ensuring residents feel safe and are safe in their own homes. This paper examines the advice that has been given by the government and traces how this advice has had disastrous consequences for the mortgage lending market for flats located in high-risk residential buildings. This has been compounded by the unfortunate effect that the EWS1 form has had on the same market. The paper opens with a review of the independent expert advisory panel set up to provide advice and make recommendations to the Secretary of State for Housing, Communities and Local Government on urgent building safety measures that should be carried out to high-risk residential buildings with aluminium composite material (ACM) external wall cladding. The panel formulated the much-criticised advice note 14 which provided guidance to building owners to take general fire precautions with non-aluminium composite Material (non-ACM) cladding in their external wall systems to ensure that the systems are safe. Although advice note 14 was superseded in January 2020 by the Ministry of Housing, Communities and Local Government’s consolidated advice document, the binary approach to defining safe external wall systems is still adopted. This has caused unintended consequences for the valuation of flats in high-risk residential buildings as many valuation surveyors take the position that if compliance with the consolidated advice document cannot be demonstrated, then the flats within that building will have a valuation of £nil. The industry’s response has been to produce the EWS1 form which was intended to unblock the market. This aim has not been achieved, however, and the paper details why the EWS1 form has, to date, failed and suggests ways of restoring confidence within the market.

Life cycle energy assessment and carbon dioxide emissions of wall systems for rural houses

Abstract Wall systems have a wide range of embodied energy due to the diversity of materials available. This paper analyzes the expenditure of energy and carbon dioxide emissions in internal and external wall systems (IEWS) of a rural residence of social interest in Cascavel, state of Paraná, Brazil. The methodology proposed by NBR ISO 14040 was used to perform a life-cycle energy assessment (LCEA) and the carbon dioxide emissions assessment (LCCO2A) of these systems. Four scenarios were considered: reinforced concrete structure and ceramic blocks wall system, load-bearing masonry with concrete blocks, steel framing and reinforced concrete walls molded on site. As a result, it was found that it is possible to reduce energy consumption up to 25% by opting for reinforced concrete walls molded on site. In regards to CO2 emission, it was verified that the difference is even greater, being able to reduce emissions by almost 32% when opting for this same scenario.

The Impact of Internal Insulation on Heat Transport through the Wall: Case Study

This paper presents a case study on how to improve the energy efficiency of an institutional building of significant heritage value through retrofitting the external wall system. This building is located in Upper Silesia, Poland. Due to the architectural value of the facade, thermal insulation had to be applied from the inside. As part of this publication, basing on the measurements and simulations, the authors present the results involving the improvement of energy efficiency of the insulated wall. On this basis, they also demonstrate the impact of insulation from the inside on the change of humidity inside the room. The tests were carried out both quantitatively by means of heat flux measurement and qualitatively by means of infrared temperature measurement. The research was supported by numerical modeling. The obtained results indicate that the thermal insulation used in the form of mineral insulation boards applied from the inside improves thermal insulation of the wall. Thus, heat losses through the examined envelope were limited. Computer simulations indicated that no condensation may occur under the condition considered.

Influence of the Coating System on the Acoustic, Thermal and Luminous Performance of Brazilian Buildings

This work presents an extensive numerical simulation to analyze the influence of the coating layers on the performance of construction systems, in order to make the constructions projects feasible, not only economically but also technically. Through numerical simulations based on a defined reference model, the present work studied the influence of different layers of floor, roof and internal and external wall systems, on the acoustic, thermal, and luminous performance of buildings in Brazil. The results showed the materials and elements with the greatest influence on: lighting performance are the internal finishes of the environment and the type of glass used in the external windows. On thermal performance, all elements of the roofing system and façades, especially an absence of external cladding and the use of thermal blankets on the roof, have greater influence. The acoustic performance of the façade function on the external windows and acoustic performance of the floor system are mainly influenced by the thickness of the structural element and the use of a ceiling and acoustic blanket; acoustic performance of internal walls is affected by typology of the structured element of the wall and thickness.

Numerical investigation of the energy efficiency of a serial pipe-embedded external wall system considering water temperature changes in the pipeline

Pipe-embedded external wall using low-grade energy has been shown to significantly reduce the cooling or heating load of buildings. However, previous studies have generally focused on the heat transfer between water pipes and pipe-embedded wall and paid less attention on the energy use of water distribution. In this study, a numerical model of serial pipe-embedded wall (SPW) considering water temperature changes in the pipeline is developed, and the load reduction and energy efficiency of the SPW are studied numerically under different climates and structures. The influence of flow velocity and flow path on the performance of SPW is also investigated. The results show the following: (1) the SPW retains a satisfactory load reduction rate, which is only slightly less than that of the parallel pipe-embedded wall (PPW); (2) the coefficient of performance (COP) of the SPW is 10 times higher than that of the PPW after considering water distribution; (3) the water temperature affects the indoor load more than the sol-air temperature does, and the SPW has load reduction potential compared with the conventional wall when the water temperature is below 30 °C in summer or above 12 °C in winter; (4) increasing the flow path or flow velocity alone will not always result in better energy efficiency for a SPW system. There exists an optimum flow velocity or flow path that will maximize the energy efficiency of a SPW system.

A research on straw bale and traditional external wall systems: Energy and cost-efficiency analysis

A research on straw bale and traditional external wall systems: Energy and cost-efficiency analysis

A Cradle to Handover Life Cycle Assessment of External Walls: Choice of Materials and Prognosis of Elements

This research focuses on a comparison of 20 external wall systems that are conventionally used in Spanish residential buildings, from a perspective based on the product and construction process stages of the life cycle assessment. The primary objective is to provide data that allow knowing the environmental behavior of walls built with materials and practices conventionally. This type of analysis will enable promoting the creation of regulations that encourage the use of combinations of materials that generate the most environmentally suitable result, and in turn, contribute to the strengthening of the embodied stages study of buildings and their elements. The results indicate that the greatest impact arises in the product stage (90.9%), followed by the transport stage (8.9%) and the construction process stage (<1%). Strategies (such as the use of large-format pieces and the controlled increase in thickness of the thermal insulation) can contribute to reducing the environmental impact; on the contrary, practices such as the use of small-format pieces and laminated plasterboard can increase the environmental burden. The prediction of the environmental behavior (simulation equation) allows these possible impacts to be studied in a fast and simplified way.

Cost optimization for public school building projects during design stage using value engineering

During the past ten years, various systems of building components have been applied in public school projects in Iraq, with no systematic method used for selection and evaluation, but only based on the designer’s experience. This paper displays evaluation and selection techniques based on value engineering methodology to find the optimal cost for school building projects in Iraq during design stage. The most important criteria for performance, constructability and sustainability criteria, which based on the Leadership in Energy and Environment Design used in this assessment were obtained from a survey of 49 professional designers and consultants, adoption of the Super Decisions Software Program, which uses analytical hierarchy process (AHP) for determining the relative importance of the main criteria and sub-criteria, that allows the decision-makers to evaluate the suitable alternatives of design for the external wall system in Iraq’s school buildings was built.

Comparative analysis of energy related performance and construction cost of the external walls in high-rise residential buildings

In the design phase of a high-rise residential building, stakeholders should adopt the proper external wall system by considering energy performance and IEQ as well as construction cost and structural stability. The energy related performance and construction cost of external walls affect the life cycle cost. Therefore, also a value analysis of the LCC in terms of the energy performance is required. The purpose of this study was to evaluate the energy related performance and construction cost of external walls in high-rise residential buildings, which are the currently staple external walls, using reinforced concrete (RC), glass fiber reinforced concrete (GFRC) and cellulose fiber reinforced cement (CFRC). All the wall systems have the same doors and windows in their bodies for equal comparison of energy efficiency and construction cost. The energy efficiency of the CFRC external walls was high while the construction cost for RC external walls was low. The value assessment considering the LCC and the residents’ health revealed that RC external walls were most satisfactory up to 6 years after construction, GFRC from 6 years to 26 years, and CFRC thereafter, respectively. The findings of this research will be valuable for stakeholders deciding on an external wall system.

Analysis of Heat Transfer by Thermal Bridge of Corner Wall in a New Glass Regenerated Pumice External Wall System

This paper was based on heat insulating members made by a new type of waste glass regenerative pumice, with the characteristics of light weight, permeable water retention, ventilation, heat insulation, fire retardant, etc. In the external wall heat insulating system of building envelops, the thermal bridge of external wall corner was simulated with ANSYS. The temperature field and flux field distribution will be shown respectively of non-insulation, self-insulation, internal insulation and external insulation. Through comparing the heat preservation of different insulation forms, the external insulation was better than internal insulation and self-insulation. Besides, considering the imperfection of calculating the wall average heat transfer coefficient in current energy saving standards, a simplified method was presented to calculate the linear heat transmission coefficient with ANSYS. The two coefficients were compared to serve the latest research.

The influence of the external walls thermal inertia on the energy performance of well insulated buildings

Energy conscious building design consists in controlling the thermophysical characteristics of the building envelope such as, firstly, thermal transmittance ( U-value). However, besides the U-value, the envelope thermal inertia should also be considered. The literature studies report very different estimations regarding the energy saving potential associated with the use of an adequate inertia, ranging from a few percentages to more than 80%. Therefore, this study aims at assessing the parameters enhancing or damping the role of thermal inertia, providing a variety of results. For this purpose several external wall systems with the same U-value but different dynamic properties were investigated to calculate the associated achievable energy savings. A parametric analysis was performed in progressive steps, by running the models of a virtual Test Cell and of a sample building. Both design parameters (heat transfer surface, solar control) and operational ones (ventilation rates, HVAC functional regime) were varied. It was found that the highest energy performance wall system has a proper combination of the dynamic thermal transmittance and thermal admittance values, although not necessarily the best ones. Moreover, it was shown that thermal inertia effects are enhanced if it is coupled with other energy saving measures and an efficient building use.