Timber Cladding Research Articles

Hygrothermal performance of timber-framed walls in Turkey – Long-term monitoring

The increasing energy consumption emphasizes the urgency of sustainable building practices. Worldwide, there is a tendency towards local, natural, durable, and recyclable materials like timber. Furthermore, timber's excellent thermal insulation and natural hygroscopic properties enable it to efficiently regulate indoor humidity levels, ensuring stability and comfort. In Turkey, timber construction declined significantly in the 20th century due to the shift towards vertical reinforced concrete, however, recent years have witnessed a renewed interest driven by earthquake concerns and global inclination. Despite this resurgence, timber construction practices are still limited, and the hygrothermal performance of exterior walls in both restoring traditional timber buildings and constructing new ones is often disregarded. Furthermore, there is a lack of scientific research in this area. Understanding the hygrothermal behaviour of these structures is essential for meeting modern energy efficiency standards. This study evaluates the hygrothermal performance of prevalent practices in timber-framed constructions in Turkey. Long-term monitoring in a full-scale test cabin exposed to real climatic effects provides insights. Findings indicate the exterior plywood sheathing on the North-west facing walls being more susceptible to moisture, particularly when the indoor relative humidity is elevated. South-east facing walls are better at drying, but air barrier membrane slows down drying. Timber cladding with ventilated cavity offers improved protection but its high exposure to rainfall in North-west, and solar radiation in South-east, implies potential performance degradation over time. Installing suitable vapour retarders and additional exterior thermal insulation particularly to the North-west facing walls could possibly reduce risks associated with moisture, as well as preventing thermal bridges.

Life cycle assessment of hemp-lime concrete wall constructions: The impact of wall finish type and renewal regimes

Using sustainable building materials is one of the key methods for minimising the negative environmental impacts of the global construction industry. Bio-based buildings building materials, such as hemp-lime concrete, are considered more sustainable, as they make use of a renewable raw material and can sequester CO2 from the atmosphere. Studies have shown that hemp-lime concrete can have a favourable global warming potential, though the life cycle of building materials affects a wide variety of negative environmental phenomena that should also be considered. Studies examining the life cycle of hemp-lime concrete have so far primarily focused on the material itself. Though the exterior surface of a hemp-lime concrete wall needs to be protected and have a finish applied to it, few studies have considered the environmental impacts of coated hemp-lime concrete wall constructions. Using life cycle assessment methodology, through a wide range of environmental impact categories, the study analysed the environmental impacts of applying lime putty and sand coatings to a hemp-lime concrete wall in pessimistic, average and optimistic scenarios, It also compared the environmental impacts of four types of appropriate wall finishes and the impacts of applying varying finish renewal regimes in the use phase. It was found that applying lime putty and sand finishes to the exterior and interior surface of a hemp lime concrete wall increased the total global warming potential by 19.054–30.793 kgCO2eq and had a noticeable effect on all other impact categories. It was found that while no one finish type could be considered globally superior to the others, in a majority of circumstances applying lime-based coatings resulted in lower embodied environmental impacts, than applying a ventilated façade with timber cladding.

A comparative life cycle assessment of ETICS and ventilated façade systems with timber cladding

The aim of this work is to evaluate the environmental impact of different solutions for building facade retrofitting. Based on Sustainable Construction, this study is carried out by applying the Life Cycle Assessment (LCA) methodology based on ISO 14044:2006 standard requirements. A “cradle-to-grave” life cycle analysis is developed for each solution, comprising the extraction of raw materials to the disposal phase, and then a comparative analysis was performed by considering the same functional unit: 1 m2 of building facade for a 40-year time horizon. Four retrofit solutions are assessed: two External Thermal Insulation Composite Systems (ETICS), differing only in the insulation material, expanded polystyrene (EPS), and insulation corkboard (ICB); and two ventilated facade systems with different types of timber cladding, thermally modified timber, and painted timber. The data included in the inventory phase is mostly taken from technical documentation and from the Ecoinvent database, complemented with scientific literature and estimations when necessary. The LCA was performed using the SimaPro software applying both EPD (2018) and ReCiPe 2016 Endpoint (H) methods. Results of this study show that, phase-wise, the production and maintenance of the components materials have higher contribution in terms of environmental impact. On the other hand, by comparing the various solutions, the ventilated facade retrofit solution with heat treated timber cladding is the one that shows the highest environmental impact in almost every single category, whereas the cladding solution with painted timber finish is the one that shows the best environmental performance.

Stress/Strain Behaviour of Mechanical and Adhesive Joints in Timber Façade Applications

This paper compares the stress and strain behaviour of mechanical fasteners and elastic adhesive connections in timber façade applications. Two common designs with timber cladding are introduced. The traditional façade planks and multilayer large-format solid wood panels were selected. The resistance of a reference façade section with mechanical fasteners or adhesive bond to wind suction is determined according to the recommendations of European guideline ETAG 034. The pressure/suction chamber allowing hermetic closure was used. The sample deformation was measured at 15 locations, this also allowed to determine the elongation of the adhesive layer at break. The failure loads reached with the adhesive joint exceeded 20 kN/m2 in both combinations of façade cladding. On the other hand, the sample with a large-format panel and mechanical fasteners showed the lowest failure load at 12 kN/m2. The results confirmed that bonded joints are a suitable solution for large-format cladding, whereas an increase in the number of mechanical fasteners will be a more convenient solution for façade plank applications.

“Free-Standing, Wooden, Upright”: The Evolving Cladding and Structure of the New Zealand House, 1858–1981

The timber-framed, weather-board-clad, corrugated-iron-roofed, stand-alone building has become the image of New Zealand housing. Its evolution is explored using census data from 1858 to 1981 for walls and from 1961 to 1981 for the roof. Four wall claddings (wood, brick, boards and concrete) were used in two-thirds or more of dwellings. The 1981 census reported 46 percent had timber cladding but analysis shows 85 percent had timber framing (structure). Timber cladding has been replaced by materials including brick-veneer and fibre-cement boards. From the 1970s, concrete walls became more widely used, replacing both structure and cladding. In 1981, 90 percent of roofs were corrugated, galvanised iron or tiles, while 55 percent of all dwellings had both a corrugated-iron roof and timber framing. While popular opinion considered timber construction as little better than temporary, the ready availability of timber and industry creativity in these seismically active islands have ensured the ongoing importance of timber housing.

Experimental study of fire spread between multiple full scale informal settlement dwellings

Internationally, informal settlements (also known as slums, favelas, shantytowns, ghettos, etc.) are expanding rapidly which have been associated with numerous large fires (where more than 10,000 people can be left homeless in a single disaster [1]), and an increase in fire related injuries and deaths. As a result of an increase in fire related incidences, various proposed interventions have been funded from governmental or private sources. However, many interventions have been unsuccessful because of technical, political, economic, social or practical issues. It is with the above mentioned in mind that this paper seeks to provide an understanding of fire behavior between multiple informal settlement dwellings (ISDs) as a baseline for future research and experiments. The paper starts by defining informal settlements in terms of construction and continues to look at the potential causes and hazards associated with informal settlement fires. The following two full-scale informal settlement dwelling burn experiments were conducted; (a) three ISDs clad with steel sheeting and (b) three ISDs clad with timber. The heat fluxes and temperatures of both experiments are shown and compared to understand the effect of cladding materials (i.e. timber cladding versus steel cladding, which are mostly used in informal settlements) on fire spread. Some general behavioral observations made during the full-scale experiments are given and discussed (i.e. how fire spreads, collapse mechanisms, etc.). Fire spread times are reported for both experiments, and range between 4 and 9 min (i.e. from the start of flashover in the first dwelling to the end of flashover in the last dwelling). These experiments are one of the bigger ISD experiments conducted to date and are the first experiments that measured heat fluxes for ISDs, which is crucial to understand fire spread. An important finding in this paper is that there is a critical separation distance of 3.8 m needed to prevent fire spread between dwellings.

Development of Durable Exterior Insulation Finishing Systems Based on Composite Timber Technology for Building Facades

Today, the requirements to thermal insulation of buildings and structures are increasing. Insulation has become an essential part of regulatory thermal protection of buildings. The analysis of the advantages and drawbacks of the existing insulation systems has shown that the most suitable system is the one with the insulation layer located outside the building. Such system of insulation is based on the use of an additional layer, called finishing or cladding, placed on top of the insulation layer to ensure the protection of buildings against atmospheric agents. The purpose of this study was to develop a material for exterior finish cladding of buildings. We developed a composite timber cladding system in the form of laminated composite material consisting of a substrate (base), a binder and a decorative layer. Manufacturing process comprised four stages. Atmospheric effects were modeled according to the GOST climatic test methods. For the rational use of material resources we calculated the optimal material consumption per unit area for the decorative layer. Durability of cladding depends on the substrate material. Under the effect of atmospheric agent the durability of cladding decreases. Heat and ultraviolet exposure causes decrease in durability of cladding after the completion of resin polymerization, which initially leads to an increase in durability. The impact of aggressive media solutions also results in reduced durability of cladding. Durability of cladding depends on the strength characteristics of the substrate. An operation life of cladding is determined by the difference between the mass of cladding with optimal material consumption per unit area for the decorative layer and the mass of similar cladding with the least possible material consumption per unit area for the decorative layer from an aesthetic perspective. The operational life of the developed cladding is at least 15 years. The cement chipboard-resin compound has low adhesive strength, which leads to the conclusion about the impossibility of using cement chipboard as the substrate for decorative cladding. High humidity deformation limits the use of wood particleboards and MDF as a substrate for cladding. Thus, we recommend using WBP plywood as a substrate for the cladding. The economic rationale is based on the comparison of the following materials used for exterior finishing systems: plywood, facing bricks, porcelain stoneware and vinyl siding.

Development of Performance-based Standards for External Timber Cladding

This paper reviews the background to, and development of, new British Standards for external timber cladding. The standards are being produced because timber has become a widely used external cladding material in the UK and this has highlighted that existing standards on the topic are inadequate. When fully published, the BS 8605 series will offer performance-based specifications and guidance on the main issues affecting external timber cladding. The standards involve multi-compliant performance measures; several technical conflicts had to be addressed.

Special Issue on Timber in Fire

Timber is amongst the oldest building materials used by humankind. We have been building with timber for millennia, and in its various forms timber has consistently remained a key structural and building material in most cultures (along with masonry and, more recently, concrete and steel). However, various conflagrations in largely timber-built towns and cities around the world throughout the history of civilization—typically called the ‘‘Great Fires’’ (e.g. of Rome, Constantinople, Hangzhou, Utrecht, Amsterdam, London, Baltimore, Tokyo, etc.)—led to the use of timber structural and cladding materials being reduced or explicitly restricted within dense conurbations, with a preference for non-combustible structural framing, cladding, and roofing materials—particularly for multistory and high-rise construction. In most places, timber has remained a critically important and widely used building material in a range of applications, however during recent centuries the structural use of timber (either as heavy timber elements or light timber framing) has typically been limited to low-rise construction of smaller volume buildings with fewer than four-to-five storeys; the use of timber cladding has also been widely restricted or avoided. However, spurred on by the sustainability and constructability credentials of timber as compared with concrete, masonry, or steel—and by the development of novel engineered timber materials and prefabricated systems incorporating engineered timber joists and trusses, glued-laminated timber (glulam) and cross-laminated timber (CLT)—timber has experienced an accelerating resurgence/emergence as a primary material in multi-storey buildings [1]. A range of publications during the past 5 years has highlighted the opportunities to build large, multi-storey buildings in engineered timber [2–4]. Timber buildings of up to nine or ten storeys are increasingly being proposed internationally, and numerous proposals have been made for predominantly timber—or hybrid timber-steel or timber-concrete—buildings of 30 storeys or more [2]. Timber is also increasingly being proposed by architects and engineers for innovative, sustainable, and attractive building facades and cladding systems.

Air infiltration in walls with direct-fixed claddings

This research examines the extent to which drainage and ventilation drying can remove water that has leaked through claddings on walls with no specific drainage cavity. In this study, tracer gas and zonal computer models were used to measure and predict air infiltration in the space between the wall underlay and the cladding and in the insulated spaces in 16 wall specimens. Half of the walls were clad with weatherboards direct fixed to the frame over a synthetic flexible wall underlay, and the remaining eight had ‘barrier’ or sheet claddings. A companion paper describes drainage and drying measurements in the same walls. Tracer gas measurements showed that average infiltration through weatherboard claddings (0.2 L/s) was much higher than behind sheet claddings (0.03 L/s). The range of day-average infiltration measured behind weatherboards (0.02–1 L/s) actually overlapped earlier measurements in bottom-vented cavity walls (0.1–2 L/s), and this is thought to partly explain the successful track record of direct-fixed weatherboard claddings in New Zealand. The airflow characteristics of leakage paths through claddings and at junctions between the timber frame, cladding, lining and underlay were also measured and used in a zonal model to calculate infiltration rates into the insulated spaces and behind the different claddings. There was acceptable agreement between measured and calculated infiltration, and this supports the next step of applying the computer models to whole buildings to better understand the heat and moisture consequences of air infiltration in New Zealand walls.

ENVIRONMENTAL LIFE CYCLE ASSESSMENT OF ANALOGOUS NEW ZEALAND ‘EXEMPLAR HOUSE’ DESIGNS

ABSTRACT To reduce the environmental impact of residential construction a holistic understanding of the building life cycle is necessary. Life Cycle Assessment (LCA) is well suited to the task of calculating the impacts associated with building products and systems so it is used in this study to assess building material options for a typical New Zealand house design. The LCA and underlying data adhered to international standards and framework. Four house designs comparing concrete and timber flooring, steel and timber framing and fibre cement and timber cladding were investigated. The different designs were modified to have the same thermal performance using NZS4214:2006. Consequently the difference in environmental performance can be attributed to the wooden building products. Substituting steel with timber framing results in a 20–30% decrease in global warming emissions, eutrophication and photochemical oxidation, but an increase in land and water use. Exchanging concrete with timber flooring results in...

Moisture conditions in timber cladding: field trial data for Sitka spruce

Exposure trials on timber cladding are valuable for informing facade designers. This paper describes a trial using Sitka spruce (Picea sitchensis). Sitka spruce is the only UK-grown timber available in sufficient volume to supply the growing cladding market, but its suitability is unclear. Data indicated that the moisture content range in timber cladding was wider than generally accepted. The minimum of around 10% moisture content appeared to be similar for all details tested. The maximum was influenced by construction detailing but was around 30%. From a theoretical standpoint, the range, and rate, of moisture content fluctuation observed meant that the commonly quoted average value was largely irrelevant. The mode was a more representative statistic; most of the data were skewed towards the wood's fibre saturation point. Sitka spruce is, therefore, at risk of fungal decay and is only suitable as external cladding in the UK if treated with preservative.

Assessing the ventilation performance of a naturally ventilated livestock building with different eave opening conditions

In livestock housing permeable windbreak materials are regularly used at eave openings to reduce the adverse effects of windy outdoor conditions on the indoor environment. Two materials generally used for this application include space boarding, i.e. a traditional timber cladding system, and ventilated cladding, i.e. a profiled steel sheeting system with louvers cut into the protruding ribs. In this study computational fluid dynamics (CFD) models were developed to investigate the ventilation performance and thermal environment of naturally ventilated calf buildings with unrestricted, space boarding and ventilated cladding eave opening conditions. The effect of altering the eave opening height on both the indoor environment and ventilation characteristics of the building has also been investigated. It was found that ventilated cladding performed the best in terms of ventilation efficiency and thermal comfort during wind driven ventilation, as the high resistance of the opening condition prevented the short-circuiting of air from the windward to the leeward opening. For high porosity eave opening conditions, increasing the eave opening height was found to decrease the average air velocity at animal level due to a change in size and location of the primary air recirculation zone. It was also found that the resistance and the height of an eave opening determine whether or not the leeward eave opening acts as an air inlet.

The design and construction of Itford Farm Bridleway Bridge

Until recently, users of the South Downs Way National Trail had been finding it increasingly difficult and dangerous to cross the busy A26 trunk road and the provision of a segregated crossing had become increasingly necessary. On behalf of the Highways Agency, InterRoute embarked on the design and construction of a suitable crossing. A structural timber beam or truss bridge was initially investigated but this was later rejected in favour of a structural steel solution with timber cladding. A steel truss superstructure was used for ease, speed and convenience of construction, and timber was used for its aesthetic qualities on most of the visible parts of the bridge. Effort was made, within the constraints of the budget, to design a bridge in harmony with its rural setting, a designated Area of Outstanding Natural Beauty. The chosen configuration, a three-span arrangement with curves in both vertical and horizontal axes, was selected to harmonise with the rolling hills of the Sussex Downland.

Tradition and innovation: timber as rainscreen cladding

This paper describes the use of timber as a rainscreen cladding on David Chipperfield's River and Rowing Museum at Henley. The extensive use of green oak in this way is the key to a precise and beautifully crafted building and was the result of collaboration between the architects and the Timber Research and Development Association. This use of timber represents a major shift in the work of David Chipperfield from concrete toward a wider palette of materials. Henley is also an important example of a recent trend in the development of timber as an external cladding material. Timber cladding as a rainscreen will be discussed in the context of the Henley project in terms of its performance factors and the design and construction process, and analysed with a view to drawing some conclusions for its future use.

A Large Span Timber Dome

The paper is about a dome that consists of 22 laminated timber arches, purlins and cladding. The structure was analyzed numerically and experimentally. Numerical analysis also dealt with geometric non-linearity. The stiffening effect of the cladding was examined by a model test. Before their erection the individual parts of the structure were subjected to load test. The finished structure incorporates instruments for monitoring the frequency of vibrations excited by the ambient factors.