FPInnovations a effectué un essai en laboratoire afin d’étudier la teneur en humidité (TH) du bois lamellé-croisé (CLT) découlant du coulage de chapes de béton, et l’efficacité avec laquelle un enduit imperméabilisant et une membrane permettent de de prévenir cette humidification.
FPInnovations conducted a laboratory test to investigate the potential wetting of cross-laminated timber (CLT) from the pouring of concrete topping, and the effectiveness of a water repellent coating and membrane in preventing such wetting.
Cross-Laminated Timber (CLT) is an engineered mass timber product manufactured by laminating dimension lumber in layers with alternating orientation using structural adhesives. It is intended for use under dry service conditions and is commonly used to build floors, roofs, and walls. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail connectors), and even result in decay and loss of strength, construction moisture is an important consideration when building with CLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of CLT during building construction and identify appropriate actions to mitigate the risk.
Two of the major topics of interest to those designing taller and larger wood buildings are the susceptibility to differential movement and the likelihood of mass timber components drying too slowly after they become wet during construction. The Wood Innovation and Design Centre in Prince George, British Columbia provides a unique opportunity for non-destructive testing and monitoring to measure the ‘As Built’ performance of a relatively tall mass timber building. Field measurements also provide performance data to support regulatory and market acceptance of wood-based systems in tall and large buildings. This report covers vertical movement and roof moisture performance measured from this building for about three and a half years, with sensors installed during the construction.
The report first describes instrumentation. The locations selected for installing displacement sensors for measuring vertical movement comprised of the following: glued-laminated timber (glulam) columns together with cross-laminated timber (CLT) floors on three lower floors; a glulam column together with a parallel strand lumber (PSL) transfer beam on the first floor; and a CLT shear wall of the core structure on each floor from the second up to the top floor. Sensors were also installed to measure environmental conditions (temperature and relative humidity) in the immediate vicinity of the components being monitored. In addition, six locations in the timber roof were selected and instrumented for measuring moisture changes in the wood as well as the local environmental conditions. Most sensors went into operation in the middle of March 2014, after the roof sheathing was installed.
The monitoring showed that the wood inside the building reached an average moisture content (MC) of about 5% in the winter heating seasons and about 8% in the summer, from an initial MC of about 13% during the construction. Glulam columns were extremely stable dimensionally given the changes in MC and loading conditions. With a height of over 5 m and 6 m, the two glulam columns monitored on the first floor showed very small amounts of vertical movement, about 2 mm (0.04%) and 3 mm (0.05%), respectively, over a period of about three years and a half. Assuming the two monitored columns are representative of the other columns along the column line, the cumulative shortening of the six glulam columns along the height of the building would be about 12 mm (0.05%), not taking into account deformation at connection details or effects of reduced loads on upper floors. The CLT wall was found to be also dimensionally stable along the height of the building. The measurements showed that the entire CLT wall, from Floor 1 to Floor 6, would shorten about 19 mm (0.08%). The PSL transfer beam had a reduction of about 12 mm (1%) in the depth, i.e., along the building height. The CLT floor panels also showed considerable vertical movement of about 5 mm (3%) in the thickness direction. All the differential movement was expected and taken into consideration in the design and construction of the building.
In terms of the roof performance, two locations, both with a wet concrete layer poured above the plywood sheathing, showed wetness during the construction but continued to dry afterwards. The satisfactory drying performance can be attributed to the interior ventilation function designed for the roof assemblies by integrating strapping between the sheathing and the mass timber beams below.
Le bois lamellé-croisé (CLT) est un produit massif de bois d’ingénierie qui est fabriqué à partir de multiples pièces de bois de dimension assemblées en couches orthogonales avec des adhésifs structuraux. Ce produit est conçu pour des conditions de service sèches et est couramment utilisé pour construire des planchers, des toits et des murs. Comme l’humidification prolongée du bois peut causer des taches, de la moisissure, des variations dimensionnelles excessives (parfois suffisantes pour provoquer la défaillance des attaches), et même la pourriture et la perte de résistance, l’humidité est un facteur important dans la
construction avec le CLT. Le présent document a pour but de fournir de l’information technique pouvant aider les architectes, les ingénieurs et les constructeurs à évaluer les risques d’humidification du CLT pendant la construction de bâtiments et à prendre les mesures appropriées pour atténuer ces risques.
Implementation of cost-effective moisture management strategies is an important consideration for any mass timber project to reduce the risk of dimensional instability, discolouration, mold, and decay. On-site strategies can include protection by tenting, tarping, or wrapping mass timber components as well as the use of membranes, coatings, and water repellents. Moisture uptake from exposed end grain is a particular concern though it can be effectively managed by applying coatings or water repellents that reduce moisture uptake. This document aims to provide technical information to help architects, engineers, and builders use on-site moisture protection tools to reduce moisture risks.
Fifteen structural composite lumber (SCL) products including laminated-veneer lumber (LVL), laminated strand lumber (LSL), oriented strand lumber (OSL), and parallel strand lumber (PSL) provided by Boise Cascade, LP, West Fraser, and Weyerhaeuser were tested for moisture-related properties in this study, also covering four reference materials: 16-mm Oriented Strand Board (OSB), 19-mm Canadian Softwood Plywood (plywood), 38-mm Douglas-fir and lodgepole pine solid wood. Water absorption, vapour permeance, vapour sorption, and dimensional stability were measured with limited replication by following relevant standards for a purpose of assisting in improving building design and construction, such as hygrothermal modelling of building envelope assemblies, design for vertical differential movement, and on-site moisture management.
Pour tout projet de construction en bois massif, il est important de mettre en place des stratégies rentables de gestion de l’humidité afin de réduire le risque d’instabilité dimensionnelle, de décoloration, de moisissure ou de carie. Parmi les stratégies utilisées sur les chantiers, on compte l’emballage des composantes en bois massif ou l’utilisation de tentes ou de bâches de protection, de membranes, de revêtements ou encore de produits hydrofuges. L’absorption d’humidité imputable à l’exposition du bois de bout pose un problème particulier, mais il peut être géré efficacement par l’application de revêtements ou de produits hydrofuges qui diminuent l’absorption d’humidité. Le présent document présente de l’information technique pouvant aider les architectes, les ingénieurs et les constructeurs à utiliser des outils de protection contre l’humidité sur le chantier afin de réduire les risques associés à l’absorption d’humidité.
Practical solutions are needed for on-site moisture management of mass timber construction. Six groups of cross-laminated timber (CLT) specimens, together with reference specimens including plywood, OSB, and nail-laminated timber were assessed for their wetting and drying behaviour. The focus of this study was to assess the effectiveness of water repellents and membranes installed on CLT in preventing the wetting that can be caused by, for example, rain during outdoor exposure, installation of wet concrete topping, or sitting on a damp concrete slab. Seven water repellent products covering a range of formulations and three membranes including a self-adhered vapour-permeable membrane, a self-adhered vapour-impermeable membrane, and a lumber wrap were assessed as potential temporary moisture protection measures. Implications for moisture protection practices based on the test were summarized at the end of this report.