Rendered rainscreen walls - cavity ventilation, ventilation drying and moisture-induced cladding deformation
type: CreativeWork
description: Over the past five years, moisture damages in external walls of wood frame structure and rendering on insulation as a cladding has been a widely debated subject which has received a lot of attention. In the light of this, the interest in an alternative construction method where rendering is applied on boards instead of insulation has increased. In this method, carrier boards are mounted on battens so that an air cavity is formed between the cladding and the backup wall structure. Provided that this cavity is open at the top and bottom, wind and thermal forces will create air circulation which means that moisture in the wall can be convectively removed. Under real conditions, ventilation rates in wall cavities are affected by many factors and there is a lack of knowledge regarding both its magnitude and significance for the drying process. Consequently, uncertainties arise during the analysis and moisture safety design of ventilated external walls. The main objective of this study was to increase knowledge of the significance of the cavity design for ventilation rates and convective moisture transport in a cavity behind rendering on a board. Special attention has been paid to the investigation of differences depending on two types of cladding support systems that are often used in practice – vertical wooden battens and perforated horizontal metal battens. Another objective of the study was to investigate how a cladding made up of rendering and boards is deformed on exposure to moisture changes. Understanding of the deformation behaviour is fundamental in assessing the risk of the occurrence of cracks and other defects that affect the appearance and durability of the rendered façade. In the theoretical part of the study, applicable equations for the modelling of air flow, heat balance and moisture balance in ventilated cavities were identified. The experimental part comprised an investigation of some important fluid mechanical parameters in a full scale setup in the l…
abstract: Over the past five years, moisture damages in external walls of wood frame structure and rendering on insulation as a cladding has been a widely debated subject which has received a lot of attention. In the light of this, the interest in an alternative construction method where rendering is applied on boards instead of insulation has increased. In this method, carrier boards are mounted on battens so that an air cavity is formed between the cladding and the backup wall structure. Provided that this cavity is open at the top and bottom, wind and thermal forces will create air circulation which means that moisture in the wall can be convectively removed. Under real conditions, ventilation rates in wall cavities are affected by many factors and there is a lack of knowledge regarding both its magnitude and significance for the drying process. Consequently, uncertainties arise during the analysis and moisture safety design of ventilated external walls. The main objective of this study was to increase knowledge of the significance of the cavity design for ventilation rates and convective moisture transport in a cavity behind rendering on a board. Special attention has been paid to the investigation of differences depending on two types of cladding support systems that are often used in practice – vertical wooden battens and perforated horizontal metal battens. Another objective of the study was to investigate how a cladding made up of rendering and boards is deformed on exposure to moisture changes. Understanding of the deformation behaviour is fundamental in assessing the risk of the occurrence of cracks and other defects that affect the appearance and durability of the rendered façade. In the theoretical part of the study, applicable equations for the modelling of air flow, heat balance and moisture balance in ventilated cavities were identified. The experimental part comprised an investigation of some important fluid mechanical parameters in a full scale setup in the l…
author: Falk, Jörgen
language: eng
keywords: Materials Engineering
date published: 2014
date modified: 2026-07-24T02:59:49Z
provider: University of Lund
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Building Materials, LTH, Lund University