Wall Base Ventilation Research Articles

Time Domain Reflectometry (TDR) technique – A solution to monitor moisture content in construction materials

Measuring moisture content in building materials is crucial for the correct diagnosis of buildings’ pathologies and for the efficiency evaluation of the treatment solution applied. There are several different techniques available to measure the moisture content in construction materials. However, perform long-term minor-destructive measurements is still a great challenge. The TDR – Time Domain Reflectometry – technique is commonly used for moisture content measurements in soils, but is considered a relatively new method with regard to its application in construction materials. In the present state of research, the current use of the TDR technique for monitoring moisture content in all types of consolidated porous building materials is not possible yet. Indeed, the empirical conversion functions proposed for soils are mostly not suitable for building materials. Furthermore, to successfully use the TDR technique, a good contact between the TDR probe and the material under study is required, which may be difficult to achieve in hard materials. In this paper, the TDR technique was implemented in two limestone walls constructed in the lab to test experimentally the efficiency of a wall-base ventilation channel to speed up drying after a flood. Each wall was equipped with four two-rod TDR probes for continuous monitoring the moisture content in both situations: with and without the ventilation channel. All the equipment used, procedures followed during the drilling until the probes’ final installation, as well as the individual calibration required for each probe are explained in detail. Instead of using unsuitable functions proposed for soils, the evaluation of the moisture content from the apparent relative dielectric permittivity measured was established using as reference method the gravimetric method. The results obtained suggest that the TDR technique is suitable for moisture content monitoring in consolidated porous building materials.

New technique for treating rising damp in historical buildings: Wall base ventilation

Abstract Intervene in historic constructions increasingly requires extensive and objective knowledge of what one will be working with. The multifaceted aspect of the works needed on this kind of constructions tends to encompass a growing number of different tasks, with the imperative need to know the causes of many of the problems that affect these buildings and the possible treatments that can solve them. Moisture transfer in walls of old buildings, which are in direct contact with the ground, leads to a migration of soluble salts responsible for many building pathologies. We know that many of the techniques currently used to reduce rising damp are not much effective, when dealing with walls of considerable thickness and heterogeneous materials, as is the normal case of historic constructions. Bearing this in mind, a new technique to treat rising damp in historic constructions has been developed and patented in Portugal. The technique consists of ventilating the base of walls through a natural ventilation process or by installing a hygroregulated mechanical ventilation device. The process of development and validation of this new technique will be presented as well as the most recent studies to improve it. A detailed presentation of the diagnosis, design and works made on a historic building in the north of Portugal, will be done. Some system limitations and some corrections that needed to be performed will also be presented.

Ventilation system for drying out buildings after a flood: Influence of the building material

ABSTRACTPortugal’s most striking buildings were usually built near waterways and on floodplains due to easier access to water supply. This proximity, besides causing an increased probability of pathologies due to rising damp also brings a higher exposure to the risk of flooding. After the occurrence of a flood, all building elements below the flood water level will remain with high water contents, with all the negative consequences that this fact can cause, namely, the degradation of the materials. Therefore, it is very important to promote the fast drying of these building elements to prevent worse consequences, either structural, safety, or heritage conservation. In a recent investigation undertaken under a collaboration project involving the University of Coimbra and University of Porto, an innovative treatment system to combat rising damp in historical buildings was developed: the wall-base ventilation system. Currently, investigations have focused on analyzing the technical feasibility of adapting this system for drying out walls of historical buildings after floods.

The Rising Damp in Cultural Heritage: From Physical and Numerical Analyse to Practical Application

The main goal of this work is to present a complete review of rising damp treatment in building heritage using a technique developed in our group to estimate and mitigate the height of the rising damp front and to predict the improvements of some experimental treatment techniques. The paper present a mathematical and a numerical analyse of the problem; an experimental and a practical application of the technique developed. This work is distributed into six main sections, in addition to this general Introduction: This book chapter is divided in several sections. Initially, it is presented the “state of the art” synthesis, where it is studied the techniques traditionally used for the rising damp treatment, showing the existing limitations on its application in monumental heritage and in old or ancient buildings, with specific characteristics. Then, it is performed the idea and the operating principle of the new technique, known as the wall base ventilation system, on the basis of previously conducted studies. An analytical, numerical and “in-field” study it is presented based in a case study described in detail. Finally, it is done a critical analysis of the results obtained, projecting the future work.

Treatment of rising damp in historic buildings: Experimental campaign of wall base ventilation and interface effect analysis

Abstract The treatment of rising damp in historical building walls is a very complex procedure. In this work it is presented an extension of the continuous “in situ” results of the rising damp treatment conducted in a Portuguese historical church, using the wall base ventilation technology. The results, registered over four years, clearly reveal the best ventilations periods and indicate that the best solutions must correspond to admit outside air during summer periods and inside air during winter periods. Furthermore, another important aspect was to better understand the difference in absorption behaviour between walls with and without joints when the rising damp treatment is conducted. It also presented an experimental campaign and a critical analysis of water absorption in samples of clay brick with and without joints and joints with different contact configurations (perfect contact, hydraulic continuity and air space between layers). The results showed that when the moisture reaches the interface, the wetting process gets slower due to the interfaces hygric resistance. This resistance was more pronounced for joints with air space between layers and less for joints with hydraulic continuity.

Project design abacus for wall base ventilation drying systems to control dampness

ABSTRACTDampness is an important degradation issue especially in old buildings and monumental heritage, particularly a rising one as the result of capillary movement of water in the lower sections of walls and other ground-supported structures by capillary action. There are several methods to treat this kind of dampness among which is the wall base hygro-regulated ventilation system an interesting solution for high thick walls with considerable heterogeneity.A significant number of studies have been undertaken around this method which have been implemented and validated in several heritage buildings. Such achievement has led to the adoption of the HUMIVENT patent system which aims to increase evaporation through peripheral channels on the base of the ventilated walls. A pre-sizing design program was also created and was called HUMIVENT PREDIM.This study aims to develop a set of auxiliary abacus for pre-sizing wall base ventilation systems. This approach aims to provide fast and expeditious systems sizing in the design and rehabilitation project offices. It allows an easy awareness in the several parameters that influence the wet front and the preliminary ventilation system design. It is a very useful tool for designers allowing them to obtain pre-sizing without extensive knowledge of the program and the associated parameters and with quick understanding of the drying process optimization. For better awareness of the abacus’ potentiality and use, an application example is provided thereof. It is concluded that the abacus can straightforwardly be used for sensitivity studies and for the selection of the best solution in each case.

Ventilation system for drying out buildings after a flood: Influence of the air change rate on the drying process

ABSTRACTIt is currently considered that climate change caused by the intensification of the greenhouse effect will worsen extreme weather events such as floods. Indeed, floods are extreme weather events that are at risk of occurring more often and with greater intensity in the coming decades.For historical reasons, particularly easier access to water supply, some of Portugal's most striking buildings were built near waterways and on floodplains and are therefore much more likely to suffer flooding. The occurrence of a flood can suddenly increase the moisture content in various building elements, which causes damage. It is very important that the moisture level of the walls is reduced as quickly as possible after a flood has occurred.This article presents the results of a numerical analysis undertaken in a collaborative project involving the Institute for Research and Technological Development in Construction Sciences (ITeCons) and the Civil Engineering Department of the Faculty of Science and Technology of Coimbra University. The main objective was to perform a numerical simulation to validate the efficiency of a wall-base ventilation system as a technique to improve the drying out of walls of historical buildings after a flood. In this article we present the results of the latest investigations that have been carried out on the influence of the air change rate in the ventilation channels on the drying process.

Implementation and Monitoring of Higroregulated Wall Base Ventilation Systems to Control Rising Damp

This work describes the implementation of two higroregulated wall base ventilation systems in a church in the North of Portugal for the treatment of rising damp and presents the results of four years of the systems monitoring. It is a work developed by LFC – Laboratory of Building Physics of FEUP, where the main goal is to validate and optimize this treatment technique. It was assessed the functioning and effectiveness of the implemented systems, minimizing the likelihood of condensation inside them and maximizing the drying process through the adoption of higroregulated systems. With the monitoring carried out it is possible to conclude that, for the analyzed climate, it is better to adopt a seasonal operation, where the air is admitted from the exterior, during the warm months, and in the cold months the air is admitted from the interior of the Church.

Wall-Base Ventilation System to Control Rising Damp: A Case Study of Vilar de Frades Historical Church in Portugal

Moisture transfer in the walls in direct contact with the ground leads to the migration of soluble salts, which are responsible for many building pathologies. The treatment of rising damp in historical heritage walls is a very complex procedure. The traditional techniques currently used to minimize rising damp are, in most cases, slight effective or too expensive, especially when dealing with walls of considerable thickness and/or heterogeneous materials such as the historical monuments. The main purpose of this work is to present the experimental results of the rising damp treatment conducted, over 3 years, in the Vilar de Frades Church, in northern Portugal, using the wall-base ventilation technology. The results showed that, for this particular climate conditions, the best solution is to operate seasonally, with outside air admitted to the system during summer months and inside air admitted to the system during winter months.

Rising Damp: Optimization of the Wall Base Ventilation System

Rising damp constitutes one of the main causes of monumental heritage and old buildings degradation, especially, its thick walls with heterogeneous composition. The LFC-FEUP has been developed important research in rising damp domain. In recent years, was validated and experimentally characterized the operation principle of a technique called "wall base ventilation system" for the treatment of rising damp in monumental heritage and ancient buildings consisting of circulating air at the base of the buildings walls with high thickness and heterogeneity in its constitution, with a saturation distant relative humidity. The studies previously developed allowed the interest and viability of the proposed system, taking time to develop a methodology for optimizes it. In this paper it is presented the optimization of the wall base ventilation system based on some important physical parameters. To optimize the system, it was developed a 2D evaporation model that describes the moisture transfer between the system and the wall as well as the water vapour transport throughout the system (Evaporation and Transport Model – ETM). It was also used and adapted another 2D model, to describe the rising damp phenomenon in buildings walls, considering the wall base ventilation system (Rising Damp and Evaporation Model – RDEM). Finally, the design model was developed, using both models(ETMandRDEM) and some experimental validation was done, which allowed the comparison between the levels archived by the wet front analytically and experimentally.

Wall base ventilation system to treat rising damp: The influence of the size of the channels

One of the major causes of pathologies in our historic buildings is the presence of moisture, particularly rising damp. Since these constructions tended to be built near water lines, to facilitate their supply, and because their walls are mainly made of high porosity materials, the presence of rising damp is constant. Although many historic buildings in Portugal have already been the targets of interventions to eliminate pathologies, the fact is that it has not been possible to do it properly. The treatment techniques available nowadays are quite diverse but all of them have low applicability to historic constructions. Research has been carried out, in this past years, at the Department of Civil Engineering of the University of Coimbra in collaboration with Department of Civil Engineering of the Faculty of Engineering of the University of Porto to try and solve this problem. An old but poorly studied technique has been investigated experimentally and numerically in the past few years: ventilation of the base of the walls. It was experimentally validated to limestone walls 20 cm thick. Numerical investigation has been carried out in order to analyze the influence of different parameters on its efficiency. In this paper we present the results of the latest investigations that have been carried out about the influence of the size of the ventilation channel on its efficiency.

Analysis and Monitoring of the Drying Process of a Hygro-Regulated Wall Base Ventilation System Implemented in a Historical Church to Control Rising Damp

Treating rising damp in the walls of historic buildings is a very complex procedure and the traditional techniques currently used to minimize rising damp are not effective or too expensive, in particular when dealing with walls of considerable thickness and heterogeneous materials. This work presents the results of an in situ application of the hygro-regulated wall base ventilation system to control rising damp in a historical church located in northern Portugal. The main purpose is to validate the wall base ventilation technology for treating rising damp in very thick and heterogeneous walls. The analytical model used well describes the observed features of rising damp in building walls, verified by in-field tests, which contributed to simple sizing of the hygro-regulated wall base ventilation system to be implemented in historical buildings.

Degradation Control of Walls with Rising Damp Problems

Degradation in walls of Historical Building with rising damp is a complex problem to solve, due to the thickness and heterogeneity of those walls. The traditionally treatment techniques used (such as watertight barriers, injection of hydrofuge products, etc.) show, sometimes, to be ineffective or too expensive, justifying the need to find a new approach. Experimental studies validate the effectiveness of a new treatment technique applied to the walls of old buildings wall base ventilation system. Building Physics Laboratory (LFC) is developing a model of this technique. The sizing of the treatment system is based on knowledge of the characteristics of the wall, of the geometry of the ventilation system and of the building being dealt with. In this work it is described the moisture transfer process between the moving air flux, inside the system, and the wall. Experimental results were used to validate the mathematical solution and the values obtained are very similar.

Rising damp in building walls: the wall base ventilation system

This work intends to validate a new system for treating rising damp in historic buildings walls. The results of laboratory experiments show that an efficient way of treating rising damp is by ventilating the wall base, using the HUMIVENT technique. The analytical model presented describes very well the observed features of rising damp in walls, verified by laboratory tests, who contributed for a simple sizing of the wall base ventilation system that will be implemented in historic buildings.

Characterization of a Hygro-Regulated Wall Base Ventilation System for Treatment of Rising Damp

The treatment of rising damp in the walls of historical buildings is very complex, due to the thickness and heterogeneity of the walls. The techniques traditionally used for dealing with this problem (such as watertight barriers, injection of hydrofuge products, etc.) have sometimes proved ineffective, and that is why it is necessary to find a new approach. In recent years, the Building Physics Laboratory at the Faculty of Engineering, University of Porto has been conducting experimental research on the effectiveness of the wall base ventilation system, using natural or mechanical higro-regulate systems to reduce the level of the damp area. This experimental research and the simulations that were performed, clearly show that wall base ventilation is a system with potential. This paper presents the characterization of the hygro-regulated systems operation based on experimental studies developed in laboratory, which allowed the influence of the velocity of the air, condensation risk and the possibility of salt crystallization.

A Wall Base Ventilation System Applied at Different Wall Geometries—Numerical Simulation of the Evaporative Process

This work describes the moisture transfer process between a moving air flux and a saturated cylindrical pillar, in alignment with the direction of flow. Numerical solution of the partial differential equation describing moisture conservation gave the concentration field near the saturated surface and the mass transfer flux was integrated to give values of the Sherwood number as a function of the relevant parameters. An expression is proposed that accurately describes the dependence found numerically between the value of the Sherwood number and the values of Peclet number and aspect ratio, L/d 1, of the cylindrical pillar in contact with a wall base ventilation system, the Humivent device. For large enough cylinder diameter, the problem degenerates into mass transfer from a planar surface and the same equation applies, with L/d 1 = 0. The importance of the equation was demonstrated through the application of a practical example, namely, in the drying process of a porous media.

The “Humivent” Device for Rising Damp Treatment

Humidity is one of the main causes of decay in buildings, particularly rising damp. The treatment of this phenomenon in historical buildings is very complex due to the thickness and heterogeneity of the walls. Moisture transfer in the walls of historical buildings is in direct contact with the ground leads to the migration of soluble salts, which are responsible for many building pathologies. Traditional methods of dealing with this problem (chemical or physical barriers, electro-osmosis, etc) have proved to be somewhat ineffective or are too expensive. In the recent years, experimental and in-field research into the effectiveness of wall base ventilation systems (natural or hygro-regulated-HUMIVENT device) to reduce the level of rising damp, conducted at the Building Physics Laboratory, Faculty of Engineering, University of Porto, has yielded interesting results. This paper presents recent patents and publications in the rising damp area and describes a new system called HUMIVENT for treating rising damp in historical buildings based upon a hygro-regulated wall base ventilation system. Finally, we analyse the results obtained in laboratory and the following implementation of the system in a church in Northern Portugal. It was a defined criteria to avoid condensation problems inside the system and crystallizations/dissolution problems at the walls.

Mathematical analysis of the evaporative process of a new technological treatment of rising damp in historic buildings

The treatment of rising damp in historic buildings walls is very complex, due to the thickness and heterogeneity of those walls. The traditionally techniques used to deal with this kind of problem (such as watertight barriers, injection of hydrofuge products, etc.) show, sometimes, to be ineffective, justifying the need to find a new approach. Experimental studies in the area of rising damp validate the effectiveness of a new treatment technique applied to the walls of old buildings. The results of the experiment show that the presence of a wall base ventilation system on both sides prevents the damp front from reaching Level 9 ( i. e., a height of 61.5 cm). This work describes the moisture transfer process between a moving air flux and a saturated wall, by both advection and diffusion. Numerical solution of the partial differential equation describing moisture conservation gave the concentration field near the saturated surface and the mass transfer flux was integrated to give values of the Sherwood number as a function of Peclet number. A mathematical expression is proposed (given as Eq. (21) in the paper) to describe accurately the numerical dependence between the value of the Sherwood number and the values of Peclet number.

Wall base ventilation system as a new technique to treat rising damp in existent buildings

In existent buildings, rising damp is particularly difficult to treat, due to the thickness and heterogeneity of the walls. Traditional methods of dealing with this problem (chemical or physical barriers, electro-osmosis and so on) have proved somewhat ineffective. In recent years, numerical and experimental research into the validation of a new technique: wall base ventilation system, to reduce the level of rising damp, conducted at the Building Physics Laboratory, Faculty of Engineering, University of Porto, has yielded interesting results. This article describes and analyses the results obtained following the implementation of hygro-regulable wall base ventilation systems in laboratory and in churches in Portugal. It was defined with criterions to avoid condensation problems inside the system and crystallizations/dissolutions problems at the walls.

Treatment of rising damp in historical buildings: wall base ventilation

Intervention in older buildings increasingly requires extensive and objective knowledge of what one will be working with. The multifaceted aspect of work carried out on buildings tends to encompass a growing number of specialities, with marked emphasis on learning the causes of many of the problems that affect these buildings and the possible treatments that can solve them. Moisture transfer in walls of old buildings, which are in direct contact with the ground, leads to a migration of soluble salts responsible for many building pathologies. We feel that many of the techniques currently used to minimise rising damp are not effective, in particular when dealing with walls of considerable thickness and heterogeneous materials. This paper will present the results of a project developed at the Building Physics Laboratory (LFC) at the Faculty of Engineering of Porto University. The project focussed on performing experiments to validate a new technology for treating rising damp in walls of historical buildings: wall base ventilation. We will also present some of the results obtained in the numerical simulations carried out [Torres MI, Freitas VP. Rising damp in historical buildings. Research in building physics—Proceedings of the Second International Conference on Building Physics, Leuven, Belgium; 2003. p. 369–75; Torres MIM. Rising damp in historical building walls. Ph.D. thesis, Coimbra, FCTUC, 2004 [in Portuguese].].