Vapor Retarder 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.

Timber-framed exterior walls insulated with wood shavings: A field study in a nordic climate

Wood processing residues provide a possibility to produce thermal insulation material with low environmental impact. This paper deals with the hygrothermal performance of timber-framed exterior walls with wood shavings as insulation material. The presented study consisted of field measurements of five exterior wall structures with two different types of wood shavings insulation and three reference walls. The study was performed in cold Nordic climate, where hygrothermal conditions at outer parts of a wall structure are critical. Untreated wood shavings and wood shavings coated with pulverized clay were compared as insulation materials. Different wind barriers as well as a water vapour barrier and sheathing acting as vapour retarder were also used. Results indicated no suitable conditions for mould growth inside any wall. The thermal resistance of wind barriers as well as the clay-coating of wood shavings had positive effect on the hygrothermal performance of the test walls. Wood shavings proved to be suitable insulation materials for well-insulated structures from the hygrothermal point of view, when the overall design, construction and maintenance are carried out in a proper way.

Classification and simplified design rules concerning the moisture performance of capillary active insulation materials

Conventional interior insulation systems protect the wall from condensation in winter by the help of vapor barriers or vapor retarding insulation materials. However, these solutions also reduce the drying potential of the walls towards the inside. This can be a disadvantage if wetting from the outside due to rain or other influences takes place and the drying potential to the outside is not sufficient. In such cases, so called capillary active materials can be an alternative, because they provide additional drying potential to the inside in summer thanks to a rather low vapor diffusion resistance. In winter they work without vapor retarders because they can store and wick water away from the condensation plane back towards the interior by capillary action. In practice, there are currently many different materials under the label "capillary active" with a correspondingly wide range in terms of moisture storage, liquid transport and vapor diffusion resistance and it is difficult to decide, whether material is suitable for an application or not. There is still missing a common definition of the performance of such materials. While for most other materials already simplified design and application rules for the application as interior insulation are available, capillary active interior insulation materials still require an individual design, normally by the help of hygrothermal simulation. In order to simplify also their practice application, a classification of the moisture performance of capillary active interior insulation, considering the influencing parameters of relevance on the moisture level at the critical interface between wall and interior insulation was developed. On this basis, also a simplified verification process as well as design rules for the main practical application fields become possible, which allows designers to choose an appropriate system for the specific situation.

Hygrothermal performance of natural building materials: Simulations and field monitoring of a case study home made of wood fiber insulation and clay

This contribution presents temperature and relative humidity data monitored over nearly two years for a case study building made of natural building materials. The case study building is a single-family house located in Denmark made of wood fiber insulation, wood fiber boards and indoor clay plaster without any membranes. Three different types of cladding systems have been tested: 1) mineral plaster rendering; 2) wood cladding applied directly over wood fiberboards; 3) wood cladding with a ventilated cavity. Monitored data is provided and compared with simulations performed with a commercial hygrothermal software. The moisture content and mold growth index are calculated from monitored data. The data indicates that the hygrothermal performance of the roof is excellent (RH < 70%); the hygrothermal performance of the walls with the three different cladding systems is good; one out of two sensor groups in the floor exhibits a moisture content up to 18% at the cold side of the insulation during summer and fall. Securing sufficient and evenly distributed crawlspace ventilation is recommended for eliminating concerns of eventual mold growth. Measurements show that materials employed in this house respond quickly to moisture changes, more quickly that simulated data. This work highlights the need for validating and adjusting WUFI simulation results with measured data to provide reliable results for building envelopes composed of highly hygroscopic plant-based materials. For these assemblies in these conditions, including a vapor retarder is not needed for achieving a satisfactory hygrothermal behavior.

Hygrothermal performance of highly insulated external walls subjected to indoor air exfiltration

The study comprises three laboratory tests in which typical Finnish highly insulated (HI) walls were exposed to concentrated leakages of indoor air under steady outdoor temperatures of 1–5°C. Airflows with a relative humidity of 50% and at rates of 1–3 L/min were directed close to the wooden frames inside the walls. The thermal resistance ratios between the exterior sheathing(s) and the whole wall (Γ) were 20%–22% and 1%–10% for the HI and baseline (BL) walls. The HI walls that presented Γ values of at least 20% were observed to be resistant to air exfiltration, and their durability was not affected by the addition of a gypsum sheathing outside the wooden frame or a more permeable vapor retarder. This is related to the negative linear correlation that exists between the moisture accumulation rate in wood-based material and the dew point depression (DPD) value. The developed approach, called the DPD method, shows that a significant degree of moisture accumulation does not occur even for DPD values of as low as −2°C if the exterior sheathing is vapor permeable. The airflow does not penetrate into the rigid mineral wool sheathing, which helps to avoid interstitial condensation. Regardless of thermal transmittance, the HI and BL walls with maximum Γ values of 1% were exposed to a high relative humidity and even interstitial condensation because the DPD values were often below −2°C. For these walls, the mold index analysis and visual observations confirmed the local risk for mold growth on the opposite side of the leakage point. In practice, long-term mold growth may be limited if the seasonal periods during which the outdoor temperature is 1–5°C last for a maximum of about 1 month every year.

Performance of smart vapor retarders under hot and humid summer conditions

Today, there are many variations in water vapor control membranes including smart vapor retarders (SVRs), that function as vapor barriers but whose water vapor resistance drops when the ambient relative humidity becomes high. In the first half of this study, the change in water vapor resistance against ambient relative humidity in both directions was measured using the wet-cup method for the four types of two-layer SVRs consisting of hydrophobic and hydrophilic membranes and one type of vapor retarder. All the SVRs showed high water vapor resistance under an ambient relative humidity of 60% or less and low resistance above 75%. Additionally, a clear directional dependence of the water vapor resistance was observed for all SVRs. In the latter half of the study, two sets of small-scale field tests were conducted for six types of membranes, including polyethylene foil, under hot and humid summer weather conditions in Japan. The relative humidity dependence and water vapor diffusion direction dependence indicated by the cup method were validated and confirmed. In addition, the water vapor resistance in the ambient relative humidity range of 70–75% obtained by the cup method was strongly related to the retention of dryness of the specimens in the field tests.

농촌주택 및 목조주택 표준모델 구조체의 습·열 환경 성능 개선 방안

The purpose of this study was to investigate whether the standard models for rural housing and wooden housing model have performance for hygrothermal and to propose a way of improvement relevant to hygrothermal performance for those models. All of the models to be analyzed were found to have some parts that were absent of stability in terms of performance for hygrothermal. In the process of analyzing the causes and proposing improvement measures, the following conclusions were derived. Fist, The exterior surface of the structure should be composed of a structure with good moisture permeability, and for the interior surface, a variable vapor retarder paper should be applied in consideration of the reverse condensation phenomenon in summer. Second, in terms of performance for hygrothermal, applications of external insulation plaster finish to the exterior wall or of ventilation method using a rafter vent on the roof should be avoided. Third, a rain screen method with a ventilation layer should be applied to the exterior wall, and a method of constructing ventilation layer separated from the insulation layer with a vapor retarder paper should be applied to the roof. Fourth, the application of insulation materials having capillary action, such as wood fiber insulation board or cellulose insulation board, contributes to more stable performance for hygrothermal.

Interstitial hygrothermal analysis for retrofitting exterior concrete wall of modern heritage building in Korea

Retrofitting modern heritage buildings aims at not only energy conservation, but also restoration and preservation of an architectural artefact. However, if envelope construction is adjusted and HVAC systems are replaced, the temperature and humidity profiles and air-tightness can also be transitional, thus condensation could occur on the surface and/or inside the structure. It is continuously emphasized to assess retrofit measures’ expected transitions in the hygrothermal performance of envelope and their potential condensation problems, prior to actual retrofit. The present study measured the surface moisture content of the concrete structure and built environment of three modern heritage buildings in Seoul. These results were used as the initial conditions for the hygrothermal analysis of insulations and vapor retarder. One modern heritage school was chosen for retrofit, then mock-up test, ISO 13788 steady-state analysis, and dynamic simulations by WUFI were used to analyze the risk of interstitial condensation in the exterior wall, according to the initial moisture content of concrete wall and whether the vapor retarder had been installed. For modern heritage buildings with fully dry concrete walls, the mock-up test verified that the risk of interstitial condensation between the concrete and insulation is low, regardless of whether the vapor retarder had been installed. Per ISO 13788 steady-state analysis and WUFI transient simulation, if PF board was used as the internal insulation for concrete exterior wall, the chance of interstitial condensation was also low, regardless of the initial moisture content and the use of a vapor retarder.

Influences on the drying behavior of a concrete ceiling below a cold attic

The article describes the current state of a project examining the influences on the moisture distribution in cold attics above concrete ceilings of residential buildings. Considerable research has been done on moisture damages in cold attics, especially in Scandinavia and North America, focussing on spaces above wooden ceilings. The project (ongoing until Sept 2021) underlying the article deals with cold attics above concrete ceilings resting on masonry walls, a frequent variant in Austria. Research was triggered by a regional Austrian building industry association to shed light onto recent detrimental moisture accumulation in the wooden wall plate (= bearing for the rafters along the eaves) and in the two EPS insulation layers on top of the ceiling. Suspected reasons for the moisture problems and for the local moisture distribution are 1) a too small diffusion resistance of the vapour retarder covering the ceiling, 2) insufficient (natural) attic ventilation and 3) convection, e. g. in the gap between the polystyrene blocks. In order to rank these potential causes by influence and also to find a practical solution a two stage experimental approach was chosen: 1) A handy small scale replica (order of dimension: 1m) of the situation was exposed to the according indoor and outdoor climate in a climate chamber. Different vapour retarders on top of the ceiling were chosen. 2) A larger 1:1 replica has been erected as well but not yet delivered monitoring data. In parallel, a hygrothermic model taking convection into account was established and simulations carried out. The project will deliver a contribution to the Austrian standard on moisture safety 8110-2 on how to judge the moisture safety of joints via simulation.

Improving Energy Performance of Historic Buildings through Hygrothermal Assessment of the Envelope

The intervention on historic buildings through building energy retrofitting has become one of the current challenges of improving energy efficiency. Nonetheless, this building typology presents certain complexities. Among them, one of the most relevant is the protection on their façades due to the historical and/or artistic values of a given façade and, therefore, the addition of external thermal insulation is restricted. However, at the same time, in several of those buildings indoor surfaces do not present that architectural value, and then internal thermal insulation becomes a promising strategy for improving their thermal performance. Nevertheless, its application must be carefully evaluated to avoid possible pathologies caused by moisture problems. This paper aims to identify constructive solutions for interior insulation of walls free from moisture problems. For this purpose, a comprehensive analysis of a series of constructive solutions based on internal insulation has been carried out through hygrothermal simulations. The results show how the application of water-repellent impregnation becomes essential to guaranteeing the integrity of the envelope. In addition, the combination of insulations with or without inner membranes, such as smart vapor retarders or vapor diffusion barriers, has been evaluated detecting the solutions that best fit the objective. Finally, taking advantage of the great potential of 2D simulation tools, the post-processing of the data has been performed to apply the wood decay model, and thus assess the behavior of a very conflictive point in this type of intervention, i.e., the wooden beam-ends. The results in this critical point have shown how the application of the proposed constructive solutions becomes essential to guarantee the integrity of the element and how the application of traditional solutions could lead to a hazard that must be avoided.

Effect of forced convection on the hygrothermal performance of a wood frame wall with wood fibre insulation

Wood-based thermal insulation materials have interesting hygroscopic characteristics because of their high moisture capacity. The present paper investigates the moisture conditions in wood-frame walls with wood fibre thermal insulation. The effect of forced convection of moist air into the construction is studied in particular. Laboratory measurements were carried out on a full-scale wall model divided in five sections with various configurations. The wall sections had different combinations of exterior air barrier, thermal insulation and interior vapour retarder. Each section was prepared with an air leakage to simulate supply of moist air to the wall construction through forced convection. The measurement results provided insight in the moisture conditions in the wall and internal distribution of moisture in the wall sections. The results show that walls with wood fibre insulation may have the same risk of high moisture levels as walls with mineral wool insulation. However, the results indicate that wood fibre insulation absorbs condensation and melting water, while the mineral wool does not. Hence, the results imply that the wood fibre insulation has the benefit of distributing the moisture over a larger volume than the mineral wool insulation. Furthermore, the investigations indicate that using an exterior air barrier with high thermal resistance results in a generally lower moisture level in the wall construction, which can be considered favourable regarding risk of mould growth.

Water vapor transmission properties of acrylic organic coatings

In this work, we evaluate the water vapor transmission rate (WVTR), the permeability (P), solubility (S), and diffusion (D) coefficients of Paraloid B44, Paraloid B72, and Incralac coatings in the temperature range of 5–35°C. The Arrhenius function—diffusion activation energy and preexponential factor—has also been determined from the data: D_{B44} = 35.2;{text{cm}}^{2} ;{text{s}}^{ - 1} exp left( { - 25;{text{kJ mol}}^{ - 1} /{text{RT}}} right); D_{B72} = 9.5;{text{cm}}^{2} ;{text{s}}^{ - 1} exp left( { - 23;{text{kJ mol}}^{ - 1} /{text{RT}}} right); D_{text{Incralac}} = 622.8;{text{cm}}^{2} ;{text{s}}^{ - 1} { exp }left( { - 28;{text{kJ mol}}^{ - 1} /{text{RT}}} right). These resins are important coating materials, for example, for conservators to protect metallic artifacts, such as statues, against corrosion. Despite Paraloid B44 and B72 resins being considered as reference materials in conservation practice, that is, new coating materials (either water vapor retarders or transmitters) are often compared to them, there are no comprehensive data for the quantities describing the vapor permeability (P, S, D) of these materials. The measurements are based on the ISO cup-method using substrate/coating composite samples. The strength of this technique is that it can also be used when the coating is non-self-supporting; nevertheless, P, S, and D can be deduced for the coating layer itself, and it seems to be a standardizable procedure for comparative performance testing of coating materials. Paraloid B72 layers exhibited higher WVTRs—from 39 to 315 g m−2 day−1 as the temperature increased from 5 to 35°C—compared to Paraloid B44 and Incralac coatings—from 17 to 190 g m−2 day−1, respectively. The transmission rate parameters were also compared to the results of corrosion tests. Incralac was the most effective corrosion inhibitor, and the performance of the B44 was better than the B72, which is in good agreement with the transmission rate tests.

Hygrothermal Analysis of Masonry Wall with Reed Boards as Interior Insulation System

When the masonry walls of buildings under heritage protection need to be restored and thermally improved, the only option is to use an interior insulation system. This is also the riskiest method of insulating walls in cold climates. Capillary active interior insulation systems have been proven to be the most reliable, minimizing the risk of mold growth and decay caused by condensation. They have also been proven to be less risky in wind-driven rain. The building studied is situated in a heritage-conservation area in downtown Tartu, Estonia, and therefore cannot be insulated from the exterior. This paper compares the hygrothermal performance of four different interior insulation systems with and without a heating cable and vapor barrier. In the first case, Isover Vario KM Duplex UV was placed between reed panels. In the second case, reed panels were used without the vapor barrier. Data loggers were applied between the reed panels and the original wall and inside the room to measure temperature and relative humidity in one-hour intervals. Exterior temperature and relative humidity values were taken from the Estonian University of Life Sciences Institute of Technology weather service station. In addition to the measurements taken in the case study building, calculations were made using heat-air-moisture (HAM) Delphin software to simulate the situation. The use of a smart vapor retarder (Isover Vario KM Duplex UV) with reed panels in the interior insulation system reduced the relative humidity level inside the wall. The vapor retarder improved the drying-potential compared to the interior insulation system without the vapor barrier.

Fungal damages in Norwegian massive timber elements – a case study

ABSTRACT Massive timber elements are new in Norway, but their use is increasing. More knowledge is needed regarding the moisture performance of massive timber elements. There is uncertainty regarding the need for vapour barriers or retarders, and construction tents are rarely used despite the elements’ sensitivity to moisture. Twelve massive timber cases from the Mycoteam database, evenly distributed between the construction phase and use phase, have been studied. The types and causes of damage are compared, and remedial measures studied. Examination was challenging, and long electrodes in pre-drilled holes were found as a feasible method for moisture measurements. Drying took place from one week to several months, depending on wetting and drying conditions. The main cause of moisture intrusion was insufficient protection from precipitation, either during construction or due to constructional errors. Fungal growth was observed in all but three cases, while decay was found in six cases. High moisture content within elements did not cause fungal growth if the surfaces were dry. Decay in outdoor exposed elements was mainly caused by Gloeophyllum sepiarium, whereas Antrodia sp. was most common in elements not exposed outdoors. More research is needed regarding fungal damage in massive timber elements in combination with other materials.

Interior thermal insulation systems based on wood fiberboards: experimental analysis and computational assessment of hygrothermal and energy performance in the Central European climate

Two interior thermal insulation systems based on wood fiberboards are analyzed. The first system is composed of soft and hard fiberboards, the second one utilizes a capillary active fiberboard with incorporated water vapor retarder. The hygrothermal and energy performance of the systems in the climatic conditions of Central Europe is assessed using a combination of experimental and computational methods. A laboratory critical experiment is performed at first. The measured temperature and moisture profiles are then used for the validation of computational model of coupled heat and moisture transport, which is applied for hygrothermal and energy simulations. After the successful validation procedure, the model is used for the annual assessments. The energy assessment of the two-layer system shows excellent results from the point of view of energy savings (79 % improvement) but its hygrothermal assessment reveals possible shortages related to excessive hygric straining of the wall on the exterior side. The capillary active insulation system with water vapor retarder, which is able to keep moisture in the envelope within the hygroscopic range, exhibits only slightly worse energy performance (66 % improvement) but much better hygric performance than the two-layer system.

Prediction evaluating of moisture problems in light-weight wood structure: Perspectives on regional climates and building materials

Most of the construction techniques and materials used in Korean wooden houses are based on those used in North America and Europe. In order to prevent moisture problems in wooden houses, it is necessary to evaluate the hygrothermal behavior of the building envelope. In this study, the hygrothermal performance of light-weight wood structures was analyzed using the WUFI simulation program in 20 regions of Korea. As the results, since there is a clear distinction between summer and winter in Korea, the location of the vapor resistance materials should be considered, and the 2 × 6 structure was found to be the most stable for installing the vapor retarder and the weather-resistive barrier on the inside and outside of a wall. In addition, the water stability of the light-weight wood structure was affected by the hygrothermal climatic conditions in each region. The OSB surface is influenced by the amount of driving rain, but the vapor-retarder layer is more significantly affected by summer heavy rain. Therefore, consideration of the regional climate conditions, the hygrothermal properties of building materials, and the location of building materials are needed to ensure the water stability of the walls in the light-weight wood structures.

Generic algorithm to assess moisture susceptibility of simplified wall assemblies

A simplified wall assembly consisting of four material elements is considered. Optional vapor retarder and thermal resistances are located between the elements. A simplified numerical model is presented to perform probability-based risk analysis using the Monte Carlo method. The risk assessment of the wall assembly considers the interior and exterior climatic loads. The moisture transport mechanism accounted for in the analysis is diffusion. A prescribed rain load is assumed to be transferred directly to a chosen outer susceptible material element in the construction. A case study with a wooden wall structure is analyzed and the probability distribution of the time of wetness is presented for a case using 30 different climatic years, randomly varying indoor moisture excess, indoor temperature, and rain leakages. The results show that, in the case investigated in this paper, the simulations converged after 600 years. The proposed simplified model, combined with the use of Monte Carlo simulations, offers better opportunities for a systematic assessment of risk compared with the currently used simulation programs using only a design year.

Numerical analysis of hygrothermal properties and behavior of Korean based cross-laminated timber (CLT) wall system to deduce optimal assemblies

Cross Laminated Timber (CLT) is attracting worldwide attention, due to its durability, usability, and many other advantages. However, since CLT is made of timber, analysis of the hygrothermal performance is essential. In this study, the basic hygrothermal values are measured to obtain the exact hygrothermal performances. The values are put into the simulation with various assemblies which has hygroscopic effects. The effectors are the type of insulation, the presence of the vapor retarder, the climate condition and the type of standards. The final goal of this paper is to find the optimal CLT assemblies. The thermal conductivity, thermal transmittance coefficient, and water vapor resistance factor were measured. The thermal transmittance coefficient of the wall system was measured by using TCi and facing thermo-hygrostat, and applied in the simulation. The water vapor resistance was measured by conducting dry-cup test. In addition, the various conditions that affect the thermal moisture behavior were applied to the simulation for getting stable hygrothermal results. As a result, the standard of Passive house and Domestic wooden house, the climate condition, the presence of breathable water proofing paper, and the insulation alternatives of Expended Polystyrene (EPS) and Extruded Polystyrene (XPS) were applied. It was concluded that breathable waterproofing paper should be installed inside, and the applications of both XPS and EPS made no difference to moisture but the application of Mineral Wool was adversely affect to hygrothermal performance of the CLT wall system. The thickness of insulation should be designed according to the Passive house standard (0.15 W/m2K) rather than the Domestic (Korea) Wooden house standard (0.21 W/m2K).

Hygrothermal behaviour of timber frame walls finished with a brick veneer cladding

In this study, two typical timber frame walls with brick veneer cladding have been constructed at KU Leuven to investigate the hygrothermal response of these constructions in a moderate sea climate. Main topic of research is the contradictory criterion for the wind barrier when it comes to the risk on interstitial condensation for winter and summer conditions: in winter a vapour open wind barrier is appropriate, in summer a more vapour tight. Therefore, similar walls but with different types of wind barrier have been investigated. In one set-up a vapour open bituminous impregnated wood fibre board is used as wind barrier, whereas in the second set-up a more vapour tight wood fibre cement board is used. The study shows that a high relative humidity can be expected at the interface between insulation and wind barrier during winter conditions, leading to a high mould growth index. In contrast, the relative humidity at the interface between insulation and inner vapour retarder during summer is lower than expected. This can be caused by the buffering capacity of the hygroscopic materials in the wall.

Advanced modelling of vapor resistance of moisture dependent vapor retarder

Moisture dependent vapor retarders (smart vapor retarders) are widely used in building construction especially roofs in order to prevent moisture accumulation or to support drying out processes. The current modelling approaches mainly use only a relative humidity dependent vapor resistance. Recent studies have shown more complex behavior like direction depending flow or vapor pressure gradient depending flow. This paper shows a new procedure for including all these effects into physical model. Furthermore description of necessary measurements with evaluation of results and selection of a proper model with parameter adjustment will be shown based on three different example membranes. Finally the implementation of this model into a hygrothermal simulation code is described