Moisture management and monitoring in modern timber construction

Timber construction, deeply rooted in the history of construction, is experi­encing a renais­sance and is now more than ever in the focus of builders, archi­tects and executing companies. Its role in residential, commercial, indus­trial and educa­tional construction, but also in infra­structure, exemplified by the construction of wooden bridges, has expanded signi­fi­cantly over the years and is seen more than ever as an essential element of forward-looking construction. This develo­pment is driven by an incre­asing awareness of ecolo­gical sustaina­bility and resource efficiency. However, timber construction also faces specific challenges, in parti­cular the suscep­ti­bility of wood as a building material to moisture and moisture during the construction phase and the subse­quent use of the building. If moisture and moisture protection in modern timber construction fails unnoticed and long-lasting, there is a risk of massive damage that makes a mockery of all the desired sustaina­bility goals. Overall, there is a danger that the current enthu­siasm for building with wood will lead to incre­asing rejection of this construction method. A deep under­standing of the properties of wood as a material, careful planning and execution of construction projects and innovative monitoring techniques are therefore crucial to secure the desired sustaina­bility and use goals of buildings built in timber construction in the long term.

Histo­rical develo­pment of timber construction

Tradi­tional timber construction methods, such as those found in half-timbered houses or log houses, were often charac­te­rised by regional construction methods and available materials. These designs were simple, functional and adapted to local condi­tions and climatic condi­tions. The natural breat­ha­bility of the open wooden surfaces and the air permea­bility of the construction ensured a balanced moisture balance inside the buildings, and the steep compartment shapes, which usually overhang widely, ensured that rainwater was safely drained away from the building. Good prere­qui­sites for a long service life.

Change to modernity

In contrast, modern timber construction is charac­te­rized by a radical change in archi­tec­tural language and construction techniques. Modern cubic archi­tecture, with its clean lines and minimalist shapes, has also had a strong influence on timber construction. This develo­pment led to a move away from tradi­tional roof shapes towards flat roofs with thin, membrane-like seals and incre­asingly extensive insulation layers, which are incre­asingly used for roof gardens, terraces, photo­voltaic systems or rainwater retention. Today’s energy-optimised and airtight construction methods pose new challenges, especially for timber buildings. While this design contri­butes to improved energy efficiency, it also compli­cates the natural moisture transport processes and thus makes the structure more suscep­tible to moisture and moisture, regardless of the under­lying causes. Inacces­sible water­pro­ofing layers and water-bearing pipe systems in the construction make it difficult to syste­ma­ti­cally detect faults as a prere­quisite for prompt repairs, while at the same time the incre­asingly intensive use of roof surfaces for roof gardens, terraces, photo­vol­taics and rainwater retention leads to new damage risks for moisture protection, which, when they occur, often remain undetected for years and then often only be detected on the basis of the usually signi­fi­cantly conse­quential damage, which not infre­quently already endangers the stability. A blessing in disguise is at play when component failure triggered in this way is limited to pure material damage.

Increase in the size of buildings in modern timber construction – increase in risks due to moisture

Further risks due to moisture and moisture in modern timber construction arise from the incre­asing size of the buildings. With the advent of techno­logies that make it possible to construct larger and more complex struc­tures from wood, the dimen­sions of timber struc­tures have expanded considerably. This is expressed in large residential complexes, multi-storey office buildings and extensive educa­tional and cultural insti­tu­tions, which are built entirely in timber construction.

As a result of this develo­pment, even the construction of the building, at least in our rainy latitudes, can lead to a considerable effect of preci­pi­tation on the building that has not yet been protected from moisture or only tempo­r­arily. Hydrau­li­cally setting building materials and water-based paints and coatings, often also accidents and careless handling of water on the construction site, do the rest to generate high moisture loads in the building, without it being immediately visible where the wooden structure is moistening and damage to the wooden components begins.

These and other aspects, such as the usage behaviour after completion of the building, mean that the risk of moisture-induced damage to a wooden building has a long-term proba­bility of 100% compared to other risks such as fire or burglary, if only because materials such as water­pro­ofing and water-bearing piping systems in the building usually have a shorter lifespan, than the planned lifespan of the building itself and as a result of mecha­nical ageing over time. In addition, accidental occur­rences, both during construction and during use, can almost at any time cause water­pro­ofing or water-bearing systems in the building to lose their function and thus trigger extensive conse­quential damage to the building unnoticed.

Need for effective moisture management

In view of these risks, effective moisture management during the construction phase and during the use of wooden buildings is crucial to avoid capital damage and the resulting loss of resources. Such moisture management includes both preventive measures such as the protection of the wooden elements against moisture and moisture, but also a suitable monitoring concept for the early detection of occurring defects in conjunction with early, proactive damage repair.

The imple­men­tation of effective moisture management is therefore of funda­mental importance for damage-free construction with wood and a long-term damage-minimized use of timber struc­tures. It helps to ensure the sustaina­bility and safety of these impressive struc­tures and should always be on the agenda when projects in timber construction are planned respon­sibly and imple­mented with the claim of freedom from damage and sustaina­bility.

Modern monitoring solutions for moisture protection

Modern monitoring solutions in timber construction aim to detect primary damage as quickly as possible, i.e. if possible, in real time, regardless of where exactly moisture and moisture are spreading, and to observe the develo­pment of the damage over time. Advanced systems use a combi­nation of long-lasting, if inacces­sible, passive sensor technology, energy-optimized data acqui­sition and trans­mission systems together with databases and evaluation software, which usually work centrally on cloud servers, to determine in real time when and where damage has occurred in the building, to report this to the respon­sible autho­rities and to collect data for the obser­vation of the temporal and spatial develo­pment of the effect of moisture. Provide. In this way, real-time monitoring systems create exactly the infor­mation advantage that is needed to be able to carry out damage repair measures quickly and in a targeted manner before far-reaching conse­quential damage occurs.

If possible, flat-acting sensor technology arranged directly under sealing layers is preferable to linear or point-based sensor technology, as it usually enables the fastest and most reliable detection of faulty condi­tions without water having to spread over a wide area in the construction in order to be detected.

Planning and imple­men­tation of effective monitoring

The planning and imple­men­tation of an effective monitoring concept that is suitable for the respective property is a cross-sectional engineering task and requires extensive experience in various specialist areas such as building construction, building physics, materials science, measu­rement and control technology, building automation and software.

In view of the complexity of this task and in order to ensure a long-term, use-related function of the monitoring solution to be imple­mented, it is therefore advisable to involve an experi­enced specialist company in such projects in good time. These experts not only have the necessary technical knowledge, but also have practical experience in the imple­men­tation and long-term operation of such systems and thus make a signi­ficant contri­bution to the successful imple­men­tation of an optimal monitoring solution. It should be noted that the systems offered on the market differ funda­men­tally due to the under­lying physical operating principles, the response relia­bility and speed and the possible service lives and the resulting long-term functional relia­bility and efficiency. System selection and design should therefore always be carried out in compliance with the requi­re­ments placed on the system in terms of overall function­ality, perfor­mance and durability.

Monitoring in practice

An important area of appli­cation for monitoring systems is the metro­lo­gical leak monitoring of flat roofs used. The illus­tration shows a typical modern flat roof with extensive greenery and a warm roof structure under­neath of a three-field sports hall still under construction.

Even now, before the PV system is installed, the water-bearing water­pro­ofing is no longer visible. A conven­tional visual inspection with regard to leaks is therefore no longer possible, and even externally applied test proce­dures reach their physical limits due to the many built-in and installed parts of the roof. At the same time, new drainage concepts, e.g. with rainwater retention on the roof, lead to a sharp increase in the hydraulic gradients acting on the water­pro­ofing, not only in the short term as a result of heavy rainfall, but in the longer term due to the deliberate retention of rainwater compared to a freely weathered flat roof with a slope, which greatly accele­rates water ingress into the roof structure even in the event of small leaks.

Due to the thickness of the insulation material packages required today and in view of the dismantling and disposal costs required for the roof structure in the event of a damage-related renovation, but also the wear layers and systems on them, such roofs, which are still mostly erected without systems for early damage detection, pose a signi­ficant risk – a problem that is now a problem that is now a problem due to the now ubiquitous obligation to green and use photo­voltaic systems of roof surfaces takes on new dimen­sions.

In addition, moisture management on the construction site is often inade­quate, with the result that moisture-sensitive building materials are exposed to the weather unpro­tected for longer periods of time before they are installed.

The system used essen­tially consists of an electri­cally conductive contact layer that is arranged over the entire surface below the water-bearing water­pro­ofing and, via an associated sensor matrix and a connected measuring unit, conti­nuously measures the electrical potential distri­bution below the water­pro­ofing at short intervals, which results when a measuring voltage is applied to the wet outside of the water­pro­ofing. Since the surface seals used in the construction sector are usually electrical non-conductors, an electric current flow in the described structure is only possible from a purely physical point of view where there is a conductive connection between the wet outside and the contact layer below the water­pro­ofing — this is usually where the water­pro­ofing shows leaks.

In order to detect this, the measu­rement data is automa­ti­cally sent by the measuring unit via the Internet to a database server, stored there and evaluated with regard to the temporal course and spatial distri­bution in a kind of tomographic repre­sen­tation. If specified voltage values are exceeded and certain distri­bution patterns are detected, the system reports a leakage alarm and the leakage position is automa­ti­cally calcu­lated.

In contrast to other methods, e.g. point sensors on the vapour barrier, the system can detect water ingress into the roof structure very quickly and reliably and locate it with a high degree of accuracy. The practical suita­bility of the method is also supported by the fact that the successful sealing of leaks can also be observed directly in the measu­rement data, which is an invaluable support for search and repair work. Furthermore, the system can also display the spatial distri­bution of moisture in the roof structure and thus provides additional infor­mation about the hygro­thermal processes below the water­pro­ofing.

Physi­cally, the method is based on today’s standard control proce­dures for the conti­nuous long-term monitoring of seals at hazardous waste landfills, such as the BAM-approved geologger® seal control system.

Under the brand name smartex® mx, it has been successfully used for the real-time monitoring of flat roofs of various sizes, construction methods and uses for more than 25 years now. Due to its fast response and high positioning accuracy, it is the best available technology for monitoring flat roofs, especially in timber construction, where safe and fast detection and the most precise positioning possible are parti­cu­larly important.

A small monitoring solution for flat roof-like water­pro­ofing of balconies, canopies, dormers and for green flat roofs of prefa­bri­cated houses, which is based on the same physical principle as the smartex® mx system, has been offered by ProGeo since 2015 under the name smartex® is and has already been delivered and installed more than 4,500 times.