The basic requirement for a building without moisture problems and mould infestation is its construction in accordance with the applicable regulations (recognised rules of technology, building regulations of the Länder (German federal states), model building regulations of the Ger-man government). These in particular include the avoidance of thermal bridges and leaks in the building envelope, moisture barriers for com-ponents that come into contact with the soil, potential special structural protection measures in flood areas, and structural requirements for use (ventilation, ventilation systems, heating systems). It is recommended that the building envelope and water-carrying installations are inspect-ed for potential leaks prior to use.
Likewise, the heat protection of the outer envelope must be verified to avoid thermal bridges. Thus, a check of the insulation in the first winter using thermographic analysis of the indoor space can show where there may be thermo-technical weak spots.
During construction, it must be especially ensured that the existing trapped moisture is adequately dried and/or flashed out (see Section 4.1.1) and that no damp building materials are used (see Section 4.1.2).
If existing buildings are renovated, additional aspects must be taken into account (see Section 4.1.3). In addition, regular inspections of buildings also help prevent problems (see Section 4.1.4).
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4.1.1 Prevention of mould infestation caused by trapped moisture Building materials containing water as an essential component are built in or used in new and extensively refurbished buildings. For ex-ample, a solidly built detached house consisting of masonry walls, ce-ment plaster, basece-ment walls and concrete floors contains several thou-sand litres of water ‘incorporated’ into the structure. Drying processes and long-term intensive ventilation must be applied to transfer some of this water to the outdoors (see also Section 3.1.9). Final drying may take up to several years depending on the structure and building tech-nology used.
There has been a tendency over the years to shorten the building process and move occupants into buildings as quickly as possible in all seasons for economic reasons. In the past, care was taken to allow rough build-ings to dry over the winter months before commencing internal finish-ing work. Previously less water was used (brickwork and beamed ceil-ings instead of concrete) and buildceil-ings were less airtight. Air exchange was more efficient due to the frequent use of open fireplaces, thus drying generally proceeded more quickly. Today, however, drying-out houses is much more difficult and time-consuming due to wide-spread central heating and the building regulations requiring airtight designs.
Trapped moisture, which mainly occurs using monolithic construc-tion methods and poured screed (see Secconstruc-tion 4.1.1), must be prop-erly flashed out before the internal finishing work takes place.
It is inappropriate to place dividing walls and facing form works on still damp screed because moisture is absorbed by the materials and is difficult to remove.
Complete drying of the components can take up to several years (see Section 3.1.9.).
When constructing a building, care should be taken that the internal fin-ishing work only takes place when the building moisture has been suffi-ciently removed. A detailed ventilation and heating plan must be pre-pared for the construction phase, particularly when building takes place in the winter.
Special problems occur in connection with screed laying in buildings with drywalls, where (partially hidden) mould often grows on the plas-terboard. The introduction of internal plaster and floor screed after the installation of windows is a common cause of mould in new ings. If the moisture has not been sufficiently released from the build-ing material to the outside, mould can grow (see Figure 17). In addition
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to plasterboard panels, this often affects wooden components in the roof area. Specified ventilation must be applied during screed laying. Exces-sive ventilation may weaken the screed drying process while too feeble ventilation can lead to mould growth risk.
4.1.2 Avoid damp building materials
Building materials should be stored dry and installed in a dry condi-tion. Building practice shows, however, that building materials are of-ten stored outdoors unprotected (also in the rain) and installed while still wet.
Special care has to be taken on building construction. Materials delivered to the building site should be stored dry and installed in a dry condition. Unprotected storage and wet installation of insulation materials, dry construction elements and wood-based panel sare particularly problematic. Materials installed in a wet condition are difficult to dry off later and can lead to concealed mould infestation.
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4.1.3 Avoiding moisture and mould during refurbishment
If existing utility rooms are converted into living spaces or for a different purpose of use, it must be checked how, and to what extent this affects the building physics. A basement or extension room used as a storage room in an old building and built accordingly can cause significant prob-lems if the internal finishing work is restricted to installing wall cover-ings and new floor covercover-ings without checking and, if necessary, reduc-ing the permeability of the external walls and the underfloor membrane to moisture ingress. In addition, layered structures must also be checked from a building physics point of view. Rooms in old buildings compris-ing a concrete floor slab and masonry walls can easily tolerate the pen-etration of small amounts of moisture because the existing non-airtight doors and windows and wall openings enable sufficient air exchange.
However, if the originally uncoated or lime plaster coated brick walls are clad with dry components and the floor is covered with a floating screed and relatively impervious surfacing, the moisture penetration through the soil into the walls and underfloor cannot be released into the indoor air to the same extent as before. This can lead to damp accumulation and plasterboard walls: wall plaster or the insulation in the floor can be mi-crobially colonised.
When installing rooms or components such as stairs, it must be ensured that the building envelope is protected against water penetration (driv-ing rain, ground water pressure) or soil moisture. Gaps often occur in the building seal, in particular in the joints between old and new compo-nents, which can cause significant damage. The problem may become fatal when the seal cannot be easily improved after building an exten-sion, e.g. when a garage is attached to an existing building directly and the damp proof seal in contact with the earth is damaged. In this case, the site needing repair lies directly under the garage and is not accessible from the outside without demolishing the new building.
Specialist planners should be consulted when such conversion measures are undertaken to account for the complexity of building physics issues and the different structures.
4.1.4 Building inspection in everyday use
Technical products exposed to environmental conditions are usually in-spected regularly. This is mandatory for vehicles and commercial instal-lations. Regular inspection is also helpful in buildings to avoid problems cause by dampness and mould. In addition to structural inspections (see preliminary remark in Section 4.1), inspections play an important role in everyday use.
Pipes in houses should be checked regularly. However, this is technical-ly complicated and difficult with water pipes laid under the plaster. Rust particles in, or the corresponding discoloration of the water may be clear indications of the need to renew pipes.
Often, damage is caused by easily removed causes such as rain gutters clogged with foliage. If the gutter gets clogged (see Figure 18), water runs down the façade, it can penetrate the walls and cool outer parts of the building envelope. In winter, additional frost damage may be the result into which driving rain can later penetrate.
Silicone joints are ‘maintenance joints’ in wet areas and must be re-placed after a certain period of use as they will lose their sealing func-tion. Water from the shower can then easily penetrate into the wall be-hind the bathtub or shower tray through leaky silicone joints and cause substantial damage, mostly invisible, especially to permeable and wooden structures.
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TIPS for the prevention of water damage on and in buildings:· Regularly check gutters and façade.
· After a storm, have the roof inspected.
· Check whether old water pipes need to be replaced as part of a refurbishment.
· Pay attention to possible water leakage from heating systems (pressure drop, check water consumption).
· Pay attention to peeling and leakage of silicone seals in the bathroom area (shower, bath tub).
· Further information can be found in the “Instructions for use for houses” of the Aachener Institut für Bauschadensforschung1.