In the construction of new buildings and larger renovations, there is generally an increased risk of water damage and condensation, and thus the danger of microbial colonization on building components. Rainwater can penetrate due to the often only makeshift protection of the building (rainwater damage in the roof area and upper floors, water ingress from the construction site into basement rooms). Especially at winter construction sites, condensation caused by water from the installed concrete components and masonry, from freshly applied plasters, screeds over weeks can lead to relative humidity above 90%. As a consequence, mold infestation can occur, usually on the wooden beams of the roof structure and on mineral fiber insulation, plaster surfaces, and gypsum plasterboards. Problems often arise also from incorrect airtightness layers or damage to the vapor barrier foil by subsequent trades (cable penetrations, exhaust air ducts, connections of solar systems). In cases of heavy moisture exposure in the finished state, the insulation layers in the floor construction: polystyrene or organic fillings made of cereal husks or wood fibers can also mold very quickly due to draining water.
Through an adapted construction process, sufficient drying times, proper moisture management, intermediate cleanings without brooms and ventilation as well as quick and proper handling of water damage, microbial consequential damages can be minimized or avoided.
From the BGH ruling, high legal requirements for a "mold-free condition" can be derived for builders. With normal construction practice, this abstract legal claim can rarely be reconciled, since wooden components or other organic building materials can already show small mold or bacterial infestations upon delivery, and an absolutely mold-free building is only theoretically conceivable. The specifications of the Federal Environment Agency (mold guideline 2017, among others) mainly refer to hygienic impairments caused by mold damage and are therefore only partly applicable for the assessment of contractual claims and the acceptance of a defect-free building. The justified claims not to accept microbiological damages therefore require a thorough investigation for possible microbial damages, a clear delimitation of damage, and a reliable assessment. This is the basis for appropriate remediation solutions. The damage condition must be documented in detail, as well as the measures carried out and the findings of the technical follow-up inspection.
For remediation of mold problems during construction, developing and coordinating an approach jointly supported by the builders and the developer is often the right way. If there is agreement on the remediation approach, effective and sustainable measures can be implemented within a few weeks, resulting in a defect-free, hygienically safe building. Agreement on a timely remediation is usually better than years of legal disputes before regional courts with high costs for court experts and lawyers, additional loss of use/rental costs, and an uncertain outlook, as courts today decide very differently on the recognition of new building defects, even with clear findings.
We offer our 20 years of project experience for damage documentation, development of remediation solutions, and a mediating role between builders and developer.
Causes of Mold in New Buildings / During Renovations
Typical damages during the shell construction phase are heavy precipitation entries or water ingress from outside: Through storm events, periods of heavy rain, or defects in the building sealing or installation, thousands of liters of water can penetrate the shell during construction. In the case of adding stories to existing buildings, wetting and mold growth on plaster surfaces and wooden beams of the existing building can occur due to concreting on the top floor slab. Another possible damage scenario is rainwater entering through basement openings or at the foundation base and causing flooding in the basement.
Construction measures in existing buildings that already show microbial preliminary damage to roof trusses, ceilings, or basements have proven particularly mold-prone, since new or re-colonization happens faster there than on newly installed building materials.
Condensation damage often occurs in new buildings during the winter months, mostly shortly after the consecutive installation of wall plasters and screeds. If sufficient drying times between these construction activities are not observed, it is difficult to ventilate the thousands of liters of incorporated water out of the building without damage. With ongoing condensation or humidity levels over 90%, visible mold infestation on component surfaces can appear after about 5 - 7 days. In case of defects in the airtightness layer or incorrect execution, adjacent rafter fields can become wet. Particularly vulnerable to mold from condensation damage are gypsum plasters, gypsum plasterboards, Fermacell boards, wood fiber boards such as OSB and chipboards, lost formwork. But also less susceptible surfaces entangled with construction dust, such as the underside of concrete floor slabs, masonry, plastic window frames, and screed surfaces, can develop mold.
Once dark or colored colonies are visible signs of infestation, spore release and transport must also be expected. From this point, contamination of primarily unaffected areas can also occur. Therefore, sealing off the infested rooms and building parts is important, and uncontrolled drying of infested surfaces with warm air circulation should be avoided.
Only through quick and proper action can permanent defects in the building fabric and possible health hazards for users be prevented.
Health hazards from mold in new buildings
Depending on the damage process, moisture availability, and the colonized surfaces, a damage-typical infestation usually forms in new buildings. On surfaces with direct water impact (water damage / shell construction damage) on lightweight panels, wood, and organic fillings in the floor, typical water damage fungi such as Stachybotrys, Chaetomium, or Trichoderma dominate, which are generally considered more critical health-wise. In the areas affected by condensation damage, usually less demanding and less critical fungi such as Cladosporium, Penicillium, Aspergillus, or Alternaria develop. These fungi are considered less critical from a health perspective than the aforementioned water damage molds. Condensation molds should not be tolerated as infestation surfaces in new buildings, even if they sometimes occur in outdoor air.
Assessment of mold infestation in new buildings, regulations and guidelines by the Federal Environment Agency (UBA), etc.
Currently, there are no binding public guidelines (Federal Environment Agency, building legislation) regarding the usual microbiological condition of new buildings. The current UBA mold guideline 2017 and the subsequently published explanatory publications by the UBA evaluate mold infestation in the roof structure and in attics and basements not used for residential purposes as rather uncritical from a hygienic point of view, with low requirements for use category III (source: Mold guideline of the UBA 2017):
Nevertheless, significant primary infestation on component surfaces in the roof or cellar constitutes a legally remediable defect because it does not correspond to the usual delivery condition. Various craftsmen are responsible for the mold-freedom of their work as long as acceptance has not yet taken place. They must therefore also protect the components they installed from condensation and mold after the completion of their work.
Based on the BGH roof truss ruling, new buildings should be free of primary infestation and elevated spore deposits. Whether a proven health hazard results from increased indoor air or surface concentrations of mold spores and consequently a health risk is derived is initially secondary in the legal assessment.
An absolutely spore-free condition cannot be achieved under normal construction site conditions and can therefore hardly be demanded by the builder, as outdoor air also introduces typical mold spores such as Cladosporium, Alternaria and, to a lesser extent, Penicillium and Aspergillus, meaning these spores are incorporated.
Due to this legal gray area, qualified and reliable expert investigations and assessments assume particular importance. Through targeted sampling, selection of appropriate sampling and analysis methods, and correct classification of findings, it must be checked whether significant and thus remediable microbial damage exists in the object under investigation or only minor discolorations and spore contaminations that can be classified as inconspicuous usual condition. This assessment can determine whether a building becomes the subject of a legal dispute for 5 years or is completed and inhabitable after a short interruption for remediation.
After remediation, the usual background concentrations should not be exceeded, and no defects in terms of unremediated preliminary damage should remain that deviate from the normal, unremarkable delivery condition. Also, dried or disinfected infested areas with inactive, i.e., non-cultivable mold residues are associated with health risks for users according to earlier publications of the Federal Environment Agency:
"Moisture damage with mold growth can demonstrably lead to health problems. Therefore, the Federal Environment Agency (UBA) recommends proper remediation: This includes elimination of the causes that led to the moisture damage and thus to mold growth, cleaning of mold-infested materials where this is not possible, their removal, and final fine cleaning of the entire apartment to remove remaining mold spores." /15/
Currently, there is a largely uniform assessment in Germany regarding which mold spore concentrations are typically found in inconspicuous/uncontaminated new building materials. The strictest limit is in the most recent publication from the BLEI Institute 2014 /20/, which specifies concentrations below 1000 CFU mold spores/g as "no evidence of colonization/background." Other publications provide this limit as 5000 CFU mold spores/g (Laboratory Environmental Mycology/Trautmann) or 10,000 CFU mold spores/g (Federal Environment Agency, Laboratory URBANUS).
Based on the personal project experience of the undersigned over the past 15 years in new buildings, the usual background concentrations of undamaged polystyrene impact sound insulation also lie below 10,000 CFU mold spores/g for incubation.
Source: IGU Ingenieurbüro Gesundheit + Umwelt