10-year retention obligation? Don't risk illegible receipts due to improper storage. The guide to secure long-term archiving.
Despite the digital transformation, the paperless office is still an illusion for many Swiss SMEs and private individuals. Important contracts, deeds, tax documents and balance sheets exist in physical form and must remain so. While digital data ‘only’ requires backups, paper has completely different requirements. From a chemical point of view, it is a challenge. It does not tolerate any errors in ambient temperature, humidity or lighting.
The problem is exacerbated by the legal situation. According to the Swiss Code of Obligations (CO Art. 958f), business records and accounting documents must be kept for ten years. In the case of real estate documents or certain tax-related documents, this period is often as long as 20 years. Ten years is a long time for a material that consists of plant fibres and decomposes slowly but surely.
Most archives end up pragmatically where there is space: in the basement. But what may be good for wine is often death by instalments for files. Paper is hygroscopic. This means that it adapts its moisture content to the ambient air. When paper absorbs moisture, the fibres swell. This results in wavy paper, stuck pages and, in the worst case, mould growth.
In older buildings in particular, the humidity in the basement is often well above the recommended 45 to 55 percent for paper. As soon as the 60 percent mark is permanently exceeded, a microbiological process begins. So-called mildew stains form – yellow-brown discolouration caused by fungal spores that irreversibly damage the paper. Added to this is the ‘cellar smell’: paper absorbs odours extremely quickly. A contract that smells musty does not make a professional impression during an audit or sale.
For a long time, silverfish were considered the classic pests in bathrooms and basements. But archives now have a new, more dangerous enemy: the paperfish (Ctenolepisma longicaudata). Unlike silverfish, which love moisture, paperfish prefer drier conditions – exactly how we want to store our files.
The paperfish has spread rapidly in Europe in recent years. It feeds on cellulose and starch. This means that it eats paper, cardboard and the glue on book spines. The damage is often devastating, as the insects not only nibble at the surface, but eat their way through entire stacks of files, destroying the text in the process (‘hole eating’). Conventional corrugated cardboard moving boxes are no obstacle for these pests, but rather a welcome buffet and nesting place at the same time.
In addition to moisture and pests, the chemical composition of paper also threatens its durability. Many types of paper, especially inexpensive printer paper or older newspaper, contain wood and lignin. Under the influence of UV light (daylight or fluorescent tubes), the lignin oxidises. We all know the result: the paper yellows and becomes brittle.
Another problem is ‘acidity’. Paper decomposes over time when the pH value becomes acidic (acid corrosion). This is accelerated by incorrect storage, for example in simple cardboard boxes or wooden shelves, which themselves emit acidic vapours.
If you want to ensure that your documents are still legible and presentable after ten years, you should observe the following principles:
Climate control is a must: the storage room should have a constant temperature (ideally 14–18 °C) and a relative humidity of 45 to 55 per cent. Large fluctuations stress the material more than constant, slightly suboptimal values.
Avoid cardboard: Do not store important long-term files in banana box-sized moving boxes. Use acid-free archive boxes or, even better, sealable plastic boxes. These offer mechanical protection against silverfish and provide better protection against water damage (e.g. burst pipes in the basement) than cardboard.
Metal instead of wood: Metal shelves are more suitable for file storage than wooden shelves, as they do not emit harmful gases and do not provide a breeding ground for pests.
External storage: If your own basement is damp, you risk losing your business records. An external, professional storage facility (self-storage) is often the safest solution. Here, the climate and pest control are monitored, which guarantees the physical integrity of your files.
Paper seems patient, but it is not. If you want to comply with legal retention periods and preserve important documents for posterity, you cannot simply ‘forget’ files in the basement. Proper packaging and a controlled indoor climate are the life insurance for your documents.
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