How Calgary dryness and chinooks affect paper, tape and static in storage

What to take away

Calgary dryness and what it does to paper

Calgary sits in a semi-arid prairie. Indoor air in January can fall below 20 per cent relative humidity in a heated house, and a basement suite with a forced-air furnace can run drier than the outdoors. That is the condition your paper lives in for five months a year.

Paper is hygroscopic. It holds water in its fibre structure and exchanges that water with the air. When the air dries, the sheet gives up moisture, shrinks slightly, and stiffens. Newsprint, cheap office paper from the 1970s and 1980s, and anything printed on acidic stock goes first.

The Canadian Conservation Institute lists incorrect relative humidity as a primary agent of deterioration, because both too little and too much moisture drive chemical and physical damage. You can read its guidance on incorrect relative humidity for the mechanism.

What you see at home is not dramatic. A deed from 1955 feels crisp and slightly cockled. A folded letter cracks when you open it. Photographic emulsions curl at the edges. None of it looks urgent until a corner snaps off in your hand.

Temperature matters alongside moisture. Warm rooms speed the chemical reactions that yellow and embrittle paper, which is why the conservation literature treats incorrect temperature as its own agent rather than a footnote to humidity.

Cold and dry is not automatically safe, either. The combination of low moisture and low temperature makes some plastics and rubber components shed or crack, a problem that archive materials fail quietly tends to describe before you notice it on the shelf.

Chinooks, rapid humidity swings and adhesive failure

A chinook can lift Calgary temperatures by 15 degrees or more in a day. Indoor relative humidity moves with it, sometimes by 20 points inside a week. Paper can adapt to dry air. It copes badly with being yanked back and forth.

Each swing makes the sheet swell and shrink. Fibres fatigue. Cockling becomes permanent, and the paper stops lying flat. This is the part of southern Alberta archive storage that surprises people who moved here from a humid province.

Adhesive failure and tape are where the swings show up fastest. Pressure-sensitive tape, the kind on every roll in a kitchen drawer, has a rubber or acrylic adhesive layer that dries out and oxidizes. In a dry room it loses tack and lifts at the edges.

Then the chinook arrives. The paper expands, the tape does not expand at the same rate, and the bond shears. You find curled tape flags on the backs of photographs and along the folds of letters.

Worse is the tape that holds. After a decade it cross-links, turns yellow-brown, and sinks into the paper. Removing it takes solvent or a scalpel, and either one can take surface fibres with it. The carrier and adhesive also off-gas as they age.

Physical forces count as a deterioration agent in their own right during this kind of handling. The Canadian Conservation Institute sets out how physical forces cause damage when objects are pulled, peeled or flexed, which is exactly what tape removal involves.

The wider framework is worth knowing because it tells you what to watch. The CCI groups agents of deterioration into light, humidity, pests, pollutants and the rest, and a Calgary storage room usually has three of them working at once.

Static in southern Alberta homes and how to handle it

Static in dry homes is not a minor annoyance. Below about 30 per cent relative humidity, synthetic materials accumulate charge, and photographic film, sleeves and plastic negative pages are synthetic.

Charged sleeves attract dust, and dust on an emulsion is abrasive. Slide a print out of a charged polyethylene sleeve and you can pull surface particles with it. The same charge lifts toner from laser-printed pages and photocopies.

You feel it as a snap when you touch a metal shelf. The fix is not a humidifier in every room. It is grounding yourself before handling, and choosing enclosure materials that do not build charge.

Touch a grounded metal object, a tap or a file cabinet, before you open a box. Work on a bare table rather than carpet. Avoid pulling sleeves apart quickly; peel them slowly so charge has time to dissipate.

For enclosures, paper and board hold less static than clear plastic. Polyester and polyethylene sleeves are useful for frequent handling but attract dust in a dry room. Materials described as acid-free, buffered, inert behave better over decades than general office supplies.

If you are unsure whether a cupboard is too dry or too damp, watch for the humidity signs that show up before damage does: curling edges, lifting tape, and a faint crackle when a page is turned.

Humidity targets for a dry-winter archive

Conservation guidance generally settles on a moderate band for mixed paper collections: roughly 35 to 50 per cent relative humidity, held steady, with temperature in the range of 18 to 21 degrees Celsius. Stability matters more than hitting a precise figure.

A Calgary house in February may sit near 15 to 20 per cent. That is far below the band, and a single portable humidifier in a closed room is the practical way to close the gap without humidifying the whole house.

Do not overshoot. Pushing a cold basement room to 60 per cent invites mould on the walls and on the boxes. The goal is a middle setting you can hold all winter, not a number you hit once.

Whole-home measures help indirectly. Air sealing and better insulation change how much dry outdoor air the furnace pulls in, and NRCan's home energy efficiency guidance covers the upgrades that affect indoor moisture.

Measure before you buy equipment. A cheap hygrometer left on the shelf for a week tells you more than a single afternoon reading. For a home archive, start with the archive mistakes comparison of measuring tools, then add a thermometer-hygrometer pair and a log.

Record the reading weekly through the winter. If the room swings more than ten points in a week, treat that as the problem to solve, not the absolute number.

Handling changes for brittle paper and tape

Brittle paper handling is a set of habits, not a technique you learn once. Support the sheet from underneath. Never lift a page by one corner, and never let it hang from your fingers.

Work flat. A hard table with a sheet of clean blotting paper underneath gives the page full support. If you must move it, slide a stiff card under the sheet first and carry both together.

Stop at the fold. If a letter will not open without resistance, do not force it. Place it in a sleeve and let a conservator humidify and flatten it later, which is far cheaper than repairing a torn leaf.

For tape, resist the urge to pull. Old tape that has dried can often be lifted with gentle local warmth from a hair dryer on low, but the adhesive residue stays. That residue is the part that stains.

When you must store something taped, interleave it with acid-free paper so the adhesive does not transfer to neighbouring pages. Sheets in contact with deteriorating tape are the ones that develop brown mirror-image stains.

Steps for a taped or brittle item you need to keep:

The comparison between flat storage and other arrangements is worth reading before you commit shelf space. Document storage choices affect how much handling a fragile item receives over its life.

A Calgary dry-season storage checklist

Run this in October, before the furnace starts running hard, and again in March when the chinooks are frequent.

Two habits carry most of the benefit. Keep the room steady, and handle less. Every time you open a box in a dry Calgary winter, the contents lose a little moisture and gain a little dust.

Common questions