Relative humidity and paper storage

Hello, When storing paper in the print shop, should I be shooting for 35%-55% relative humidity? I have recently moved my shop and wanted to see if anyone can recommend an ideal relative humidity to aim for, particularly for storing papers.

My past locations have been uninsulated garages/shops. I have stored all of my paper inside the house where heat and humidity are under control for fear that temperature and humidity fluctuations would ruin paper stocks (stored in flat files).

The new shop is our garage, concrete slab, with insulation, drywall, and a heat source when necessary. Drywall and insulation are still going in, but humidity has fluctuated between 55 and 65% over the last few days. We are an hour north of Seattle in the pacific northwest.

I know real life applications can vary from ideal ranges, so I’m open to hear what is working for you.
Thank you!

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I try to stay in the 50% to below 60% range in summer, and let it go down naturally a little more in winter. However, it is probably more important to maintain a constant humidity than to maintain any specific humidity, within reason.

Paper will take on or give off moisture with humidity changes. When it does that, it expands with added humidity and contracts with reduced humidity. It expands and contracts quickest at the edges, and this is why it can wrinkle around the edges with humidity changes. A rule of thumb in commercial pressrooms is to let any incoming paper shipments acclimate for at least 24 hours (or longer) before using it.

Regarding your cement garage floor, I know from bitter experience that moisture will go through cement very easily and increase the humidity in your garage. I would recommend that if you can still seal the floor with a good sealer like epoxy, it is well worth it. The floor in my shop isn’t sealed, and last year, as well as the humidity problem, I had a severe summer mildew problem. This year I maintained the humidity between 50-60% with a dehumidifier and had no problem. (I live in southern Canada between Buffalo NY and Detroit, MI).

If you can get a copy of the book “What the Printer Should Know About Paper” originally by the Graphic Arts Technical Foundation, it is well worth it, for all kinds of important things to know about paper. The used book sites have it for less than what you can get a new copy for. Just Google it.

Hope this helps

The most important thing is maintaining the same humidity through storage, press runs and finishing. Any changes will result in curling, misfeeding and misregister.
If I recall correctly, the GATF book said air conditioning was invented to solve paper problems in early lithographic printing plants. It was normal then to take large press sheets and hang them by quires in a conditioning room in order to achieve consistent relative humidity through a press run, and to test a stack of paper a sword hygrometer was the tool needed.

A good dehumidifier will lower the humidity to whatever percent you set and keep it there. I have an Aprilaire whole house unit hooked into my central HVAC system. It works well. Aprilaire has smaller, free-standing units that are energy efficient. Check out Amazon or Sylvane in Ga where I bought mine. Long term, a cheap unit from a big box retailer will fail.

I am not running it for paper storage, bur rather to deal with mildew issues for a vacation home in the mtns,

But remember, a dehumidifier is really an air conditioner that will use a good bit of electricity if it runs a lot - don’t be shocked when you get your first power bill.


Of course in the US with continent wide weather variation,
it all depends where your paper is. But a cautionary tale for you from the UK, where the weather used to be vaguely stable, and 65% Rh was good for many months of the year.
Now the late greatly lamented Curwen Press, had made a
fundamental management mistake way back in buying
two TWO colour A1 presses. Rather than a 4 coloiur. Of course they fitted the room easily … But come a day when you had done a two colour pass by Friday night, and the second two didnt fit register on Monday morning. Oh Dear Get the platemaker to remake those two plates with a whisker of space added in the gutters and repeat indefinitely … how to ruin a business. No air con of course.
It was amazing to see an A1 sheet bigger by about a sixteenth of an inch over a week-end! This was decent stock too not rubbish. Sigh. Such a fine firm too. Pallets straight from the milll came with probs as well, rather than via the merchant trade.!