I can say that if any of the open reel tapes he has are acetate-based, being stored in sealed boxes, over time, acetic acid will be released from the resin base, releasing a vinegar smell that could eventually result in the tapes deteriorating, each becoming a glob mess. Acetate-based tapes must be able to “breath”; in other words, to be able to vent the vinegar odor. Any of his reel tapes, if any are polyester- or mylar-based, should fare OK over the long haul.
A friend who had a very large recordings collection (though that was nearly all LP records), had an off-site storage room in a dry, public climate-controlled rental facility. There, temperatures were able to be maintained with little to no concern about harm coming to the collection. As far as a garage subject to lack of control of extremes of temperature are concerned, I personally would have concern about storage of any audio media over a long period of time. I would recommend that he look into storage of his audio media in a public, climate-controlled rental facility such as that what I mention.
In terms of concern about potential for long-term damage because of extremes in temperature, I would rank them from greatest to least:
1) Acetate-based open reel tapes
3) Polyester-based and mylar-based open reel tapes
5) Shellac pressings
> On Oct 27, 2020, at 4:21 AM, Jon Samuels <[log in to unmask]> wrote:
> A friend of mine asked me a question I was unable to answer, so I thought
> I'd ask if anyone out there has any specific knowledge. He's storing
> shellac pressings, open reel tapes, CDRs and DATs in an unheated garage in
> the Northeast of the U. S. Temperatures in Winter can go below 0 degrees
> Fahrenheit, and are often in the single digits above 0. The materials are
> stored in heavy duty, sealed plastic boxes. Will any harm come to any of
> the materials by being stored in Winter in that environment? He
> currently has no other place to store this material. I'd like to give him
> some wise advice, if I can.
> Thanks in advance.
> Jon Samuels