Insulated modular storage without environmental controls

Paula Sagerman <redfish [at] together__net> writes

>The Brattleboro Historical Society (VT, USA) would like to use part
>of an old barn for storage of archival materials if there is a way
>to protect the materials from deterioration.  We have paper,
>textiles, furniture, etc.  In order to protect the building
>envelope, we are considering building a "box within a box" using
>insulated, sheet-rocked walls and ceiling.  However, there will not
>be any climate control. Are any materials safe in this situation?

I'm presently investigating an off-site storage area similar to your
own for a private client in Pennsylvania. Our barn has a small
amount of electric heating already in place. This keeps the
temperature just above freezing in winter, which is necessary
because there is also plumbing on-site. I'm happy to share with you
the findings of my investigation. I hope the information is useful
for your own.

The box within a box approach can be a sound one, provided that both
boxes are reasonably secure. Before addressing any environmental
challenges to your modular storage, you should first be satisfied
that the issues of pest control, fire and security are resolved for
the entire site. Inspect the barn that you are using from the
outside in. Look for defects in the roof and siding. Any evidence of
wet building material is cause for alarm. Inspect the perimeter for
signs of poor foundation drainage. If the outer shell is not capable
of shedding water, then you will have RH problems within the whole
building interior, regardless of what kind of box you build inside.

Most indoor environmental damage results from climate control
equipment, so you are probably better off most of the time  with a
temperature and RH not too different from the great outdoors. If you
watch the weather channel, you might notice that even when the
temperature is very low outdoors, the RH is usually somewhere
between 40% and 60% as it is even on the hottest days of summer and
this should be sufficient for storing fairly robust materials (no
ivory-inlaid card tables, for instance!). When we bring that air
indoors and cool it or heat it to our human comfort preferences,
that's when we see the sustained levels of extremely high or
extremely low RH that cause the most damage. There are exceptions
like when it's rainy or foggy or in a transition from a hot day to a
cool night. In these situations, the RH approaches 100%.

You likely will want to avoid freezing temperatures. There are also
periods of time where the air outdoors is saturated and condensation
will form on any surface cooler than the air around it. Bear in mind
that insulation slows down the transfer of heat, it doesn't stop it
entirely. Like a Thermos bottle, it keeps hot things hot and cold
things cold for a short while. Under the right conditions (that are
not rare!) your sheet-rock and insulation construction might create
a cold, humid micro-climate in the archive box that could
periodically soak the stored collection with condensation. This
situation would most likely arise during the spring and fall when
temperature and relative humidity fluctuate the most. Just a few
hours in such conditions can be far more devastating than successive
summers of air conditioning or repeated winters of un-humidified
heating.

The first, most important step you can take in this process is to
monitor your candidate area. If the site is remote and your visits
are infrequent, I would recommend a few inexpensive dataloggers like
the HOBOs sold by Onset. They're only about $100 for a Temperature
and RH logger that will give you the critical information you need
to know. Pay close attention to dew-point or absolute humidity
values because RH percentages on their own can be misleading. You
may even want to build a small, sheet-rock box about 1 cubic foot in
size insulated to the same R-value that you plan to use, place it in
the barn with a data logger in it right now (while the weather is
lousy) and see what happens over the next month! (This sounds like
fun!) You might also include some rodent and bug traps to see what
kind of creatures may want to make unauthorized visits to your
archive.

Considering the climate you have in Brattleboro, you will not be
able to enjoy premium environmental conditions without the help of
significant heating, humidification and dehumidification equipment.
A source of heat is I think, unavoidable. A small humidistatically
controlled heater can prevent the condensation events. I think this
method is used with some success at the Shelburne Museum. I believe
that with a reasonable amount of work, you can have moderate RH
conditions in your "box-within-a-box" about 90% of the year. Good
Luck,

Craig Oleszewski
Project Manager
Art Preservation Services



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                  Conservation DistList Instance 13:44
               Distributed: Wednesday, February 16, 2000
                       Message Id: cdl-13-44-007
                                  ***