Environment in historic house

Christine Cross <ccross1 [at] execpc__com> writes

>I am currently working on the restoration of a 1930s home in
>Wisconsin, USA. We have recently upgraded the existing HVAC system.
>My question concerns RH levels. I had always been told that optimum
>RH in a historic house was 50% with a temperature between 65 and 70
>degrees Fahrenheit year round. The project architect feels this RH is
>too high and will infiltrate the plaster and begin to rot the wall
>studs. What should we do? Any suggestions for sources concerning
>this topic?

Your architect is correct. 50% RH in a 1930's house during a
Wisconsin winter will cause condensation within the walls (and
eventual mold problems and deterioration of the house) unless an
excellent vapor barrier was installed within the walls when the
house was recently restored. Although 50% RH has been a general
guideline for conservation of artifacts, this level is not safe for
older buildings in cold climates. At Shelburne Museum, we employ
several different methods of climate control to preserve our
historic buildings and the artifacts they contain. Briefly stated,
in the buildings that we heat, humidify, and dehumidify we maintain
50-60% RH at 72-76 degrees F in the summer and 35% RH at 55-60
degrees F in the winter. Temperature and humidity levels are
gradually reduced and increased with the seasons. There is quite a
bit of information on climate control for historic houses, much of
which is referenced in an annotated bibliography found at:
<URL:http://palimpsest/byauth/kerschner/ccbiblio.html> I will also
e-mail you copies of two articles on the work we have conducted at
Shelburne on climate control for historic houses over the past 12
years.

Richard L. Kerschner
Director of Preservation and Conservation
Shelburne Museum
PO Box 10, Route 7
Shelburne, VT  05482
802-985-3348 Ext 3361


                                  ***
                  Conservation DistList Instance 14:36
                Distributed: Wednesday, January 3, 2001
                       Message Id: cdl-14-36-005
                                  ***