Split Rock Lighthouse Humidity Control Building Assessment
Project Type: Building Assessment, Two Harbors, MN
Client: Minnesota Historical Society
LHB conducted an evaluation of the Split Rock Lighthouse exterior wall cavity and the results of temperature and humidity monitoring conducted using monitors located just inside the air circulation grills.
The existing exterior wall of the lighthouse consists of uninsulated brick with a ventilated interior cavity and a steel-reinforcing frame. The cavity ventilation system consists of interior perforated grills located at the base and mid points and exterior hooded openings at the top, just below the light. Environmental condition monitoring equipment is installed just inside the lower grills and measures the temperature and relative humidity of the air entering the cavity. LHB performed visual inspection of the cavity through the use of a boroscope.
A low cost solution would be to seasonally open and close the vent openings. Closing them in the summer with high air moisture content and opening them in the winter with low air moisture content. This solution would reduce annual moisture uptake and remove moisture from the wall system over time to equilibrium. This solution would not limit relative humidity to within the recommended range for conservation due to natural variation in humidity.
A moderately priced method for removing moisture is to provide multiple portable desiccant dehumidifiers, perhaps one per cavity at the base of the lighthouse during low use seasons to remove excess moisture from the summer ventilation and prevent relative humidity from entering the danger zone during winter.