Improving the Thermal Performance and Durability of Historic Masonry Buildings

Historic buildings are less energy efficient than modern structures due to the nature of their construction. Although envelope improvements can reduce operating energy, such retrofits can potentially accelerate the deterioration of the historic facade. Consequently, the challenge is to improve the energy performance while maintaining a durable facade.\nThis research proposes a retrofit approach for historic buildings that addresses both energy consumption and durability of the masonry facade. To improve energy performance, an 1879 historic solid masonry home was retrofitted using an innovative Nested Thermal Envelope Design (NTED). An envelope controlling heat, moisture and air movement was constructed around Core and Perimeter zones that were independently operated. Conditioning the entire house provided 36% space heating energy savings below the Ontario Building Code 2012, while turning off the heat to the Perimeter areas increased savings to 68%.\nTo address durability concerns arising from insulating the masonry walls, the use of a vented airspace installed between the masonry and the thermal insulation was explored. The vented airspace at the first field trial increased the drying potential of the historic masonry during the winter when the brick was most vulnerable to freeze-thaw damage. An estimated 1.1 kg/m2/a was removed at South and East walls. The second field trial showed drying between 4.3 kg/m2/a and 5.7 kg/m2/a at the South and 0.08 kg/m2/a wetting at the North. In situ moisture content levels of the brick varied between 10% - 15% while laboratory testing of similar brick revealed a saturated\nmoisture content of 29%. Both field trials showed that the vented airspace\ndrying potential was influenced by facade orientation and solar radiation levels.\nAn alternative way of constructing the airspace was then tested in the laboratory to explore the use of air permeable insulation in lieu of a clear airspace. Walls constructed with rock wool insulation and vent holes, but with no clear airspace, removed between 52% - 90% of moisture, depending on the insulation density and vent hole area. Walls featuring a clear airspace removed between 59% - 95% of moisture. These laboratory tests showed that enough air was able to move through the air permeable insulation thereby improving the drying potential of the walls.

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