Ramblings: Insulation Tips

The excerpt below is from the 2014 Ramblings issue and features general rules for insulation. We are currently in the process of creating a resource guide focusing on issues prevalent to the island’s old houses, such as insulation. This guide will be available online for easy access. Stay tuned for more information.

ramblings photoInsulate the attic first. Heat rising through the attic and out the roof is a major source of heat loss and for many houses this step—along with window and door storms and weather-stripping—will be adequate for making your house comfortable and more energy efficient. If the attic space is not heated, insulating between the floor joists is typically the best solution. This will involve carefully taking up the floorboards and just as carefully reinstalling them.

Second, consider insulating from below—the basement and/or crawl space. Insulating these areas is complicated due to the possibility of trapping moisture, but proper installation of insulation can ensure a more comfortable living area and protection for the wood elements. In unfinished spaces without a furnace or heating source, insulation in the basement’s ceiling or first-level floor joists is possible. Vapor barriers should generally face upward to avoid trapping moisture in the insulation. In areas where there is a furnace or in a heated basement, ceiling insulation is usually not recommended. Adding a vapor barrier on the ground is also critical for crawl spaces and other areas where the ground is exposed beneath the house.

Don’t add wall insulation. It is surprising to most people, but insulating the exterior walls of a historic house on Nantucket is not recommended due to the high potential of trapping moisture in the wall and causing serious damage. In addition, there is a high cost for remediation when problems arise. Introducing insulation in wall cavities without a vapor barrier and adequate ventilation will lead to disaster—insulation will become saturated, lose its thermal properties and actually increase heat loss. Well-meaning property owners who add wall insulation also greatly increase the risk of doing more damage to their historic house and creating potential health risks. Trapping moisture in the cavity will advance rot and deterioration of wood elements that are not visible, such as sills, and can introduce mold. In addition, some blown-in installation has been known to damage building elements as it expands, including plaster keys that hold the historic plaster in place.
Wall insulation has been successfully installed during major renovations when vapor barriers and adequate air infiltration will be maintained or reintroduced. However, to preserve a building’s historic plaster, removal of the exterior shingles or clapboard is highly recommended to access the area and to repair any wood rot or damage. Damaging the interior plaster is not a preservation solution; plaster, unlike wallboard, “breathes” and with proper maintenance can survive for centuries—examples of this abound on Nantucket. Ensuring that an insulated wall area is well vented inside and out is critical, and in some cases dehumidifiers have been added to help ensure moisture is held in check. If wall insulation is still desired after knowing the risk and conducting an assessment, well-qualified professionals familiar with historic houses should be engaged to complete the work.

To read the complete 2014 issue of Ramblings click here.