Restoration of historic buildings is tricky business. Among other challenges, preservation concerns severely limit façade alterations.
Restoration often includes deep energy retrofits which generally increase the thermal resistance (R-value) of the envelope. For existing structures adding insulation to the exterior is generally preferred over the interior as adding insulation from the inside will reduce its floor area. But for historic structures this approach is self-defeating.
Vacuum insulation has been used widely in non-building applications like refrigerators, thermos containers, and thermal doors. Its use in building envelope insulation is fairly new and still in R&D. Vacuum Insulated Panels (VIPs) are composed of two stainless steel plates which sandwich a core of vacuum and fumed silica.
VIPs possess 5-10 times the R-value of conventional insulation. Hence the thickness of wall sections may be far less than conventional insulation, effectively increasing the floor area. The resulting space savings alone are estimated to be $152 per foot of wall assuming a value of $182 per square foot of space.
Moreover, it has also been proven that the VIPs can add to the structural strength of the wall which then reduces the material necessary for structural members.
VIPs however are not perfect. Their stainless steel edges conduct heat, thereby reducing efficiency–though this has been largely mitigated by replacing its straight edges with serpentine ones. Other problems arise out of the panels’ fragility, allowing gases to enter its core and potentially rendering them useless. Gases will ultimately penetrate the VIP which limits their lifespan to less than 40 years.
VIP installations remain elusive owing to their high cost and a lack of proven history. Researchers believe these issues will be eliminated with enhanced technology and that VIPs will play a far more significant role in the future.