We designed a siding renovation project for the Brooklin School, a K-8 facility in Brooklin, Maine. The project was completed in the summer of 2016.
Built in the late 1990s, the Brooklin School is a stick-built single story building. The structure is composed of a steel frame with wood stud exterior walls and engineered wood roof trusses. The wood clapboard siding had been failing for a number of years, particularly at corners and near grade. The building envelope was typical of buildings built at that time and before: 1/2-inch plywood sheathing, a poorly installed fabric air barrier, and wood siding. Siding renovation projects such as this are an opportunity to install an air barrier and continuous exterior insulation.
We took the exterior down to the plywood sheathing. Rotted plywood, particularly at the base of the building, was removed and replaced. In this next photograph, one can see the fluid-applied air barrier installed over the existing plywood sheathing. The plywood joints have been taped, and the air barrier is obviously producing a seamless barrier from the sill plate to the soffit. The window nailing fins have been wrapped in the air barrier as well.
After the air barrier has sealed the building against air infiltration, we can increase the envelope's thermal efficiency even further by adding continuous rigid insulation outside the air barrier. On this project, we are using foil-faced polyisocyanurate, which has an R-value of about 7 per inch. The contractor has correctly sealed the seams on the insulation with foil tape. A fluid-applied air barrier in conjunction with exterior insulation allows vapor inside the wall cavity to migrate to the outside of the air barrier as a vapor. The vapor does not change to liquid until it is outside the air barrier, which is impermeable to liquid water. Condensed water will travel down the outside of the air barrier and exit the building envelope.
Fluid applied air barriers may seem overkill on low-rise light commercial and institutional projects. However, the quality control inherent in fluid applied air barriers alone makes them worth while. It is very easy to inspect the fluid applied air barrier and see that it has created a monolithic membrane. The cost premium over fabric air barriers is between one and three dollars per square foot. For an envelope renovation project that is coming in around $30 per square foot, this means we paid somewhere between three and ten percent more for the fluid applied air barrier. The premium has given us a theoretically better product based on ideal material properties, but it has also given us a product which is demonstrably less prone to installation troubles.
We are using Matthews Brothers triple-glazed windows- Clara Starrett with glazing class 5, factory-installed casing for single units. The fiber-cement lap siding is pre-finished, and fastened with 2-1/2-inch stainless steel nails. Additional trim, including the roof fascia and the skirt at the bottom of the wall, are vinyl.