Insulation and Outsulation

We enjoy building custom homes and never build the same house twice. At the beginning of a new project, we worth with our customers to set specific goals for that house and then find the best  building products that will help us meet those goals.

In the two houses we are currently building in Falls Church, we have installed Dow SiS panels on the exterior of the house in place of more standard materials like plywood or OSB (oriented strand board). This structural foam insulation board serves three purposes. The first is that it acts as our house sheathing. It takes the place of OSB and eliminates the house wrap. The second purpose is that it serves as a drainage plane. With the SiS panels installed, there is no need to install a house wrap to drain rain and moisture -- it is installed with the sheathing. The SiS board, when properly sealed, serves as both a structural panel and house wrap. The third reason to install this product is that it provides 'outsulation'. This insulates a thermal break on the outside of the structure of the house.

Even the best-insulated houses have what are called “thermal breaks” or “thermal bridging.” This is when heat energy (hot or cold) is directly channeled outside of the building envelop by a break, such as a 2x4 stud in an external wall. A 2x4 stud has an R value (a measure of thermal resistance used to assess the efficiency of insulation – the higher the number the better) of about 4.3, which means that in relation to the rest of the wall system (which is probably around R-15), it is the weak link. The thermal break is a large area that helps heating and cooling energy escape from your home. Think about how many wooden studs there are in one 8 foot wall -- probably 8 to a wall and 36 studs in a room.  Calculate the energy loss (and increased heating/cooling costs!) throughout the house because of the thermal breaks caused by all of those studs, and you can see how putting more insulation on the outside of a stud could be beneficial.

Insulation and outsulation are important, but they are only part of the energy equation. A house is a whole system. This system includes the HVAC, the windows, the thermal envelope and the breathability of a house. More on these topics to come……..