When you build a custom home to high-performance or passive home standards, one of the primary objectives is to lower the home’s heating and cooling costs. In traditional construction, heat loss through your walls, roof, and windows can drive up your heating bill. It might surprise you to learn that most heat loss is through the walls – about 35 percent! And, even though warm air rises, you’re losing ten percent more heat through your walls than out your roof. The opposite holds true when temperatures outside are hot. A standard home will absorb heat through the walls at higher rates, even though the sun is beating down on the roof. Why? Because the heat is transferring in from the outside through walls that aren’t properly insulated, and through a process called thermal bridging.
Technically, thermal bridging is the transfer of warm air from a warm environment to a cooler one. For high-performance building, as it applies to energy efficiency, thermal bridging is used in reference to the building envelope, including window and door inserts, where heat is conducted along solid elements. For example, in conventional home construction, a 2 x 6 wall has 2 x 6 studs acting as conductors of heat moving in or out depending on the time of year. Conductive materials and poorly insulated materials allow the transfer to happen more easily. Plus, more wall insulation does little to mitigate the loss or gain.
A particularly susceptible area to thermal bridging is the framing around windows. The more complex the framing, the higher likelihood thermal bridging can occur. In the winter months, combine this with the heat loss radiating through standard windows, and you can see your heating bill soar over 25 percent. In the summer, the combination of solar heat gain through a window by radiation, along with the potential of thermal bridging along the window frame by conduction can create the equivalent warmth of radiant heaters throughout your home. Combating these uncomfortably warm indoor temperatures with fans and air conditioning units will drive up your energy bill.
It may seem obvious, but when building an energy efficient home, avoiding thermal bridging is especially important. The inherent nature of energy efficient design includes a highly insulated and air-tight building envelope. If energy efficient techniques are utilized without a thermal bridge-free model, the thermal bridges end up having the opposite effect, negating the positive gains of high-performance home construction.
More seriously, thermal bridges in an airtight environment have the detrimental effect of trapping moisture in the form of condensation. Condensation can cause mold growth, affect indoor air quality, deteriorate insulation, and contribute to rot and structural damage.
By taking high-performance building to passive home standard, the building envelope becomes virtually thermal bridge-free. Advanced framing techniques, combined with the latest in building technologies like Structurally Insulated Panels (SIPS) and Moisture Barriers will keep your home operating at peak performance, and comfort. Homes remain cooler during summer months, and warmer during winter months.
Passive home design also eliminates thermal bridges at the windows but combining high-performance windows with assembly technologies designed with air-tightness at their core. Think of the windows in a passive home like those on a ship; you don’t want them leaking. Because windows and doors are big holes poked through a meticulously engineered and constructed wall assembly, they are the most likely points in the system for thermal bridges.
Fortunately, windows in a passive home won’t be tiny like a ship’s windows. Large, beautiful, triple-paned and high-performing windows are a signature aesthetic of modern home design. You’ll be able to embrace all that natural light for its passive solar benefit during the winter months without worrying about losing heat through the windows. In the summer, these high-performance windows use advance technologies to reduce solar radiation and reflect unwanted heat so you can enjoy the summer day without having to pull down all the blinds.
Combining the latest in building envelope technologies and techniques with the best in energy efficient windows are just two of the ways Clarum addresses thermal bridging to reduce seasonal energy use in the custom homes we build.
Interested in learning more about Clarum’s approach to extreme performance home envelopes? Give us a call at 650.322.7069 or check out our High-Performance Home Building Guide.