Practically every building in the modern world is insulated, but many aren’t built to optimize their insulation due to thermal bridging. Thermal bridging is a phenomenon wherein gaps in building insulation allow heat loss and moisture to move from the outdoors to the indoors, creating uncomfortable indoor spaces and potentially damaging conditions within wall voids. Areas at highest risk of thermal bridging include connection points, like studs against exterior sheathing material, exterior walls joining floors, exterior walls meeting each other, or even openings that abut windows and doors.
The mechanics of thermal bridging
Thermal performance of any structure depends heavily on how well the building envelope is insulated -- everybody knows that. What fewer people realize is that there are multiple points along the outside of a building where heat transfer is likely to occur due to a change in thermal conductivity between different materials.
Take a wooden building with wooden wall-stud construction as an example. It’s a familiar enough structure, built from dimensional lumber, sheathed with a sheet material like plywood or oriented strand board (OSB), with pre-cut batt insulation installed in the gaps between the studs. It’s easy to assume the R-factor, or the insulation value, of that wall is the same as the insulation that’s installed on it, right?
Sadly, because in this situation, there’s no insulation between the wood studs and the exterior sheathing, there’s an approximately two-inch gap in insulation coverage every 16 to 24 inches, depending on the framing. Raw lumber naturally conducts heat more readily than batt insulation material, allowing more heat to move into and out of the structure through each stud. That lumber is acting as a thermal bridge.
The same applies to other types of structures, including those with steel studs and masonry wall materials. Without insulated sheathing to cover each of the insulation gaps, called a "thermal break," even the tightest building envelopes can experience massive heat loss at these thermal bridges.
Why eliminate thermal bridges?
It might seem like not such a big deal to leave thermal bridges where they are, especially if you’re planning on renting or selling a structure. After all, ignoring the problem can save you on building costs, and it could be years before anyone begins to notice an issue. Aside from damage to your reputation, eliminating thermal bridges (which can account for as much as a quarter of the wall in wood-stud-framed construction!) creates structures that last longer.
Heat loss is only one of many problems created by thermal bridging. Many structures also experience interstitial condensation, or moisture within wall voids. Internal condensation can cause serious longer-term damage to wall systems, as well as mold accumulation that can turn your building into a dangerous structure. This could create a liability situation for you, especially if you choose to rent that building to tenants.
Speaking of tenants, though, choosing to prevent or eliminate existing thermal bridges means decreased energy consumption, and, ultimately, happier tenants who realize the value your units bring to their families and businesses. There are even certifications for buildings that are highly energy efficient that may help attract a greener crowd.
How to eliminate thermal bridges
The easiest way to eliminate the thermal bridging effect is to install a layer of rigid foam or other continuous insulation thermal barrier on the outside of your structure. If you’re not building from the ground up, it may be a little trickier, but choosing insulated vinyl siding, for example, can create much the same effect. As long as the thermal envelope is unbroken and consistent, you’ll notice a marked improvement in energy efficiency. Adding an additional vapor barrier can further protect the building from condensation inside the exterior wall.
The Millionacres bottom line
Thermal efficiency may not be the hottest selling point for a structure, but the performance of the systems contained in a freestanding building or unit that’s devoid of thermal bridges can make a huge difference to how well it serves as an investment property. Keep in mind that tenants will often pay more for a more efficient unit that hasn’t developed odd smells from condensation inside the walls.
The things you might brush off can make a big difference to a choosy renter or buyer who has already seen several properties. A property with proper thermal efficiency, however, won't have any off-putting aromas and can lead to higher lease prices.
In addition, units that you intend to keep for the longer term will need less maintenance, and the building will age better overall with a very consistent thermal envelope. All structures age, but some will age much more noticeably and quickly -- these are generally the ones where important (and difficult to reach) areas like wall voids are considered during construction or remodeling.
** Also referenced all the provided articles on thermal bridging, as well as personal experience as a residential builder.