Thermal Bridging and Issues with Windows

As a homeowner, heat loss is or should be a big concern. Energy escaping through the building envelope (walls, roof, floor) means more energy is required to maintain a consistent temperature or better said – comfort -within your home. It also means higher utility bills whether you’re building a new home or looking to refurbish an existing home. One of the most significant considerations should be how to make your home more comfortable but also more energy-efficient – less costly to operate. Which leads us to the topic of Thermal Bridging!

What is thermal bridging?

In a heating climate and similar to air infiltration, thermal bridging results in heat loss and occurs when heat escapes from the inside of the building to the outside, via conduction and through the building envelope. If you’ve ever been in a house that has a “drafty” spot or just constantly feels cold, that’s likely the result of thermal bridging as much as or even more than air infiltration. Even airtight homes can have a heat-losses of 20 to 50 percent due to thermal bridges.

Types of Thermal Bridges

There are several types of thermal bridges that designers, builders, and homeowners should be aware of and the following are three common types:

  • Repeating or Systematic thermal bridges: A common cause of heat loss are repeating thermal bridges which are predictably found inconsistent breaks in the thermal envelope allowing heat to pass through easily. It’s important to keep these in mind during a building’s design. Common Examples include wood and steel studs, steel wall ties, ceiling joists, and insulated suspended floor joists.
  • Non-repeating thermal bridges: This method of heat loss doesn’t follow a pattern in the way that repeating thermal bridges do. A non-repeating thermal bridge tends to pop up in specific areas impacted by an interruption or break in the construction. Common culprits include things that penetrate the thermal envelope to include windows and doors, structural beams, pipes and cables, and cantilevers.
  • Geometrical Thermal bridges: Generally found where the building envelope changes directions and where the materials meet, Geometric thermal bridge examples include wall corners, wall to roof and floor junctions.  The more complex a building design is, the more geometric thermal bridging will be prevalent.

Regardless of the source, avoiding thermal bridges wherever possible is essential – and knowing where your home is losing heat can help you take the proper measures needed to reduce the problem.

Thermal Bridging and Windows

Often, it is windows that are a major culprit when it comes to heat loss and thermal bridging in the home. Standard or code minimum windows often represent a compromise. “We” accept their lower thermal performance because we enjoy the view, natural light, and ventilation they provide. However, when adding high-performance windows with higher R-values (lower U-values), windows become less of a concern for thermal bridging, especially when properly installed.

In an existing home, an expert can determine the state of a home’s windows by doing an inspection. They know what to look for in terms of damage, deterioration, and condition. Knowing a window’s age is a big help as well. Most older windows did not have high-performance glazing nor did manufacturers generally consider thermal bridging in the frames and spacers.

With new construction or existing homes, to reach your energy and comfort goals, it is important to consider high-performance windows. The thermal image below shows the thermal bridging – shown in blue/purple. This is likely why you have seen condensation on windows.

This image below shows the thermal bridging – shown in blue/purple.
The magic of thermal imaging!

Note also high-performance windows help with other variables to include sound attenuation. They reduce the sound coming from the busy street in front of your house for example.

Thermal Bridging Results in Condensation – and Mold

Four variables come into play with condensation: outdoor temperature, indoor temperature, your home’s humidity level, and the indoor surface temperature of an exterior building envelope component. Since outdoor temperatures are not something we have control over, we focus on what is in our control. Windows that have well-insulated frames, multi-panes of gas-filled glass and have higher performance spacers will help increase the interior surface temperature of the windows. Higher interior surface temperatures help to effectively prevent the condensation of moisture on your windows preventing mold from growing. This subsequently improves your air quality. We would be remiss if we didn’t also mention the importance of ventilation systems which improves indoor air quality.

Check out this SIGA Fentrim F for preventing condensation

How To Prevent Window Thermal Bridging

  • Glass: Pursue options that included triple or even quad glazing.
  • Gas: Gas filled glazing is no joke. Argon gas is cost effective and provides a good boost in performance over air-filled units. Krypton gas, while more costly, provides an excellent increase to performance.
  • Frames: Select frames made of low conductive materials. Aluminum frames without thermal breaks are a complete no-no for energy efficiency and comfort. Aluminum is a tremendous conductor of heat. Better options are wood, fiberglass, and PVC with insulating air chambers. These frames are even better if they are insulated. Note, thermally broken aluminum is a good option depending on how good the thermal break is.
  • Spacers: Selecting windows with better spacers can help prevent thermal bridging in the windows as well. These spacers separate the panes of glass and appear where there are divided lights. Avoiding spacers made of aluminum and steel, and selecting stainless steel and various composite materials are much better options. Warm Edge, Super Spacer, and Swiss Spacer are some of the composite spacers that are available.
  • Installation: Proper window installation including air sealing and insulation around the windows will significantly reduce the amount of energy loss. To reduce thermal bridging around windows, Thermal Buck is a great product for the installation.

Final Thoughts

Bringing awareness of thermal bridging to all of your construction partners will aid in your goal. An architect can design to minimize thermal bridges. By not paying attention to the details on the construction site or if there is a lack of training, reaching your goals will be difficult.

If you’re looking for ways to minimize thermal bridges and select high-performance windows for your project, contact us today.

SIGA Majrex: A Skin Like the Cactus

What can we learn from the cactus related to building science? The cactus “skin” has essentially two perm ratings. The cactus absorbs vapor through its skin at night, and in the daytime when temperatures rise, that same skin prevents the moisture from escaping. The skin of the cactus allows moisture to migrate inward, but not outward.
SIGA has learned the answer to keeping walls dry by incorporating the unique characteristic of the skin of the cactus to collect and store water. In our buildings, we want the opposite to happen — prevent moisture from getting into our walls and allow it to migrate out. SIGA’s new product Majrex does just that.

While a cactus needs water to survive, our walls do not. In fact, moisture in our walls has the opposite impact — effectively “killing” our walls instead of nurturing them. So, the goal is the reverse of the cactus.
Humidity/moisture is higher inside our buildings due to such activities as cooking, showering and many other sources, even breathing. That moisture gets into our walls through a couple mechanisms, including air infiltration. With air infiltration, air and the moisture it carries travels from the interior of the building into the walls. That moisture within the air then condenses on cold surfaces in the interior of the walls — like a “sweaty” glass of ice water on a humid summer day. While it is best to keep the air out of our walls in the first place, some air will get in regardless carrying moisture with it.

At the point we have condensation in our walls, we absolutely need that moisture to dry or migrate out of the walls. Moisture in our walls causes mold, mildew and dry rot. In a typical home, if we were to add up all the cracks in the walls, corners and around the windows and doors, we have a hole equal to a 3-foot by 3-foot window open 24 hours every day of the year. Not only does this make us cold, but it also empties our pockets. Most importantly, it enables moisture to get into our walls with air as its transport mechanism.

SIGA patented its unique, one directional moisture transport and named it Hygrobrid technology. With this technology, SIGA developed Majrex, a “smart” interior membrane. Majrex has two different perm ratings. The perm rating from interior of the building to the interior of the walls is less than 0.097. In the other direction, from the interior of the wall to the interior of the building, the perm rating is greater than or equal to 4.25. Unlike other “smart” membranes that react to humidity and become more permeable to moisture, Majrex is essentially vapor open one way and nearly vapor closed the other. Combined with the SIGA Majvest air and weather barrier on the exterior with its 68-perm rating, we can effectively keep air and moisture out of our walls and effectively enable our walls to dry to the interior or to the exterior.

 

Majrex offers the benefits of:
1. Making our walls airtight so air and moisture cannot get in.
2. Making sure walls are vapor open, enabling moisture to migrate out of the walls.

Unfortunately, we often hear from building practitioners that walls need to breathe, and there is a very important distinction we would like to make. We do not want air going into our walls, because that very air is the culprit which brings moisture into our walls. We do not want them to “breathe.” Instead, we want them to be vapor open.

Simply put, Majrex is a directional membrane which allows moisture out of our walls and prevents it from coming in. Thanks to the cactus, SIGA has learned the secret to keeping our walls dry.

For more information or to order SIGA Majrex, call us at 720.287.4290

Source: sigacover.com