High-Performance Windows & Air Infiltration

Generally speaking, windows are the weakest link in our building envelopes. When evaluating windows, often the insulative specifications (R-value / U-factor) are the primary focus. Just as important are the air infiltration rates. Code-built homes often lose 20 to 40% of the heat in the home through air infiltration. Windows and doors are a significant source of this heat loss. 

For windows and doors, air infiltration is defined as a volume of air (cubic feet per minute) divided by the window area (in square feet) when subjected to a 25mph wind (blowing perpendicular to the window) – Cubic feet per minute per square foot at 25mph windspeed.  As of 2017, window manufacturers were only required to report air infiltration numbers if the windows were to be labeled Energy Star. 

An Energy Star Compliant window allows air infiltration to be as high as 0.30 cfm/sq ft

Now some quick math for a 10sqft window:

0.30cfm/sqft x 10sqft = 3.0cfm total air infiltration allowed. 

To think about this another way: A basketball has a volume of 0.26 cubic feet. 

3.0cfm / .26 cubic feet = 11.5 basketballs per minute or 690 basketballs per hour from a single window. Imagine how much air this equals for a typical home of many windows. 

Now let’s compare an Advantage or Alpen High-Performance windows to an Energy Star compliant unit:

While we can’t prevent a basketball from being thrown through a window, let’s talk about how Advantage and Alpen prevent these air infiltration “basketballs”.

  1. Gaskets & Seals – While fixed units have the best infiltration rates, operable units must also be considered. Any sliding window uses a friction type gasket material to seal the window for air and weather. Over time this material can break down and will not perform as well as a compression seal. Consider awnings, casements, and tilt-turns which use compression seals rather than hung or sliders that use a friction type gasket. We always recommend against sliders and hungs and for fixed, casements, awnings, and tilt-turns. 
  2. Hardware – Consider the window hardware used to seal the windows. With a friction fit, there isn’t a practical way to better seal a window other than applying slight pressure or replacing the weatherstripping. With a compression style, minor hardware adjustments can be made to place more or less pressure on the seals, and while weatherstripping can be replaced, typically minor adjustments are all that is required to achieve an excellent air seal. 

High-Performance windows help create comfortable, quiet, high-performing homes conserving energy for future generations. We are burning through our fossil fuel resources rapidly and bad windows and doors are a primary source of wasted energy use.   If you have any questions about air infiltration or other aspects of high-performance windows, please call us at 720.287.4290 or send us an email. info@aebuildingsystems.com

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.

What Are Construction Thermal Bridges in Buildings?

Do you have a random “cold spot” in your dining room or perhaps in an area where a sweater is always needed, no matter how high the thermostat is set?  Thermal bridges may be at play.

If you don’t work in or around construction, you may have never heard the term “thermal bridging”–but you’ve likely felt its effects. In a nutshell, it’s the movement of heat across an object that is more conductive than the materials around it.

Thermal bridging not only causes a loss of heat within the space, it can also cause the warm air inside to cool down. As we approach the coldest season of the year, this means higher utility costs and potentially uncomfortable shifts in temperature inside your home or building.

Keep reading to find out exactly how thermal bridging works and what you can do to stop it:

What is thermal bridging?

When heat attempts to escape a room, it follows the path of least resistance. Likewise, the same process occurs during the summer, only in reverse, allowing heat to enter your otherwise cool building.

Thermal bridging happens when a more conductive material allows an easy pathway for heat flow–usually where there is a break in (or penetration of) the insulation. Some common locations include:

  • The junctions between the wall and the floor, roof, or doors and windows.
  • The junction between the building and the deck or patio
  • Penetrations in the building envelope to include pipes or cables
  • Wood, steel, or concrete envelope components such as foundations, studs, and joists
  • Recessed lighting
  • Window and door frames
  • Areas with gaps in insulation

Impacts and risks assumed due to thermal bridging

What does all of this mean for you? In addition to poor climate control, there are several other lesser-known (but still serious) effects caused by thermal bridging.

Thermal bridges can increase the risk of condensation on internal surfaces, and also cause condensation within the walls.  Both can lead to mold growth, which in turn can cause unpleasant odors, poor air quality, and most importantly long-term health problems. Additionally, unchecked condensation may eventually cause rot and structural damage.

Thermal Bridging in windows

Thermal bridging can have a significant effect on the energy efficiency of windows. The frames and spacers are the primary culprits.  Spacers are the, typically metal, “strip” that goes between and separates the glass on double and triple pane windows.  Different materials have different conductivity and impact the performance of the windows differently.  Condensation on a double pane window is generally due to the spacers.

With retrofit situations, knowing exactly how old a window is, as well as the component materials, can provide you with a general idea of its efficacy. Unfortunately, if your windows are rather dated or just poorly made, it is nearly impossible to add thermal breaks into an existing framing system.

Issues with roofs and foundations

By their very nature, roofs and foundations present a large number of challenges in terms of maintaining a thermal boundary. Drains, vents, and holes for pipes and wires (amongst other things) create unavoidable penetrations in the building envelope and insulation. Heat transfers from the building into the ground or from the building into the air are often inevitable, though they can be minimized.

Strategies and methods to reduce thermal bridges in buildings

Bottom line? In new construction, design it right which a whole topic in itself. With existing homes, if you suspect there is thermal bridging occurring in your space, you need to eliminate or reduce the effects as much as possible.

Proper planning, design, and construction can help remedy thermal bridges in new structures. However, if you live in an older home, there are still steps you could take. These strategies include:

  • Performing an energy audit to identify thermal bridges in your home
  • Installing double or triple pane windows with argon or krypton gas, better spacers and insulated frames
  • Updating and/or adding insulation to your home – ideally adding a continuous insulation layer.
  • Installing storm doors (especially if you have metal doors)
  • The ultimate remedy is to complete a deep energy retrofit that addresses everything and more than mentioned in this blog

Studies show that in an otherwise airtight and insulated home, thermal bridges can account for a heat loss of up to 30%. Whether you’re building a new home or retrofitting an existing structure, care should be taken to avoid unnecessary breaks or penetrations so that the possibility of thermal bridging decreases.

If you’re looking for ways to minimize thermal bridges in your next project or existing home, contact us today.

High-Performance Windows

If eyes are the windows of the soul, then windows are the eyes of the energy-efficient home.

Generally, windows are the weak link in the walls of a home. “I love putting plastic on my windows to keep cold air out and warm air in,” said no one ever. That is why considering the brand and style of the windows in a home is just as important as deciding insulation and exterior materials.

The goal is comfort and operational cost saving, and the goal for builders and architects is providing both.

High performance windows are necessary in keeping with Passive Haus standards of efficiency: design, minimal thermal bridging, air tight, super insulated, optimized glazing, energy recovery ventilation and passive gains.

So we have learned that code built homes often lose 20 to 40% of the heat in the home through air infiltration, and windows and doors are a significant source of this heat loss.

To better grasp just how significant, imagine the volume of a basketball as our measure of air infiltration. According to the National Fenestration Ratings Council (NFRC), the maximum allowable air infiltration in a window, with the outside wind at 25 mph, is 0.3 CFM (cubic feet of air)/sq. ft. Air infiltration for a 10 sq. ft. standard window at the allowable maximum is 3.0 CFM or 11.4 basketballs per minute. At sixty minutes, one window allows in 684 basketballs per hour.

If you have (30) 10 sq. ft. windows, that equals 342 basketballs per minute or 20,520 basketballs per hour. That is a substantial amount of heat loss.

How do we reduce the basketballs?

Consider installing Alpen or Advantage Woodwork High-Performance windows. With a high-performance window, air infiltration at a 25 mph wind is <= 0.01 – 0.05 CFM (cubic feet of air). A 10 sq. ft. high performance window is at 0.10 CFM or .38 basketballs per minute or 22.8 basketballs per hour.

Therefore, (30) 10 sq. ft. windows equals 11.4 basketballs per minute or 684 basketballs per hour. We just went from 20,520 to 684 basketballs per hour. To summarize, that’s approximately a 97% reduction of air infiltration from what the NFRC says is acceptable.

The bad news is loss of air through a structure’s windows is like opening the windows and tossing our hard-earned money out of them. The good news is high performance windows fixes that problem.

The overall quality and performance of windows like Alpen or Advantage High-Performance windows is also superior. What makes these windows even more unique are their individual components, designed to combat heat losses (winter) and gains (summer):

  1. Frames – High performance windows have durable, low conductivity frames which generally include insulation. These frames offer better thermal performance. The R-value of most standard frames is r-2 to r-3.5. High performance window frames are r-4 and up to r-7, 8, and 9.
  2. Seals – High performance windows generally have multiple seals, which promote not only weather tight but also air tight seals.
  3. Glazing – IGUs (insulating glass units). Glazing can have double, triple and even quad glass. High performance IGUs have special coatings that high performance window manufacturers leverage to optimize heat gain from the sun in colder months and reduce heat gain and over-heating in the warmer months.
  4. Spacers – Depending on the material used, the spacers in between the IGUs can help increase the interior surface temperature of a window up to 15 degrees. For example, a galvanized steel spacer in a fixed high profile Alpen 525 window is rated R-5.9, whereas a stainless-steel spacer in a fixed high profile Alpen 625 window is R-6.7. Also, high performance window spacers reduce condensation on the edge of the glass (which reduces opportunity for mold and rot) and increases the inside glass surface temperatures, therefore improving comfort.
  5. Gas – There is “gas between the glass,” as it is denser than air and a reliable barrier to heat loss. Argon or Krypton gases are often used. Argon is much less costly, but Krypton increases performance and is often used in Passive House projects.

While ROI (return on investment) is important, comfort and unnecessary energy use are the primary reasons people pursue high performance windows.

High-Performance Windows help create high performance homes which conserve energy for future generations.  We are “burning” through our energy resources (coal and oil) rapidly.  Why not own a comfortable, energy efficient home that is also super quiet and will likely last much longer than your neighbor’s home?   And … let’s conserve our resources for future generations.

Please do not hesitate to call us at 720.287.4290 to learn more.