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 Walls and SIPs

When building an energy efficient home, High Performance wall assemblies are critical components, and can be grouped into a couple of categories: 1. Built on-site advanced wall assemblies and 2. Prefabricated walls, to include SIPs.

Note that this blog post is largely dedicated to Polyurethane SIPs.  

ICFs, Insulated Concrete Forms, are a good option and are manufactured by several companies. Faswall and Nexcem have an interesting woodchip product. There are pros and cons for ICFs, and it is important to understand both.

Advanced Wall Assemblies

The goal is to improve the wall construction of conventional, stick built homes with advanced wall assemblies to include double stud, stagger stud or continuous insulation walls.

Double stud walls consist of two stud-framed walls set up next to each other to form an extra thick thermally broken wall cavity that can be filled with insulation. Because the interior and exterior framing are separated by insulation, thermal bridging is reduced or, ideally, eliminated.

Stagger stud walls use top and bottom plates that are normally 2×6 (5.5”) – 2×12 (11.25″).  Vertical 2 x 4 studs are then staggered alternately on each side of the plates. This is a good option for extra insulation, reduced thermal bridging and sound-proofing of spaces as well.

Another option is standard construction with a Continuous Insulation (CI) layer. In CI, builders add a continuous layer of insulation across the exterior of all structural members to reduce or eliminate thermal bridges, except for fasteners and service openings. Insulation is installed generally on the exterior of the building and is an integral part of the building envelope. Comfortboard 80 is an excellent vapor open product that can be used for a CI approach. Mineral Wool is generally favored, as foam tends to have low perm ratings and generally the desire is for our walls to dry to the outside.  Often folks using a CI approach do not use enough insulation to move the dew point outside of the wall assembly.  It is critical to have a vapor open approach if the dew point falls within the stud cavity.

Prefabricated Walls

Prefabricated walls are built in a factory, transported to the building site and craned into place. Manufacturers of these types of walls include:

Phoenix Haus, which designs and produces open sourced housing templates for walls that save energy, provide better insulation and allow homes to be more efficient with or without solar energy.

Build SMART simplifies the process of building a high-performance, energy-efficient structure with factory-manufactured modular components. Continuously insulated panels come with pre-installed, energy-efficient windows and doors and are delivered to the building site.

SIPs – Structural Insulated Panels. There are several types of SIPs out there. Generally, the difference between SIPs is the insulation.  Most are made with OSB (oriented strand board) skins, but some SIPs have different skins to include metal or MgO (Magnesium Oxide) skins. Most often, the insulation is EPS or Polyurethane.  However, there are some that are made with mineral wool, PolyIso (Polyisocyanurate) or XPS (extruded polystyrene).

Some SIPs are not considered structural (e.g. most metal SIPs), and they might be referred to as Sandwich Insulated Panels.

SIP panels made of EPS, XPS or PolyIso are glued together generally with Polyurethane adhesive. SIPs made with Polyurethane foam are adhered together with the foam itself creating a tremendous bond and a very strong wall panel solution.

Thermocore SIPS are made with polyurethane insulation core with interior and exterior skins of OSB. Panels are precisely and custom manufactured to the architectural drawings. Included in the SIPs are door and window bucks, headers, sub facia and electrical conduit boxes. Also, beam pockets and additional structure like 2x, LVL or steel posts can be built into the panels.

Construction with Thermocore SIPs is quicker than framed homes. The time from foundation to dried-in is significantly reduced. Labor costs are lower, which is ideal in places where available labor is scarce, costly, unreliable or poor quality. Thermocore SIPs are stronger than framed walls, with lower thermal bridging.

Thermocore SIPS often have higher material cost, the electrical requires pre-planning and can be considered less environmentally friendly due to foam, which is a petrochemical product.

The thermal performance values of SIPs and lower labor costs often make up for the initial cost and planning. SIPs help to achieve a more air tight building as well. In the Passive House and Zero Energy industry, where energy efficiency, comfort and clean air are the goals, Thermocore SIPs are an optional building solution.

For more information on SIPS, call us at 720-287-4290.

Sources: U.S. Department of Energy, Greenbuildingadvisor.com, Thermocore.com

What is Passive House?

Passive House or PassivHaus – The Comfort of Energy Efficiency

Passive House (or PassivHaus in Europe) is an energy efficiency standard that was developed in Germany but has its foundation in North America. The goal of Passive House is to reduce the energy required to heat a building by 70-80%, relative to current code-built buildings. The same goes for reducing cooling energy use in a cooling climate like Phoenix, AZ. Three primary design considerations and several secondary principles are critical. Also, it is important to highlight that in addition to energy savings, Passive House Buildings offer a healthier, quieter and much more durable and comfortable building. In commercial buildings, let’s not forget how all these things convert into a productivity factor, which effectively contributes to the ROI. The Passive House approach is rigorous yet very feasible with the right attention to detail from design through construction. PassivHaus buildings in Europe and increasingly in North America are being certified every day. Parts of Europe have and will be making PassivHaus the required building code, as are parts of North America.

In the 1970s, Wolfgang Feist traveled to the US and Canada to learn about various buildings that were being constructed in response to the energy crisis. Some had Passive Solar Design approaches. Others were highly insulated and some included double stud wall construction. Still others, like the Saskatchewan Conservation House, had many of the principals found in today’s Passive House buildings. However, the Passive Solar Design approach often suffers from overheating even in the winter. Many of the super insulated and double stud homes had issues related to moisture, such as rot and mold in the walls. From his studies and the practical application of what he learned, Dr. Feist eventually developed the PassivHaus standard and built the first PassivHaus in 1991. The standard has two primary objectives. The first is heating loads must meet 4.75 kBTU/sf/yr. Most existing and even some new homes are 40 to 70 kBTU/sf/yr. The second is air tightness must be below 0.60 ACH50. Most existing homes are 4.0 to 15.0 ACH50 and even worse.

The three primary design considerations are SuperInsulation, low air infiltration and minimizing thermal bridging. The insulation levels are generally based on the specific climate for the project and can vary due to many circumstances. It is not unusual to have below grade foundation and slab and above grade wall insulation in the r-40 to r-60 range. Roof/ceiling insulation can often vary from r-65 to over r-100. Air infiltration rates are a standard and are tested or commissioned at 0.60 ACH 50. This is very tight and very achievable with proper attention to detail. Finally, thermal bridging often requires eliminating or reconfiguring cantilevers, insulating footers and rethinking some of the designs like balconies and bump outs that we see in many North American homes.

For several years, AE Building Systems (AE) has been bringing this mindset to a wider audience. Basic principles such as increased thermal performance, reduced air infiltration, and reduction of thermal bridging are keys to providing efficiency and comfort. AE has brought together separate building envelope components into a cohesive system that can meet these efficiency requirements and provide comfortable, durable and healthy buildings.

Most people do not understand why they are uncomfortable. We know we are cold or hot but not entirely why. There are several reasons and following are a couple examples. A standard window with a u-value of 0.30 is considered energy efficient. However, on a 7-degree F day, the indoor surface temperature on the u-0.30 window will likely be below 60 F. With a cold surface, our bodies are literally robbed of its heat due to radiation. Heat travels to cold and our bodies radiate heat to the cold surface making us feel cold. In addition, cold windows and walls often create convection currents within the building to include our living rooms and bedrooms. Air next to a cold wall or window drops and warm air in the space rises creating a very local convection current or microclimate that most believe are drafts. A similar condition is stack effect where warm air rises to the upper levels in a building while cold air drops to the lower levels. In some homes, there is often a 10 to 15 degree temperature variance between lower and upper levels. Higher performance windows and walls will increase the interior surface temperatures to levels that reduce the potential of the walls and windows to literally “suck” the heat off your body. At the same time, improving the interior surface temperatures will reduce the potential for convection currents and stack affect or microclimates within the building.

Several secondary considerations are important. First, high performance windows are crucial. Windows are the weak spot in our building envelopes. Windows with u-values as low as u-0.11 (r-9) are often necessary for achieving the Passive House standard. Passive Solar or solar heat gain is important, but it is also important to optimize and not maximize south facing glazing – to minimize the potential for over-heating. Also, it is critical to incorporate mechanical ventilation. Most leaky homes get fresh air through the cracks and holes in the walls. This is not where you want to get fresh air. Energy Recovery Ventilation (ERV) systems bring in fresh air and transfer the heat to the incoming fresh air effectively keeping the heat where it belongs while filtering the air. Also, a shoebox design is often incorporated with Passive House. Bump outs and corners invite thermal bridging and air infiltration. These feature, while they have aesthetic benefits, do not contribute to energy efficiency and comfort. Moisture management is also critical. Moisture most often enters walls in the form of vapor or humidity in the air. When the walls are cold, the vapor condenses on the interior of the wall. While Passive House buildings are largely air tight and have minimal thermal bridging, it is important to pay attention to how walls might have condensation and more importantly how they will dry. Also, “House” is a literal translation of Haus. Haus in German means “place of inhabitation” and Passive House applies to schools, office buildings, etc. Existing buildings are not excluded and passive house applies to retrofitting buildings. The retro-fit requirements are not as stringent, but achieving them can be quite rigorous depending on the building conditions. Finally, spec homes or homes built to be sold can pay off. Having a realtor who knows how to market this type of special building is extremely beneficial.

AE Building Systems has been delighted to have had the opportunity to provide products to several Passive House projects as well as other standards or objectives, including Zero Energy buildings. There are several important considerations, and we do our best to help our clients through the process.