If you’re looking to build a high performance home, insulation is likely to be forefront in your mind. But the insulating material you use is just one part of your insulation strategy. If you want your new home to be warm and air-tight, you also need to tackle thermal bridging.
Let’s start with the basics. The R-value of your insulation is a measure of how well it resists heat flow. The higher the R-value, the better the material is at keeping heat in your home. Simple right? Well, not quite.
As with many technical rating systems, the R-value of an insulation system is based on specific test conditions – i.e. it’s a theoretical value. The actual R-value of the completed, installed product will vary based on both the design of the building and the quality of the installation.
Building research shows that in some cases the R-value that’s achieved in reality can be a half to a third lower than the level you would expect based on the product label. Much of this discrepancy may be down to thermal bridging. If you invest in a costly, high R-value insulation product, but don’t take thermal bridging into account then you’re effectively throwing part of the value of that insulation (and your money!) away.
What is thermal bridging?
Thermal bridging occurs when part of a wall, roof or floor transfers heat more rapidly that the surrounding material. This point then acts as a pathway for heat to escape the building more rapidly.
Thermal bridges may occur when you have a break in the wall insulation, where the insulation is compromised in some way (e.g. it gets wet) or, most commonly, when the insulation is penetrated by a material that has a higher thermal conductivity.
If you remember back to high school physics, you may recall that materials such as steel and concrete are good conductors of heat. Much better than, say, glass or plastic (materials that we typically use for insulation). When these conductors penetrate the wall insulation, then you are likely to get thermal bridging.
A classic example of this is the use of steel studs to bridge an insulated wall. The steel creates a pathway for heat to travel out of the home at a much higher rate than the rest of the wall.
Why is it important to get rid of thermal bridges?
The main reason we focus on thermal bridging in construction is to reduce heat loss from the building. This will reduce the energy needed to heat your home (reducing your bills) and make it more comfortable to live in. The more we insulate our homes, the bigger the impact of any heat loss areas. For example, in highly-insulated homes, thermal bridging can be responsible for up to 30 percent of the heat loss from the home. So it’s worth paying attention to!
But heat loss isn’t the only issue. A cold patch of wall cools the air that comes into contact with it, creating air currents which you experience as drafts. Drafts have a negative impact on comfort levels and you may find yourself turning up the heating simply because of this cold air flow.
Thermal bridging can also affect the air quality in your home. Cold patches on walls or ceilings increase the likelihood of condensation, which can lead to mold growth. In a worst case situation, this could result in interstitial condensation that could lead to more significant structural damage within the wall itself.
How to identify thermal bridging in your home
You don’t need expensive equipment to detect thermal bridging in your home. In fact, you’ve probably already noticed it. Stand next to one of your windows on a cold day and you’ll feel a noticeable difference in temperature compared to the rest of the room (unless you have high-end triple glazing!). Even running your hand over the wall can highlight colder areas.
If you want more measurable evidence, then you could use a thermal imaging device such as the FLIR ONE Thermal Imaging Camera Attachment to identify cold spots in your house.
Top tips for reducing thermal bridging in your new home
The good news is that if you’re conscious of the need to minimize thermal bridging, there’s a lot you can do to prevent it. The first step is in the design of your building:
- Consider what materials you can use for your exterior framing and where conductive materials may be safely eliminated. You can find more detail on efficient framing strategies on the Fine Homebuilding website.
- Use materials with low heat conductivity wherever possible. Wood studs aren’t an ideal solution, but they’re less conductive than metal. You can improve things further by applying strips of insulation over wood studs to provide a thermal break.
- Watch out for ‘penetration’ thermal bridges, such as steel or concrete beams or parapets that pass through the wall assembly. Look at incorporating a thermal break element to provide continuous insulation.
- Another option is to consider is an exterior insulation system that wraps rigid foam insulation around the main frame of the building, avoiding the problems of studs altogether.
- Finally, you should take thermal bridging into consideration when determining what level of insulation performance you want to achieve. If you know what the impact of thermal bridging is likely to be, you can specify the right material to achieve the performance you want.
Construction is equally important. Make sure your builder understands what you’re trying to achieve with your high performance home and that they have the skills to build what you’re after.
Common issues to look out for include discontinuities in the insulation, particularly at junctions and around openings. Insulating materials such as rigid foam should be cut to fit tightly together with any gaps sealed to prevent heat loss. If you’ve opted for site blown insulation, use a specialist contractor to make sure all areas are properly filled.
Many builders are now up-skilling to better deliver high performance homes. However, if you’re in any doubt it’s worth hiring a specialist contractor. At SEED we build high performance homes across Virginia, Maryland and the DC area. If you’re looking for a general contractor for your high performance home, we’d love to hear from you.