What is Thermal Bridging?
Thermal bridging is the progress of energy (heat) through a material that has more conductivity than any of the objects surrounding it. The more conductive material creates a “bridge” which is essentially the path of least resistance for the energy (heat) to move across.
It is worth remembering that the golden rule – heat will always want to go where it is cooler.
Thermal bridging can undermine all of your insulation efforts and can contribute to energy loss in your van, which means you have to work harder to keep it cool.
Spending all of the money, time and effort to insulate your van, but then not bothering to properly plan for thermal bridging is like doing the hundred yard dash, only to trip over your shoe laces just before the finish line!
Trust me, we’ve been there. When I was building out our Ford Transit Jumbo, I was deep into the van insulation rabbit hole, so much so I was having dreams about it. One specific area of the process that had me perplexed, at least at first, was thermal bridging, what it was, and why it was so important.
Thermal bridging is a concept that, if you’re not prepared for, can undermine all of the hard work you will put into insulating your van.
Why does thermal bridging happen in a van?
Thermal Bridging occurs when the van builder (you) creates a pathway of least resistance for heat flow between the exterior of the van, and your interior space. This happens by not properly taking all conductive surfaces within the van into account.
In my research for our own van build I watched a LOT of Youtube videos, and most completely missed one important element of planning when insulating.
The internal ribs of the van are a serious insulative weak point!
These are ribs that run both up the internal walls as well as across the ceiling in most vans. They are made of metal and are directly connected to the exterior car metal. It is this connection that makes them so important.
Metal is a super conductive material, so by leaving the ribs of the van uninsulated, they will simply be a thermal bridge, and in hot climates, carry the heat from the van’s external surface past your insulation and into your interior.
In colder climates this same thermal bridge will also allow heat to escape the interior and make its way into the cooler outside atmosphere, leaving you shivering cold when you wake up freezing at 2am.
How do I stop Thermal Bridging In My Van? Best Insulation Practices.
To stop thermal bridging, you want to make sure you are properly insulating the premade thermal bridges in the van, such as the internal ribbing that sticks out from the external sheeting.
You can stop thermal bridging in your van in 2 ways.
- By adding additional insulation on top of the internal ribs of the van. However, this will encroach on your living area size.
- By filling the internal ribs with insulation. We used polyester batts in our van conversion. They can be ripped apart easily and stuffed into the ribs. Worked a treat.
You also don’t want to create more heat transfer super highways (thermal bridges!) by doing something like connecting metal cupboard framing directly to the van walls or ribs, or by drilling self tap screws straight into the van ribs. If you do, then every screw becomes its own little thermal bridge, and will assist the transfer of heat.
Do I really need to worry about Thermal Bridging in my van? Is it a big deal?
Thermal bridging is worth planning against, but let’s not get completely paranoid. There is actually a mathematical limit on how much transfer of heat can occur, and this is based on factors such as;
- how large your van is.
- how large the surface area of the thermal bridges are (such as the internal ribs of the van).
- The thermal difference between exterior and interior of your van.
If you used a self tapping screw to connect a cupboard to one of the van ribs, even if the screw passed through a layer of insulation, you would have created a thermal bridge.
But – the reality is that the surface area of that screw that is exposed to the inside space of the van is bloody tiny! And would never really pass on enough heat to make any real difference to this interior temperature.
Thermal bridging is worth planning against, but let’s not get completely paranoid.
If you are half buried in snow overnight and it is -20 out, then yep, a high level of thermal bridging paranoia is totally worth it.
Also, it’s worth remembering that your windows are a major point of thermal bridging. So if you are spending all of this time mitigating thermal bridging of th evan ribs and your bolts and self tap screws, only to leave your windows uncovered, then you need to re-think your strategy!
How We Stopped Thermal Bridging In Our Van
In our Ford Transit van conversion, we did a series of things to mitigate thermal bridging.
I’ll use the ceiling insulation as a good example.
We had ceiling ribs that dropped down from the roof about 1 ¼ inches.
- in-between each metal ceiling rib, we used 1 inch Polyiso board. This provided good insulation for the ceiling, but still left the metal ribs exposed.
- To stop the ribs being a thermal bridge, we stuffed the ribs full of Polyester insulation, and then we covered the ceiling ribs with 12mm ply board.
- Then, when we attached our 12mm pine tongue and groove ceiling, and were able to secure it to the ply board and not the metal ribs themselves. This stopped any screws becoming thermal bridges too.
There you have it, all you need to know about Thermal Bridging and how to minimise its effects.
Happy building!