Friday, 8 February 2013

Thermal bridging exposed on a snowy day

I wasn't planning on writing a blog post today but what else is there to do on a day when everyone is taking a snow day and most of the city is closed. Shovelling, I suppose, is an option but the snow plow hasn't been by what's the point? Moving the snow twice doesn't make it twice the least not for me! I will admit that the city looks beautiful right now though.

It's beginning to look a lot like Christmas...again!

8½ inches fallen in 7 hours...and still counting!

Let's just heat the great outdoors with that thermal bridging!
I wanted to write this post to illustrate a perfect example of the result of thermal bridging in a conventionally built home.  Each piece of a house's framing material acts as a thermal bridge, a conduit for heat to leak through the wall. Thermal bridging is more significant than many realize. This photo shows the outdoor patio area of the 2010 better-than-code-built addition at our house in the city. Admittedly, we knew nothing about Passive House when we were planning and building this addition back in 2009, therefore thermal bridging was never taken into consideration. That is totally obvious when you look at the photo and see how the snow is melting within the 18-24 inch (45-60 cm) band closest to the house. The concrete floor inside is radiantly heated and that heat is being sucked right out of the 22°C (72°F) interior floor and into the -5°C (23°F) exterior stone patio because there was no thermal break, in the form of insulation, implemented under the patio door and between the interior and exterior floors. The patio door, although very good, is only double paned and is also losing more heat than it would with the third pane, typical of passive house rated windows. No wonder the floor's heat system comes on as often as it does! 

Just goes to show that energy efficiency can, literally, go right out the window, or wall, or floor if thermal bridges are not dealt with properly. Here we thought we were building a very energy efficient addition 2 years ago. Today's snow day certainly shot down those beliefs. This is very concrete proof that conventional building techniques have a long way to go to live up to their energy efficiency claims. Eliminating thermal bridging is one of the most important characteristics of a passive house. I always understood the concept. Now I see it.

This kind of heat loss will not happen in a passive house. Insulating a passive house takes thermal bridges out of the equation and heat then remains inside the house longer, rather than finding its way easily to the outdoors.

A little extra, well-placed, insulation can reduce heating (and cooling) requirements significantly.

Graphic thanks to Fine Home Building

Luckily, we will not be experiencing the kind of heat losses in our new house that you see in the above photo of our current house. We can thank the wall anatomy details designed specifically for Casa Tortuga. You will notice several extra layers making up the super-insulated wall structure of this passive house. Thermal bridging is eliminated, therefore eliminating the heat losses we are seeing now in our city house.

Wall anatomy of Passive House Casa Tortuga.

Copyright © 2013 Vert Design, Chris Straka

How all the layers go together. That's a lot of insulation!
Copyright © 2013 Vert Design, Chris Straka

Now that looks like a really warm and cozy house. I can't wait!

Well, it's still snowing after all the time it has taken to write this post. Maybe it's time to go tackle some of the thigh-high drifts out there. Ras gave up when she saw the snow plow's contribution at the end of the driveway. It's time for me to put my 9 layers of insulation on and go out to brave the windy, wintery, white stuff! Ugh!!


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