The Chainsaw Retrofit


The Passivhaus approach can be implemented when retrofitting existing buildings as well as when building new ones. Heating energy use in an existing building can be reduced to 10% of what it was prior to renovation. There are (of course) a number of challenges. In western Washington, achieving Passivhaus in an existing building will require:

  1. Adding additional insulation in walls, roofs and floors.
  2. Replacing windows.
  3. Improving air tightness.
  4. Installing a balanced heat recovery ventilation system.

Clearly this is not a trivial or inexpensive undertaking. However, when a planned renovation will involve new siding, windows, and furnace anyway, it is worthwhile investigating an upgrade to Passivhaus performance. Let’s say like many of our clients you are interested in having a ground source heat pump as your source of heat. In one of our projects, we found that by going to Passivhaus we could obviate the need for the ground source heat pump altogether, so we could save that money, and use it to pay for much of the cost of the additional insulation and better quality windows. It will still cost more (10%-20%) to get to Passivhaus, but the investment you make in the envelope of your house will pay dividends for the life of the structure.

The “chainsaw retrofit”–so called because this approach involves removing the overhangs of the existing house with a chainsaw!–is one way to add the additional insulation. Matt Wasse in our office has created an animation to illustrate how this approach works. Have a look:

Try you have trouble playing the video.