Window Coverings


The temptation has always been there for eco-house builders. It’s those damn windows; they are just so useless once the sun goes down. There must be some way to insulate them once they no longer need to be seen through, right?


The answer is yes, but not cheaply. The biggest problem is moisture. If you insulate a window from the inside without a perfect air seal between the heated space and the cavity between the window covering and the window, moisture-laden air will flow into said cavity. When that happens, the moisture will condense on the window. Take it from green building pioneer Rob Dumont:

Back in the 70s I had a small house with lots of south windows. I experimented with interior rigid insulation on the windows. Some observations:

You need a very tight air and vapour barrier on the warm side of the insulation. I did not have either, and condensation would readily form on the window. I used a 2 inch thick piece of beadboard as the insulation. The windows were double glazed sealed units with an R value of about R2. Even more condensation would form on the window when the insulation was removed, as the warm, moist air could then, unimpeded, hit the window.  The condensation would run onto the sill. I actually got quite sick from the mould that grew on the lower corners of the windows. Never again.

R Value

We felt compelled to buy window coverings as soon as we moved into the Mill Creek NetZero Home  read more... »

Preserving Original Wood Windows While Improving Their Insulation Value


dining room window

Note from Conrad:This is a guest post by fellow Edmontonian Alice Harkness. Thanks for your excellent work Alice!

I experimented last winter with a very simple way of upgrading the insulation value of the beautiful original windows of my house: I added a third, Low-E glaze between the double hung window and the storm window.


There is a 3/4 inch thick space inside the storm window created by the stop (the strip of wood that serves as the outside edge of the channel for the upper double hung window, and backing for the storm). Here’s what I did:  read more... »

Passive Solar Design


(MCNZH concrete floor being bathed by sun through a 9’x6’ window)

The most important design considerations for cold climate building are insulation, building envelope, and passive solar design. Given our lofty goals for the Mill Creek NetZero Home (MCNZH), we pushed hard to maximize our return on every one of these fronts.

The MCNZH collects 54% of its annual space heat through passive solar design – that’s 8747 kWh or 31.5 Gigajoules. It does so by:

  1. having huge south windows that are specially manufactured to maximize solar heat gain
  2. containing a large amount of thermal mass to absorb the solar heat when the sun shines
  3. having movable solar awnings that allow 100% of the sunlight to hit the windows during the heating season (the awnings are strictly speaking not a passive part of the solution).

I’ll discuss the first two bullets on this list, given that I’ve already described the movable awnings at length.  read more... »