In this home we chose to install Pella 250 series windows with triple pane glass, argon gas, and low-E coating.  The triple pane glass is about 50% more energy efficient than the double pane Energy Star rated windows we used to install (the new windows are still Energy star rated, just better).  The U-factor of the glass in the windows we used is 0.20, compared to an Energy Star window with a U-factor of about 0.30 – 0.35.  Since the U-factor is the inverse of the R-value (one divided by the U-factor), the windows in our home are R-5, or the equivalent of 1″ foam insulation.


The windows also have argon gas inserted between the panes of glass.  Since argon is a very heavy gas (much heavier than air), it slows down the “convective looping” between the panes.  This is heat that is lost in the winter when air or other gas picks up heat from the inside pane and then “loops” in the space and gives off the heat to the outside pane.   The reverse is true in hot months, when the gas between the panes slows down the heat transfer from the outside in.

The low emissivity, or Low-E, coating on the glass acts to control solar heat gain into the home.  The special coating reflects solar rays in the summer when the sun is high in the sky and at a sharp angle to the glass.  In the winter, the angle of sunlight is lower, and the coating lets the rays in.  This helps the home gain some heat in the winter and keep the heat out in the summer.  Yet another example of the home saving energy without mechanical means.

One comment I often hear is that the materials we use, especially the windows, are expensive, and therefore drive up the cost of the home.  The Pella triple pane windows on this home cost about $2700, whereas a set of double pane windows (which are 33% less efficient) would have been closer to $1900.  Yes, we spent about $800 more for the better windows, but amortized over a 30 year mortgage, this will cost the homeowners an additional $2.22 per month, a small price to pay for superior performance and comfort.  And windows are an integral part of the home that aren’t changed out every 10-15 years like a water heater or appliances.  They should last 50 years or more, so doing it better from the start makes sense.


The last step in installing windows (and doors) is applying the flashing, or materials that keep water out of the building around the windows.  This has to be done absolutely perfectly or there is the potential for water to leak into the building and cause major damage.  This is a step often done improperly in homes even to this day,and something we take very seriously, since the consequences can be hundreds to thousands of dollars in damage down the road.  Vinyl siding keeps most of the water away from the house wrap but not all, and changes in weather can also cause moisture to collect behind the siding.  If this flashing isn’t done right,  you won’t know until you start seeing evidence inside the home, and by that time  the damage to the sheathing, framing, drywall, etc. is pretty severe.  You can see in the photo above how we used Dow Weathermate flashing tape (blue) around the sides and top of the window, then overlapped the house wrap (light blue) to create a drainage surface that keeps water out.  If you’ve done your flashings right, in theory, you could never install siding and water would still not get in.  An added benefit to all of this flashing is that it helps air-seal the home, which is another way to prevent heat loss.  The home works as a system, and all parts are related.

Wall Insulation

Once all of the trades were roughed in and inspected and framing was inspected, we began the insulation in the exterior walls.  We ran into a bit of a challenge with this home when it came to choosing and installing the insulation we would use.  We prefer dense-packed cellulose over fiberglass insulation because it performs better due to the way it slows down air flow in the wall cavities.  When you slow down the movement of air inside the walls, you greatly slow down heat loss by convection (loss of heat from air to a solid, like drywall and wall sheathing).  Fiberglass is not a bad product, but it lets air flow through it fairly easily (think of a cheap furnace filter; made of fiberglass).  So we chose dense-packed cellulose.

Note: we could have used a damp-spray cellulose material, but we have found in the past that the foam sheathing does not allow the insulation to sufficiently dry, leaving wet areas of insulation in the walls.  Even with dehumidifiers running in a home for two weeks the insulation still has a moisture content that makes us nervous.  With a tight, high-performance home, moisture in the walls is a very bad thing, and can lead to mold issues down the road.  We also had the option of damp sprayed fiberglass, but again we were concerned about added moisture into the structure.

The trouble came when we discovered that the staggered stud walls that we had built, although excellent at heat loss prevention, made it significantly more challenging to insulate than a standard framed wall.  Generally with cellulose, the material is blown into each stud cavity under pressure, causing the insulation to fill the cavity nice and tight.  By building the staggered stud walls, the stud cavities are no longer enclosed, but rather open to the next cavity, and the next, and so on.  It becomes impossible to create any pressure and pack the insulation in.  See the photo below that illustrates our dilemma:


Help came from Mark Lee of Better World Builders here in Kalamazoo.  His company does very high quality energy improvement work, and is acting as our insulation contractor on the ZERH project.  Mark came up with a way of using a fabric material (made for this purpose), stapled to the sides of the studs, to create enclosed cavities that would accept the dense-packed insulation.  His crew did a great job of installing the material, filling the insulation tightly around all of the framing, wires, electrical boxes, and other items in the walls.  The photos below show the fabric in place in the walls:

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With the 2 inches of dense foam on the exterior walls as sheathing and the dense-packed cellulose inside the walls, we end up with an R-value of about 32, or about 78% better than the 2012 energy code, which won’t be adopted here in Michigan until early next year.  This should insure energy savings and a comfortable living space for the life of the home.