In conventional home construction as used in subdivision or tract homes, a single 2 in x 4 inch wood framing stud forms the exterior walls.  The 3-1/2 inch thickness affords fiberglass insulation values of

R-12.  However, even this minimal requirement suffers from being non continuous.  That is, it only fills the spaces between the studs and does not run continuously.  While wood is considered to have some insulation, it is only R=1.4 per inch.  So for a 3-1/2in stud, R=3.6.  Consider such an exterior wall 12 ft long and 8 ft high with studs on 16 in centers.  Calculation shows that of the total area of the wall equalling 96 sqft, nearly 12 sqft is solid wood connecting outside siding to inside drywall.  With 12% of the wall having only an R-3.6 insulation value, it explains why such exterior walls feel cold to the touch on a cold winter day or night.  This lack of insulation reduces the room comfort index in the same but more exaggerated way as a large exterior glass surface does in cold weather.  A higher room temperature is then needed to compensate for the reduced comfort index.

Recognizing this limitation, higher end builders realized a 2in x 6in stud placed on 24in centers would reduce the loss because only 7% of the wall would have a value of R- 7.7 and the rest of the wall's value would be R-17.  However, in Canada, where temperatures dip to minus 50 degrees F. even this measure falls short.  The solution is a double framed wall eliminating all direct wood contact between the external siding and the internal drywall, yielding a continuous insulation result.  Depending upon the location the thickness of the double wall is adjusted for more or less insulation to match the weather pattern.

In our home, a double wall approach with minimal thickness was selected for additional energy efficiency and for increased room thermal comfort.  Following is a picture of the framing approach used.  We spaced our inner wall about 2in from the outer wall, a little more than in the picture.


Here are some important points to note in this design approach:

  • The most important feature is the thermal break afforded between the two walls,

  • We suspended 6in batts of unfaced fiberglass insulation on the inside of the outer wall,

  • Next we fastened 4in batts between the studs of the inner wall,

  • The resultant wall insulation value is R-30 and inside surfaces of exterior walls remain at room temperature due to the thermal break.  This improves home thermal comfort by reducing the radiant heat lost from occupants bodies to exterior walls that are colder or hotter than the conditioned air set by the thermostat.

  • Importantly, the inner wall excludes the load bearing double headers required over windows and doors in the outer wall, allowing for 4in of insulation in those inner wall spaces,

  • From an aesthetic point of view, the double wall yields attractive window wells of about 10in,

Shown by Appointment only,
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