Insulation short circuit

Insulation · Walls Above Grade · printed page 251 (PDF page 252)

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Insulation – Short Circuits in Walls

Text in the illustration

insulation is sometimes added to the exterior of a wood frame wall without adding insulation in the stud cavity
this can be a waste of time because convective currents circulate through the empty stud cavity and carry heat out the top of the stud wall
it's kind of like wearing a hat a foot above your head
shingles
roof rafter
attic space
roof sheathing
escaping heat
insulation
ceiling joist
wall stud
drywall
gutter
fascia
soffit vent
new siding
rigid insulation added
old siding
convective loops allow heat to escape out the top of the wall cavity
empty stud cavity
cross section

Generated explanation

The cross section depicts a wood-frame exterior wall meeting an insulated attic floor and sloped roof at the eave. Rigid insulation and new siding have been added outside the old siding, while the stud cavity remains empty behind the interior drywall. A large looping arrow shows convective circulation within the empty wall cavity and heat escaping at the top of the wall toward the roof. The illustration identifies this as an insulation short circuit that undermines the benefit of the added exterior insulation. Roof shingles, sheathing, a rafter, gutter, fascia, and soffit vent establish the surrounding eave assembly.