Many superinsulated wall designs
are well over 6 inches thick. Most
window manufacturers, however,
will only provide jamb extensions
for up to a 2x6 wall. Moreover,
wider extension jambs are prone
to damage during shipping and
carry all the headaches associated
with special-order materials.
An alternative is to trim out the
window in place. The details
described here can be adapted to
fit a variety of thick wall styles.
They represent a technique used
by Neil Carter of Charleston,
Maine, who builds very fat
walls—sometimes 16 inches
thick. Carter specs the highest Rvalue
window available. Instead
of using a jamb extension, he
builds window wells with sides
that angle out from the window
into the room. He has found this
detail to be