Cracking
Clapboards
by William A. Lotz
We have known for several years
that there is a compatibility problem
between wood clapboards and
extruded-polystyrene sheathing.
When the two products are installed
tightly together, the clapboards can
fail by splitting, shrinking, cupping,
curling, and popping the nails.
The failure of the clapboards is
more severe on the sides of the
building that get sun-especially
morning sun. The problems are
worse when the siding has a dark
stain or dark paint, or is left
Splitting (above) and nail popping (right) are
common on horizontal wood sidings installed
directly over foam sheathing. One solution is
to put the foam on the inside.
unfinished. The problem is also
worse when the nails are driven too
hard.
The foam-insulation manufacturers
claim