Preventing Posts From Heaving
To the Editor:
There are several concepts in the
answer about pergola posts (On the
House, 2/02) that need some work.
First, it is a myth that frost doesn’t
grip and act on smooth surfaces.
When Sonotubes first became popular,
this was a common misconception.
Every year I replace Sonotube
footings that have heaved and
turned over. The only way to prevent
uplift with Sonotube piers is to
add a flared footing at the bottom
(below frost) and to add hooked bars
from the footing up into the
Sonotube form. Without the bars,
frost will indeed snap off and lift the
pier. Without hooks on the bottom,
frost will actually draw the bars right