Miller, production supervisor for Common Vision Inc. in Hamden,
Conn., responds: Beveled
siding will not bend properly around your curved walls because
of the gap created by lapping each piece over the piece below.
You are, in effect, increasing the circumference of the wall at
the lap. Your clapboard is tight to the sheathing at the top of
the board (the thin part) and therefore is a true 4-ft. 8-in.
radius. At the bottom, however, the lap means you are bending
around a 4-ft. 8 1/4-in. radius. What happens is that the ends
of the clapboard rise above the horizontal course line if you
keep the board tight to the sheathing, or you get a gap between
the sheathing and the top edge of the clapboard.
I have found two ways to deal with this without soaking or
steaming the wood. The easiest is to use a non-beveled rabbeted
siding — one that makes full contact with the sheathing
across its back, not just at the top edge (see illustration).
Since most rabbeted sidings come in 3/4-inch thickness, you may
have to have this milled in 1/2-inch stock so it’s
flexible enough to bend around the wall.
A more labor-intensive method, but one that works with
clapboards, is to cut the siding to a shape that will bend
around the wall and still stay horizontal (use 6-inch-wide
clapboards for this). To get the right shape, nail a starter
strip around the bottom of the wall, then scribe a line around
the wall at the height of the top of your 4-inch clapboard.
Make a mark in the exact middle of a length of 6-inch clapboard
and tack it to the wall with one nail so that its top edge
touches the scribed layout line at the center mark. Then, with
a person on each end of the clapboard, bend it around the wall
so that its top edge is pressed flat to the wall. You will see
that the ends fall below your horizontal line. Tack the
clapboard to the wall so that each end is an equal distance
below the line. Now scribe horizontal lines for the bottom and
top of the clapboard. Remove the clapboard and cut to these
lines; the clapboard will have a flattened U shape. Cut as many
pieces as you need to that particular curve; the length of the
pieces doesn’t matter.
In cases where the length of the curved clapboards
isn’t great (for example, if you’re siding between
windows), it’s possible to start with a curved board, and
make a number of successively less curved boards, until, maybe
ten boards later, you are working with straight boards that are
arching as you put them on. The change from curved to straight
is gradual enough that no one can tell that your boards arch up
off the horizontal line. Ten boards from the soffit, you need
to start cutting progressively more curved boards until the
last one is the right shape and lies parallel to the soffit
again. I did this recently on a three-story tower with 4-inch
clapboards and I only had to cut the 20 boards; the rest came
straight out of the bundles. No one can see the arch unless I
point it out.