Over the years, the eyebrow dormer on my client's 1926 colonial
had seen its share of bad Long Island weather. Though the trim
was structurally sound, the paint finish was in sad shape. To
protect the window from deterioration and minimize future
maintenance, I suggested to the owner that we clad the
weathered trim boards with 1/2-inch Kleer PVC trim
(866/553-3770, www.kleerlumber.com). While PVC can be
easily machined and sanded, just like wood, it's a lot more
durable; best of all, I knew I could heat-bend it to fit the
graceful curves of the dormer.
Initially, I thought I would be able to measure the dormer's
radius and use math to lay out, cut, and shape the material on
the ground. But after taking a few measurements from different
areas of the eyebrow, I realized that the carpenter who had
originally built the dormer had freehanded some of the trim;
there was no way I could mathematically plot my curves.
Complicating matters further, the width of the trim varied from
6 1/2 to 8 inches wide.
Since I didn't want to spend hours sitting on the roof scribing
the trim in place, I made a felt-paper template that I could
carry down to a workspace in the driveway, a technique I've
used to make copper roof flashings. With an accurate template,
I could replicate the trim on the ground.
To build the template, I stapled up sections of 30-pound
asphalt felt paper so that they covered all the dormer trim
without sagging or wrinkling. Then I used a sharp utility knife
to cut out the borders of the trim (see Figure 1).
Figure 1. Using two
pieces of 30-pound felt and a utility knife, the author makes a
template of the existing dormer trim (top). A plumb cut at top
center (bottom left) and a horizontal measurement across the
width (bottom right) allow the template pieces to be realigned
on the ground.
In warm weather, 30-pound felt paper is pliable enough to fold,
so cutting the roof outline accurately was just a matter of
working the paper up under the roof edge and slicing along the
top edge of the trim. The paper is stiff enough to provide a
reliable template that won't stretch or distort when spread out
on the worktable.
To help keep the template sections properly oriented, I cut a
plumb line through both pieces of paper at the top middle of
the template. I also snapped a reference line across the entire
dormer while the felt paper was still in position, then made a
couple of marks along this line on either side of the window
and accurately measured the distance between them. Starting
with the plumb cut and with this measurement for reference, I
reassembled my template on the ground in the same position it
was in on the dormer (Figure 2).
Figure 2. The author
reassembles the two felt-paper sections using the plumb cut
(top) and the measurement between the two reference points
Bent, Not Cut
Because I was working with a 4-foot-by-8-foot sheet of PVC
trim, I could have overlaid the template on my trim stock,
marked the outline, and cut out the pieces with a jigsaw. But I
wanted a clean look that didn't require a lot of sanding, so I
decided to heat-form the trim instead.
I've used Heatcon's heat-forming kit (800/556-1990,
www.heatcon.com) to bend PVC and other
types of plastic trim into shape on a number of different
projects (see "Bending Trex," 7/06). The technique is actually
pretty simple: A pair of temperature-controlled heating
blankets are used to warm up lengths of plastic trim so that
they become pliable enough to be molded into shape. The proper
molding temperature varies according to the material being
used, but runs somewhere between 250°F and 300°F. To
prevent over- or undercooking the material, the kit comes with
an infrared thermometer.
On this project, I fastened sawn strips of PVC to my worktable
— using the template as a guide — to form the inner
and outer profiles of the dormer trim (Figure 3). These strips,
which were about an inch wide, were flexible enough to bend
smoothly around the template without being heated. To allow the
new trim to completely cover the old trim and create a reveal,
I held the inner strip an extra 5/8 inch away from the template
along the bottom edge.
Figure 3. To make a form
for the trim, 1-inch-wide PVC rippings are screwed to the
worktable, with the felt-paper template serving as a guide
(above). The PVC trim is warmed with heat blankets; scraps of
drywall prevent heat loss and speed up the process
To deal with the changing width of the original handmade trim,
I formed the new trim in two overlapping layers. The lower
piece follows the curve of the window, while the upper piece is
shaped to the roofline.
After screwing the forms down and ripping lengths of trim to
width from a 4x8 sheet of 1/2-inch PVC, I fired up my two
6-inch-wide by 6-foot-long Heatcon heat blankets. To help
minimize heat loss and speed up the heating process, I
sandwiched the heating blankets and trim between scrap pieces
of drywall. Once fully heated to around 295°F, the PVC trim
was easily shaped to the outline of the forms (Figure 4).
Figure 4. Once the PVC
trim has been heated to 295°F, it's flexible enough to be
placed in the form and molded into shape (top). The eyebrow
trim is actually made up of two overlapping layers; the author
forms the lower window section first (middle), then the upper
roof section (bottom).
Because the length of the workpieces was limited by the
blankets' 6-foot length, I fabricated each layer from three
pieces of trim. Fitting the pieces together on the ground with
my template as a guide made final installation up on the roof a
I screwed the dormer trim in place with 2-inch stainless-steel
trim screws and used Bond&Fill Structural two-part PVC
filler (877/822-7745, www.bondfill.com) to fill the holes and
butt joints (Figure 5).
Figure 5. After
fastening the lower trim layer in place with stainless-steel
trim screws, a crew member scribes and fits additional PVC
window trim and siding, and installs blocking to support the
upper layer of trim (top). Protected by its weatherproof PVC
outer layer, the eyebrow dormer is ready for another 80 years
of service (bottom).
We also created "clapboards" out of the same 1/2-inch PVC stock
to replace the siding we'd removed from the dormer, then
scribed-to-fit two short lengths of vertical window casing.
Although PVC trim can be finished to match existing trim work,
in this case we left it unpainted.Mike Sloggatt is a
remodeling contractor in Levittown, N.Y.