Next, slide a shingle ripper under the shingles
and mark that angle onto the face of the trimmer
around the RO, gently breaking the self-sealing
rafters on each side of the opening. Bevel-cut the
Doors, Windows, and Skylights
149
1. After snapping chalklines to
2. Unless you are highly skilled with a reciprocating saw, 3. Standing outside the cutout area, pry up the sheathing outline the rough opening, use a
like this pro, use a circular saw to cut through the roof
and pass it through the hole to your helper inside. By the
utility knife with a hooked blade to
sheathing. To avoid gumming up a blade, remove the
way, many old-timers don’t like sneakers because nails
cut the shingles. Then use a shingle
building paper before cutting. Be sure to wear eye
can pierce the thin soles; on the other hand, sneakers can
ripper (left) or a flat bar (right) to pry protection.
improve your footing. Your call.
up the shingle nails and remove the
shingles within the cutout area. Knee
pads are a must for most roof work.
top edges of the doubled headers at that same
angle. Once you’ve headered off the top and bot-
tom of the RO, double up the trimmer rafters
along the sides of the opening, using as long a
board as possible. (Space is tight in an attic.)
Finally, install studs running from the RO in
the roof to the RO in the ceiling below. If you
install the four corner studs first, you can run
4. After removing the sheathing, the
installer used a hooked blade to cut
taut strings between them to align the interven-
back the shingles more precisely so
ing studs. If the lightwell sidewalls are plumb,
the Velux skylight’s mounting
rather than flared out, you will have saved your-
brackets could sit on the flat plane of
self a lot of work.
the roof sheathing, rather than on an
uneven shingle surface.
P R O T I P
Cut the length of the lightwell
a little long. It’s difficult to know
exactly where the grooved lower
edge of the skylight curb will
meet the finish surface on the
plumbed lower wall, so you’re
better off cutting the opening
long and shimming it up as
needed, using thin pieces of
plywood. Ultimately, 1⁄2-in.
drywall edges should fit perfectly
The same lightwell after the roof has
into curb grooves.
been opened: Note the doubled
headers around all sides of the
Here, all four lightwell walls will flare Different skylight, same installer.
opening. Because all walls flare, this
out toward the bottom (none plumb). Here, he frames out the lightwell
is a complicated piece of framing.
Using his level as a straight-edge, the before cutting a hole in the ceiling
installer marks the rafter cuts; the
because it was raining. First, he
level runs from the edge of the roof
headered off the ceiling joists, then
opening to the doubled headers in
the rafters around the roof opening,
the ceiling opening. After cutting the before angle-cutting the studs
rafters, he’ll attach a doubled header
between the two openings. (He cut
behind the cutline.
the four corner studs first.)
150 Chapter 6
Skylight: Sloping Roof, Flat Ceiling
Positioning a sloping skylight above a flat ceiling is an inexact sci-
then push a nail up through each corner of the rectangle into the
ence. Situating the skylight between rafters is easy enough, but
space above.
because lightwells typically flare out, sizing and positioning the ceil-
go into the attic or space above to find the four corner nails and
ing opening can be tricky if you’ve never done it before. Here are a few
determine if there are wires, pipes, and ducts that would be a problem
tips to demystify and simplify the process.
to relocate. Avoid positioning skylights where roof planes converge, by
Don’t overdo. As with hot sauce, so too with skylights: A little
all means. If the space over the ceiling is inaccessible, turn off the
goes a long way. letting light into a space dramatically transforms it,
electricity and use a cordless recip saw to punch a hole big enough for
so err on the conservative side when sizing them. Skylights placed on
your head, so you can take a better look before enlarging the hole further.
north- and east-facing roofs will yield the most even light, whereas
If you can position skylight openings to avoid cutting rafters or
openings on south- and west-facing roofs can get quite harsh and hot,
ceiling joists, do so. If you must cut more than one rafter, have an
making shades must-haves on those sides. When adding skylights, give
engineer review your plans. Otherwise, double up headers and trimmers
a thought to how those ceiling openings will look at night, too—in
around the rough opening to redistribute loads, and use steel connec-
too many cases like a large black hole. Some designers add tiny leD
tors to ensure solid connections.
lights inside a lightwell to give it a softer, romantic light.
Refine your design. Do you like the lightwell shape? (you might
Size them small. the most common sizes are 141⁄2 in. or 301⁄2 in.
want to make a foam-core model.) Remember, you can flare the sides of
wide—which fit in the spaces between two or three rafters set 16 in.
the lightwell, too—there’s no law that says they must be vertical—but
on center, respectively. (the fewer rafters you cut into, the better.)
that will simplify construction. Compound-angle cuts on all studs can
let’s say that both skylights are roughly twice as long as they are wide: be a monster to do correctly.
the smaller skylight (14 in. by 28 in.) will have an area of 2.7 sq. ft.,
When you have a better sense of the lightwell’s location, enlarge
whereas the larger one will have 12.5 sq. ft. things get interesting,
the hole in the ceiling, but don’t cut it to its final size yet. to mark the
though, when you add a flared lightwell from the skylight to a ceiling
corners of the opening in the roof, drive 16d nails up through the
below. Measure a flared lampshade’s width top and bottom and you’ll
sheathing. Note: thus far you’ve cut into finish surfaces only, not into
see how flaring radically increases surface area. So the bottom of a
framing.
flared lightwell can easily be double or triple the area of a skylight.
Parting thoughts: Operable skylights can be a great source of
get it on paper. Using graph paper, make a roughly to-scale
natural ventilation, especially in attic bedrooms and the like. Skylights
drawing (side view) that shows your roof (with the correct slope), a
with center pivots can be turned around for easy cleaning, whereas
skylight in it, and the distance between the head of that skylight to
units hig
h in the ceilings can be opened and closed via tiny motors
the ceiling plane. Because the angle of the lightwell flare is undecided
activated by wireless controls. there are lots of accessories and
at this point, use the drawing on p. 148 as a guide. From this sketch,
options, so visit www.velux.com or some other makers’ sites to see
extrapolate how large the opening in the ceiling will be.
what’s available. And don’t forget to look into glazing options that
get it on the ceiling. Using pieces of painter’s tape, mark the
provide somewhat greater energy efficiency.
four corners of that imaginary lightwell onto your ceiling. the four
sides of the lightwell rectangle should be parallel to walls in the room.
Move the tape until you like the size and shape of the opening-to-be.
INStAllINg AND
That done, the outside installer screws the bot-
P R O T I P
FlASHINg SkylIgHtS
tom legs of the brackets to the sheathing.
Wrapping the curb with building paper or self-
A cordless framing nailer is
Follow the manufacturer’s instructions when
adhering membrane underlayment gives you an
great for framing skylights, espe-
installing and flashing your skylight so the war-
extra layer of protection before installing the
cially for toenailing 16d nails
ranty will be honored should the unit leak.
when there’s little room to swing
Installations shown are fairly typical.
unit’s apron, side flashing, and head flashing.
a hammer. And you won’t need to
Screw the mounting brackets to the sides of
Apply 12-in.-wide strips of underlayment, one on
drag a 100-ft.-long compressor
the skylight curb; most brackets are adjustable.
each side, folding each so that it runs up onto the
hose up into the attic.
Then, with one worker on the roof and one in the curb about 2 in. Apply the bottom piece first,
attic, pass the skylight out through the opening.
which overlaps the shingles below, then place the
As the worker outside raises or lowers the brack-
side pieces and, finally, the top piece. If possible,
ets until the top and bottom of the unit are level,
slide the top piece of self-adhering membrane
the worker inside centers the unit in the opening. up under the building paper so you adhere it
directly to the sheathing. Slit the folded strips
Doors, Windows, and Skylights
151
where they overlap the curb corners so the strips
where water will run. Rather, nail overlapping
lie flat, and apply a dab of roofing cement to
pieces of step-flashing to the curb only and high
adhere the slit pieces.
enough so the nails will also be protected by curb
caps. If necessary, trim the last (uppermost) piec-
Install the apron flashing first. It runs along
es of step-flashing so they don’t extend beyond
the lower edge of the skylight and overlaps
the curb.
the shingles below it. Holding the apron snugly
against the curb, attach it to the curb—not the
Install the head flashing by slipping its upper
roof—using a single screw (or nail) on each
flange under the next full course of shingles above
side. Although it’s usually not necessary to caulk
and pressing the head flashing snugly to the
under the apron’s lower flange, follow the
curb. Attach the head flashing to the curb with
manufacturer’s advice. Ideally, the apron will line one screw or nail at each corner. Then install a
up with a course of shingles, but in renovation
strip of building paper—or a second strip of self-
work that’s not always possible.
adhering membrane—over the head flashing’s
flange before shingling over it. Note: Stop the
Install step-flashing along the sides, weaving
flashing strip and shingles 21⁄2 in. to 4 in. above
the L-shaped flashing between shingle courses.
the skylight curb so there is a clear expanse of
Ideally, shingle courses should stop 1⁄4 in. shy of
metal to clear leaves and accelerate runoff.
the curb so that water can run freely along the
sides. The vertical leg of each piece of step-flash-
Installing cladding (curb caps) is the last step.
ing should extend up high enough so it will be
These pieces cover and seal the tops of apron and
protected from rain by curb caps; the horizontal
side (step-) flashing and, on some models, the top
leg should extend under the shingles at least 4 in. of the head flashing as well. Follow your sky-
As with all flashing, avoid nailing in the channel
light’s installation guide religiously. In some fixed
zzzzzz Skylight Cladding
Head flashing
3
Cladding
2
Apron
2
1
Step-flashing
Cladding covers and seals the top legs of apron and step-flashing and—on some operable
models—it covers the head flashing as well. Read installation instructions closely. Numbers
on the cladding indicate the installation sequence.
152 Chapter 6
models, the head flashing is the last piece to go
on, covering the upper ends of the side cladding
pieces. Details vary, but caps snap or screw on.
Better-quality units have self-sticking foam gas-
kets that are applied to the top of the curb before
the caps are installed, which reduces air and dust
infiltration.
Finish off with a couple more tasks. To reflect
light, lightwells should be covered with drywall
and painted a light color. Insulate around the
lightwells to reduce heat loss and condensation.
Because condensation is common around sky-
lights, cover the lightwell with water-resistant
(WR) drywall, often called greenboard for its
color. Stiffen the well’s outside corners with
metal corner beads.
Velux units have integral curbs and proprietary flashing kits. This one is “directional”—that is, with
a top and bottom. Having slipped head flashing under shingles above, the installers will slip the
unit’s head underneath. Small l-shaped brackets along the curb will mount to the sheathing.
Once the unit’s mounting
brackets are screwed to the
sheathing, wrap the curb with
building paper or self-
adhering membrane as
described in the text. Here, the
Head flashing has two pieces, a base and a cap. Slip the
apron’s bottom flange
base piece under the course of shingles above as shown,
overlays the shingles below.
then hold the base snug to the curb and attach it with a
single screw or nail at each corner.
Working from the bottom up, apply l-shaped step-
flashing along the side. each overlaps the one below and
is nailed with a single nail to the side of the curb. The
uppermost pieces of step-flashing slide up under the head
flashing. When these in
dividual pieces of step-flashing
are in place, a continuous cap piece will cover each side.
Doors, Windows, and Skylights
153
7 Exteriors
It still takes a skilled eye to install
siding, but pneumatic nailers have
largely replaced hammers and drill
drivers. Wear safety glasses when
using this tool.
and door headers, vent hoods, and outdoor out-
The exterior wall of a house is a multi-
lets. Finally, various sealants or caulks fill gaps,
layered membrane that weatherproofs a house
bond materials together, or cut air infiltration. Of
in much the same way a roof does. In addition
course, windows and doors are exterior elements,
to protecting underlying elements from damage
too, but they are discussed in greater detail in
by sun and wind, the exterior intercepts and
chapter 6.
directs water away from sheathing and framing.
Although gutters may be considered part of the
The visible exterior layer consists of siding
roof, they are discussed at the end of this chapter
and trim. Beneath the siding, ideally, is a water-
because gutters are attached to the exterior and
resistive barrier, typically building paper or
help protect it. Gutters also direct water away
plastic housewrap. In addition, flashings seal
from foundations, thus reducing moisture in
transitions from one material to another or direct basements and crawlspaces and forestalling mold.
water around potential dams, such as window
154
zzzzzz Water-Resistive Barrier and
Window Flashing Details
As you install the WRB and flashing, always do so in a manner that will
divert water away from the sheathing and framing behind it. Because
water flows “downhill,” materials above should overlap those below.
Self-adhesive
Self-adhesive
Upper course of WRB
over flashing tape
flashing tape
Head flashing
flashing tape
overlaps ends
Metal cap flashing
of jamb flashing
(Z-flashing)
WRB strips
folded lengthwise
2 in. to 4 in.
seal corner
4
Head casing
WRB
covers sheathing
Jamb casing
WRB
(building paper
2
or housewrap)
Corner board
Renovation 4th Edition Page 35
