Soffits and Ventilation

Perforated soffit panels play an important role in proper attic
ventilation, and they prolong the life of the roof.
Thermal Convection
Warm air rises. In the home, moist, warm air from the living
area can move into the attic and work its way up to the roof
ridge. If the roof has ridge ventilation with adequate venting at
the soffit, the hot air will rise up and out of the house. If the
attic is not properly ventilated, the heat builds up. In the winter,
this build-up promotes the formation of ice dams in areas that
get snow. In the summer, heat build up can deteriorate the
roofing insulation, sheathing, and shingles.
The American Society of Heating, Refrigeration, and Air
Conditioning Engineers (ASHRAE) and Housing and Urban
Development (HUD) have set standards for attic ventilation:
1 sq. ft. of net-free ventilation area for every 150 sq. ft. of attic
floor space. If approximately half the open ventilation area
is in the upper portion of the roof (the ridge) and half is
in the lower area (the soffit), the standard changes to
1 sq. ft. for every 300 sq. ft. of attic floor space. This is
because the high-low balanced system equalizes the air
flow and ventilates more efficiently.
If customers begin to notice attic condensation or an
appreciably warmer attic after new vinyl siding and soffit have
been installed, they will attribute the problem to the siding, not
inadequate ventilation. And that’s why it’s important for you to
tell homeowners about the need for adequate ventilation.
Soffit Vents
There are many types of ventilation, but the most effective is a
combination of soffit and ridge vents. Cool air is drawn into the
attic through soffit vents, while the ridge vent allows the warmer
air to rise and flow out the top. CertainTeed offers five lines of
ventilated soffit panels: Beaded, T3-1/3" InvisiVent, Ironmax,™
Universal, and Value. If specified and installed properly, all will
provide adequate soffit ventilation.
To determine the amount of ventilation you’ll need, check the
local building code. How often to vent the soffit depends on the
width of the overhang and how many square feet of airspace a
particular panel provides. Typically, two solid soffit panels are
installed for every one vented panel. That is, every third panel is
vented. If you are ever in doubt about how many ventilated
panels to install, err on the side of installing more than you
think you need.
Installing Soffit
You can use solid vinyl panels or perforated vinyl panels for
soffit installations. Perforated panels provide ventilation, which
helps to reduce heat buildup in the summer and ice dams in the
winter. In buildings with roof ridge vents, you should install
ventilated soffit. Check local building codes to determine the
amount of ventilation required. In high wind load areas, you
should also check local building codes to determine
if application methods differ.
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Objectives
In this chapter, you’ll learn about attic ventilation and how
vented soffit contributes to it.
• Thermal convection
• Placement of vented soffit
• Open eave installation
• Closed eave installation
• Installing fascia
• Installing porch ceilings
12. Soffits and Ventilation
The procedure used to install soffit depends on the construction
of the eaves:
• Open eaves—eaves with exposed rafters or trusses—are
typical of new construction. You will also have to use open
eave installation procedures if you have to remove damaged
soffit at a remodeling project.
• Enclosed eaves—eaves with soffit in place—are typical of
remodeling projects.
Installation over Open Eaves
The first step in installing soffit is to install the proper receiving
channels. You have several options for receiving channels. You
can use accessories such as F-channel or J-channel, or you can
make channels using coil stock. The best approach is to select a
method that works most effectively with the construction
techniques used to create the eave. Examine figures 1–4 and
find the one that most closely resembles the construction
methods used on your particular project.
If no F-channel is available, J-channel can be modified to create
F-channel. Simply cut slots in the nail flange area where it
would be nailed to the wall. After cutting the nail flange, bend
the flange back and nail to the wall. When installing Beaded T2"
panels, use 3/8" H-bar or 3/8" J-channel.
Installing Receiving Channels
Install the receiving channels following the details shown in
figures 1–4. Nail the channels every 16", positioning the nail in
the center of the slot. Do not nail tightly. If you’re using Beaded
T2" panel as soffit, nail both the channel and the soffit every
8"–12" to create added support.
If the eave span is greater than 16", you will have to install
nailing strips (as shown in figure 4) and install the receiving
channels on the nailing strips.
If the soffit will turn a corner, cut and install the channel so
there is 1/4" for expansion at each of the adjoining walls.
Insert the panel into the channel on the wall, then into the
channel at the fascia board. You may have to flex the panel
slightly to insert it into the second channel. Make certain the
panel is perpendicular to the wall, then nail. Depending on the
installation method you’re using, you’ll nail either to a nailing
strip or to the fascia board.
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fascia cap or
coil stock
fascia cap or
coil stock
open truss
F-channel
soffit
16"-24"*
open truss
F-channel
J-channel
soffit
16"-24"*
open
rafter
F-channel
J-channel
soffit
soffit
add nailing
strips
add
framing
16"-24"*
16"-24"*
FIGURE 2
FIGURE 1
FIGURE 4
FIGURE 3
* To determine the maximum permissible span, consult individual
product specifications and local building codes.
Installing Soffit
Measure from the wall to the fascia board. Then subtract 1/2" to
allow for expansion. Mark this dimension on a soffit panel and
cross cut the panel using a power circular saw with a reversed
fine-tooth blade. Cut
one or two panels at
a time, carefully
advancing the saw
through the vinyl.
Insert the panel into
the channel on the
wall, then into the
channel at the fascia
board. You may have
to flex the panel
slightly to insert it
into the second channel.
Make certain the panel is perpendicular to the wall, then nail.
Depending on the installation method you’re using, you’ll nail
either to a nailing strip or to the fascia board.
If you’re nailing to the fascia board, use small-headed nails.
Drive the nail through the nail flange and “V” groove. This
is one of the rare instances when face nailing is permissible.
Once a soffit panel is face-nailed, it will expand only in one
direction—in this case, toward the receiving channel. Be
sure to leave space for the full expansion allowance in the
receiving channel.
If you’re using a nailing strip (as in figure 4), do not nail
tightly—allow movement for expansion.
Continue installing the panels by locking and nailing the soffit
in place. Make certain soffit panels are fully locked along their
entire length.
Turning a Corner
To turn a corner, measure
from the channel at the wall
corner to the channel at the
corner of the fascia board.
Subtract 1/4" for expansion. If
necessary, install nailing strips
to provide backing for the
lineal. Cut and install soffit
double channel lineal or Hbar.
Miter the corner soffit
panels and install as described above.
Completing the Installation
To complete the installation, apply utility trim and fasten
aluminum fascia cap or formed aluminum coil stock with
painted trim nails. If you must face nail fascia, drill holes
for the trim nails to allow for expansion and to reduce
denting of the aluminum.
Installation over Enclosed Eaves
If the existing soffit is rotted or damaged, it’s best to remove
it completely before installing vinyl soffit. Then use the
instructions for open eaves.
If you’re installing perforated soffit panels and the existing soffit
doesn’t have openings for ventilation, cut an adequate number
of openings. Then complete the installation as described for
open eaves.
The procedure used to install soffit over an enclosed eave is
almost identical to that used for an open eave. The major
difference is the installation of the J-channel. Determine the
method you’ll use to install soffit at the fascia board (see figures
5 and 6). When installing J-channel at either the wall or the
fascia board, nail the J-channel every 12"–16".
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fascia
soffit
panels
bent
aluminum
coil stock
nail into slot
nail into “v”
soffit
H-bar
fascia
miter soffit
panels
fascia cap or
coil stock
nailing
strip
soffit J-channel
enclosed
eave
J-channel
soffit
enclosed
eave
FIGURE 6
FIGURE 5
Turning a Corner
If the soffit is to turn a corner, cut and install J-channel so there
is 1/4" for expansion at each of the adjoining walls and
adjoining fascia boards. Miter the corner soffit panels and
install as described above.
Installing Triple 3-1/3" InvisiVent
and Solid Soffit
Installation over open eaves
In most situations, T3-1/3" InvisiVent and Solid Soffit should be
installed like our standard soffit products. However, when T3-
1/3" soffit is installed over open eaves, follow these installation
techniques.
Install receiving channels
There are two ways to install receiving channels for soffit.
The best approach is to select a method that works most
effectively with the construction techniques used to create
the eave. Examine the illustrations, and find the one that
most closely resembles the construction methods on your
particular project.
Use either 3/4" J-channel or 3/4" F-channel, or you can make
receiving channels using coil stock.
Install the receiving channels following the details shown in the
illustrations.
Nail the channels every 12" to 16", positioning the nail in the
center of the slot. Do not nail tightly.
NOTE: If you are concerned about excessive insect
infiltration with ventilated soffit, cover the opening with
corrosion-resistant mesh or other screening before
installing the soffit.
Install soffit
Nail the soffit every 16" or 24", depending upon local building
codes and stud spacing. T3-1/3" soffit will span up to 24"
without additional nailing strips.
Installation over existing soffit
When installing T3-1/3" InvisiVent and Solid Soffit over an existing
solid wood soffit, you must cut openings into the existing
soffit to provide adequate airflow through the soffit. The goal is
to have at least 9 square inches of net free air per lineal foot of
soffit. Removing a center portion of the existing soffit will provide
the desired airflow.
Using a saw, cut along the length of the existing soffit. Leave 2"
to 3" from both the wall and the fascia so that you will have
enough wood surface to securely fasten the soffit.
Remove the center portion of the existing soffit.
Install the soffit as described above.
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F-channel
soffit
fascia cap or
coil stock
open
rafter
add framing
J-channel
soffit
Installing Fascia
The wooden fascia board that encloses the front of an eave also
needs protection from the weather. To provide this protection,
you can install vinyl or aluminum fascia panels.
There are two procedures for installing vinyl fascia panels—
one for installations that include soffit, one for installations
without soffit.
Installations without Soffit
1. Fasten undersill trim in place along the top of the
fascia board.
2. Use a snap lock punch to create tabs along the top
edge of the fascia panel.
3. Hook the bottom of the fascia panel under the bottom
of the fascia board. Push the top edge into the undersill
trim, as shown, or behind the drip edge.
4. Secure the panel to the bottom of the fascia board with
white trim nails. Nail at the slot openings only (see
illustration). Do not face nail the fascia panel.
5. When overlapping fascia panels, first cut a notch in the
underneath panel. The notch should be 1/2" deep by
1-1/2" long. Slip the notched panel into the adjacent panel.
6. To turn a corner, you must first fabricate a corner piece.
• Cut a length of fascia panel so it extends 6" beyond
the corner.
• Mark a vertical line to indicate the position of the corner
and cut a 90° V-notch centered on the vertical line.
• Score along the vertical line and fold.
• With a snap lock punch, create tabs along the upper edge
of the panel. The tabs must be raised on the outside face
of the panel.
7. Fit the panel on the corner, making sure to overlap the
preceding panel.
Installations that Include Soffit
1. Fasten the undersill trim in place along the top of the
fascia board.
2. Fasten F-channel along the bottom outside of the fascia
board as shown.
3. The fascia panel will have to be rip cut to fit over the fascia
board and F-receiver.
• To determine the width of the panel, measure from a slot
in the undersill trim to the bottom of the F-receiver.
• Deduct 1/4" and cut as shown in the illustration.
• Use a snap lock punch to create tabs 1/8" below the cut
edge. Punch tabs every 6", with the tab raised on the
outside face of the panel.
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CertainTeed Vinyl Siding Master Craftsman Education & Development Program
undersill trim
vinyl fascia cap
fascia
board
nail in slot opening
undersill trim
fascia
board
F-channel
4. Install the panel by hooking the bottom of the fascia panel
under the F-receiver and pushing the top into the undersill
trim as shown.
5. Secure the panel to the bottom of the fascia board with
white trim nails. Nail at the slot openings only. Do not face
nail the fascia panel.
6. When overlapping fascia panels, first cut a notch in the
underneath panel. The notch should be 1/2" deep by
1-1/2" long. Slip the notched panel into the adjacent panel.
7. To turn a corner, you must first fabricate a corner piece.
• Cut a length of fascia panel so it extends 6" beyond the
corner.
• Mark a vertical line to indicate the position of the corner
and cut a 90° V-notch centered on the vertical line.
• Score along the vertical line and fold.
• With a snap lock punch, create tabs along the upper
edge. The tabs must be raised on the outside face of the
panel as shown.
8. Fit the panel on the corner, making sure to overlap the
preceding panel.
Aluminum Fascia
The techniques used to install aluminum fascia panels are
similar to those used with vinyl—with three exceptions:
1. There is no special undersill trim to use with
aluminum fascia.
2. Aluminum fascia is made without nail slots, so you
have to pay attention to proper nailing techniques.
3. Corners are handled differently.
Follow this four-step procedure to install aluminum fascia:
1. Install drip edge, gutter or all-purpose trim along the top of
the fascia board to receive the top edge of the fascia panel.
2. Slip the fascia panel in place; then fasten the underside of
the panel.
3. For best appearance and to avoid bending the aluminum,
first drill a slightly oversized hole. Then, using a light touch,
fasten the fascia with painted trim nails.
4. Nail every 24", keeping nails lined up with the soffit
V-grooves.
5. At outside corners, bend a 1" flange at a 90°angle so it turns
the corner. Then cut the overlapping fascia at a 45°angle.
Position the panels and fasten.
NOTE: If you need a piece of nonstandard size fascia
board, use a portable break to form it from aluminum
trim sheet. Install and attach it using the same
techniques you need for standard fascia panels.
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1/8"
measure
minus 1/4"
6"
Installing Porch Ceilings
The procedures used to install a porch ceiling are in many ways
similar to those used to install soffit. These procedures vary
slightly, depending on whether you’re working on new
construction or a remodeling project.
New Construction
1. Begin by installing receiving channels on all four sides of
the porch. If you are using F-channels, fasten them to the
existing walls. If you are using J-channels, you will have to
install a nailing base.
2. If you plan to use light blocks to attach external light
fixtures, install them to adequate backing.
3. Plan the layout of the ceiling panels to achieve an even
balance or to align with adjacent work.
4. If the ceiling panels will run parallel to the ceiling joists,
you will have to install additional 1" x 3" wood furring
nailing strips. Install these nailing strips perpendicular to
the ceiling joists, placing a strip every 12" to 16".
5. Invert J-channels and fasten them to the underside of wood
strips along the perimeter of the ceiling area.
6. Install the first panel into the channels at one end of the
porch. Be sure to leave room for expansion. Fasten every
12" to 16", positioning the fasteners in the centers of slots.
Do not fasten tightly.
7. Install the remaining panels. When cutting the last panel of
the first course, be sure to allow room for expansion.
For areas where more than one panel length is needed, use a
soffit H-bar. If necessary, rip cut the final panel and use a snap
lock punch to create tabs every 8" to 10" along the cut edge.
Attach undersill trim and insert the panels into the receiving
channel.
Remodeling
Before you begin, check to be sure the existing ceiling can serve
as a solid nailing base. If the existing ceiling is solid, remove all
existing moldings and fixtures from the ceiling and begin by
fastening inverted J-channels along the perimeter of the ceiling
area. Then follow the steps for new construction. (Since you are
working on a solid ceiling, you will not have to install the
additional nailing strips called for in step 4).
If the existing ceiling is not solid, install nailing strips to provide
a secure nailing base. Then install J-channels. You will have to
install additional nailing strips if your ceiling panels are to run
parallel to the ceiling joists. If so, follow the instructions for
new construction.
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Summary
• The most effective attic ventilation is a combination of
vented soffit and ridge vents.
• Check local building codes for the amount of ventilation
you’ll need. Typically, two solid soffit panels are installed for
every vented panel.
• When installing soffit on open eaves, you can use a
combination of J-channel, F-channel, and coil stock as
channels to receive the soffit.
• For installations on closed eaves, use J-channel and either
aluminum fascia cap or firmed coiled stock as receiving
channels.
• Fasten most soffit every 16". Ironmax can be fastened
24" o.c.
• You should also install vinyl or aluminum fascia panels to
protect the wooden fascia boards that enclose the front of
an eave.
• Begin installing porch ceilings on new construction by
installing either F-channel or J-channel. If more than one
length of panel is needed, use a soffit H-bar.
• When remodeling, you can fasten J-channel directly to the
ceiling if it is solid.