Table 3-4.-Plank Decking Estimating Factor
traditional designs have considerable y more. Much of the
boards are to be used, multiply the total roof area by
1.16. To determine the total number of board feet
needed, add 5 percent for trim and waste.
Plywood Sheathing
To determine how much plywood will be needed,
find the total roof area to be covered and divide by 32
(the number of square feet in one 4-by 8-foot sheet of
plywood). This gives you the number of sheets required
to cover the area. Be sure to add 5 percent for a trim and
waste allowance.
Decking or Planking
To estimate plank decking, first determine the area
to be covered, then refer to the chart in table 3-4. In the
left column, find the size planking to be applied. For
example, if 2- by 6-inch material is selected, the factor
is 2.40. Multiply the area to be covered by this factor
and add a 5 percent trim and waste allowance.
Wood Fiber Roof Decking
To estimate the amount of weed fiber decking
required, first find the total roof area to be covered. For
every 100 square feet of area, you will need 6.25 panels,
2 by 8 feet in size. So, divide the roof area by 100 and
multiply by 6.25. Using our previous example with a
roof area of 2,310 square feet, you will need 145 panels.
EXTERIOR TRIM
LEARNING OBJECTIVE: Upon completing
this section, you should be able to identify the
types of cornices and material used in their
construction.
Exterior trim includes door and window trim,
cornice trim, facia boards and soffits, and rake or
gable-end trim. Contemporary designs with simple
cornices and moldings contain little of this material;
exterior trim, in the form of finish lumber and moldings,
is cut and fitted on the job. Other materials or
assemblies, such as shutters, louvers, railings, and posts,
are shop fabricated and arrive on the job ready to be
fastened in place.
The properties desired in materials used for exterior
trim are good painting and weathering characteristics,
easy working qualities, and maximum freedom from
warp. Decay resistance is desirable where materials may
absorb moisture. Heartwood from cedar, cypress, and
redwood has high decay resistance. Less durable species
can be treated to make them decay resistant. Many
manufacturers pre-dip materials, such as siding,
window sash, door and window frames, and trim, with
a water-repellent preservative. On-the-job dipping of
end joints or miters cut at the building site is
recommended when resistance to water entry and
increased protection are desired.
Rust-resistant trim fastenings, whether nails or
screws, are preferred wherever they may be in contact
with weather. These include galvanized, stainless steel,
or aluminum fastenings. When a natural finish is used,
nails should be stainless steel or aluminum to prevent
staining and discoloration. Cement-coated nails are not
rust-resistant.
Siding and trim are normally fastened in place with
a standard siding nail, which has a small flathead.
However, finish or casing nails might also be used for
some purposes. Most of the trim along the shingle line,
such as at gable ends and cornices, is installed before
the roof shingles are applied.
The roof overhangs (eaves) are the portions of the
roof that project past the sidewalls of the building. The
cornice is the area beneath the overhangs. The upward
slopes of the gable ends are called rakes. Several basic
designs are used for finishing off the roof overhangs and
cornices. Most of these designs come under the category
of open cornice or closed cornice. They not only add to
the attractiveness of a building but also help protect the
sidewalls of the building from rain and snow. Wide
overhangs also shade windows from the hot summer
sun.
Cornice work includes the installation of the
lookout ledger, lookouts, plancier (soffit), ventilation
screens, fascia, frieze, and the moldings at and below
the eaves, and along the sloping sides of the gable end
(rake). The ornamental parts of a cornice are called
cornice trim and consist mainly of molding; the molding
running up the side of the rakes of a gable roof is called
gable cornice trim. Besides the main roof, the additions
and dormers may have cornices and cornice trim.
3-8
