Wood-frame house construction, chapter 5, Specialty features

Wood-frame house construction, chapter 5, Specialty features
Chapter 5
SPECIALTY FEATURES
Page
Fireplaces, wood stoves, and chimneys . . . . . . . . . . . . . . 144
Fireplaces ( 144 ), Wood stoves ( 145 ),
Chimneys ( 147 ).
Garages and carports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Garages ( 151 ), Carports ( 152 ).
Porches and decks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Porches ( 152 ), Decks ( 154 ).
Driveways and walkways . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Driveways ( 160 ), Walkways ( 162 ).
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Specialty Features
The topics discussed in this chapter include a variety of
specialty features that are included in some but not all
home construction plans.
Fireplaces, Wood Stoves, and Chimneys
The installation of fireplaces, wood stoves, and the
chimneys that they require for operation involves significant structural considerations relating to safety and efficiency. Basic information is provided below.
Fireplaces
From the standpoint of heating, fireplaces could be considered a luxury, their heat production efficiency being
estimated to be only 10 percent. However, they are often
desired as a decorative feature. As indicated in the next
two sections, improved efficiency can usually be obtained
by the installation of a factory-made circulating fireplace.
This metal unit, enclosed by masonry, allows heated air
to be circulated throughout the room in a system separate
from the direct heat of the fire.
Satisfactory fireplace performance can be achieved by
following several rules relating the fireplace opening size
to flue area, depth of the opening, and certain other
measurements.
It is generally recommended that the depth of the fireplace should be about two-thirds the height of the opening. Thus, a 30-inch-high fireplace would be 20 inches
deep from the face to the rear of the opening.
The flue area (inside length times inside width) should
be at least one-tenth of the area of the fireplace opening
(width times height) when the chimney is 15 feet or more
in height. When less than 15 feet, the flue area should be
one-eighth of the area of the opening of the fireplace.
This height is measured from the throat (fig. 129) to the
top of the chimney. Thus, a fireplace with a 30-inch
width and 24-inch height (720 in2) would require an 8- by
12-inch flue, which has an inside area of about 80 in2,
when the chimney height is 15 feet or over. A 12- by
12-inch flue liner has an area of about 125 in2, and would
be large enough for a 36- by 30-inch opening when the
chimney height is 15 feet or over.
Steel angle iron should be used to support the brick or
masonry over the fireplace opening. The bottom of the
inner hearth, the sides, and the back should be built of a
heat-resistant material such as firebrick. The outer hearth
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should extend at least 16 inches out from the face of the
fireplace and be supported by a reinforced concrete slab.
This outer hearth provides protection against flying sparks
and should be made of noncombustible materials such as
glazed tile. Other details relating to clearance, framing of
the wall, cleanout opening, and ash dump are also shown
in figure 129. Hangers and brackets for fireplace screens
are often built into the face of the fireplace.
The back width of the fireplace is usually 6 to 8 inches
narrower than the front. This helps to guide the smoke
and fumes toward the rear. A vertical back wall about 14
inches high tapers toward the upper section or throat of
the fireplace (fig. 129). The area of the throat should be
about 1 ¼ to 1 1/3 times the area of the flue to promote
better draft. An adjustable damper is used at this area for
easy control of the opening.
The smoke shelf (top of the throat) is necessary to prevent back drafts. The height of the smoke shelf should be
8 inches above the top of the fireplace opening (fig. 129).
The smoke shelf is concave to retain any slight amount of
rain that may enter.
Fireplaces with two or more openings (fig. 130) require
much larger flues than conventional fireplaces. For example, a fireplace with two open adjacent faces (fig. 130A)
would require a 12- by 16-inch flue for a 34- by 20- by
30-inch (width, depth, and height, respectively) opening.
Local building regulations usually specify sizes for these
types of fireplaces.
Air-circulating firebox forms. The heating capacity
of a fireplace can be increased by using steel aircirculating firebox forms. These usually form the firebox
sides and rear, plus the throat, damper, smoke shelf, and
smoke chamber. The sides and back of the circulator are
double, enclosing a space within which air is heated. Cool
air is introduced into this space near the floor level and,
when heated by the hot steel, rises and returns to the
room through registers located at a higher level.
Air-circulating firebox forms can also prevent smoke
from entering the room. The volume of air drawn up the
chimney is substantial and is normally replaced by cold
air infiltrating through cracks in the house. In modem
tight house construction, however, the caulking and
weatherstripping that reduce air infiltration also hamper
the chimney draft, with the common result that smoke is
drawn into the room. This problem is solved by installation of an air-circulating firebox, along with glass doors
Figure 129 – Masonry fireplace components.
across the fireplace front that prevent room air from
entering the firebox.
The firebox form is set on a firebrick floor laid on
reinforced concrete. The chimney flue is begun at the top
of the form, and, facing the room, decorative masonry is
laid around the unit opening. Small fans are often
installed to increase the heating efficiency of the unit, and
the inlets and outlets are covered with decorative grates.
Zero-clearance prefabricated fireboxes. Factory-built
fireplace units can be ordered that include all fireplace
and chimney components from the hearth to the chimney
cap. These are called “zero-clearance units” because they
can be installed on wood floors and against wood framing
(fig. 131). Such units must have an inspection label on
them from a third-party testing agency (such as from UL,
Warnock-Hersey, or PFS Corporation) to qualify for use.
The units have steel walls and include insulation that protects wood structures from excessive heat. They frequently include dampers, screens, glass doors, circulating
fans, and external air supply ducts. Some are of
freestanding contemporary type. Others can be placed on
raised hearths and faced with stone or brick to provide a
traditional appearance, or they can be covered with
sheetrock and trimmed in wood. Their insulated steel
chimney pipe can be housed in a wood stud chimney
utilizing the same style of siding as the house.
Wood stoves
Some types of wood stoves are freestanding; others are
designed for insertion into fireplace openings. Their air
intake is controlled to produce efficient, slow, and more
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Figure 130 – Dual opening fireplace:
or for space heating. Water can be pumped to various
locations or circulated through convection.
Some wood stoves have glass doors, which make them
appear more like a fireplace. They can be set on brick,
tile, or stone hearths and surrounded with walls of the
same materials.
Wood stoves can be connected either to insulated steel
or to masonry flues (fig. 132).
As the use of wood stoves has increased in popularity,
failure to observe proper fire safety precautions in construction and installation has resulted in fires and accidents. In particular, it must be recalled that wood and
other combustibles can be heated to the flash point without direct contact between the hot stove and such combustible material. Sufficient heat to ignite combustibles
can be passed from the stove across air spaces through
convection and radiation, or through intervening noncombustible materials such as masonry that are in contact with
combustible material. The following paragraphs describe
precautions that should be taken against fire.
Pipe insulation. When an uninsulated metal pipe or
thimble passes through or comes in contact with walls, ceiling, or framing, at least 6 inches of fiberglass insulation
should be packed between the pipe and such materials at
all points of passage or contact. The fiberglass insulation
should not have paper facings. Cement, stone, brick, or
asbestos cannot serve as substitutes for such insulation,
because all these materials can conduct sufficient heat to
bring adjacent combustibles to the flash point.
complete combustion than is possible with fireplaces, with
little loss of room air up the chimney. Airtight wood
stoves can provide a combustion efficiency of 30 to 40
percent (a gas furnace is typically 80 percent efficient).
Some models are made of steel or cast iron, which radiates heat. Others are enclosed in thin steel jackets, allowing air to circulate between the stove and the jacket. The
cooler outer jacket provides a desirable safety feature. Air
enters and leaves the space between stove and jacket
through vents and heats the room through convection (see
the technical note on heat flow and insulation). Fans are
sometimes employed to improve circulation. In some systems the heated air is collected in a plenum and distributed to other rooms through ducts. To assure safe
operation when properly installed, such units should have
a label indicating they comply with safety standards as
tested by a third-party testing agency.
Some models contain coils through which water circulates; the heated water can be employed for domestic uses
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Clay thimbles. Clay thimbles should not be run directly
through concrete block or other nonflammable masonry.
The thimble, masonry, or both, may crack, allowing heat
to rise within the masonry cavities and ignite the wood
sill. For passage through nonflammable block or masonry,
an insulated steel pipe should be used. Alternatively, a
steel pipe can be passed through the thimble, using any of
a variety of techniques to maintain an air space between
the two pipes. This air space should be open to the basement room.
Safe distance from walls. Manufacturers of various
types of stoves specify the minimum distances from walls
and other combustible materials judged safe for their
stoves. These specifications should be carefully followed.
In general, freestanding wood stoves should be kept at
least 3 feet from combustibles, including wood studs covered with gypsum board and half-bricks. If a stove is
placed closer to a wall or other combustible material than
the minimum distance specified by the manufacturer, a
steel heat shield should be placed-between the stove and
such materials, with air space on both sides of the shield.
Figure 131-Zero-clearance fireplace in external wood chimney.
Safe distance from ceiling. Uninsulated steel flue
pipes should not be closer than 3 feet from ceilings.
Hearths. Freestanding wood stoves should be set on
brick or concrete hearths. Bricks of standard 2¾-inch
thickness or 3 inches of concrete should be used. Other
hearths may be used only if specified in the stove
manufacturer’s installation instructions.
Chimneys
Chimneys can be constructed of masonry units supported on a suitable foundation or of lightweight insulated
stainless steel pipe. They must be structurally safe and
capable of producing sufficient draft for fireplaces, stoves,
and/or other fuel-burning equipment. Steel flue pipe
should bear a label signifying approval by Underwriters
Laboratories, Inc., or other third-party testing agencies.
The chimney should be built on a concrete footing of
sufficient area, depth, and strength for the imposed
load. It is usually freestanding, and is constructed in such
a way that it neither supports nor is supported by the
structural framework of the house. The chimney footing
should be below the frost line. For houses with a basement, the footings for the walls and fireplace are usually
poured together and at the same elevation.
The size of the chimney depends on the number of
flues, the presence or absence of fireplaces, and the
design of the house. Each fireplace should have a separate
flue. For best performance, flues should be separated by a
4-inch-wide brick spacer (withe) placed between them
(fig. 133A).
Certain house designs include a room-wide brick or
stone fireplace wall that extends through the roof.
Although only two or three flues may be required for
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Figure 132 – Wood stove:
heating units and fireplaces, several false flues may be
added at the top for appearance.
Flue sizes conform to the width and length of a brick
so that full-length bricks can be used to enclose the flue
lining. Thus, an 8- by 8-inch flue lining (about 8½ in by
8½ in, outside dimensions) with the minimum 4-inch
thickness of surrounding masonry will use six standard
bricks for each course (fig. 134A). An 8- by 12-inch flue
lining (8% in by 13 in, outside dimensions) will be
enclosed by seven bricks at each course (fig. 134B), and
a 12- by 12-inch flue (13 in by 13 in, outside dimensions)
by eight bricks (fig. 134C).
The height of the chimney and the size of the flue are
important factors in providing sufficient draft. In addition,
the greater the difference in temperature between chimney
gases and outside atmosphere, the better the draft. A
chimney constructed within the house framework has better draft than a chimney constructed in an exterior wall
because the masonry retains heat longer.
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The height of a chimney above the roofline usually
depends on its location in relation to the roof ridge. If the
chimney is within 10 feet of the roof ridge, the top of the
flue liner must extend a minimum of 24 inches above the
ridge and must be a minimum of 36 inches above the
highest part of the roof next to the chimney. When the
chimney is more than 10 feet from the roof ridge, the top
of the chimney must extend a minimum of 24 inches
above the highest point on the roof within 10 feet of the
chimney and at least 36 inches above the highest point on
the roof next to the chimney (fig. 133B). For flat or lowpitched roofs, the chimney should extend at least 3 feet
above the highest point of the roof.
To prevent moisture from entering between the brick
and flue lining, a concrete cap is usually poured over the
top course of brick (fig. 133C). Precast or stone caps
with a cement wash are also used.
Flashing for chimneys is illustrated in figures 93 and
135. Masonry chimneys should be separated from wood
framing, subfloor, and other combustible materials. Framing members should have at least a 2-inch clearance and
should be firestopped at each floor with a noncombustible
material (fig. 136). Subfloor, roof sheathing, and wall
sheathing should have a ¾-inch clearance.
A cleanout door is included in the bottom of chimneys
for fireplaces and other solid fuel burning equipment. The
cleanout door for the furnace flue is usually located just
below the smokepipe thimble, with enough room for a
soot pocket.
Flue linings. Rectangular fire-clay linings or round
vitrified (glazed) tile are normally used for chimney flues.
Local codes usually require vitrified tile or a stainlesssteel lining for gas-burning equipment.
Rectangular flue lining is made in 2-foot lengths and in
various sizes from 8 by 8 inches to 24 by 24 inches. Wall
thicknesses vary with the size of the flue. Linings of a
smaller size have a wall 5/8 inch thick; larger sizes vary
from ¾ inch to 1 3 / 8 inches in thickness. Most commonly,
vitrified tiles 8 inches in diameter are used for the flues
of the heating unit, although larger sizes are also available. This type of tile has a bell joint.
Flue lining should begin at least 8 inches below the
thimble for a connecting smoke or vent pipe from the furnace. For fireplaces, the flue liner should start at the top
of the throat and extend to the top of the chimney.
Flue liners should be installed so far ahead of the brick
or masonry work, as it is carried up, that careful bedding
of the mortar results in a tight and smooth joint. When
diagonal offsets are necessary, the flue liners should be
beveled at the directional change in order to have a tight
joint. It is also good practice to stagger the joints in adjacent tile.
Standard flue blocks are available for building less
expensive chimneys. These blocks are 8 inches high by
16 inches square or larger, with holes in the center sized
to fit standard flue liners. Other blocks have half-circular
holes on one side; two of these form a circular hole
through which a thimble can be placed.
Figure 133 – Chimney details:
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Figure 134 – Chimney brick and flue combinations:
Insulated steel chimneys. Insulated steel chimneys are
made in tubular sections from 12 to 36 inches long. Sections are fastened together to form a long pipe. Triplewall pipe consists of three pipes with spaces between
them through which air circulates to remove heat. The
inner pipe is made of stainless steel; the outer pipes are
galvanized. Another type consists of double-wall stainless
steel pipe with asbestos insulation between the walls.
Both types come with a full line of accessories including
tees, wall supports and brackets, roof supports and flashing, storm collars, caps to keep rain from going down the
flue, and spark arrestors. Both types can be fully exposed
to weather or enclosed in wood chimneys. Wood chimneys normally consist of conventional stud walls covered
with sheathing and siding. The entire top, 2 feet square or
larger, is covered with galvanized flashing through which
the last section of insulated steel pipe extends.
Unlike clay flues, which could crack in flue fires, steel
chimneys do not crack when subjected to the heat of such
fires. If creosote buildup is ignited in a steel flue, the fire
can burn until the creosote burns off, and if the manufacturer's installation recommendations have been followed,
the flue should not be damaged.
Figure 135 – Chimney flashing.
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Figure 136 – Chimney clearances for wood frame construction.
Garages and Carports
Garages can be classified as attached, detached, or
basement. A carport is a roofed, open structure for
sheltering vehicles.
Garages
An attached garage has a number of advantages. It can
give better architectural lines to the house, it is warmer
during cold weather, and it provides convenient space for
storage. It also provides covered protection for entering or
leaving vehicles and a short, direct entrance to the house.
An attached garage is also less expensive to build than a
detached garage because it shares one wall with the house.
Where there is considerable slope to a lot, basement
garages may be desirable. Such garages generally cost
less than those above grade.
Detached garages are independent structures built on a
slab foundation. The specifications for the slab foundation
are generally the same as those for an attached garage.
Size. Many car models are 215 inches long, and
larger, more expensive models are usually over 230
inches-almost20 feet-inlength. While the garage need
not necessarily be designed to take all sizes with adequate
room around the car, it is good practice to provide a
minimum distance of 21 to 22 feet between the inside
faces of the front and rear walls. If additional storage or
work space at the back is desired, greater depth is required.
The inside width of a single garage should never be less
than 11 feet; 13 feet is more satisfactory. The recom-
mended minimum outside size for a single garage, therefore, would be 14 by 22 feet. A double garage should be
not less than 22 by 22 feet in outside dimensions to provide reasonable clearance. The addition of a shop or storage area would increase these dimensions.
For an attached garage, the foundation wall should
extend below the frost line and about 8 inches above the
exterior final grade level. It should be not less than 6
inches thick. The sill plate should be anchored to the
foundation wall with anchor bolts spaced about 8 feet
apart, with at least two bolts in each sill piece. Extra
anchors may be required at the sides of the main door.
If fill is required below the floor, it should be sand or
gravel. If some other type of soil fill is used, it should be
well compacted. If these precautions are not taken, the
concrete floor may settle and crack.
The concrete floor should be not less than 4 inches
thick. It should be laid with a pitch of about 2 inches
from the back to the front of the garage. Welded wire
mesh is often used to help control surface cracks. However, unless it is placed in the top third of the concrete, it
has little value.
The garage floor should be set about 1 inch above the
drive or apron level. It is desirable to have an expansion
joint between the garage floor and the driveway or apron.
The framing of the side walls and roof and the application of the exterior covering material should be similar to
that of the house. Interior studs can be left exposed or
covered with some type of sheet material. Building codes
require that the wall between the house and the attached
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garage be covered with fire-resistant material. Local
building regulations and fire codes should be consulted
before construction is begun.
Figure 137 – Sectional overhead garage door.
Doors. The overhead sectional type of garage doors
are used most commonly (fig. 137). They are made in
four or five horizontal hinged sections and have a track
extending along the sides under the ceiling framing with a
roller for each side of each section. They are opened by
lifting and are adaptable to automatic electric opening
with remote control devices.
The standard size for a single door is 9 feet wide by
6½ feet or 7 feet high. Doors for two-car garages are
usually 16 feet wide.
In design, the door most often used is the panel type
with solid stiles, rails, and panel fillers. A glazed panel
section is often included; translucent fiberglass and
embossed steel or aluminum are also available. Clearance
from the top of the door to the ceiling must usually be
about 12 inches, although low-headroom brackets are
available that can reduce required clearance to 6 inches.
The header beam over garage doors should be designed
for the total dead load and live load that may be imposed
by the roof above. If floor loads are also carried by this
header, the floor live loads must also be considered.
Three 2- by 12-inch boards, 18 feet long, are often
required for 16-foot doors. If a load-bearing truss is used
in the gable-end wall over a garage door, no header is
needed.
To keep the garage warmer in cold climates, overhead
door units can be ordered with insulation kits and
weatherstripping for the perimeter of the door. Weatherstripping is typically made of vinyl for head and side
jambs and rubber or vinyl for contact with the floor.
Carports
Carports are often built with 4- by 4-inch solid wood
posts (6- by 6-in posts in areas with heavy snow load) at all
corners and at other intermediate points determined by the
size of the load-bearing headers. Typically, there are four
posts (with three spaces) in the long direction. The headers
that span between the posts are normally 2 by 8 inches, or
2 by 12 inches on two-car ports in heavy snow areas.
Metal post bases are often used to fasten posts to the
concrete slab. The load-bearing header is either bolted or
nailed to the posts. Connectors must be able to resist
strong wind uplift forces. Clearances should be the same
as for garages, to allow for the possibility that the carport
will be closed in at a later date.
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Carports are usually attached to the house. To improve
their appearance and utility, storage cabinets are often
built on the open side or at the end.
Porches and Decks
Porches or decks should be joined to the main house by
means of the framing members and roof sheathing. Rafters,
ceiling joists, and studs should be securely attached by
nailing, bolting, or lag-screwing to the house framing.
When additions are made to an existing house, it may
be desirable to remove siding or other exterior finish so
that the framing members of the addition can be easily
fastened to the house. In many instances, siding can be
cut to the outline of the addition and removed only where
necessary. With wood or plywood siding, metal joist
hangers are sometimes applied directly to the siding, but
only at points where the attachment is to be made to
framing members behind the siding at the point of application. Footings should be of sufficient size, with bottoms
located below the frost line, and the foundation walls
should be anchored to the house foundation when possible.
All lumber used outside, especially joists, flooring,
posts, and lattices, should be either pressure-treated or of
a species with natural resistance to decay, such as redwood, cypress, and cedar.
Porches
Some porches have roof slopes continuous with the roof
of the house. Other porch roofs may have just enough
pitch to provide drainage and may require continuously
sealed roofing or hot-tar built-up roofing rather than shingles. Basic construction principles for porches are similar,
however, and a general description can cover various types.
Figure 138 shows the construction details for the juncture
of a concrete slab floor and the house foundation wall. An
attached porch can be open or fully enclosed. It can be
constructed with a concrete slab floor, insulated or uninsulated, or with wood floor framing over a crawl space
(fig. 139). Construction details should comply with those
previously outlined for various parts of the house itself.
where termites may be present (see the section on protection against decay and termites in chapter 8). A fully
enclosed crawl space foundation should be vented or have
an opening to the basement.
Framing and floors. Porch floors, whether wood or
concrete, should have sufficient slope away from the
house to provide good drainage. Weep holes or drains
should be provided in any solid or fully sheathed perimeter wall. Open wood balusters with top and bottom railings should be constructed so that the bottom rail is free
of the floor surface.
Wood for porch flooring should have good decay and
wear resistance, be nonsplintering, and be resistant to
warping. Species commonly used are cypress, Douglasfir, western larch, southern pine, and redwood.
Wood floor framing should be at least 18 inches above
the soil. It is good practice to use a soil cover of polyethylene or similar material under a partially open or a
closed porch.
Lattice or grillwork around an open crawl space should
be made with a removable section for entry in areas
Columns. Roof support for enclosed porches usually
consists of fully framed stud walls. Because finished
coverings are used on both interior and exterior, the walls
are constructed much like the walls of the house. In open
or partially open porches, however, solid or built-up posts
or columns are used. Solid posts, normally 4 by 4 or 6 by
6 inches, are used mainly for open porches. A more finished column can be made up of doubled 2- by 4-inch
Figure 138 – Porch concrete slab floor.
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Figure 139 – Porch crawl space floor.
lumber covered with 1- by 4-inch boards on two opposite
sides and 1- by 6-inch boards on the other sides
(fig. 140A). An open railing may be used between posts.
decorative railings can be used for an open porch
(fig. 141B). This type can also be used with full-height
removable screens.
A large house entrance often includes columns topped
by capitals. These factory-made columns are ready for
installation when they reach the building site.
All balustrade members that are exposed to water and
snow should be designed to shed water. The top of the
railing should be tapered, and connections with balusters
should be protected as much as possible (fig. 142A). Railings should not contact a concrete floor, but should be
blocked to provide a small space beneath. When wood
such as the blocks must be in contact with the concrete, it
should be pressure-treated to resist decay.
The bases of posts or columns in open porches should
be designed so that no pockets are formed that can retain
moisture. In single posts, a steel pin can be used to locate
the post, and a large galvanized washer or similar spacer
can be used to keep the bottom of the post above the concrete or wood floor (fig. 140B). Alternatively, a variety
of metal post bases are available at lumberyards. One
should be selected that provides space for drainage under
the end of the post (fig. 140C). The bottom of the post
should be treated with water-repellent preservative (WRP)
to minimize moisture penetration. Single posts of this type
are often made from a decay-resistant wood species or
pressure-treated wood.
Balustrades. Porch balustrades usually consist of one
or two railings with balusters between them. A closed
balustrade can be used in combination with screens or
combination windows (fig. 141A). A balustrade with
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Connection of the railing to a post should be made in a
way that prevents moisture from being trapped. One method
provides a small space between the post and the end of
the railing (fig. 142B). When the railing is painted or
treated with water-repellent preservative, this type of connection should provide good protection. Exposed members, such as posts, balusters, and railings, should be all
heartwood stock of decay-resistant or pressure-treated wood.
Decks
A variety of wood species can be used for building
decks. For long life and reduced maintenance, either
Figure 140-Post details:
pressure-treated wood or wood with natural resistance to
decay, such as redwood, cedar, or cypress, should be
used. Some woods that are easy to work, such as hemlock, most pines, spruce, and Douglas-fir, have either low
resistance or only moderate resistance to decay and insect
attack. Such species can be used for deck construction if
they are pressure-treated.
is in place and measurements cannot easily be made,
some other point of reference should be used that can be
transferred to the outside. For example, the measurement
from the top of the inside floor to the bottom of a window sash can be transferred to the outside from the bottom of the same window sash. One inch should be added
to this measurement to locate the top of the decking.
Decks should be designed to withstand heavy loads
because they tend to be places where many people congregate. Local building codes should be checked in case
they specify minimum load-bearing requirements for live
load (people, snow, furniture, equipment, etc.) and dead
load (the deck itself). If there are no code requirements,
assume a live load of 40 pounds per square foot (lb/ft2)
and a dead load of 10 lb/ft2. Spacing of posts, beams, and
joists should be based on these requirements. Span tables
for floor joists such as are shown in the section on floor
framing should be consulted.
Next, a measurement should be made down from the
top of the deck to a distance equal to the thickness of the
deck flooring plus the height of the deck joists. This point
represents the bottom of the deck joists. The bottom of
the deck joists can be located in this manner at both ends
of the proposed deck, and a chalk-line string snapped
through the points.
Layout. Most decks are attached to the house,
although some are freestanding. For those that are
attached to the house, the top of decking should be
located 1 inch below the inside floor level. If no doorway
Joist spacing should be marked along the length of the
chalk line. The outside face of the first floor joist will be
in line with the end of the deck. Beginning with the outside face of the first-floor joist, a distance of 15¼ inches
should be measured to mark the beginning face of the
second joist. Thereafter, the beginning faces of the floor
joists should be marked at 16-inch intervals. The final
mark at the end of the deck marks the outside face of the
final floor joist.
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Figure 141-Types of balustrades:
Several methods can be used to attach the deck floor
joists to the house along the chalk line. The simplest
method is to attach joist hangers directly to the siding
with lag screws (fig. 143). The lag screws must penetrate
either the floor framing members or the wall studs of the
house. The bottoms of the joist hangers are aligned with
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the chalk line, and the sides of the hangers are aligned
with the marks indicating deck floor joist spacing.
Another method is to attach a header joist to the side of
the house with lag screws that are long enough to penetrate the floor framing or wall studs of the house
(fig. 144). The bottom of the header joist should be
aligned with the chalk line; its height is the same as the
deck floor joists. Metal joist hangers should be nailed to
the header joist with their bottoms aligned with the bottom edge of the joist. The sides of the joist hangers
should be aligned with the marks indicating deck floor
joist spacing.
Figure 142 – Railings:
A third method is to attach a 2- by 4-inch or 2- by
6-inch wood ledger to the side of the house with lag
screws (fig. 145). The top of the ledger should be aligned
with the chalk line. No joist hangers are required since
the deck floor joists rest on top of the ledger.
If either the header joist method or the ledger method is
chosen for use against wood siding, flashing must be
installed. A circular saw should be used to cut through
the siding at the top and along the entire length of the
header or ledger. The siding should be pried out with a
flat bar, and Z-flashing installed to prevent water accumulation between the wood siding and the header or ledger
(figs. 144 and 145).
If the deck floor framing is attached to a brick or block
wall, lead anchors and expansion bolts should be used in
place of lag screws.
The deck floor framing should be assembled on the
ground by nailing a header joist to the ends of the floor
joists on the side of the deck away from the house, using
16d hot-dipped galvanized nails, three per joist. A second
header joist should then be nailed to the first. The floor
joists should be lifted and the ends placed into the joist
hangers or onto the ledger. The header joist should be
Figure 143 – Deck attachment to house with joist hangers.
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Figure 144-Deck attachment to house with header joist.
Figure 145-Deck attachment to house using ledger.
Footings for the deck support posts should be deep
enough to extend to undisturbed soil below frost line
(fig. 146). One method of digging footing holes is to use
a post-hole digger. A 6-foot steel bar may be useful for
loosening the soil. An 8-inch-diameter hole is sufficient
for 4- by 4-inch posts.
When the post footing holes have been dug, the deck
should again be raised, leveled, and temporarily braced.
The joist ends at the house should then be permanently
nailed to the hangers or ledger.
If concrete footings are used, the holes should be filled
with concrete and post anchors fastened in the concrete. It
may be worthwhile to check the location of the anchor
with the plumb line. It should be remembered that the
plumb line will probably be at the outside comer of the
post, and the anchor should be positioned accordingly.
Four- by four-inch pressure-treated posts should be cut to
fit between the anchor and the deck joists, and nailed to
the joists (fig. 146A).
raised until the deck floor framing is level, and temporarily braced with 2 by 4 posts.
The deck should be squared with diagonal measurements and a temporary brace placed across the framing to
maintain squareness. From a ladder, a plumb line should
be dropped to locate footings and posts, and stakes should
be driven at these points. The deck should be set on the
ground while post holes are being dug.
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Curing of the footings requires about 7 days. When
they have been cured, the temporary deck bracing can be
removed and the support posts set on and nailed to the
anchors.
As an alternative to the use of a concrete footing, about
4 inches of gravel can be placed in the bottom of the
hole, its depth measured, and the post cut, set in the hole
on top of the gravel, and nailed to the deck floor framing.
The hole should then be backfilled with gravel, and the
gravel tamped (fig. 146B).
Figure 146 – Deck posts and footing:
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Flooring. Starting from the house, chalk-line string
should be snapped for placement of deck flooring. If
2- by 4-inch lumber is used, marks should be made every
4 inches; if 2- by 6-inch lumber is used, marks should be
made every 6 inches. For a 12-foot-deep deck, 36 2 by
4’s or 24 2 by 6’s are needed. The marking provides a
½-inch space between boards. The first ½-inch space
should be adjacent to the house. This allows rainwater to
drain past the decking.
Corrosion-resistant nails should be used. Two 16d nails
should be driven at each deck-joist intersection. If nails
are driven at about a 30° angle, they are less likely to
loosen. Three 16d nails should be used at butt joints.
Decking boards should be inspected visually for
straightness as they are being placed. Any boards having
a slight edgewise crook can be straightened somewhat by
nailing one end and bending the board into place as it is
nailed. Occasionally, a pry bar may be needed to
straighten difficult boards. Boards that are slightly bowed
should be laid with the crown up to prevent the accumulation of water. It may sometimes be necessary to discard
boards that are badly deformed.
Railings. Railings must be sturdy enough to withstand
the weight of people leaning against them. They should
also be designed to prevent children from falling through.
Local codes may specify minimal height and maximal
space between rails.
In an extended post deck, the posts extend 36 inches up
through the deck flooring and serve as the major rail posts.
Many builders use 2- by 2-inch rail posts, spaced
6 inches on center and lag-screwed to the deck header or
to an edge joist. A vertical 2- by 4-inch board at the top
of the 2 by 2's and a horizontal cap board complete the
top of the railings. Edges of the cap board can be routed
to give the board a more finished look and to minimize
splinters (fig 146).
Driveways and Walkways
Driveways and walks should be installed prior to such
landscaping as final grading, planting of shrubs and trees,
and seeding or sodding of lawn areas.
Concrete and bituminous pavement are most commonly
used in the construction of walks and drives, especially in
areas where snow removal is important. In some areas of
the country, a gravel driveway and a flagstone or precast
concrete walk may be satisfactory, thereby reducing cost.
Driveways
The grade, width, and radius of curve in a driveway
are important in establishing a safe entry to the garage.
160
When attached garages are located near the street on rela-
tively level property, driveway width is the basic consideration. Driveways that are long and require an area
for turnaround require careful planning and design. Figure
147 shows a driveway and turnaround that allow the
driver to back out of a single or double garage into the
turnaround, and proceed to the street or highway in a forward direction. This is much safer than having to back
onto the street or roadway, particularly in areas of heavy
traffic. As shown in figure 147, a double garage should
be serviced by a wider entry and turnaround.
Driveways that must be steep should have a near-level
area 12 to 16 feet long in front of the garage for safety.
Driveways that have a grade more than 7 percent (7-ft
rise in 100 ft of length) should have some type of pavement to prevent erosion.
Two types of paved driveways are the slab or full-width
type, which is more common, and the ribbon type
(fig. 148). When driveways are fairly long or steep, the
full-width type is the most practical The ribbon driveway
is cheaper and perhaps less conspicuous because of the
grass center strip between the two concrete runners. However, it is not practical if there is a curve or turn involved
or if the driveway is long.
The width of the slab driveway should be 9 feet, although
8 feet is often considered acceptable (fig. 148A). When
the driveway is also used as a walk, it should be at least
Figure 147 – Driveway with turnaround.
Figure 148 – Driveway derails:
10 feet wide to allow for a parked car as well as a walkway. The width should be increased by at least 1 foot at
curves. The radius of the drive at the curb should be at
least 5 feet (fig. 148A). Relatively short double driveways
should be at least 18 feet wide, and 2 feet wider when
they are also to be used as a walk from the street.
ordinarily required on sandy undisturbed soil but should
be used in all other conditions. Concrete should be about
4 inches thick. Lengths of 2 by 4 are often used for side
forms to produce a 3½-inch-thick slab. The side forms
establish the elevation and alignment of the driveway and
are used for finishing the top surface of the concrete.
The concrete strips in a ribbon driveway should be at
least 2 feet in width and located so that they are 5 feet on
center (fig. 148B). When the ribbon is also used as a walk,
the width of strips should be increased to at least 3 feet.
Under most conditions, the use of steel reinforcing is
good practice. Steel mesh, 6 by 6 inches in size and
installed in the upper one-third of the poured concrete,
normally prevents or minimizes cracking.
A 5-bag or 5½-bag commercial concrete mix is
ordinarily used for driveways. However, a 5½-bag to
6-bag mix containing an air-entraining mixture should be
used in areas having severe winter climates. Pouring a
concrete driveway over an area that has been recently
filled is poor practice unless the fill, preferably gravel,
has settled and is well tamped. A gravel base is not
Isolation joints, sometimes called expansion joints,
should be used (a) at the junction of the driveway with
the public walk or curb, (b) at the junction with the
garage slab, and (c) about every 40 feet on long driveways. The purpose of the isolation joint is to separate two
adjacent concrete sections that may move relative to each
other. The isolation joint should be filled with a material
161
such as asphalt-impregnated fiber sheathing. The joint
Concrete walkways should be constructed in the same
filler material should be set ½ inch below the concrete
general manner as concrete driveways. They should not
surface to allow placing of a sealant at the top to make
the joint watertight.
be poured over filled areas unless such areas have settled
and are very well tamped. This is especially true of the
areas near the house after basement excavation backfill
has been completed.
Control joints should be provided at 10- to 12-foot
intervals. These crosswise grooves, cut into the partially
set concrete, predispose the concrete to crack in a controlled fashion along these lines during the cold weather
rather than to form irregular cracks in other areas. In
order to be effective, the control-joint depth should be
approximately one-quarter of the concrete thickness.
Blacktop driveways, normally constructed by paving contractors, should also have a well-tamped gravel or crushed
rock base. The top should be slightly crowned for drainage.
Walkways
Main walkways generally extend from the front entry to
the street or front sidewalk, or to a driveway leading to
the street. A 5-percent grade is considered maximum for
sidewalks; any greater slope usually requires steps. Walks
should be at least 3 feet wide.
Figure 149 – Sidewalks on slopes:
162
The thickness of the concrete over normal undisturbed
soil should be about 4 inches. A 2 by 4 is commonly
used as a side form. As described for concrete driveways,
control joints should be used and spaced on 4-foot
centers. Isolation joints should be used to separate the
walkways from steps, driveway, and the public sidewalk.
When slopes to the house are greater than a 5-percent
grade, stairs or steps should be used. This may be accomplished with a flight of stairs at a terrace, a continuing
sidewalk (fig. 149A), or a ramp sidewalk (fig. 149B).
Such stairs should have 11-inch treads and 7-inch risers
when the total stair size is 30 inches or less. When the
rise is more than 30 inches, the tread should be 12 inches
and the riser 6 inches.
For a moderately uniform slope, a stepped ramp may
be satisfactory (fig. 149B). Generally, the rise should be
about 6 inches to 6½ inches and the length between risers
sufficient for two or three normal paces.
As with all concrete sidewalks and curbed or uncurbed
driveways, a slight crown should be included in the walk
for drainage. Joints between brick or stone may be filled
with a cement mortar mix or with sand.
Walks can also be made of brick, flagstone, or other
types of stone. Brick and stone are often placed directly
over a well-tamped sand base. However, this system is
not completely satisfactory where freezing of the soil is
possible. For a more durable walk in cold climates, the
brick or stone topping should be embedded in a freshly
laid reinforced concrete base (fig. 150).
Walkways made of pressure-treated wood can be used
in conjunction with decks. Two 2- by 4-inch boards can
be fastened to the ground, 24 inches on center, with steel
rebar stakes, to which 2 by 6 decking is attached. Such a
walkway can lead to the wood steps of the deck.
Figure 150 – Offer sidewalks:
163
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