Weekend Cabin Retreat Project
Sill and Floor Construction
Sacramento City College
EDT 300
Kenneth Fitzpatrick, P.E.
EDT 300 - Sill and Floor Construction
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Objectives
 Recognize
platform and balloon
framing.
 Plan the appropriate floor support
using joists or trusses for a
structure.
 Determine proper joist sizes using a
typical span data chart.
 Describe the components of a floor
system.
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EDT 300 - Sill and Floor
Construction
Objectives
 Demonstrate
an understanding of the
principles involved in post and beam
construction.
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EDT 300 - Sill and Floor
Construction
Types of Framing
 Methods
of floor framing vary from
one section of the country to
another.
 Builders in a given area may use
different methods, based on personal
preference and experience.
 The basic types of floor framing are
platform and balloon framing.
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EDT 300 - Sill and Floor
Construction
Platform Framing
 Platform
framing is popular for
several reasons.
 It
can be used for both one- and two-story
structures and is easy and fast to
construct.
 Shrinkage is uniform throughout the
structure. A firestop is automatically
provided.
 Construction is safe because the work is
performed on solid surfaces.
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EDT 300 - Sill and Floor
Construction
Platform Framing
 In
platform framing, the sill is the
starting point in constructing a floor.
 A sill is the lowest member of the
frame of a structure,
 Rests
on the foundation
 supports the floor joists or the uprights
(studs) of the wall.
 The
sill in most residential
construction is a 2 x 6.
 (actual
6
dimensions 1 1/2" x 5 1/2").
EDT 300 - Sill and Floor
Construction
Platform Framing
 Platform
framing utilizes a method of sill construction known as box sill
construction.
 The
box sill consists of a 2 x 6 plate
(also called a sill or mudsill) and a
header that is the same size as the
floor joists.
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
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EDT 300 - Sill and Floor
Construction
Balloon Framing
 Balloon
framing was once used
extensively, but in recent years has
diminished in importance.
 Its distinguishing feature is that the
wall studs rest directly on the sill
plate.
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EDT 300 - Sill and Floor
Construction
Balloon Framing
 Two
types of sill construction are
used:
 The
solid or standard sill.
 The T-sill.
 The
studs are nailed directly to the
sill and joists in solid sill construction.
 No header is used.
 Joists are supported by a ribbon and
nailed to the studs on the second
floor level.
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EDT 300 - Sill and Floor
Construction
Balloon Framing
A
firestop must be provided between
the studs.
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EDT 300 - Sill and Floor
Construction
Balloon Framing
 In
T-sill construction, a header is
used, which also serves as a firestop.
 The studs
 Rest
on the wall plate.
 Are nailed to the header as well as the sill
plate.
 The
sill may be very wide, to provide
a good base for the joists to rest on.
 Solid sill is used more extensively in
two story homes.
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EDT 300 - Sill and Floor
Construction
Balloon Framing Advantages
 Small
potential shrinkage.
 Vertical Stability.
 Can be used for two-story homes with
brick veneer or stucco exterior wall
finishes.
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EDT 300 - Sill and Floor
Construction
Balloon Framing Disadvantages
A
“less than desirable” surface to
work on during construction.
 Firestop blocks must be used.
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EDT 300 - Sill and Floor
Construction
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Construction
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EDT 300 - Sill and Floor
Construction
Joist and Beams
 Joists
provide support for the floor.
 Usually made from a common soft
wood such as
 southern
yellow pine
 fir
 larch
 hemlock
 The
or spruce.
size of floor joists ranges from a
nominal size of 2 x 6 to 2 x 12.
 Spacing from 12" to 24".
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EDT 300 - Sill and Floor
Construction
Joist and Beams
 The
size joist required for a given
situation will depend on the
 length
of space
 load to be supported
 specie and grade of wood
 and distance the joists are spaced apart.
 Spacing
of floor joists may be 12, 16,
or 24" o.c. (on center).
 A spacing of 16" o.c. is most common.
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EDT 300 - Sill and Floor
Construction
Joist and Beams
 Span
data for floor joists is
presented in tables.
 The span data presented assumes a
maximum deflection of 1/360th of
the span with a normal live load.
 This is the amount which most codes
require.
 The normal live load is 40 pounds per
square foot.
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EDT 300 - Sill and Floor
Construction
Floor Systems
A
floor system may also be
constructed using girders or trusses
 usually
4 x 6, 4 x 8, or 4 x 10 depending on
the span) in the place of floor joists.
 The purpose of this approach is to use
fewer support members (joists).
 The
typical spacing of girders or
trusses in this system is 48" o.c. with
1 1/8" thick tongue-and-groove
plywood as the floor decking.
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EDT 300 - Sill and Floor
Construction
Floor Systems
 The
distance which joists must span
is usually so great that a beam or
load-bearing wall is needed to reduce
the span.
 The beam may be
a
solid timber
 a built-up beam from dimension lumber
 a metal S-beam.
 Load-bearing
walls may be concrete
block, cast concrete, or frame
construction.
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Systems
 Partition
walls that are supported by
the floor joists require added
support.
 It is good practice to double the
joists under parallel partition walls.
 If space between the joists is used
as a cold air duct, solid blocking is
used between the joists.
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EDT 300 - Sill and Floor
Construction
Floor Systems
 Openings
in the floor for stairs and
chimneys require double joist
framing.
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Systems
 Cross
bridging is commonly used to
stiffen the floor and spread the load
over a broader area.
 Bridging boards are ordinarily 1 " x 3"
in size with the ends cut at an angle
so they fit snugly against the joist.
 They are nailed securely in place
midway between the beam and wall.
 Metal bridging is also available.
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Systems
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EDT 300 - Sill and Floor
Construction
Floor Trusses
 Engineered
wood floor trusses for
light-frame construction are widely
used for residential structures.
 minimum
of depth
 lightweight assembly
 easy to handle.
 The
open web construction reduces
transmission of sound through
floor/ceiling assemblies.
 Makes installation of plumbing,
heating, and electrical systems easy.
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EDT 300 - Sill and Floor
Construction
Floor Trusses
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EDT 300 - Sill and Floor
Construction
Floor Trusses
 Computers
are used to design modern
engineered floor trusses to assure
load capabilities for a given design.
 Each truss has a built-in camber so
that the floor/ceiling will be level
once a load is applied.
 Stress-graded lumber is used in their
construction so that a minimum
amount of material is required.
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EDT 300 - Sill and Floor
Construction
Floor Trusses
 Some
trusses are fabricated with
lumber chords and patented
galvanized steel webs, instead of the
typical wood webs.
 The webs have metal teeth which are
pressed into the sides of the chords.
 A reinforcing rib withstands both
tension and compression forces.
 Engineered wood floor trusses are
usually fabricated from 2 x 4 or 2 x 6
lumber and generally spaced 24" o.c.
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EDT 300 - Sill and Floor
Construction
Floor Trusses
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EDT 300 - Sill and Floor
Construction
Subfloor
 Plywood,
tongue-and-groove boards,
common boards, and other panel
products are used for subfloors.
 Plywood is advantageous.
 large
size of plywood
 short time required to nail the sheets in
place
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EDT 300 - Sill and Floor
Construction
Other Subfloor Materials
 One-half
inch thick plywood
 Composite board
 Waferboard
 Oriented strand broad
 Structural particleboard,
 These
be used when joists are
spaced 16" o.c.
 Some builders prefer 5/8 in. stock.
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EDT 300 - Sill and Floor
Construction
Other Subfloor Materials
 When
these products are used, the
joist spacing must be is very
accurate.
 All edges of the panels must be
supported.
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EDT 300 - Sill and Floor
Construction
Other Subfloor Materials
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EDT 300 - Sill and Floor
Construction
Subfloor Materials
 Some
localities combine the subfloor
and underlayment (usually
5/8"particleboard) into a single
thickness that is generally 1 1/8"
thick.
 The sheets have tongue-and-groove
edges and require no blocking
between the joists.
 A single thickness sheet of 3/4"
tongue-and-groove plywood may also
be used for some applications.
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EDT 300 - Sill and Floor
Construction
Subfloor Materials
 Plywood
should be installed with the
grain direction of the outer plies at
right angles to the joists.
 It
is stronger when positioned in this
manner.
 Panel
products should also be
staggered so that end joints in
adjacent panels break at different
joists.
 A slight space must be allowed
between sheets for expansion.
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EDT 300 - Sill and Floor
Construction
Subfloor Materials
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EDT 300 - Sill and Floor
Construction
Subfloor Materials
 Subfloor
panels may also be glued and
nailed to the joists.
 Structural
tests have shown that stiffness is
increased by 25 percent with 2 x 6 joists
and 5/8" plywood.
 Gluing
advantage
 squeak-free
structure
 eliminates nail-popping
 reduces labor costs.
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EDT 300 - Sill and Floor
Construction
Cantilevered Joists
 Home
designs where a section of the
floor projects beyond a lower level
are called cantilevered joists.
 These joists are parallel to the
overhanging area
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EDT 300 - Sill and Floor
Construction
Cantilevered Joists
 Rule
of thumb for necessary length
of cantilevered joists:
 Extend the joists inside at least
twice the distance they overhang
outside.
 If
the inside distance is too short the floor
may sag along the outside wall.
 If
a ledger strip is used, locate it
along the top of the inside double
header joist since the force will be up
rather than down.
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EDT 300 - Sill and Floor
Construction
Cantilevered Joists
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EDT 300 - Sill and Floor
Construction
Framing Under Slate or Tile
 Areas
which have ceramic tile, slate,
or stone floors require a substantial
base.
 If a concrete base is provided, the
floor framing must be lowered to
provide for the concrete.
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EDT 300 - Sill and Floor
Construction
Framing Under Slate or Tile
 Several
techniques are used:
 A smaller
size joist may be used and the
space between joists reduced to provide
adequate support.
 This is a common solution to the problem.
 Another technique is to use one or more
beams under the section to support the
added weight.
 The
dead weight may be as much as
40 or 50 pounds per square foot in a
bathroom with a tile floor and heavy
fixtures.
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EDT 300 - Sill and Floor
Construction
Framing Under Slate or Tile
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EDT 300 - Sill and Floor
Construction
Framing Under Slate or Tile
 The
concrete base for the tile or
stone should be
 reinforced
with wire mesh
 cast on a plywood subfloor covered with
building paper.
A
special type of concrete is
generally used. a mixture of 1 part
portland cement and 6 parts sand,
known as a cement mortar mix.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Large
framing members (posts,
beams, planks) are spaced farther
apart than conventional framing
members
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Post
and beam construction provides
a greater freedom of design than
conventional framing techniques.
 The system is basically simple, but
presents problems related to
 larger
structural sizes
 framing connectors
 methods of joinery.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Most
of the weight is carried by the
posts.
 The walls are called curtain walls.
 Curtain walls provide for wide
expanses of glass without the need
for headers.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Wide
overhangs are also possible by
extending the large beams to the
desired length.
 Spacing of the posts is determined by
the design of the building and the
load to be supported.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 The
foundation for a post and beam
structure may be
a
continuous wall
 a series of piers where each post is to be
located.
 Size
by
of footings will be determined
 the
weight to be supported
 soil bearing capacity
 local building codes.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 The
size of posts required will be at
least 4" x 4".
 If the floor is also to be supported
by the posts, they should be at least
6" x 6".
 Vertical height of the posts will be a
factor in determining the size.
 Again check local codes.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Beams
may be solid, laminated,
reinforced with steel, or plywood box
beams.
 Spacing and span of the beams will be
determined by the size and kind of
materials and load to be supported.
 In most normal situations, a span of
7'-O" may be used when 2" thick
tongue-and-groove subfloor or roof
decking is applied to the beams.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Thicker
beams must be used if a span
greater than 7'-O" is required.
 Two systems of beam placement are
possible with post and beam
construction.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 First
system: the longitudinal method.
 Beams
are placed at right angles to the
roof slope.
 Roof decking is laid, therefore from the
ridge pole to the eaves line.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Second
system: the transverse
method.
 The
A
beams follow the roof slope and
decking runs parallel to the roof ridge.
post and beam structure has a
limited number of joints.
 Fastening small members by nailing
does not provide a satisfactory
connection.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 Metal
plates or connectors are used.
 These
are fastened with lag screws or
bolts.
 Decking
planks for the roof and floor
range in thickness from 2 to 4 inches.
 The planks are usually tongue-andgrooved along the edges and they may
be tongue-and-grooved on the ends as
well.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
 It
is customary to leave the
underside of the planked roof
exposed.
 If added insulation is required, it may
be placed above the decking and
under the roofing material.
 Rigid type insulation should be used.
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
Construction
Post and Beam Construction
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EDT 300 - Sill and Floor
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