Transcript Light Frame Construction

Light Frame
Construction
History
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Light wood frame construction invented in 1830
in Chicago by George Washington Snow
He recognized that closely spaced vertical
members used to fill space in walls of heavy
timber was strong enough to carry weights
Small boards and framing members became
inexpensive due to new milling practices
Machine made nails became cheap compared to
hand forge nails
Called balloon frame because it seem so thin
Balloon Frame
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Joist – Floors
Studs – Walls
Rafters – sloping
roofs
Disadvantages
• Fire strips required
• Studs are to long to
be erect efficiently
Platform Frame
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Floor
Wall – Load bearing
Floor
Wall – Load bearing
Attic/roof
Advantages
• Short studs
• Automatic fire stops
• Convenient working surfaces
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Disadvantages
• Each platform constitutes of a
thick layer of wood whose
grain runs horizontally
• Leads to vertical shrinkage –
leads to distress in exterior or
interior finish surfaces
Platform Frame Sheathing
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Is the key component for platform
framing
• The end nails that connect the
plates to the studs have little
holding power against uplift of the
roof by wind but the sheathing
connects the frame into a single
strong unit from foundation to
roof.
• The rectilinear geometry of the
parallel framing members has no
useful resistance to wracking by
lateral forces such as wind, but
rigid sheathing panels or diagonal
sheathing boards brace the
building effectively against a
surface to which shingles boards
and flooring are nailed for finished
surfaces.
Foundation for light Frame
Structures
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Foundations for light framing originally
made of stone or brink – are now made
in most cases of site cast concrete,
concrete block masonry or preservative
treated wood
Concrete and masonry foundations are
highly conductive of heat and usually
must be insulated to meet code
requirements concerning energy
conservation.
Wood foundation is easily insulated in the
same manner as the frame of the
building it supports
Further advantages claimed for wood
foundations are that they can be
constructed in any weather by the same
crew of carpenters that will frame the
building and they allow for easy
installation of electrical wiring plumbing
and interior finish materials in the
basement.
Establishing the position, shape
and size of building
Details of Foundations
Planning the frame
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Architectural floor
plans serve to indicate
the locations and
dimensions of all walls,
partitions and
openings
Exterior elevations are
drawings that show
the outside faces of
the building with
vertical framing
dimensions indicated
as required.
Sections are also
drawn that cut
completely through the
building showing the
Erecting the Frame
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Notice the basic simplicity
of the building process
• A platform is built walls
are assembled horizontally
on the platform and tilted
up into place and another
platform or a roof is built
on top of the walls
• Work is accomplished
without the use of ladders
or scaffolding and
temporary bracing is
needed only to support
the walls until the next
level of framing is installed
and sheathed.
Attaching the frame to the
foundation
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The sill preferably preservative treated or
naturally decay resistant wood is bolted to
the foundation as a base for the wood
framing .
A single sill is all that is required by most
codes but in better quality work the sill is
often doubled for greater stiffness
The top of the foundation is usually
somewhat uneven, so at low spots the sill
must be shimmed with wood shingle
wedges to be able to transfer loads from
the frame to the foundation
A compressible fibrous sill sealer should be
inserted between the sill and the
foundation to reduce air infiltration through
the gap.
The normal foundation bolts are sufficient
to hold most buildings on their
foundations, but tall frames in areas
subject to high winds or earthquakes may
require more elaborate attachments.
Floor Framing and Bridging
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The standard joist spacing are 16
or 24 o.c., measuring from center
tot center of the joists
Any of these spacing
automatically provides a joist at
every panel end
Sub flooring should be glued to
the joists to prevent squeaking
and increase floor stiffness
Plywood and OSB panels must be
laid with the grain of their face
layers perpendicular to the
direction of the joists because
these panels are considerably
stiffer in this orientation
Sheathing and sub flooring panels
are normally manufactured 1/8”
Bridging which is cross bracing or
solid blocking between joist at
midspan in a tradional feature of
floor framing
Floor Framing and Bridging 2
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Its function is to hold the joists
straight and to help them share
concentrated loads
Although many building codes no
longer require bridging, it should be
used on better quality buildings
because it makes a noticeable
difference in the rigidity of a floor.
Where needs of joists butt into
supporting headers as around stair
openings and at changes of joist
direction for projecting bays end nails
and toe nails cannot carry the full
weight of the joists and sheet metal
joist hangers must be used.
Manufactured I joists and floor
trusses are increasingly used in place
of sawn joist because they can span
farther between supports and they
tend to be straighter.
Wall framing Sheathing and
Bracing
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Some building codes require
blocking to be installed at the
mid height of the studs in wall
frames that are taller than 8
ft. The purpose of this
blocking is to stop off the
cavities between studs to
restrict the spread of fire.
Headers over window and
door openings must be sized
in accordance with building
code criteria. Typically, a
header consists of two
nominal 2 inch members
standing on edge separated
by a plywood spacer that
serves to make the header as
thick as the depth of the wall
stud.
Roof Framing
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Pitch is specified as a
ratio of rise to run
Rise is the vertical
dimension and run is
the horizontal
In the united states
pitch is usually given
on the architects
drawings as inches of
rise per foot of run
Prefabricated framing Assemblies
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Roof trusses and floor trusses
find widespread use in
platform frame buildings
because of their speed of
erection, economy of material
usage and long span.
Most are light enough to be
lifted and installed by two
carpenters
Manufactured wall panels have
been adopted more slowly
than roof and floor trusses,
except by large builders who
mass market hundreds or
thousands of homes pre year.