Chapter 26

Structural Components

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Links for Chapter 26

Floor Construction

Wall Construction

Roof Construction

Related Web Sites

Environmental Design

3

Conventional Floor Framing

• Floor joists range from 2” X 6” to 2” X 14” and spaced at 12”, 16”, or 24”

• Mudsill rests on the masonry foundation– Provides a base for all framing

– Attached to foundation with anchor bolts

– Either 3/4” or 5/8” in diameter

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Conventional Floor Framing

FLOOR JOIST

FLOOR JOIST

SILL

MUD SILL &ANCHOR BOLTS

STEM WALL

FOOTING

FOOTING

STUDS

STUDS

FLOOR SHEATHING

RIM JOIST

FLOOR SHEATHING

CRAWL SPACE

WALL SHEATHING

SHEATHING

SOLID BLOCK

GIRDERPOST

CONC. PIER

GUSSET

SILL

SOLID BLOCK

MUD SILL &

STEM WALL

ANCHOR BOLTS

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Conventional Floor Framing

• Girder (beam) is used to support the floor– A flitch beam consists of steel plates bolted

between wood members

– Glu-lam beams are laminated with sawn lumber and more structurally stable

– Engineered wood girders consists of laminated veneer strips glued together

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Conventional Floor Framing

• Girder (beam) is used to support the floor– Steel beams are used for long spans and do

not shrink or expand

– A post is used to support beams and are 4” X 4” or 6” X 6” depending on beam width

– Steel posts do not draw moisture and remain a more true size

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Conventional Floor Framing

FLOORJOIST

RIM JOIST ORSOLID BLOCK

SHEATHING

SILL

SOLID BLOCKOVER BEARINGWALL

DOUBLE TOP PLATE

STUDS

STUDS

CANTILEVER

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Conventional Floor Framing

• Joists support the subfloor– Joists that span past a girder are cantilevered

– Joists shaped as an “I” are called trusses

– Laminated veneer lumber is used for heavy loads with single or multi-spans

– Engineered joists support larger loads with less material

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Conventional Floor Framing

FLOORJOIST

RIM JOIST ORSOLID BLOCK

SHEATHING

SILL

SOLID BLOCKOVER BEARINGWALL

DOUBLE TOP PLATE

STUDS

STUDS

CANTILEVER

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Engineered Floor System

A3

A3

L1

H1

L3

A3

F2

B2

B3

B1

H2

E2

A2

F2

L5

L3

CS

A1

A1

H1

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Floor Bracing

• Joists will tend to roll as loads are applied

• Blocking is used at the center of the joist span to help transfer lateral loads

• Sheathing is placed over the joists to form the subfloor– Face grain should be perpendicular to the

floor joists

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Floor Bracing

FLOOR SHEATHING

RIM JOIST

TOP PLATES

SOLID BLOCKING

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Post-and-Beam Construction

• Girders are supported on a post and concrete pier– Usually 4” X 6”

– Spaced at 48” o.c.

– Flooring is 2 X 6 or 2 X 8 tongue and groove boards or 1 3/32” plywood

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Post-and-Beam Construction

MUD SILL &ANCHOR BOLTS

STEM WALLFOOTING

FLOOR DECKING

SILL

GIRDERCONC. PIER

GUSSET

CRAWL SPACE

POST &

SILL

STUDS

GIRDER

FLOOR DECKING

CONC. PIER

POST &GUSSET

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Framed Wall Construction

• Bearing walls support the weight of the roof or other floors– Extra support is required under it

• Nonbearing walls have no structural purposes– Sometimes called partitions

– Can be removed without causing damage

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Framed Wall Construction

BEARINGWALLS NONBEARING

WALLS

BEARINGWALLS

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Framed Wall Construction

• Sole plate is the bottom plate and disperses the wall load to the floor system

• Studs are vertical framing members to transfer load from top of wall to floor system

• Top plates are used to hold the wall together– Two are required on bearing walls and must

lap by at least 48”

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Framed Wall Construction

• Sheathing is used as an insulator against weather

• Double-wall construction is when sheathing is applied to an exterior wall

• Single-wall construction is when a vapor barrier and no sheathing is used on an outside wall

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Framed Wall Construction

• Sheathing helps walls not to twist or rack

• Shear panel resists these forces

• Let-in braces stiffen stud walls

STUDS TEND TO SHIFTOR RACK WHENPRESSURE IS APPLIEDTO THEIR WIDE SURFACE

FORCE(WIND ORSEISMIC)

STUDS INNORMALPOSITION

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Framed Wall Construction

• Header is an opening above a door or window

• Trimmers support headers

• Subsill is on the bottom of a window

FLOOR SHEATHING

RIM JOIST

TOP PLATES

CRIPPLE (JACK)STUDS

HEADERTRIMMER

KING STUD

SUBSILL

JACK STUDS

SOLE PLATE

FLOOR SHEATHING

RIM JOIST

TOP PLATES

HEADERROUGHOPENING

CRIPPLE (JACK) STUDS

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Roof Construction

• Eave on the roof extends beyond the walls

• Cornice is the covering on the eaves

• Fascia is trim placed at the end of the rafters

• Roof sheathing covers structural members

• Skip sheathing is used with either tile or shakes

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Roof Construction

BAFFLEAT VENT

SOLID BLOCK-OMITEVERY THIRD FORSCREENED VENT

FASCIA

RAFTER

INSULATION

BAFFLEBTWN EA.RAFT

RAFTER

2 x 4 NAILER

SCREENED VENT

RAFTER

FASCIA

RAFTER/CEILING

NOTCH RAFTERTAIL TO MATCHFASCIA

2" AIR SPACEABOVE INSULATION

3-1" SCREENEDVENTS AT EACH

SOLID BLOCKWITH 2" AIRSPACE ABOVE

G.I. FLASHING

FASCIA

SCREENED VENT

NOTCH RAFTER TAIL

JOIST

RAFTER SPACE

1/2" "CCX" EXT. PLY

1/2" "CCX" EXT. PLYOR 1X6 T&G TYP.

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Roof Construction

• Finished roofing is the weather protection system

• Pitch describes the slope of the roof– Rise is the vertical distance of the slope– Run is the horizontal distance of the slope

• Span is the horizontal measurement between inside edges of supporting walls

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Roof Construction

512

RIDGE BOARDPITCH SYMBOL

OVERHANG

TOTAL SPAN

RUN

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Roof Construction

• Conventional framing involves the use of wood members placed in a repetitive fashion

• Ridge board is the horizontal member at the ridge and runs perpendicular to the rafters

• Rafters are the sloping members used to support roof sheathing and finished roofing

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Roof Construction

R10

R5

R1

R5

R1

R7

R10

H5

H6

O

H5

R3

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Roof Construction

• Common rafter spans and supports the roof loads from ridge to top plate

• Bird’s mouth is the notch cut in rafter where the rafter intersects a beam or bearing wall

• Hip rafter is used on the slopes of the hip• Valley rafter is used on the slopes of the

valley

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Roof Construction

COMMON RAFTERS

HIP JACK RAFTERS

HIPS

RIDGE

VALLEY RAFTERS

TOP PLATES

HIP

VALLEY

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Roof Construction

• Ceiling joists span between top plates and bearing walls

• Ridge braces are used to support downward action of the ridge board

• Ridge beam supports the upper end of the rafter/ceiling joists

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Roof Construction

RIDGE

COLLAR TIE @ 48" O.C.

CONTINUOUS PURLIN

PURLIN BLOCK

PURLIN BRACEAT 48" O.C.

CEILING JOIST

45Þ MAX.

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Truss Roof Construction• Truss is a component used to span large

distances without intermediate supports• Top chord supports the roof sheathing• Bottom chord resists outward thrust of the top

chord and supports• Webs span between top and bottom chords• Ridge blocks provide nailing surface for roof

sheathing

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Truss Roof ConstructionTOP CHORD

BOTTOM CHORD

WEBS

TRUSSCONNECTORS

CLEAR SPAN (INSIDE TO INSIDE)

TOTAL SPAN (OUTSIDE TO OUTSIDE)

TRUSSCLIP

RIDGE BOARD

RAFTERS

DOUBLE TRIMMER

DOUBLE HEADER

ISOMETRIC

PLAN

RAFTERS

DOUBLE TRIMMER

DOUBLE HEADER

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Truss Roof Construction

• Cantilevered truss is when the truss extends beyond the support

• Hip truss is used to form hip roofs• Vaulted or scissors truss have inclined bottom

chords• Metal hangers keep floor, ceiling, and roof

members from separating

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Truss Roof Construction

STANDARD GABLE END

CANTILEVERED STUB

MONOHIP

SCISSORVAULTED

ATTICDUAL PITCH

GAMBRELBROKENPITCH

HEADER

STANDARD GABLE END

CANTILEVERED STUB

MONOHIP

SCISSORVAULTED

ATTICDUAL PITCH

GAMBRELBROKENPITCH

HEADER

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Truss Roof Construction

STD. TRUSSES

GIRDER TRUSS

3 PANEL WINDOWSKYWALL.

HEADERTRUSS

6'-0" TYPICALVERIFY EXACT SIZEW/ MANUFACTURER.

FRAME AREA OVER RAFTERS @ 24" O.C.

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Environmental Design

• It is important to be familiar with chemicals that are commonly found in the home– Formaldehyde is a colorless gas found in

most resin-based construction products

– It can cause irritation to nose, throat, and eyes and cause headaches, coughing, and fatigue

37

Environmental Design

• Optional material can be used that does not contain harmful chemicals– Grass-based boards can be used for

sheathing

– Low-toxic products that repel moisture

– All natural carpets reduce allergy reactions

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Environmental Design

• Gas and oil heaters are more efficient, they do produce toxic chemicals and reduce the quantity of natural resources

• Electric heaters are nontoxic yet are more expensive and less efficient

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Related Web Sites• American Lumber Standards Commission,

Inc. - www.alsc.com• Gypsum Association - www.gypsum.org• The Masonry Society - www.masonrysociety

.org• Wood Truss Council of America- www.

woodtruss.com