Structure - Final Flashcards
7 functions of walls
- Transferring live and dead loads to the flooring or foundation system
- Resist racking
- Support interior and exterior finishes
- Hide electrical and mechanical systems
- Accommodate thermal insulation
- Provide sound insulation
- Provide privacy
5 Loads on walls
- Dead loads from structural members
- Snow loads
- Wind loads
- Earthquake loads
- Live loads from people, furnishings and contents of homes
6 materials for masonry walls
- Brick
- Stone
- Concrete Block
- Cinder Block
- Clay tile
- Glass Block
How are the two thickness (wythes) in masonry wall held together?
- Header bricks
- Metal ties
Masonry walls that extend above the top floor ceiling joists are prone to:
Leaning outwards
Masonry walls are strongest in which force?
Compression, Tension, Bending
Compression
10 masonry wall problems
- Cracks
- Leaning, bowing, or bulging
- Mortar deteriorating or missing
- Wavy brick walls
- Excess corbelling
- Bricks (cored) installed on their sides
- Prior repairs
- Deterioration of the masonry
- Efflorescence
- Too close to grade
General approach to cracks? 8 questions to ask
- What kind of wall is it?
- What has moved?
- Which way has it moved?
- How far?
- Is it still active?
- Why has it moved?
- What are implications?
- What should be done about it?
Step by step approach to crack analysis
- Number of cracks
- Continuity of cracks
- Type and orientation of cracks
- Amount and direction of movement
- Related problems
- Still active
- Cause
- Implications
- Recommended action
T or F
Crack analysis should be done only from the outside
False
T or F
Crack over openings do NOT always indicate severe problems
True
6 causes of leaning, bowing or bulging masonry walls.
- Inadequate lateral support
- Foundation movement
- Sagging or sloping floor systems
- Rafter spread
- Failure of ties
- Brick expansion
Cause of bulging masonry walls below windows?
Leaking water at the window has rusted metal ties
Which walls tend to expand over time, after original construction
concrete brick
clay brick
wood frame
concrete block
poured concrete
clay brick
7 causes of mortar deterioration
- Weathering
- Poor quality mortar
- Poor job of laying the mortar
- Weather was too hot
- Weather was too cold
- Mortar set too long before being used
- Additives to the mortar weakened it
What causes wavy brick wall?
The walls may have been laid up too quickly or the mason may have skimped on the amount of mortar on the back part of the bricks.
Staggering bricks so that higher bricks project out beyond bricks below, is a called:
Corbelling
Maximum limit for corbelling is?
1/3 of wall thickness (Canada)
1/2 of wall thickness (US)
T or F
Hollow concrete blocks are weaker if laid on their sides
True
T or F
Patched cracks on brick are a sure sign of serious structural movement
False
In _________ framing, the wall studs extend through the subflooring
Balloon
All of these words mean the same thing except –
a) sill plate
b) top plate
c) base plate
d) bottom plate
e) sole plate
b) top plate
T or F
Bearing walls and partition walls are built in substantially the same way.
True
T or F
Walls see vertical loads only.
False
T or F
Openings in partition walls need headers.
False
Jack studs carry __________ loads.
Header
Horizontal wood braces installed between studs to prevent buckling. They are typically installed near the mid-point of the wall.
This is a description of _________
Girts
3 functions of wall sheathing
- Support the siding.
- Stiffen the walls
- Keep wind and water out of the building
4 ways to prevent racking of exterior wood frame walls.
- Interior finishes such as drywall, plaster or plywood
- Exterior sheathings
- Panel-type sidings
- Diagonal bracing
T or F
No sheathing is needed if the building is otherwise protected from racking and weather, and the siding needs no support.
True
What is the difference between waferboard and OSB?
In waferboard, the pieces are randomly oriented. In oriented strandboard (OSB), the wafers are aligned, at least on the faces of the panel.
T or F
Adjacent pieces of plywood sheathing should be butted tightly to enhance weather-tightness.
False
T or F
Sheathing paper (building paper) should act as a vapor retarder.
False
Loadbearing wall studs should have holes no larger than:
a) 1⁄4 to 1⁄8 of width, depending on authority
b) 1⁄4 to 50% of width, depending on authority
c) 1⁄3 to 40% of width, depending on authority
d) 1⁄3 to 60% of width, depending on authority
e) 1⁄2 to 60% of width, depending on authority
C
5 differences between loadbearing wall and a partition wall
- Partition walls have no structural elements below.
- Load bearing walls rest on foundations, beams or another wall system.
- Ends of floor or ceiling joists rest on load bearing walls but not partition walls.
- Loadbearing walls often have a wall directly above. Non-loadbearing walls are less likely to have this.
- Door openings in load bearing wood frame walls have headers. Openings in partition walls do not need headers.
How far above grade should a wood frame wall with wood siding stop?
8 inches above the grade
(8 inches for siding & stucco)
(6 inches for masonry)
Exterior walls on completed houses are rarely subject to racking because they have _______________ and/or ________________ .
Interior finishes
Exterior sheathing
4 causes of wall bowing or buckling
- The walls are too tall
- Bracing is missing
- Unexpected concentrated loads
- Damaged studs
Longer studs are more susceptible than conventional length studs to:
a) settling
b) rotting
c) leaning
d) leaking
e) bowing or buckling
E
T or F
Brick veneer walls are watertight.
False
5 difference between masonry veneer wall and solid masonry wall
Veneer walls have –
1. Weep holes
2. Wood studs behind the masonry
3. No header bricks
4. No masonry arches
5. A single wythe of bricks supported on a metal angle
13 masonry veneer wall problems
- Cracked
- Bowing or leaning
- Mortar missing or deteriorating
- Stone/brick deterioration or spalling
- Weep holes missing or obstructed
- Flashings missing or ineffective
- Efflorescence
- Too close to grade
- Wavy brick walls
- Excess corbelling
- Bricks on their sides
- Sagging lintels or arches
- Temporary repairs
7 common veneer wall problem (wood frame part)
- Rot and insect damage
- Leaning or racking
- Bowing or buckling
- Excess notches, holes and mechanical damage
- Sagging top plate
- Lack of fire stopping
- Sagging headers
Rusting steel lintels over windows cause what kind of masonry crack patterns?
Horizontal cracks
T or F
The masonry veneer is a loadbearing part of the structure.
False
Function of arches and lintels are:
to Transfer load of walls over openings to the wall systems on either side
T or F
With wood frame walls, the header size is independent of the number of stories above.
False
T or F
With masonry walls, the lintel size is independent of the number of stories above.
True
End bearing for steel lintels in masonry should be at least _____ inches.
4 inches (US)
6 inches (Canada)
End bearing for headers in wood frame walls should be at least ______ inches.
1 1/2 inches
9 arches and lintel problems
- Missing
- Cracks
- Mortar deteriorating or missing
- Wood supporting masonry
- Stone or brick deterioration
- Sagging, leaning or rotating
- End bearing
- Rust
- Rot or insect damage
T or F
Masonry resting on wood is a less than ideal arrangement.
True
T or F
The top of the exposed edge of a steel lintel should be caulked.
False
Wood lintels on the exterior face of a building are particularly prone to __________ problems.
Rot and Crushing
What kinds of things are you looking for with respect to the roof structure when looking far from the house?
- A sag in the rafter or ridge system
- Dishing of the roof surface
- Spreading of rafters or the top of the walls
6 things to look for inside the attic with respect to the roof structure
- Poor end bearing
- Weak connections
- Rot or insect damage
- Mechanical damage
- Fire damage
- Cracks or sagging of interior finishes
Why might the loads on the roof structure increase when you add attic insulation?
Improved insulation means less heat loss from the building. Less heat loss from the building means less melting of snow on the roof.
5 functions of roof framing members
- Carry live loads of wind, rain, snow and people
- Carry dead loads of roof sheathing, roof coverings and roof equipment
- Support dead loads of insulation and ceiling finishes
- Laterally support building walls
- Create an attic space, ventilation space and support for soffits and fascia
__________ are sloped structural members on steep roofs that support sheathing and run from the roof peak down to the eaves. They may be two by four or two by tens and are typically spaced 12 to 24 inches on center.
Rafters
___________ are horizontal or nearly horizontal framing members on low sloped roofs that carry the sheathing, roof covering and live loads above to walls or beams. They can be thought of as low sloped rafters. Some also carry ceiling finishes.
Roof joists
__________ are horizontal members that support insulation and ceilings. They are used with rafters and may support attic floors. They often tie the bottom ends of opposing rafters together to make a structurally sound triangle of the roof assembly
Ceiling joists
Ceiling joists are often not continuous from one side of the building to the other. In this case they are spliced over a central bearing wall. Why do they have to be securely tied together?
When the roof is loaded, the rafter bottoms will try to spread apart. The ceiling joists have to resist this outward force.
How is the span of a rafter measured?
by horizontal projection from one support to another
What is the difference between a ridge board and a ridge beam?
A ridge board does not carry rafter loads. A ridge beam does.
A ridge beam will prevent rafter spreading. A ridge board will not
A ridge board is typically one by x material. A ridge beam is typically at least two by x material
Ridge beams require vertical supports below. Ridge boards do not.
3 causes of sagging rafters
- Rafters overspanned or undersized
- Too many layers of roofing materials
- Excessive loads
Difference between roof sheathing sag and rafter sag
Sagging rafters cause a dishing in the entire roof surface and/or a sag at the ridge.
Sheathing sag is a repetitive pattern across the roof between rafters, trusses or roof joists.
5 causes of rafter spread
- Ceiling joists running perpendicular to rafters
- Ceiling joists not well connected to rafters
- Ceiling joist splices not secure
- Rafters not well secured to the structure
- Ceiling joists removed to create cathedral ceilings
What is the minimum required endbearing for rafters and ceiling joists?
1 1/2 inches on wood or metal
3 inches on concrete or masonry
How do you differentiate between a roof leak and a condensation problem in attic
condensation - wide spread, uniform damage to the roof area
Leaks - run down sloped roof surfaces
Main function of the collar tie?
provide intermediate support to prevent rafter sag
What is the ideal location for a collar tie?
midpoint (half way up) the rafter span
Why is lateral support required on long collar ties and how might this support be provided?
Because collar ties are in compression, they may buckle. Lateral support helps to prevent buckling.
What is the minimum roof slope required for collar ties to be effective?
4 in 12.
What is the difference between a knee wall and a purlin?
Knee walls and purlins both provide mid-point support for rafters.
Knee walls provide support by transferring the loads down to ceilings joists and walls or beams below.
Purlins act as beams running perpendicular along the underside of rafters.
What can cause sagging of the top plate on a knee wall?
if it is a single plate and if the studs are not lined up with the rafters above.
Difference between a chord and a web?
A chord is part of the perimeter of a truss. Webs are the internal members.
4 causes of truss sag
Excess load
Overspanning
Weak connections
Cut or damaged webs or chords
Where are notches and holes commonly permitted in trusses - webs, chords or neither of these?
No where. Not allowed
What is the difference between a wood “I” joist and traditional lumber?
Wood “I” joists are engineered and manufactured wood systems that have a top and bottom chord and a web that joins them.
T or F
It is acceptable to notch a bird’s mouth into the bottom plate of an “I” joist.
False
T or F
It is acceptable for wood “I” joists to lean against each other at the peak the way rafters can
False
In both plank and panel roof sheathing, vertical joints should not run continuously up one rafter or one truss. Adjacent vertical joints should be staggered. Explain why.
The roof is stronger if vertical joints are staggered. Vertical joints are weaknesses in the roof panel. Lining up all the weakness will tend to make the roof act as several smaller panels rather than one large one.
5 causes of roof Sheathing sag
Overspanning
Excess loads
Deteriorated wood
Panel type sheathing installed in the wrong direction
Inadequate edge support
List five types of hardware that may be used to improve the ability of a home to resist earthquakes.
- Sill anchors
- Hold downs (tie downs)
- Straps
- Hangers
- Post caps
- Hurricane clips (ties)
What is a shear wall
3⁄8 to 1⁄2 inch plywood or waferboard nailed to exterior ( and sometimes interior ) stud walls of home to resist the lateral forces of earthquakes and prevent racking.
They must extend the full wall height without interruption to be effective.
They are nailed every 4 to 6 inches at panel edges and every 12 inches in the field of the panels.
All edges must rest on solid wood framing or blocking. Hold downs should be provided at each corner and each end of the shear wall.
3 key issues in hurricane resistance for houses
- Roof sheathing must be well secured to roof framing.
- Roof framing must be well secured to wall framing.
- Openings for doors and windows must be protected against flying debris.
