BCT 313 Quiz 4
What is the standard for joist spacing?
- 12", 16", 24" OC - Divisible into 48"
Sheathing
- 4'x8' OSB, plywood, Advantech/zip wall - Gives wall structure rigidity in wind and seismic activity - 1/8'' space between sheets - 6" OC edge nail - 12" OC interior nail
Roof sheathing
- 5/8" CDX or OSB for 16" OC rafters -5/8" CDX or OSB plus panel clips for 24" OC rafters
What is the difference between a ridge beam and a ridge board?
- A ridge beam is used with a tall vertical support - A ridge board is used when there are ceiling joists
What is a top plate?
- ALL load bearing walls have to have double top plates - Load bearing wall could have a single plate if it is stack framed
What is the importance of exterior non load-bearing walls
- Address their own dead, wind, and seismic loads - Typically at the end walls (gable wall)
Similarities between balloon and platform framing
- Both have sill, soleplate, sill plate, foundation sill, and mud sill
What is the importance of exterior load bearing walls?
- Contribute to the geometry of the structure - Support load elements (dead live snow) of roof, trusses, rafters, sheathing, insulation, windows, doors ect - Provide barrier and separation from weather, sound, sunlight - Provide privacy and security - Nailing base for cladding, membranes, window, doors
Steps of truss system install
- Delivered to site preassembled - Placed on clean flat surface and supported - Lifted into position - Brace first truss between ground and wall - Lift each additional truss and temporarily brace - Permanent bracing with sheathing provides top chord bracing and stabilization
What is the reality of OVE?
- Design/engineering costs are higher - More planning time to get accurate drawings and time negotiating with building inspector - Framers are unfamiliar with OVE (training, production, supervision) - Savings in lumber costs are offset by costs for splice plates, drywall clips, header hangers ect - Single plates and sills are more difficult to nail and keep straight - Some siding type requires 16" OC - No jack studs makes it hard to fasten siding near windows and doors
Wall framing includes the framing of what?
- Exterior and interior load bearing walls - Exterior non load-bearing walls (typically at end walls) - Interior non-load bearing partitions
Advantages of platform framing
- Faster, easier, safer - Uses smaller, shorter pieces - Process creates safer work platforms for each level - Less firestopping is necessary
What is a sill plate?
- Forms base of stud wall - Untreated lumber if wall is built on wood floor diaphragm but pressure treated if wall is on concrete or masonry foundation wall - Single or double
Studs
- Give wall structure and transfer loads from top plate to bottom plate - Dimensional, PSL, OSL, LSL, light gauge steel - Spaced on regular intervals - Load bearing= double plate 16" OC - Non load bearing= single plate 16" or 24" OC
ZIP sheathing benefits
- Installation eliminates multiple steps - Code-recognized built in drainage plane and air barrier - Exterior continuous insulation
Elements of ZIP sheathing and their purposes
- OSB= sheathing - Proprietary coating when taped= Drainage plane, air barrier and vapor retarder - Insulation board option
What is the importance of flashing?
- Protects against water leakage at chimney and head wall intersections - Lapped to the weather
What is the advantage of double sills and plates (as opposed to single)?
- Provides better nailing for drywall and interior trim - Better straightening ability - Leveling and squaring of sills
What is the purpose of gutters and leaders (downspouts)?
- Redirect water and prevent wetting of walls - Prevents erosion of ground beneath eaves - Integrate appearance and material aesthetic with performance - No gutters= less maintenance but additional attention redirecting water is required
Disadvantages of prefab truss systems
- Requires a crane - Cost - Reduces attic storage - Require proper on-site storage
Advantages of prefab truss systems
- Save close-in time - Increases span without posting up - Greater interior and exterior design flexibility - Efficient use of lumber
Components of framed floor system
- Sill plate - Girders, beams, joists and/or floor trusses - Band joists or rim boards - Subfloor panels
What is a truss hip system?
- Step down trusses and prime hip girder to extend the length of the roof
What is the importance of interior load bearing walls?
- Support roof and upper floors at intermediate points between exterior load bearing walls - Transfer these loads along the load path to the foundation and undisturbed soil below
How does a truss system get fastened to a wall?
- Trusses rest on top plate and are directly fastened to the top plate
Advantages of I-Joist and Floor trusses
- Used in place of traditional lumber joists - Span longer distances than dimensional lumber joists - Installed per layourtt
What must be considered when constructing a roof?
- Water management - Dead and snow loads - Wind and seismic loads - Insulation levels - Drying strategies - Shading - Fastener base for roofing materials
Disadvantages of platform framing
- Wood shrinks more tangentially and radially than longitudinally (Tall studs of balloon frame shrinks very little) -This can lead to buckling of the exterior siding or buckling and cracking of interior drywall or plaster
What are the benefits of OVE framing?
-Framing material savings with attendant labor, fasteners, and scrap savings (up to 30%) - Maximizes thermal resistance of envelope (R-6.88 to R-19)
What is the function of bridging and blocking?
-Holds joists straight - Helps joists share concentrated loads by spreading concentrated load to more than 1 joist - Increases rigidity of floor
Advantages of Band Joists (dimensional) or rim boards (engineered)
-Stabilize the floor joists: -Providing continuous edge support -Braces ends of joists against rotation - Continuous nailing base for floor decking
3 types of wall blocknig
1. Fire blocking: Stops vertical movement of fire or sparks in cavity between studs 2.. Utility blocking: Support for plumbing/mechanical elements 3. Ladder blocking: Nail base for vertical siding attachment or perpendicular partition wall
What are the two ways to connect the joists to the supporting wall or beam?
1. Joists rest on the supporting wall or beam and are fastened to it 2. Joists rest on joist hangers and the hangers are fastened to the supporting element as manufacturer and code dictates
Maxims of anchor bolt placement
1/2" diameter minimum Two per sill plate, 9"-12" from end - 3.5" from edge or OC
What is the slope of a flat roof?
1/8", 1/4" slope created with tapered insulation
How much tangential shrinkage does wood experience?
8-10%
What is statics?
A branch of mechanics concerned with elements at rest and forces in equilibrium
Define anisotropic
A physical property that has a different value when measured in different directions
How are components of framed floor system connected?
Bridging, blocking, joist hangers, anchor bolts, nails and screws, adhesives
What do girders/beams do?
Carry weight across spans that are not too long for dimensional joists, i joists, or floor trusses to carry. They transfer the weight of the elements of roof, floor and walls (dead load), weight of people and furniture (live load) and snow and ice load (snow load) downward to the foundation and to the bearing soil Can be made of dimensional lumber, LVL, PSL, or steel
What is the bird's mouth cut?
Cut in a rafter to make it fit flush on the top plate
What is the importance of interior non load-bearing walls?
Divide home into individual rooms *No contribution to structure
Typical finished floor and underlayment
Finished floor: Traditional hardwood or engineered wood Underlayment (on top of subflooring) depends on floor finish Underlayment must address acoustics, durability, and adhesion for the finish product
Roof types
Flat, gambrel, shed, gable, hip
What is the relationship between framing and finish flooring?
Framing accommodations must be designed to accommodate different thicknesses and material loads
Roof grammar
Hip, valley, ridge, dormer, eave, rake
Foundation to floor connection at side wall
In areas of high termite risk, continuous metal shield prevents termites from getting into framing from the foundation
What are pockets?
In the foundation walls where beams/girders are positioned into so that the floor joists sit directly on top of them or are attached to the side of them (with hangers)
When does backfilling take place?
It can occur before the floor diaphragm is built, but foundation walls must be braced as backfill is compacted (in lifts) so lateral pressure of soil is resisted
Load bearing header vs non load bearing headers
Load bearing: present over all openings on load bearing walls to transfer load from above horizontal direction to the vertical members at each edge. Weak point in thermal envelope because of mass Non load bearing: Can be replaced with more cost effective framing approach
Low sloped roof vs steep sloped roof
Low= Less than 4 in 12 slope or pitch Steep= Greater or equal to 4 in 12 slope or pitch
What are trimmers?
Members that run parallel to floor joists
What are headers?
Members that run perpendicular to the floor joists
What is lateral cohesive movement?
Movement of water on the surface due to non-porous material due to adhesion, cohesion and surface tension
What is capillarity?
Movement of water within thin tubes (wood) and within the spaces of a porous material (concrete) due to adhesion, cohesion, and surface tension between liquid water and the material
Subflooring
OSB or ply panels perpendicular to floor joists, staggered between rows so no joints are aligned - Base for floor finish - Combo of fastening and gluing - Tongue and groove connections between panels
What is OSL?
Oriented strand lumber: Made from flaked wood strands, less strong and less expensive than PSL, used to replace studs in tall walls because of their straightness
What is the benefit of open truss as a joist material?
Plumbing and electrical work easier, insulate better in between trusses for higher R value
What is PTL?
Pressure treated lumber - Chromated Copper Arsenate (CCA) or Alkaline Copper Quat (ACQ) - Above ground= .15lbs/CF - Ground contact= .40lbs/CF -Foundations= .60lbs/CF
What is the purpose of the floor diaphragm?
Provides lateral stability for wall when backfilled
Foundation to floor connection at end wall
The sill is bolted down and leveled on top of the foundation wall. The floor joists are toenailed to the sill
What is the purpose of a foundation/mud sill?
They are fastened to the foundation stem wall or monolithic SOG to provide a mounting surface for the floor structure (if stem wall) or wall structure (if mono SOG). They execute the structural transition from concrete/masonry to wood. They must be manufactured from PTL or decay resistant lumber to protect them from moisture
What is the purpose of floor joists?
Transfer loads of the structure to the beams, columns, load-bearing walls and other major supports Dimensional lumber, I joist, or open truss
What are hangers?
Used to attach floor joists to the side of the girder/beam (beam/girder to concrete connection)
What are springboards?
Used to plumb walls because they are unstable until next level floor diaphragm is constructed
What is roof slope or pitch?
Vertical rise in inches for every horizontal run of 1 foot in inches * 4 inches for every 1 foot for 12 inches is a 4 in 12
What is a rough opening?
Where floor joists are spaced far enough apart to allow for a finished product (staircase, chimney stack, mechanical shaft, elevator ect) to pass through the floor with small amounts of tolerance to allow for shimming of final install. Adjacent joists are doubled or tripled or engineered to compensate for the larger space between them *Put unit exactly where it is intended so it will not be compromised by the frame with expansion and contraction * 1" wider and 1/2" higher than frame
