Construction Flashcards
low slope roof
less than 2” per foot or 17% (but above 1/4” per ft)
Relatively slow drainage, small errors resulting in ponding. Membranes must be flawlessly watertight. Water vapor from the building inside or wind from outside can cause blistering, flapping, displaced or cracked membranes, But can cover buildings of any horizontal scale, simpler geometry, can be planted & occupied
Steep roof
greater than 2” per foot or 17%
Use gravity to shed water, overlap small units (shakes, shingles, thatching, etc). These smaller units can be easily repaired and replaced, and bend and flex with the roofs expansion and contraction. However they are visible
way to slope the roof
- slope the structure
- taper the structure
- tapering the insulation
Topside Roof Vent
Allows moisture vapor to escape from beneath the membrane but closes to prevent water or air from entering
low slope roof membranes
- bituminous (made from asphalt, overlapping layers)
- single-ply (rolled up plastic that we unroll)
- fluid applied (take a chemical sealant and mop or spray it on)
Emissivity
ability for the roof to shed heat, high emissivity roof means it can shed the heat quickly so its cooler
Albedo
solar reflectance, high albedo is light color & reflective (we want atleast 65% albedo)
Difference in strength b/w springwood & summer wood
Summerwood - grows slower, more strength
Springwood - grows faster, less strength
modulus of elasticity
measure of overall strength / stiffness, higher number means stronger
Plain sawn
cheaper, more likely to warp, produces less waste
Quarter sawn
finer grain (better aesthetics), more dimensionally stable, more expensive
Moisture content (MC)
how much moisture is in the wood, the less moisture the greater structural quality
MC = ((Weight when wet - weight when dry)/Weight when dry) * 100
Ex. MC15 = 15% moisture, MC19 = 19% moisture, MC15 is stronger
Wood grades
Stud grades - for studs, including load bearing
#1 structural framing - for headers and long spans
Utility grade - for blocking, etc
glue laminated wood
layers of dimensional lumber bonded together with durable, moisture-resistant structural adhesives so that all of the grain runs parallel to the longitudinal axis
Cross-laminated timber
several layers of kiln-dried lumber boards stacked in alternating directions, bonded with structural adhesives, and pressed to form a solid, straight, rectangular panel
Lightweight yet very strong, with superior acoustic, fire, seismic and thermal performance, CLT is also fast and easy to install, generating almost no waste onsite.
Laminated strand lumber
dried and graded wood veneers, strands or flakes that are layered upon one another and bonded together with a moisture-resistant adhesive into large blocks known as billets
(longer strands) not super strong, inexpensive
oriented strand lumber
OSL is made from flaked wood strands that have a length-to-thickness ratio of approximately 75. The wood strands used in OSL are shorter than those in LSL. Unlike OSB, the strands in OSL are arranged parallel to the longitudinal axis of the member
Parallel strand lumber
Dried and graded wood strands are layered upon one another and bonded together with a moisture-resistant adhesive into large blocks known as billets
In the case of PSL, long strands (longer than those used in LSL) are laid lengthwise in parallel.
strong, heavy, relatively expensive
Wood i-joists
dimensional lumber with an OSL board in between, used in floors, roofs, etc
Laminated veneer lumber
an engineered wood product that uses multiple layers of thin wood assembled with adhesives
like plywood but thicker
wood plastic composites
weather resistant, less likely to shrink and warp more flexible
How to calculate board feet?
Board feet = (nominal width (in) x nominal ht (in) x length (ft)) / 12
nominal vs actual
1 - 5/4 = -1/4”
2 - 6” = -1/2”
8 - 12 = -3/4”
oriented strand board
strongest & stiffest of nonveneered panels
most common in subfloors and exterior sheathing
fiberboard
made from the smallest grain of wood (compared to OSB and particleboard)
best for interior uses
smoothest surface
sheathing rating # / #
roof spacing OC / floor spacing OC
ex. 32/16 means spacing of 32” OC for roof and 16” OC for floor
Plywood bond classifications
Exterior - for exterior use
Exposure 1 - can handle some water, etc, but not meant to be exposed to weather long term (95% of plywood)
When do you have to treat wood?
-Wood joists are less than 18” above grade
-Wood beams or girders are less than 12” above grade
-Plates, sills, or sleepers are in direct contact with masonry or concrete which is in direct contact with the earth
-Wood framing members or sheathing are less than 8” from the soil
Types of wood treatments:
Creosote - oil based, can’t be painted, very toxic, phased out
Pentachlorophenol - oil based, can’t be painted, on telephone poles
Chromated copper arsenate (CCA) - phased out in 2004 b/c arsenic
Alkaline copper quaternary (ACQ) - less toxic, can’t be used with steel fasteners b/c copper, approved for above ground, in ground, and in water
Copper boron azole (CBA) - less toxic, can’t be used with steel fasteners b/c copper, approved for above ground, in ground, and in water
Micronized copper - powder, more natural looking, less corrosive to other metals
Carbon based pti - less corrosive to metal fasteners
Disodium octaborate tetrahydrate (DOR) - above ground only, good against termites
Sodium borate (SBX) - above ground only, good against termites
Decay resistant wood
Very - black locust, red mulberry, osage orange, pacific yew
Slightly: cypress, catalpa, cedar, chestnut, white oak, redwood, black walnut
Balloon vs platform framing
Balloon - requires fire stopping,
Platform - Newer and more common now, shorter lumber, less prone to fire spread, can frame wall horizontally
Strategies for drainage @ the foundation
dampproofing / waterproofing
Overhangs
Drip edges
Sloping ground away
Gravel fill
Rim board or band joist
Sits on top of the header or floor below or foundation
Seals the open ends o the joists
provides surface for attachment of exterior insulation, cladding, and finish elements
Transfers some of the loads to the floor below
After the attic, this is the most likely place for insulation gaps & air infiltration
Ice guard
a mat under the shingles at the outermost edge of the roof to prevent ice or water from infiltrating the roof construction
attic vent ratio
IBC requires min vent area 1/150th of attic footprint or, if theres a vapor barrier, 1/300th
Which is stronger, cold rolled or hot rolled steel?
Cold rolled steel is stronger than mild steel
How does carbon content affect metal strength / brittleness?
the more a metal has, the stronger but more brittle
-cast iron is stronger than wrought iron b/c carbon content
depth to span ratio: beam
Beam depth is generally 1/20 the span, width is ⅓ the depth
depth to span ratio: girder
Girder depth is 1/15 the span, width is ⅓ the depth
depth to span ratio: open web
Open web is 1/20 the span
Roofs, lightly loaded floors, or closely spaced can be 1/24 the span
depth to span ratio: steel decking
Steel decking depth is 1/40 the span
depth to span ratio: triangular steel truss
Triangular steel truss depth is ¼ the span
depth to span ratio: rectangular steel truss
Rectangular truss depth is ⅛ the span
Type 1 cement
normal
Type 1A cement
Normal, air entrained. Tiny bubbles introduced to the concrete and those help with durability (freeze/thaw) and make the concrete more workable, Used for exposed concrete in cold climates
Type 2 cement
moderate resistance to sulfates. for coming into contact with groundwater or below grade in sulfate heavy soil.