Structural/Rough Carpentry Flashcards
Structural/rough carpentry includes
structural framing, sheathing, blocking, anything to prep for finish work
Wood/lumber/timber
wood = comes from trees lumber = product of sawing, planing, etc. timber = at least 5 in. min. section
Adv./Disadv. of lumber
good: low cost, low footprint, easy to work, good insulator
bad: non-uniform, low strength, susceptible to moisture
Softwood vs. hardwood
soft: conifers (used for rough)
hard: deciduous (used for finish)
Lumber strength
depends on grain direction relative to load; best when load and grain parallel (eg., load on wood column); worst in bending
Lumber defects
knots (branch/limb), checks (growth rings are separated, pulled apart), pitch pocket (same as check, but filled w resin), shake (like check, but lengthwise instead of across grain), split (like check, but goes through piece of lumber, often at ends), wane (where bark was, or where chunk is just gone, usu. at corners)
warping: out of plane; bow warp - parallel, crook warp - side to side, cup = along width
Lumber grades
made by American Lumber Standards Committee; yard lumber: for structural/rough; factory/shop lumber: for finishing
Yard lumber
boards (less than 2), dimension (2 to 5), timber (more than 5)
2x2s, 2x4s (subdivided), 2x6s+
beams/stringers: 5” wide, 2”+ depth
posts/timbers: 5x5, depth not more than 2” than width
Factory lumber
grade B/better (best), C/select, D/select
common grades: no.1-no.5 (1 = best, usu. based on knots)
Nominal/Actual dimensions
1”=.75”
2-6=2.5-6.5
8-12=7.25-11.25
Moisture content
expressed as fraction of the overall weight of oven-dried wood; 30% = fiber saturation = when no water in cell cavities, but cell walls saturated = pt. when shrinkage starts to occur
Wood seasoning
Putting lumber on site, so it has time to shrink/swell to local/prevailing moisture content levels
Dry lumber
moisture content below 19% (req’d for structural lumber design values)
kiln dry = below 15%
Wood shrinking/swelling
occurs most perpendicular to grain, very little parallel to grain, most tangentially to growth rings, half as much radially
Wood stud construction
aka light frame wood construction, 2x4s or 2x6s, with a few heavier beams of built-up/heavy timber/steel members; can be platform (easier to construct) or balloon framing (less vertical shrinkage, stays parallel to wood grain)
Wood to masonry wall
hung by wood ledger + metal joist hanger or use fire cut (to prevent masonry from being pushed up/out when beam burns out)
Plywood ratings
thin wood veneer sheets glued together, usu. 4’x8’, in .25”-.75” thickness, graded by span (measures stiffness/strength of parallel to face grain - eg 32/24, max dist. roof supports/max dist. floor supports, average residential conditions), also graded by wood species (I = group I woods, II = woods 2, 3, 4), graded by quality of face veneer (N natural finish, heartwood/sapwood, free of defects, A, B plugged knotholes, C small knothole/splits, D large knotholes); can have special glues/finishes for tough environments
Types of plywood
sheathing = attached to framing to provide structural support
particleboard = small wood particle/fibers/chips (low/med/high density), mostly for backing
OSB = oriented strand board - precision cut wood strands of 4” length, .0027” thick, layered at right angles, comes in bigger panels, subject to delamn.
MDF = medium density fiberboard - fibers made by steaming wood, most dimensionally stable panels, smooth face for finishing
hardboard = inter-felted fibers, can be tempered for hardness
Blocking, bridging
blocking = pcs btwn framing for rigidity or nail base
bridging = bracing btwn joists to prevent joist buckling (can be wd blocking or metal cross braces), usu 8’ + o.c.
firestops = barriers in concealed framing spaces, can be 2”+ wood, gypsum, mineral wool
Engineered wood
smaller/waste woods to make stonger, bigger members; glue/metal fasteners/insulation used; includes plywood web joists (TJIs) (less wasteful, stronger, less shrinkage), laminated veneer lumber/structural composite lumber (thin lams parallel to length), trusses, SIPs panels, composite decking, CLTs cross-laminated timbers, glulams
Wood truss types
king post, queen post, Fink, scissor, Warren, Howe Pratt
SIPs
structural insulated panels: usu. OSB + EPS (expanded polystyrene)
other facings: plywood, Al panels, cement board, gypsum wallboard
other insulation: extruded polystyrene (XPS), urethane foam, compressed straw
thicknesses btwn 4.5”-12.25”, usu. 4’x8’ to 9’x28’
reduce construction time, improved insulation values bc reduced air infiltration, higher strength, flatter surfaces, dimensional stability
problems w/seismic anchoring, vapor barrier placement, insect damage
Composite wood decking
wood-plastic composite - planks formed from ~50% sm. wood fibers or wood flour mixed w ~50% plastic (polyethylene), along w/ colorants, stabilizers, fungicides
lasts longer than dimensioned lumber, stronger, splinter-free, recycled materials
hotter underfoot, warp prone
Cross-laminated timber
CLT, layer dimensioned lumber at right angles to make panel, very strong, resist bending, racking, act as strong diaphragm, can use smaller diameter trees since acting togther (green)
Heavy timber construction
Main framing members of bldg from large dimensioned wood or engineered wood
Glulams
Glue-laminated wood members; depths are multiples of 1.5” (2xs), higher allowable stresses bc members defect free, dried, etc.; specified by stress rating; grades are industrial (rough), architectural (medium), premium (finest)
Wood decking
aka planking, solid or lam timber spanning btwn beams, usu. TNG, spans more than sheathing (4’-20’), can be both structural & finish floor/ceiling (but hard to conceal insul, services
= heavy tiber constr.!
Wood fasteners
nails (weakest, most common - box, common wire, wire spikes), screws (flat/round head, threading makes stronger cnxn, lead holes make stronger, lag = pointed end but head like bolt), bolts (use washer at head to distribute load), metal fasteners (lightweight connectors, timber conn., split rings, shear plates to transfer loads, gang nail plates), etc.
use nailing schedule for size, number, spacing, penetration type
Wood treatments
preservatives brushed, dipped or pressure applied to fight moisture + insects
creosote (coal tar, water proof, RR ties, marine structr.), oil-borne (penta/pentachlorophenol, for utility poles, pilings, bridges, long spans over swimming pools), water-borne (ACQ/ammoniacal copper quaternary, sodium borate/SBX, etc., lesser VOCs, paintable, but don’t use w Al bc corrosive); treat all cuts w 2% copper in copper naphthenate
no longer used: CCA/chromated copper arsenate, ACZA/ammoniacal copper zinc arsenate bc of arsenic content, but were less corrosive
