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DXF2BIM — the yellow list

← Back to the 2D Drawings → BIM guide

A 2D drawing carries only some of what a model needs. Everything it does not state is a setting: a yellow field that holds a standard value or a typical-practice guess, so you can see exactly what was assumed. You can ignore the yellow list: the defaults stay applied and the measurement is determined by them, but each one is listed, tagged, and never presented as the drawing's own statement. State a value and it is kept inside your drawing set as a marking (@DEFAULT=<key>,<value>, @BY=user); remove it and the default returns.

A. What you are asked to state (the facts a drawing cannot give)

Fact Where you state it Why a default would be wrong
Units of each sheet Units section (the file header is shown, never applied by itself) a wrong unit scales the whole model
Set name (e.g. SHED) and view / level of each sheet Sheets section; suggestions from the title text wait for your tick which plan is which storey
Plan level (e.g. 0) Sheets section defines the storey
Height datum per elevation: the z of a marked line (e.g. the plinth line is 0.6096 m = 2 ft above ground, read from the column detail) Metadata → elevation sheet → @Z no drawing says which line is the datum
Which layer is what (column, footing, grade beam, beam, wall-panel hatch, fan, net, door swing, truss bar, door frame) Layers section (one choice per layer and view) a layer name is not evidence of what is drawn
Body heights nothing draws (e.g. footing depth from a detail, beam depth range) Body heights section → @BODYZ no elevation shows a buried footing
Areas to leave out (e.g. an expansion-joint strip that looks like a beam) Exclude areas → @EXCLUDE the joint would become a false beam
A stated size where a label and the drawn length disagree (e.g. a beam drawn 10 in deep, labelled 12 in) Stated sizes section → @SIZE the label's number is used; you may correct it
A details sheet (optional): a sheet of notes and schedules with no body layers add it to the set; nothing to type its text states the concrete grade, casting ratios and the footing / column schedules; it is read, never guessed, and a column schedule's below-grade section replaces a typed setting
Building type (General or Farming Shed) Element defaults → Building type selects cited type-specific defaults
Anything in section B you know better Element defaults → type a value and Set the default is a guess or a standard value, not your fact

B. The defaults used when you state nothing

std = a value with a named source in this repository or the rate pack. guess = typical practice, to be confirmed. The list below is generated from modeller/element_defaults.json (the registry the Modeller reads); the Element defaults section in the editor shows the same rows with the value in force, highlights the ones used in your model, and tells you where each value came from (default, your choice, the drawing set, or the building type).

Setting Element Unit Default Kind Basis Offered choices
building.type Building text General guess the kind of building; it selects the type-specific defaults and organises the reference component library. A person states it (@DEFAULT=building.type,Farming Shed) General, Farming Shed
beam.depth IfcBeam m 0.45 guess section depth when no label or band gives it 0.3, 0.45, 0.6
beam.width IfcBeam m 0.3 guess section width when no label or band gives it 0.2, 0.25, 0.3
gradebeam.depth IfcBeam m 0.3 guess grade beam depth 0.3, 0.45
gradebeam.width IfcBeam m 0.3 guess grade beam width when no label gives it 0.2, 0.3
column.height IfcColumn m 3.0 guess storey height when no elevation gives it 2.7, 3.0, 3.6
column.size IfcColumn m 0.3 guess square section when a column symbol gives none 0.2, 0.25, 0.3, 0.4
ceiling.thickness IfcCovering m 0.012 guess board thickness when a ceiling is implied 0.009, 0.012, 0.015
floorfinish.thickness IfcCovering m 0.02 guess floor finish thickness when implied 0.01, 0.02, 0.05
net.thickness IfcCovering m 0.005 guess netting sheet thickness; the area is drawn 0.002, 0.005, 0.01
curtainwall.mullion IfcCurtainWall m 0.05 guess typical mullion width 0.05, 0.06
door.height IfcDoor m 2.1 guess typical door set height; plans do not draw it 2.0, 2.1, 2.4
door.thickness IfcDoor m 0.04 guess typical leaf thickness for a leaf drawn as one line 0.04, 0.05
door.width IfcDoor m 0.9 guess typical single leaf; used only for a door tag with no drawn swing or gap 0.8, 0.9, 1.0
fan.depth IfcFan m 0.3 guess housing depth; the diameter is drawn 0.2, 0.3, 0.4
footing.depth IfcFooting m 0.4 guess pad footing thickness 0.3, 0.4, 0.6
footing.length IfcFooting m 1.2 guess pad footing plan length when no schedule gives it 1.0, 1.2, 1.5
footing.width IfcFooting m 1.2 guess pad footing plan width 1.0, 1.2, 1.5
member.size IfcMember m 0.04 guess square envelope for a member with no label or size 0.04, 0.05, 0.075
section.spacing IfcMember text column pitch guess a section drawn once repeats at the column pitch from its cut column pitch, 2 x column pitch
pile.diameter IfcPile m 0.3 guess typical bored pile diameter 0.3, 0.45, 0.6
pile.length IfcPile m 12.0 guess no pile length is drawn on a layout 6, 12, 18
plate.thickness IfcPlate m 0.00635 std 1/4 in, the thickness the truss section's own label states (a plate with no label takes it) 0.00476, 0.00635, 0.0095
railing.height IfcRailing m 1.0 guess typical guard height 0.9, 1.0, 1.1
railing.post_spacing IfcRailing m 1.2 guess typical post spacing 1.0, 1.2, 1.5
ramp.slope IfcRamp ratio 0.0833 guess 1:12, a typical accessible ramp 0.0625, 0.0833, 0.1
roof.slope_deg IfcRoof deg 15.0 guess typical light roof pitch; used only when no gable or section gives the slope 10, 15, 17.5, 22.5
synth.column.belowgrade.size IfcColumn m 0 guess 0 = not stated: no below-grade column is built; a column schedule that states the section (e.g. 14 x 14 in = 0.3556) sets it, an explicit value overrides the schedule
synth.column.grade_to_base IfcColumn m 0.6096 guess grade to the column base (plinth): 2 ft, the datum read from a column detail
synth.roof.overhang IfcRoof m 0.0 guess the roof is cut at the gable planes until an overhang is stated 0, 0.4572, 0.6
synth.roof.sheet_thickness IfcRoof m 0.0254 guess display thickness of a roofing sheet (1 in); the cost is by area 0.0254, 0.05
synth.slab.footprint IfcSlab text outermost grid lines guess the slab edge is taken at the outermost grid lines of the base plan outermost grid lines
synth.slab.thickness IfcSlab m 0.25 std rate pack: 'RC Slab 250mm' (viewer/rates/cidb2024_my.json IfcSlab) 0.15, 0.2, 0.25
stair.going IfcStair m 0.25 guess typical tread depth 0.25, 0.28, 0.3
stair.riser IfcStair m 0.175 guess typical riser height; a stair symbol carries no riser 0.15, 0.175, 0.19
stair.width IfcStair m 1.0 guess typical flight width 0.9, 1.0, 1.2
panel.plane IfcWall text end grid line, centred guess an elevation panel is placed on the outermost grid line of its face, centred end grid line, centred
wall.base IfcWall m 0.0 guess floor level of the storey
wall.height IfcWall m 3.0 guess typical storey wall height; not stated by a plan 2.4, 2.7, 3.0, 3.6
wall.thickness IfcWall m 0.15 std rate pack: 'Blockwork Wall 150mm' (viewer/rates/cidb2024_my.json IfcWall) 0.1, 0.115, 0.15, 0.2, 0.225
window.height IfcWindow m 1.2 guess typical window height 1.0, 1.2, 1.5
window.sill IfcWindow m 0.9 guess typical sill height above the floor 0.9, 1.0, 1.1
window.width IfcWindow m 1.2 guess typical window width; used when a plan symbol gives no width 0.9, 1.2, 1.5

Rule of resolution, strongest first: the drawing set's @DEFAULT marking → a choice made in the editor → the building type's cited override → the registry value above. A typo in a key is an error, never a silent default; a value that is not a non-negative number is refused and the default is used.

C. Building type: Farming Shed

Stating building.type = Farming Shed switches on cited values (sources: the TNAU poultry-house construction guide, and a Bangladesh agricultural-university broiler-shed lecture; both medium confidence):

Setting Value Basis
door.height 1.83 Farming Shed: preferred door 6 x 2.5 ft opening outward (TNAU)
door.width 0.762 Farming Shed: preferred door 6 x 2.5 ft (TNAU)
synth.roof.overhang 1.0668 Farming Shed: roof overhang at least 3.5 ft to keep rain out (TNAU)

It also lists the components a farming shed is expected to contain (fans, nets/pads, doors, roof, slab) and the typical ranges used for the Typology advisories (open-sided width 15–25 ft, environment-controlled 40 ft and wider, eave 6–7 ft, centre 10–12 ft). Advisories compare and never change a body or a setting; a missing expected part is reported, never invented (an evaporative pad with no drawn length is not built).

D. What Complete the building adds (amber, estimated)

Ticking Complete the building adds a floor slab and the gabled roof the drawings imply, and, where a column schedule states a section below grade, the below-grade column parts (footing top to grade at that section, grade to the base at the column's own section; synth.column.*). They are computed from drawn evidence plus the stated conventions synth.slab.* and synth.roof.* above, shown amber (derived), and their defaults are listed in yellow.

E. How evidence is shown

Evidence Meaning Where you see it
drawn measured from the drawing no mark
derived (amber) computed from drawn evidence plus a stated convention (slab, roof, a panel that inherits a thickness label, a stated beam range, fans, nets, door swings) Evidence colours checkbox on the import panel; Provenance = derived in the database
assumed (red) no drawing evidence for the body's existence or position (e.g. a truss section drawn once, repeated along the building) same checkbox; Provenance = assumed
yellow row a value the drawing did not state and a default supplied Metadata panel → All defaults; Accept all, or ignore

By default the canvas shows each body in its material's standard colour (display convention, not a measurement): reinforced concrete grey, brick masonry brick red, profiled metal roofing light blue-grey, netting green, steel sections and plates dark blue-grey, extraction fans and door sets their own colours. A material with no colour in the palette is shown neutral grey and listed.

F. Items the shed drawings left open (carried as yellow rows, never decided in code)

Item State
Truss spacing; whether the right half repeats the left assumed: a truss at every column line (red), section.spacing
Roof sheet thickness and overhang defaults 0.0254 m and 0 (synth.roof.*), overhang 1.0668 m under Farming Shed
Floor slab thickness and extent 0.25 m (rate-pack standard), outermost grid lines
Fan depth; netting thickness 0.3 m; 5 mm (the areas are drawn)
Door leaf thickness 0.04 m for a leaf drawn as one line (two drawn lines give the real thickness)
Door height drawn when the elevation's door-frame layer is typed (96 / 94 in on the shed), else 2.1 m
Four unlabelled 21.7 in swings with no open leaf listed, not built (they sweep 75°, not a door's quarter turn)
Evaporative pads not built: labelled, but no outline or length is drawn
False ceiling, slats (cross-section) not built: labelled on the section, no closed plane, size or spacing is drawn
Polythene and compacted sand under the slab not built: labelled, no thickness stated
Footing top: the detail section sums footing top to plinth to 84 in, the stated footing height (@BODYZ) puts it 69 in below the plinth the stated value is kept; the 15 in difference is listed here
Beam reinforcement not read: bars are labels on the section drawings, not a schedule (only the footing and column schedules are read)
24 in "support wall" text against the 96 / 98 in brick drawn on the elevations both kept; the brick is built as drawn
A beam drawn 10 in deep but labelled 12 in conflict row; the label's number is used
410'-0" dimension text against 1,560 in drawn conflict row in the dimension audit