Roofs

A roof is a kit like any other (panels, trim, corners and inserts), built on one number that nothing else in the pipeline can recover. Get that number wrong and every piece is wrong together, which is the good case. Get it wrong on one piece and you have a gap at the top of a building, where nobody stands and everybody looks.

Doing rather than reading?

Make a Kit Piece is the pipeline; the Class to pick is Roof. This is the reference.

Pitch is the wall segment of the roof

roofPitch is 40°. Every slope, every gable top, every dormer cheek and every verge in one kit is that angle.

You cannot see a wrong pitch in Blender

A wall segment is 4 m and the readout says 4 m. A pitch has no readout. Nobody can tell 40° from 41° by eye in the viewport, and everybody can from the street. Two slopes a degree apart meet in a ridge that does not close, and the eye goes straight to it.

MSH017 measures it for you, within roofPitchTolerance of 1°.

roofPitch

Key Value
appliesToClasses roof
measureFrom boundingBox
toleranceFrom grid.roofPitchTolerance

It is measured off the bounding box: rise over run, the Z extent against the Y extent. That is exactly right for a plain slope panel and wrong for one carrying a dormer, a valley or a return, because the box grows to hold the feature and reports the angle of the box. Hence a warning: a piece that is not one plain slope is an ordinary exception.
→ Check Your Work > When a rule is wrong

A per-project override is the way to build a kit at a different angle, like a tower, a lean-to, or a whole second town.
→ Asset Rules (Generated) > Project overrides

The other number: overhang

roofOverhang is 0.5 m: how far the eave stands out past the wall below. It is what puts a gutter clear of the wall and a shadow on it, and it is the difference between a roof that sits on a building and one that was dropped on it.

The verge uses the same number at the gable end, so the two agree by construction rather than by anybody remembering.

The parts, and which class each is

Part Class Why
Slope panel roof The field. Tiles along the ridge (X). The only class MSH017 measures.
Ridge, verge, fascia, gutter trim Runs along an edge and projects out of the plane. Exactly a wall's trim, one surface up.
Hip, valley corner Resolves where two slopes meet. One per junction, so it does not tile.
Dormer, chimney assembly A little building on a slope: cheeks, a front and a roof of its own. Ships as a prefab of Kit pieces.
RoofLight insert Lies in the plane of the slope. Fills an opening, so it pivots on the opening.
Gable wall gable See below. It is a wall.

roof-parts.svg

The words are in Roof parts. Three of them get swapped constantly: Ridge is level, a Hip slopes down and sheds outward, a Valley is the same line turned inside out and collects. An Eave is the level bottom edge; a Verge is the raking side one. A roof has both and they are different pieces.

The gable is the piece that will bite you

A gable is the triangular wall that closes the end of a pitched roof. It is a wall. It is built with
the walls, textured with the walls, and named with the walls.

Its top edge has to be the roof's own pitch, and nothing checks it

MSH017 leaves gable out on purpose. A gable's slope runs across its width and starts partway up, so the bounding box (which is all the rule is given) cannot see where the sloping begins and would measure the whole wall instead.

So the piece most likely to be wrong is the one nothing can check. That is worth saying out loud rather than papering over: build the gable from the roof, not beside it.

The arithmetic, if you build it by hand: a gable peaks in the middle of the span, so it climbs
over half its own width, not over the roof's run. At 4 m wide and 40°, that is
2 × tan 40° = 1.678 m. Use the roof panel's rise there and the verge stands off the wall by the difference.

New Kit Piece does this for you. Pick Class Gable and it hands you 4 × 0.2 × 1.678 m,
already at the pitch.

What tiles, and what does not
roof Along X, the ridge. Two panels side by side make a longer roof.
trim Along its own longest axis: a ridge along X, a verge up the rake. → Splitting a Piece > The seam itself
gable, corner Neither. One per end, one per junction.

A slope panel's connecting faces are its two vertical edges, which is what MSH013 checks once the collection says it is a roof. Its eave and ridge edges are cut at the pitch and meet trim, not another panel.

See also