Drawing a Building

This is the 2D design step. It has ten tools; four of them do the work.

How a building gets drawn

The order matters, and it is the same order you would draw one on paper.

1. Trace the outline — the walls, as seen from above.
2. Correct it — add the corner the bay window needs, slide a wall that came out a metre short.
3. Draw the roof onto it — the ridge, the hips, the valley where the wing meets the main body.
4. Say you are finished, and let the tool name the lines.
5. Build the planes — the surfaces panels are placed on.

Or skip 3–5 with a generator, which builds a hip or a gable straight from the outline. That covers most ordinary houses; it cannot describe a cross-gable, an ell, or a wing at a different pitch.

Step 1 — Trace the outline

Pick the trace tool and click the building's corners. Click the first corner again, or double-click, to close it. Escape discards a part-drawn outline — an unclosed outline is not a shape.

While you trace, the setback lines are drawn with it. They are what a traced outline gets checked against, so they come on with the drawing tools rather than hiding behind a toggle nobody finds.

Step 2 — Correct the outline

A traced roof is never right the first time.

Add corner puts a new point on a wall that already exists. This is the tool for the wall that turns out to have a bay in it, or the addition that steps back a metre. Without it the only repair was to delete the outline and trace the whole thing again.

With the arrow tool:

• Drag a corner to move it.
• Drag a wall and the wall slides along its own normal, carrying both its corners, so the angles at those corners survive.
• Drag the body and the whole building moves — see Moving things below.

Step 3 — Ridges and valleys

This is the tool most people reach for second and should reach for first on anything other than a plain rectangle. It draws the roof's own lines: the ridge along the top, the hips down to the corners, the valley where a wing meets the main body.

Lines come in runs. Each click continues the chain from the last point rather than starting a fresh line — a ridge, then the hip off its end, then the valley where the wing lands. Escape ends the run and keeps the lines.

A run never encloses anything, and that is the whole difference between drawing a roof and drawing a building.

The snap indicator

The thing that makes this tool work is knowing, before you click, what the point will attach to. As you move the cursor the map tells you:

Corners win over walls, and over a wider radius, because that is nearly always what somebody aiming near a corner meant.

Square corners and ordinary junctions

Corners are drawn two ways.

• A square marker means exactly two lines meeting at 90°, within three degrees.
• A dot means anything else — a ridge terminating in a wall, three lines at a hip, a shallow bend.

A square corner is a claim you are making about the building. Seeing it confirmed on screen is how you catch the one corner that is three degrees out before the whole roof is built on it.

Nudging a junction

Roof-line junctions can be dragged like any other point, so a ridge end placed slightly wrong is corrected rather than deleted along with everything hanging off it.

Step 4 — "Roof is drawn — name the lines"

Nothing is judged until you say you are finished, and that is deliberate. A hip roof with three of its four hips in place is already closed enough to start failing checks, so the complaints would churn under you while you are plainly still working.

Press Roof is drawn — name the lines and the tool classifies every line: eave, ridge, hip, valley, rake, gable wall. A line's role depends on the roof around it, so guessing before the shape is closed gets it wrong.

You can override any line's type afterwards from the Roof lines list, and a type you picked is left alone by later passes.

Step 5 — Build planes

Once the lines close, Build planes turns them into the roof surfaces panels are placed on. Each plane's pitch and azimuth are fitted from the geometry rather than typed in, so a cross-gable ends up with four correctly-oriented faces without anybody entering a compass bearing.

If the lines do not close, the panel says what is wrong instead of building planes fitted through corners that do not lie on them.

The generators

Make roof planes offers hip, gable and the other standard shapes, built straight from a selected outline. One click, and it covers most houses.

Two things to know:

• A generator replaces the outline it builds from, along with any roof objects placed on it.
• With several outlines on the site you have to select the one to build from. Rebuilding the wrong wing is worse than asking.

What you traced is the outline, not the roof

This is the single most important thing to understand about a plan view.

A map is flat. Every line you draw on it, and every distance measured along one, is horizontal — so what the trace describes is the building outline, not the roof surface. A pitched roof is bigger than its own footprint.

The tool accounts for it everywhere a length or an area is reported, and it does so per edge rather than by scaling everything:

• An eave runs across the slope. Its two ends sit at the same height, so its true length is the length you drew.
• A rake runs straight up the slope. On a 6/12 pitch it is about 11% longer than the line drawn for it.
• A hip does some of both, and gets the part of the stretch it has earned.

Dimension labels on the map are on-slope lengths, and so are the lengths in the Roof lines list. Roof area on the 3D step is likewise the sloped surface, not the footprint: the two differ by 1/cos(pitch) — 15% at 30° and 41% at 12/12 — and it is the sloped figure that decides how many modules fit.

Moving a corner never changes a height — only X and Y move when you drag. What changes a height is the pitch, the storeys, or a line you set by hand; see Heights, Storeys & Shade.

Trees and roof objects

Tree places a tree where you click — click where the trunk is. Its height and crown come from the preset you pick and are editable afterwards; see Heights, Storeys & Shade.

Roof object places a chimney, a vent or a unit, and it has to land on a roof plane — a roof object's height is measured from the surface it sits on.

Building traces a neighbour. It is a shading volume on the site, not part of the one you are designing, so it does not move when the building does. Give it a storey count rather than a height: nobody has a tape on the neighbour's eave, and counting floors off the imagery is the honest way there. A measured height is accepted where you have one, and it replaces the count rather than sitting beside it.

Height is what decides how far a shadow reaches, and a building to the south reaches furthest in December — the month a customer is most likely to check.

Without shade the roof reads as clear, and an unshaded roof produces a confident annual number that is simply too high. A tree that is harmless in July can dominate the array in December.

Dormers

Dormer drops one onto the roof plane you click. Its lines go into the roof graph with their roles already set, because a dormer's diagonals are valleys by construction — two surfaces meeting facing each other — and a classifier reasoning from a half-built graph calls them hips and inverts the drainage.

Three numbers describe it, and they are kept on the job rather than per dormer, because dormers on one house are almost always the same size as each other:

Sliding the setback morphs one into the other, which is easier to judge by eye than picking a name from a list.

The ridge height is inferred, and that is nearly always what you want: a dormer's ridge is level and has to arrive at the main roof, so its height above the front wall is simply how much the roof rises over the dormer's projection. On a 30° roof a 2.4 m dormer is 1.39 m tall, and no other number gives a level ridge.

A dormer that will not fit where you clicked says so, rather than doing nothing.

Splitting a face

A roof gets traced as one plane and turns out to be two — an addition framed at a different pitch, a section re-roofed in a different covering, a plane with a step in it.

Split face takes two clicks: one wall, then the wall opposite. Both ends land on the boundary, which is what guarantees two closed shapes — a cut that stopped inside the face would leave a slit rather than a division.

Both halves inherit everything the original said about itself: pitch, azimuth, covering, module override, mount. A split says this surface is two surfaces, not this surface is now unknown — you usually split in order to change one of those on one half, and making you re-enter both is how the untouched half ends up subtly different from what it was. The azimuth is inherited rather than refitted for the same reason: a bearing refitted through fewer corners drifts a degree or two, and a degree of azimuth is a real change to a production number.

Roof objects come with the halves. A vent traced onto the roof is still on that roof; the plane under it has only been subdivided.

Panels do not. The face's boundary and its setbacks both just changed, so keeping the old placements would leave modules straddling the new wall and outside the new setback — a layout that looks authoritative and is not buildable. Re-fill on the panel step in one click.

Two cuts are refused, and both say why rather than doing nothing:

• Both ends on the same wall — that carves a triangle off a straight run and leaves a piece with no area worth having. It is almost always a mis-click, and the first point is kept so the fix is one click on a different wall.
• Two corners already joined by a wall — there is nothing between them to cut.

Keepouts

Keepout traces an area modules must stay off — a skylight, a hatch, a roof access path.

The shape is the obstacle; the clearance is how far panels stay off it. Drawing the buffer instead would mean redrawing the shape every time the rule changed, and would lose the only record of where the actual obstacle is. A fire access path and a plumbing vent are the same shape and different distances.

A keepout never divides an outline and never becomes a roof plane. One drawn inside a roof face stays a no-module zone rather than cutting the roof in two around it.

Moving things

With the arrow tool:

• Click to select one thing.
• Drag on empty map to rubber-band a box. Shift adds to the selection, Alt removes from it. The point of a box round eight trees is to delete eight trees.
• Drag the body of a building and the whole building moves.

What moves with a building, and what stays

Dragging one face's ring alone would slide the outline out from under the roof graph, the keepouts, the modules and the equipment, leaving a building whose parts no longer agree about where it is. So the move takes everything that is part of the building with it:

Moves: every roof face, the roof-line graph, keepouts, roof-mounted obstructions, equipment mounted on the roof or on a wall, and conduit run on the building.

Stays: trees, ground obstructions and ground-mounted equipment. Those are features of the site. A tree does not follow a house that was traced ten metres off, and moving it would destroy the shading survey that was the reason for placing it.

A trench stays where it was dug. Its endpoints re-derive from the equipment they join, but the path between them crosses real ground with its own excavation, adders and crew. It does not relocate because the roof was corrected.

Deleting and starting over

Delete selected removes the marquee set, or the single click if there is no set. It is ordinary work and it undoes.

Clear the whole design… asks first, and says exactly what goes: the outline, the roof lines, the trees and the roof objects, and every array and circuit built on them. The address, the pitch, the module and the service panel are kept.