📌 Overview
Dormers built over the main roof and into the verandah is a common feature of many period style homes. Usually the verandah is a different pitch to the main roof, creating what we call a “bell-cast” or bell shaped roof.
In this case the main roof pitch and the verandah are different pitches — 30° and 20° respectively.
It is not difficult to create this geometry, but the process does presume a reasonable competency with Construct-Roof Smartlines. You would not do this as your first Smartlines exercise!
And here is our final result on the 3D model.
✅ Step-by-step
1) Model the main roof and verandah
Model the main roof in the usual way at 30 degrees pitch.
Add the verandah by selecting the main roof eave lines, and use values similar to below, noting:
Use [Height at Wall] to ensure that the main roof runs into the verandah roof.
Use [Distance from Last Point and First Point] to set the ends of the verandah under the eave of the main roof.
This saves having to do it later.
You will end up with a roof looking something like this.
2) Insert the dormer using Valley Gable to Hip
Next we add the Valley Gable to the Hip (yes it works on both line types).
Using values similar to below, note:
The Roof Type to Insert button is set to Gable. Selecting anything else opens up a bunch of other options that we do not need for this job.
The pitch is different (as specified by the designer).
Select OK and the gable is inserted from the main roof and over the verandah roof.
3) Drop the dormer eaves to intersect the verandah
Now we need to make the dormer eaves drop down to intersect with the verandah.
Use Mod-Roof > Drop Eave
Drop them, say, 500mm
It will now look like this.
4) Intersect the dormer and verandah planes
Next we get the software to figure out the intersection between the dormer and the verandah:
Select Mod-Roof > Intersect Planes
Set [Planes to Intersect] to [Select] (so you only intersect the planes you care about, not all planes)
Select the planes, then when finished selecting, use right mouse button to indicate that you have finished selecting, then select OK.
The planes will be cut to the edges as shown.
5) Remove planes so you can edit the linework
Now we use Construct Roof > Smartlines to modify the remaining geometry.
As you know, before we can edit linework, we must first remove the associated planes.
6) Extend verandah eave lines by 400mm
Use:
Smartlines > Trim Line to Length
Add 400mm to the verandah eave lines.
When the dialog displays the current length, simply type:
+400
Select OK and the 400mm is added.
Do this to both eave lines (the ones indicated as [1] in the original notes).
7) Draw the missing lines (and snap properly)
Use:
Smartlines > Draw Freehand
Add the missing lines.
Important:
Use the middle mouse point “snap” function to join exactly to the end of existing lines.
Do this in the locations indicated as [2] (four lines, including the apron line under the dormer).
8) Delete redundant lines
Delete the redundant lines (the ones indicated by [3] in the original notes).
Your linework is now complete.
9) Re-insert verandah planes
Simply replace the planes on the verandah (x3) and you will have a roof that looks like the final model.
✅ Final check before you apply materials
The steps are simple to complete, and with practice you will be doing all sorts of similar feats with the combination of Smartlines and Mod-Roof functions.
The most important step remains:
Use the Tools functions to check dimensions, pitch and line styles before you rush off and apply roofing materials and complete your quotation.