Menu path
Estimate > Block-Cut
🧾 What Block-Cutting does
Block-Cutting is an advanced development of the Auto-Blocking process where you determine optimal roof sheet placement and show exactly where offcuts must go as part of a block to substantially reduce waste material.
This interactive process shows what experienced roofing installers do in the field - flipping sheets around for best fit - but plans it before they get to the job site. There may be multiple 'correct' results, making this a skill-based process.
The first thing to look at is how many different ridge-to-eave lengths are there? In this example, there are three, so we are aiming for three sheet lengths in our sheet order cutting list or pack.
This Block-Cutting process is taking what roofing installers (at least those who reduce waste by flipping sheets around) actually do in the field and shows them exactly how to achieve the best fit, before they get to the job site. It is an interactive process that is ‘driven’ by the operator to get the required result.
🔧 The Block-Cutting Process
The Block-Cutting process breaks into three main steps:
Define the Block - Create the cutting template
Place the Block - Position it outside the roof area
Assign Roof Plane block-pieces - Map roof sections to the block
Step 1: Define Block
Select Estimate > Block-Cut to open the Block Cutting dialog
Set the first Block Letter, colour and number
If no roof panel is selected, you'll be prompted to select from previously defined panels
Select Define Block and click the first roof plane for the block
Choose any Block Edge Lines to stretch (or right-click Cancel if the block is correct as-is)
The block attaches to your cursor for placement outside the roof area
Step 2: Place Block
Position the block outside the roof area
Step 3: Assign Roof Planes and Repeat
The roof plane attaches to your cursor
Use F1 and F2 to rotate the plane
Use F3 and F4 to select snap points
Middle mouse button to snap the roof plane to the block corner
The plane displays as A1, A2, etc. as you assign them
🛠 Splitting Planes for Complex Layouts
Now we continue these steps for the rest of the roof. For offcuts to fit correctly, you may need to split roof planes:
Right-click to cancel the current function
Select Split Plane at Point
Select the roof plane to divide
Snap to the point where you want to split (e.g., apex of hip lines)
Return to Assign Roof Planes to Blocks and assign the split sections
F1 or F2 to rotate into the correct orientation, then snap to the corner of the block. Note that the block-piece designation automatically increments to the next number ie A2.
Split the hip end at the right using Split Plane at Point, so that two areas are created to reveal A4 and A5,
Now assign the 2 planes that were just created to Block A as A4 & A5.
Now that all of block A has been filled, we must define a new block which will be block B. Select the plane area that will define block B; select the right hand edge to stretch, and stretch the edge as shown, using the middle mouse button to snap to the corner.
Right click to cancel that operation (assuming that you stretched it correctly), and move the block to a spot outside the roof area so that block-pieces can be assigned to that block.
Once that is done and the Block-Cutting dialog box comes back up, click [>] at Block Letter to increment it to the next letter or R to reset it back to A, with Block Number Clicking [>] takes it to the next number or clicking R takes it back to 1. With Block Colour clicking > takes it to the next colour in the pallet or clicking […] lets you pick any colour in the colour table that you have set up.
Assign this block to be “B”
That gives us B1 & B2 which are obvious. Then split the planes as shown to give us B3 and then assign block-pieces B3 and B4 to the block. Next, move block-piece B5 onto our block.
Split the planes on the dormers at the bottom of the valley. And Assign those as B6 and B7. Then move the block-pieces B6 & B7 onto our block B.
Then define a new block which will be labelled C.
Continue this process for each subsequent block, splitting and assigning until they are all accounted for.
Stretch the edge back to the apex of the hip and ridge by snapping to the apex point. Then stretch the outer edge and snap to the geometry on the valley.
Can now move the block out and insert the remaining corners to create E1 and E2.
After all Blocks have been accounted for, you can use the function Place/Move Legend to annotate the Block-Cut drawing with the summary of the cutting list – for example:
Note that this shows fractions of sheets. This can be adjusted to round-up to whole numbers of sheets by changing the settings in Estimate > Allowances.
🔧 Block-Cutting Tools
Tool | Description |
Check Model | Standard model integrity check accessible during block-cutting |
Delete Free L/P | Remove redundant geometry to keep model clean |
View Plot Scale | Modify annotation text without changing block panel numbers |
View Top/ISO | Changes current view |
Save Model | Save current state without exiting block-cutting process |
Block Cutting Dimension Reference | Add panel labelling and dimension insertion (requires System Preferences setting) |
Measure b/t 2 pts | Measure distance between two points |
Measure Length of Entity | Measure length of lines or roof plane edges |
🧾 Block-Cutting Options
Option | Description |
Block Letter/Number/Colour | Set designation for each block. Auto-increments as block-pieces are applied  |
[>] button | Advances to next letter or number in sequence |
[R] button | Resets to A or 0 |
Block Colour | Any of 256 colours as defined in CAD > Defaults > Colour Table |
🔧 Roof Plane Options
Function | Description |
Split Plane at Point | Select plane, then snap to point where you want to split it |
Split Plane Mirror | Creates mirror image of split point on same plane |
Split Plane Distance | Split plane at specific distance from reference point |
Merge Planes | Remerge planes that were mistakenly split |
Reset Roof Plane | Remove incorrect annotations and start over |
Split Plane at Point
This function allows you to select a plane, in the example, the plane at the hip end (1), then middle button snap the apex of the ridge and hip for a point to split the plane through (2).
The hip end plane is split to form two block-piece planes that are available to use on the blocks as you create them.
Split Plane Mirror
There are other situations where you need a bunch of extra block-pieces defined on the roof. The command Split Plane Mirror will give you a mirror image of a split point on the same plane.
And the adjacent roof plane can be split in a similar manner to create block-pieces 3 and 4 using the same snap point.
Split Plane Distance
This function allows you to split a plane to create a block-piece of a specific distance from a reference point. Follow the prompts carefully as you must define the reference point, the distance from and the distance to the location of your split line.
In this example, we needed a split line 1200mm (~4’) from the apex point to create a block piece that suited how we intended to utilise the block pieces.
Merge Planes
This option allows you to remerge planes that you might have mistakenly split. Planes 1 and 2 will become one again.
Reset Roof Plane
Removes the annotations that might have been placed incorrectly and allows you to do it again with new annotation.
Now you see it, then you don’t.
🔧 Block Options
Function | Description |
Define Block | Auto-creates block around selected roof plane extents |
Move Existing Block | Relocate placed blocks to make room for new ones |
Modify Blocks | Access full block modification toolkit with Show/Hide Block-Cutting option |
Extend Edge | Extend the edge of a defined block to cover required area of roof |
Define Block
This function automatically creates a block about the extents of the roof plane selected, then prompts to extend the block edge, if required. If the block is the correct size, then right click [Cancel] to place the block ready for placement of block-pieces.
Move Existing Block
Once a block is placed, you may decide to place it elsewhere to make room for new blocks around the roof model.
Modify Blocks
This brings up the Modify Blocks toolkit that allows all manner of modifications to the automatically created blocks. These functions are well described in the previous section on Blocking (as distinct from Block-Cut). The key function specifically relevant to the Block-Cutting process is the option Show/Hide Block-Cutting which turns the block-cut outlines on and off.
🔧 Cut Plane Options
Function | Description |
Assign Planes to Blocks | Map block-pieces to blocks. Start with largest, most obvious piece |
Select Block | Re-select block if you've moved around the model |
Delete Cut Plane | Remove cut plane to create a new one |
Place/Move Legend | Add cutting list summary annotation to drawing |
Delete All Block-Cut Planes | Deletes all the cut planes so that you can start again. |
Assign Planes to Blocks
Once you have created your blocks and split the roof planes into block-pieces, you then assign the block-pieces to the block.
You do this typically starting with the largest and most obvious block-piece and it will be annotated block-piece 1 – in this case block-piece A1. Then select the next block-piece to be placed and this will be annotated A2 etc.
As the block-pieces are selected, they may not be oriented to suit the placement onto the block, so use function keys F1 and F2 to rotate the block-piece. If the ‘snap-handle’ is not in the correct corner, use F3 and F4 to change the handle so you can middle mouse button ‘snap’ it to the block, repeating the process until all block-pieces are placed and that block is complete.
Select Block
If you have been moving around the model and changing blocks etc, you may need to re-select the block so that you can assign the block-pieces to the correct block.
Delete Cut Plane
This function deletes a cut plane that you might have created so that you can create a new one.
Place/Move legend
After all Blocks have been accounted for, you can use the function Place/Move Legend to annotate the Block-Cut drawing with the summary of the cutting list – for example:
Note that this example shows fractions of sheets. This can be adjusted to round up to whole numbers of sheets by changing the settings in Allowances.
Additional Functions
Function | Description |
Delete All Block-Cut Planes | Start over - useful for trying alternate approaches |
Delete Selected | Delete selected items |
Move Text | Reposition annotation text for readability |
Move Group | Move entire block and block-pieces together |
Undo/Redo | Standard undo/redo operations |
Delete All Block-Cut Planes
Deletes all the cut planes so that you can start again. Sometimes you learn a more efficient way to do a job only after doing it a different way. Since this is so quick, don’t be afraid to try alternate ways to block and split planes.
Move Text
Moves the annotation text so it is easy to read.
Move Group
Allows you to move an entire block and all its block-pieces to a different part of the screen sothat the report is more easily read.
Undo
Undo the last operation.
Redo
Redo if you Undo too far or you decide that the Undo was actually correct.
🛠 Function Keys During Assignment
Key | Function |
F1/F2 | Rotate block-piece for correct orientation |
F3/F4 | Change snap handle to different corner |
Middle Mouse | Snap block-piece points to block points |
🛠 Summary of Our Process
For a roof with three different ridge-to-eave lengths, aim for three sheet lengths in your cutting list:
Define Block A for the main roof area
Split hip ends at apex points to create separate block-pieces
Assign each section (A1, A2, A3, etc.) to the block
Define Block B for different length requirements
Continue until all roof areas are assigned to appropriate blocks
Use Place/Move Legend to add cutting summary
⚠️ Critical Installation Considerations
Sheet Lap Direction: Each sheet has overlap and underlap sides. Never place two underlap edges or two overlap edges together - they cannot be installed this way.
Visual guide: Complete blocks show a thin line on one edge and thicker line on the opposite edge. Use this to determine correct piece placement when flipped.
Always consider how installers will handle individual sheets and offcuts. The layout must work practically for installation, not just material efficiency.
📊 Block-Cut Output
Use Estimate > Tally-Blocks to generate the optimised cutting list. The Block-Cut template for MS Word creates installer reports (template located in ../User folder).
Fraction settings can be adjusted to round up to whole sheets in Estimate > Allowances.
💡 Tips for Success
Start with the largest, most obvious block-pieces first
Don't be afraid to try alternate approaches - the process is quick enough to experiment
Focus on getting all laps in the same direction when pieces are flipped
Use the measure tools to verify distances before splitting planes
Save regularly using the Save Model button during long block-cutting sessions