Practical tools for measured work
Shed Dormer Framing & Cheek-Valley Calculator
Intersect a shed-dormer roof with the main roof to find tie-in location, rafter length and theoretical cheek-valley line.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Horizontal plan distance from the main-roof eave datum.
Transfer the tie-in run from the same eave and plate datums used for the inputs. Do not mix finished wall faces with framing centerlines.
How it works
The side-section solver intersects the dormer roof plane with the main roof plane. Setback is measured horizontally from the main-roof eave datum; wall height starts at the shared plate datum.
Worked example: with the default 8-in-12 main roof, 3-in-12 dormer roof, 1200 mm setback and 1800 mm front wall, the planes meet 3600 mm from the eave datum at 2400 mm above the plate.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Main roof rise
- 8
- Main roof run
- 12
- Dormer roof rise
- 3
- Dormer roof run
- 12
- Dormer front setback from eave
- 1200 mm
- Dormer front wall height above plate
- 1800 mm
- Dormer outside width
- 3000 mm
Primary result: Main-roof tie-in run: 3600.0 mm.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This is side-section layout geometry for roofs sharing one plate datum. It does not design headers, doubled rafters, loads, flashing, overhangs or structural connections. Confirm cheek-valley plan geometry and framing sizes from the project drawings.
Frequently asked questions
Why can the calculator return no layout?
The entered roof planes may be parallel or meet behind the stated front wall. Recheck both pitch ratios, the setback and the common vertical datum.
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