Shed planning · Guide 2 of 7 · 4 min readUpdated
Coordinate shed openings and header checks
Use one placement reference, distinguish unit size from rough opening, and check the assumptions behind a header candidate.
Keep one left-hand reference
Stand outside looking at the selected wall. Its frame-left edge is zero, even when the wall butts inside another wall. Choosing a unit centre or right edge changes the point being located; it does not move zero to the opposite end. Centre on wall uses half the frame length. Snap placement rounds the chosen point to the selected grid.
For example, a 30-inch-wide actual window frame with ¼-inch clearance per side needs a 30½-inch RO. If its centre is 72 inches from frame left, the RO begins at 56¾ inches. Changing from centre to left-edge entry keeps that physical position.
Choose the rough opening from the product
Exact RO mode uses supplied rough dimensions directly. Actual unit + clearances adds the entered fitting allowance to the real outside-frame dimensions. The controls start with zero clearances to avoid inventing a manufacturer requirement; enter the specified allowances before using the result. Door slab dimensions alone do not include the jamb.
The resolved opening drives framing and all area deductions. Raising a window by its top reference updates the sill, header and cripples together. Doors begin at the floor datum; any finish-floor or threshold adjustment must be included in the supplied installation dimensions.
Use a header table only within its stated scope
Manual sizing stays available for any project-specified detail. The optional automatic profile uses the 2024 Ontario Building Code, Table 9.23.12.3.-C, roof-and-ceiling row with a maximum 4.9 m tributary width, from the January 2025 compendium. It is a table candidate, not a permit or engineering approval. Verify the edition, local amendments, occupancy and all applicable conditions before enabling it.
The profile requires SPF No. 1 or No. 2 and a verified specified roof snow load up to 3.0 kPa. It uses the next higher listed snow column and exact metric opening limits. It takes no span or structural-sheathing credits. Every wall uses the conservative loaded-wall row, including the gable walls.
Only roof and ceiling loading is supported. Extra storeys, storage floors, concentrated loads, drift surcharge, unverified heavy roofing, larger supported spans and other conditions outside the table need a separate design. The profile checks the model’s roof/ceiling span and tributary width, but the person selecting it must verify local applicability and the complete load path.
Automatic mode chooses two plies and the table bearing allowance, preserving any larger entered jack pack. King-stud counts, header fillers, fastening, connections and support below remain project details. Changing to manual retains the current candidate as an editable size.
Enter the coverage that will actually be installed
Once the openings are fixed, choose the exterior finish and its trim. The dedicated siding guide compares horizontal wood, board-and-batten, vinyl lap and fibre-cement lap, then explains coverage, joints, backing and movement. Product dimensions come from the supplier; the planner's starting values are editable assumptions.
Read the complete finish order
Rough-opening dimensions describe the frame opening. Installed jambs, trim, flashing and siding clearances need their own details. Check those dimensions on site before cutting finish material. The siding guide explains what the material schedule includes and what still needs adding to the order.
Technical references
Confirm the current product literature and requirements for the material and assembly being installed.