Shed planning · Guide 4 of 7 · 5 min readUpdated
Plan shed roof framing, soffits and fascia
Compare gable and single-slope roofs, choose where water leaves the shed, and understand what overhangs, soffits and fascia contribute.
Choose the roof from the site outward
A single-slope roof concentrates runoff at one low edge. That can help keep a doorway clear of roof discharge when the low edge faces another direction. It also creates a high wall, so check that height and where the water can actually drain. A gable divides drainage between two eaves and creates a central high space, with more roof-edge and ridge details to finish.
Overhangs shelter parts of the wall and openings, but also add exposed framing, wind-sensitive edges and trim. Boxed soffits conceal the underside and create a level finished edge; open eaves show the framing and leave it needing an appropriate exposed finish. A soffit panel alone does not establish roof ventilation. Choose the roof covering and complete roof assembly before settling pitch and vent details.
Example: a door on the front wall
A roof draining toward the front can shed water directly over the entrance unless a suitable collection detail handles it. Compare a side-draining single slope with a gable whose eaves run along the sides. Check the high-wall height, drainage destination and access for cleaning gutters before choosing the version that looks best.
Read the roof geometry
The gable ridge runs from front to back. For a single-slope roof, choose the slope direction: front to back, back to front, left to right or right to left. Each option names the low and high wall. The entered low-wall height stays the same when you switch direction; the high wall rises across the selected width or depth. The floor plan marks the low and high sides, and wall framing, 3D geometry and quantities follow the selection. Pitch is the rise for every 12 inches of horizontal run. Set eave overhangs at the level roof edges and rake overhangs at the sloping edges separately. Both are horizontal measurements to the outside roof edge; they rotate with the selected slope direction.
Roof covering and sheathing estimates use the true sloped surface including those overhangs. Highest wall point refers to the wall profile above the floor. The separate Top of roof deck figure adds the entered rafter and sheathing depth, plus any high-side overhang rise. Foundation height and roof-covering thickness remain additional.
Roof area = (run across slope + 2 × eave overhang) × (length along eave + 2 × rake overhang) × √(1 + (pitch ÷ 12)²)
Keep units consistent; divide square inches by 144 to get square feet. This geometry does not size rafters, trusses, ties, connections or foundations.
Lay out the roof framing and trim
Choose rafter size and spacing, sheathing thickness, subfascia depth, fascia finish and soffit layout. These begin as editable examples, not calculated structural sizes. The gable assembly has paired rafters, a ridge board and one low tie at each interior pair; the end rafters sit over the framed gable walls. The single-slope assembly runs full rafters between the low and high walls, following any of the four directions.
The rake overhang uses fly rafters and 2×4 ladder blocks on flat, with spacing measured horizontally along the rake. Eave blocking has its own size, starting at 2×4. Each block spans the full space between rafter faces with its top flush to the roof plane. On a gable, the row moves inboard up the slope if needed to clear the low ties; the displayed position is a geometric fit, not approval of the restraint or connection detail. Choose blocking and its location from that detail. The planner flags combinations that cannot fit without crossing ties, rafters or roof edges. It does not design an overhang cantilever, a structural ridge beam, trusses, storage loading or connections.
Sloped end-wall profiles follow the uncut rafter underside. Enable a birdsmouth seat to model its horizontal bearing width and adjust the roof and wall elevations consistently. The bearing drawing shows heel depth, height above plate, notch depth normal to the grain and remaining timber. For a single slope, the high heel sits at the inside wall face; its plate elevation is shown in the detail. Fly rafters remain unnotched. Ridge pockets and other connection cuts still need their construction details. Gross rafter blanks include the extra stock needed for plumb ends. Member quantities exclude spare lumber and stock-length waste.
Fascia covers both eaves and sloping rakes. Choose boxed eaves with sloped rakes, soffits that follow the roof, or open eaves. Boxed coverage includes corner returns and, on a single-slope high eave, an outer closure below the fascia so the soffit stays below the uncut rafters. Wall receiver/backing, roof-edge flashing and ridge-cap coverage are listed separately. Panel backing, seams, trim profiles and ventilation openings need a product-specific detail.
Use Roof framing or All framing under 3D layers to expose the members. Roof plan shows their orientation; expand Rafter cross-section to see the height reference. Roof member schedule groups individual pieces by stock size and gross blank length. Soffit area is coverage, not a vent free-area calculation.
Read roof members before ordering stock
A rafter blank must contain the entire finished profile along the grain, including the extreme long points at both angled ends. The builder projects all vertices onto that axis and uses the extreme-to-extreme span, then adds the selected extra stock at each end and rounds up to 1/16 inch. It does not remove the angled-end allowance from the stock order.
For the current parallel plumb ends, the required profile span equals the same-edge slope length plus actual rafter depth multiplied by pitch/12. At 6:12, a 5½-inch-deep member needs 2¾ inches beyond its same-edge length for those end angles. The schedule distinguishes that finished span from the blank with additional end trim.
The cut profile labels both references for the plumb cut: degrees off square and degrees to the board’s long edge. They are complementary angles. Follow the actual saw’s scale and confirm a sample before production. The drawn profile is for plumb ends; seats, birdsmouths and their effect on roof height still require a construction detail.
The materials budget combines compatible wall, floor and roof blanks by actual size, then adds separation kerf when allocating whole boards. Kerf is not added a second time to the finished profile. A rafter longer than all enabled stock remains a separate quoted piece; it is not silently spliced.
Keep roof surfaces and edge trim distinct
Roof sheathing and covering follow the sloped surface including overhangs. Soffit quantities cover the selected underside areas. Fascia and edge flashing use their own edge lengths, with the surface allowance applied to the appropriate quantities.
On a single slope, high-side flashing is a separate row and that edge is removed from the other-edge flashing total. Roof insulation follows the roof inside the wall footprint, so it excludes overhangs. These quantities describe different surfaces and should not be copied interchangeably.
Review the same orientation in every view
Floor plan and Roof plan put Front at the bottom and Right at the right. The 3D side labels follow the model. Use Plan orientation for a top-down comparison, or Fit view to return to perspective. Change 3D layers to exposed roof framing or all framing to see beneath the finish.
After changing pitch, wall depth or slope direction, recheck all four wall elevations, rafter direction, low and high edges, overhangs, openings and unpriced material rows. Save the revised project and print its roof schedule with the drawings.
Price roof and wall stock together
Choose sizes, ties, bearing, bracing, ventilation and connections from the required construction detail. The model is a layout and quantity aid.