Roofs the Right Way: Footprints, Slopes, and Connections to Walls

Why “Roof by Footprint” Is the Beginner Default

For a small building, Roof by Footprint is usually the most reliable method because it keeps the roof driven by a clean 2D boundary and a small set of parameters (slope, overhang, type). That makes the roof easier to edit later, easier to document, and less likely to create messy geometry at wall intersections.

In practice, you sketch the roof perimeter (often based on exterior walls), decide which edges define slope, and let Revit generate the 3D form. You then connect walls to the roof so the model and sections show proper closure.

When to avoid other methods (for now)

• Roof by Extrusion: useful for special profiles, but beginners often struggle to keep it aligned with walls and editable.
• In-place roofs / massing tricks: can look correct in 3D but often break sections, schedules, and future edits.

Key Roof Concepts You Must Control

1) Footprint boundary vs. overhang

The footprint sketch defines the roof’s boundary. Overhang is typically controlled by the sketch line’s Overhang value (or by picking wall faces with an offset). Keep overhangs consistent and parameter-driven whenever possible.

2) Slope-defining edges

Each boundary edge can be set to Defines Slope. This is the main switch that determines whether an edge rises to form a pitched roof plane or stays as a non-sloping edge (often used for gable ends).

• Gable roof: two opposite edges define slope; the other two edges do not (they become gable ends).
• Hip roof: all perimeter edges define slope (common for simple rectangular hips).

3) Roof type properties (thickness and materials)

Roofs should be built as an assembly, not as a single “generic thickness.” Use the roof type’s structure to control layers (finish, sheathing, insulation, structure). This improves sections, details, and material takeoffs.

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Typical workflow: duplicate a roof type, then edit its structure so the thickness and materials match your intended assembly.

Step-by-Step: Create a Simple Roof by Footprint

Step 1 — Start the roof command in the right view

• Open a roof plan view (commonly the level where the roof is placed, e.g., a “Roof” level or the top level plan).
• Go to Architecture > Roof > Roof by Footprint.
• In the Options Bar, confirm the correct Level and set an initial Overhang value (you can refine later).

Step 2 — Pick walls to generate the footprint

• Use Pick Walls to trace the exterior walls.
• Set the pick option to the correct side (typically outside face) depending on how you want the roof to align.
• Apply a consistent overhang (example: 600 mm / 24 in) to start.

Tip: If your footprint is not a simple rectangle, still aim for a clean, closed loop. Avoid tiny jogs and micro-segments unless they are truly required for the design.

Step 3 — Define slopes intentionally

Select each boundary line and set:

• Defines Slope: on/off depending on roof type (gable vs hip).
• Slope: set the pitch (e.g., 6:12, 30°, or a percent depending on project units).

Gable example: For a rectangular building, turn Defines Slope ON for the two long edges, OFF for the two short edges to create gable ends.

Hip example: Turn Defines Slope ON for all four edges.

Step 4 — Finish the roof and check the result

• Click Finish (green check).
• Switch to a 3D view and orbit to confirm the roof planes look correct.
• If the roof looks twisted or unexpected, return to the footprint sketch and simplify the boundary or re-check which edges define slope.

Editing Overhangs Without Breaking the Roof

Method A — Edit footprint overhang values

• Select the roof.
• Click Edit Footprint.
• Select one or more boundary lines and adjust the Overhang value.

This keeps the roof parametric and consistent. It’s the preferred method for most beginner projects.

Method B — Use shape editing only when truly needed

Avoid using Modify Sub-Elements (shape editing) to “force” drainage or fix intersections on a simple gable/hip roof. Shape editing can complicate the roof and make future edits harder, especially when you later adjust wall locations or roof pitch.

Roof Type Properties: Thickness, Layers, and Materials

Duplicate before editing

Never edit a default roof type unless you are sure it’s not used elsewhere. Instead:

• Select the roof.
• In Properties, click Edit Type.
• Click Duplicate and name it clearly (example: Roof - Gable - Asphalt Shingle - Insulated).

Edit the structure for correct assembly

• In Type Properties, find Structure and click Edit.
• Set layer functions (Finish, Substrate, Thermal/Air, Structure) and assign materials.
• Confirm total thickness matches your intent.

Note: You don’t need to model every rafter for a beginner building model. The roof assembly layers provide correct section thickness and material data without excessive geometry.

Attach Walls to Roofs for Clean Closure

After the roof is created, walls should typically be attached so they meet the underside of the roof correctly. This improves sections/elevations and reduces manual wall top offsets.

Attach Top/Base workflow (typical: attach top)

• Go to a section or 3D view where you can clearly select walls and roof.
• Select the walls that should meet the roof.
• Use Modify | Walls > Attach Top/Base.
• Click the roof element to attach.

If the wall does not attach as expected, check that the wall is not constrained in a way that prevents attachment (for example, unusual top constraints or edited wall profiles). Keep wall profiles simple so attachment remains stable.

Detach when you need to edit the roof

If you later change roof pitch, overhang, or footprint, attached walls will usually update correctly. If you need to make a major change and walls behave unexpectedly, you can Detach Top/Base, edit the roof, then re-attach.

Keep Roof Geometry Simple and Editable

Prefer fewer, cleaner sketch lines

• Avoid tiny segments and unnecessary corners in the footprint.
• Use straight lines and arcs only where needed.
• Keep the roof as one element when possible for a simple small building.

Avoid “patching” with extra roofs unless required

Creating multiple overlapping roofs to hide problems can cause:

• Unclear intersections in section
• Extra lines in elevations
• Incorrect material takeoffs
• Hard-to-edit conditions later

If you truly need multiple roofs (e.g., porch roof + main roof), keep each footprint clean and use proper join/intersection tools rather than overlaps.

Use Sections to Verify Roof Assembly and Wall Connections

Sections are the fastest way to confirm the roof is modeled “the right way”:

• Check layer thickness: does the roof assembly read correctly?
• Check wall closure: do walls meet the roof cleanly without gaps?
• Check overhang: does the eave line match your intent?
• Check ridge/hip geometry: does it form cleanly without odd kinks?

Common problems sections reveal (and the better fix)

Practical Exercise: Model a Simple Gable (or Hip) Roof and Cleanly Attach Walls

Exercise goal

Create a roof-by-footprint for a small rectangular building, adjust overhangs, set a realistic roof assembly, and attach walls so intersections are clean in section.

Part A — Create the roof

• In the roof plan view, start Roof by Footprint.
• Pick Walls around the exterior perimeter with an initial overhang (example: 600 mm / 24 in).
• Choose one option:

• Gable: turn Defines Slope ON for two opposite edges; OFF for the other two.
• Hip: turn Defines Slope ON for all edges.

• Set the slope (example: 6:12 or 30°).
• Finish the roof.

Part B — Set roof type thickness and materials

• Select the roof > Edit Type > Duplicate.
• Edit the type Structure to include at least: finish + sheathing + insulation + structure.
• Apply the new type to the roof.

Part C — Adjust overhangs

• Select roof > Edit Footprint.
• Change overhang on one or more edges (example: make front/back 750 mm / 30 in, sides 450 mm / 18 in).
• Finish the footprint edit and confirm the roof updates cleanly.

Part D — Attach walls and verify in section

• Create or open a building section cutting through the roof (perpendicular to the ridge for a gable).
• Select exterior walls > Attach Top/Base > click the roof.
• In the section, verify:

• Walls meet the underside of the roof without gaps.
• Roof assembly layers display correctly.
• Overhang reads as intended at the eave.

Quality checklist (pass/fail)

• Pass: Roof edits are done through footprint and type properties; walls attach cleanly; section reads clearly.
• Fail: Roof relies on shape editing to force form; multiple overlapping roofs hide issues; walls use arbitrary top offsets instead of attachment; section shows gaps or confusing intersections.