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Roof Plan

A measured roof plan consists of a top-down, orthographic projection detailing the geometry and physical components of a roof structure. This bird's-eye view illustrates the specific shape, layout, and dimensions of the roofing system.

The roof plan identifies the ridges, valleys, eaves, and slopes of the entire structure. It specifies the distribution of drainage and the placement of all roofing materials. The 2D drawing outlines the precise dimensions required for calculating roofing squares and defines the spatial relationship between the various architectural features of the roof. In a Roof Plan:

1. Geometry and Layout (The Shape)

Roof Outline and Perimeter: The exact edge of the roof, showing overhangs and eaves relative to the building’s exterior walls.
Ridges and Hips: The highest horizontal points (ridges) and angled intersections (hips).
Valleys: Intersections where two roof planes meet, forming a channel for water.
Gables/Dormers: Clear definition of gable ends and any dormer windows or structures.

2. Measurements and Dimensions

Overhang/Eave Dimensions: Specific distances from the outer wall to the roof edge (e.g., 18" or 24" overhang).
Overall Dimensions: Total length and width of the roof structure.
Slope/Pitch Indicators: Arrows indicating the direction of water flow (downslope) and the pitch ratio (e.g., 4:12, 6:12).
Heights: Identification of ridge heights, parapet heights, and any level changes (crucial for flat roofs).

3. Roof Features and Penetrations

Mechanical Units: Location and size of HVAC units, fans, or solar panels.
Plumbing/Vent Pipes: Locations of all pipe penetrations.
Chimneys/Skylights: Location and sizing of chimneys, skylights, and roof hatches.
Access Points: Attic access or maintenance hatches.

4. Drainage Components

Gutters and Downspouts: Location, type, and size of gutters and where downspouts are located.
Scuppers and Drains: For flat roofs, indicate locations of overflow drains, scuppers, and drains to prevent ponding.

5. Material Annotations and Notes

Roofing Material Specification: Callouts for roofing material type (e.g., "30-year asphalt shingles," "standing seam metal," "TPO membrane").
Flashing Details: Areas requiring flashings, such as chimney saddles (crickets) or valley flashing.
Venting Notes: Locations for ridge vents, soffit vents, or attic ventilation.

6. Drawing Conventions

Scale: Typically drawn at 1/8" = 1'-0" or 1/4" = 1'-0".
North Arrow: Indicating orientation.
Dashed Lines: Often used to represent the building perimeter wall line underneath the overhangs.
Layer/Component Organization: If using CAD/BIM, organize the roof, ridges, vents, and annotations into proper layers for clarity.

Note: For complex, non-standard roofs, incorporating a 3D model view alongside the 2D plan can enhance understanding, especially for the contractor.

Key Components and Details

Roof Geometry: Shows the outline of the roof, including hips, valleys, ridges, and gables.
Dimensions & Slope: Provides precise measurements and indicates the pitch (e.g., 4:12) to ensure correct water drainage.
Structural Elements: Details overhangs, eaves, and sometimes supporting beams.
Penetrations & Accessories: Locates chimneys, skylights, plumbing vents, and, on commercial buildings, HVAC units.
Drainage Plan: Indicates gutters, downspouts, and scuppers.
Material Specification: Specifies roofing materials (e.g., shingles, tiles, metal).

Purpose and Usage

Construction Guide: Enables builders to construct the roof accurately according to specifications.
Building Compliance: Often required for planning permission and building code approval.
Material Estimation: Used by contractors to calculate accurate material quantities and labor for bids.
Visual Aid: Helps in visualizing complex rooflines during the design phase.

Roof plans are essential for ensuring a roof is structurally sound and properly waterproofed.

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