Envelope Overview

The building envelope separates conditioned interior spaces from the outdoors and unconditioned areas. Properly defining the envelope is critical for accurate load calculations.

You work with the envelope in Building Model → Envelope. The sidebar has six tabs — Walls, Windows, Doors, Roofs, Skylights, and Slabs — each with its own assign or create action.

Envelope Components

Walls

Exterior and interior wall segments on space edges. Each assigned wall carries:

• A Wall Type (U-value, mass, surface absorptance)
• A Wall Angle (surface tilt, default 90°)

Orientation and area are derived from the wall’s geometry and the building’s Plan Rotation — they aren’t editable fields on the wall. See Walls.

Windows and Doors

Openings placed on walls:

• Window Type (U-value and SHGC) or Door Type (U-value and infiltration behavior)
• Dimensions (or glazing as a percentage of wall area for windows)

See Windows and Doors.

Roofs and Skylights

Roof assignments on spaces, plus skylights placed on those roofs:

• Roof Type (U-value, mass, surface absorptance), optional Roof Pitch, and Apply roof load to ceiling only
• Skylights use a Window Type for thermal and solar properties

See Roof and Skylights.

Slabs

Floor construction for ground-coupled spaces:

• Slab Type (F-factor for perimeter heat loss, U-value for floors above unconditioned space)

Perimeter length comes from space geometry. See Slab.

Auto Create Envelope

The fastest starting point is Auto Create Envelope (the ✨ button in the Envelope toolbar). It assigns wall, roof, and slab types to unassigned exterior edges and spaces — across All Levels or the current level — and never overrides existing assignments.

You choose a Wall Type (required), and optionally a Roof Type, Slab Type, and windows as a percentage of wall area. Run it after drawing spaces, then review and adjust anything that needs a different type.

Manual Assignment

Override or fill in gaps on each tab:

Assign Walls

1. On the Walls tab, click Assign Walls
2. Choose a Wall Type (simple or multi-segment) and options such as Limit wall assignment to exterior
3. Click walls on the canvas to toggle the assignment
4. Click Done

Create Windows or Doors

1. On the Windows or Doors tab, click Create Windows or Create Doors
2. Enter dimensions (or wall-area percent for windows) and choose a type
3. Click walls on the canvas to place openings
4. Click Done

Assign Roofs

1. On the Roofs tab, click Assign Roofs
2. Choose a Roof Type, optional Roof Pitch, and whether to Apply roof load to ceiling only
3. Click spaces on the canvas to toggle the assignment
4. Click Done

Create Skylights

1. On the Skylights tab, click Create Skylights
2. Enter dimensions and choose a window type
3. Click roofs on the canvas to place skylights
4. Click Done

Assign Slabs

1. On the Slabs tab, click Assign Slabs
2. Choose a Slab Type
3. Click spaces on the canvas to toggle the assignment
4. Click Done

Envelope Checks

The project Check warns when spaces have edges but the project has no wall, roof, or slab types defined — without types, those surfaces don’t contribute to load calculations. Define types in Basis of Design → Building Data, then assign them.

Unassigned exterior edges don’t raise a dedicated alert; they simply omit transmission and solar loads for that surface. Use Auto Create Envelope or the assign actions so every exterior edge is covered.

Impact on Calculations

The envelope affects:

• Transmission loads — heat transfer through walls, roof, and floor
• Solar loads — heat gain through windows and skylights
• Infiltration — air leakage at doors and envelope openings

Best Practices

1. Define types first — set up wall, window, roof, and slab types in Building Data before assigning
2. Start with Auto Create Envelope — then adjust interiors, multi-segment walls, and special conditions by hand
3. Assign walls before openings — windows and doors are placed on walls
4. Check Plan Rotation — wall orientation for solar calculations comes from geometry plus the building’s north; set Plan Rotation on the Sheets & Maps toolbar if the plan isn’t north-up
5. Account for all openings — include windows, doors, and skylights that affect the load