Roof and Skylights
The roof is a major component of the building envelope for top-floor spaces. Roof construction significantly affects heating and cooling loads.
Roof Assignment
Section titled “Roof Assignment”Automatic Detection
Section titled “Automatic Detection”HVAKR automatically assigns roof to spaces on the top floor. Verify this assignment for:
- Multi-story buildings
- Buildings with varying roof heights
- Stepped or terraced construction
Manual Assignment
Section titled “Manual Assignment”To change roof assignments:
- Select a space
- Go to the Envelope panel
- Toggle roof on/off
- Select the roof type
Roof Properties
Section titled “Roof Properties”Roof Type
Section titled “Roof Type”Links to the roof type definition. Determines:
- U-value for transmission calculations
- Roof mass for thermal lag
- Surface absorptance for solar gain
Usually equals the space floor area. Override for:
- Sloped roofs (use actual roof area)
- Overhanging eaves
- Covered outdoor areas
Surface Absorptance
Section titled “Surface Absorptance”The roof type’s surface absorptance sets how much solar radiation the roof absorbs:
- Dark - High absorption (0.9+)
- Medium - Moderate absorption (0.5-0.7)
- Light/Cool Roof - Low absorption (0.3 or less)
Cool roofs significantly reduce cooling loads in hot climates.
Skylights
Section titled “Skylights”Skylights are windows in the roof that admit daylight and solar heat.
Adding Skylights
Section titled “Adding Skylights”- Select a space with roof assigned
- Click Create Skylights
- Enter dimensions and place skylights on the roof
- Assign a window type — skylights use window types for their thermal and solar properties
Skylight Properties
Section titled “Skylight Properties”- Dimensions - Width and height
- Position and rotation - Where the skylight sits on the roof
- Window Type - Determines the U-value and SHGC
Solar Gain
Section titled “Solar Gain”Skylights receive more direct solar radiation than vertical windows:
- Higher peak solar gain
- More consistent throughout the day
- Significant cooling load impact
Shading
Section titled “Shading”Skylight shading options:
- Internal shades or blinds
- External shading devices
- Light wells that limit direct sun
Ceiling Plenums and Attics
Section titled “Ceiling Plenums and Attics”For spaces with a suspended ceiling or attic below the roof:
- Ceiling height - Set the space’s ceiling height below the floor-to-floor height; the space above it acts as a plenum
- Apply Roof Load to Ceiling - Applies the roof load through the ceiling plane instead of directly to the space
- Temperature overrides - Roof types support summer/winter external temperature overrides for roofs below unconditioned attic spaces
Best Practices
Section titled “Best Practices”- Verify top floor - Confirm which spaces have roof exposure
- Use cool roofs - Consider high-reflectance roofing
- Size skylights carefully - Large skylights can cause overheating
- Account for plenums - Configure ceiling height correctly
- Check roof areas - Sloped roofs have larger area than floor