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 color for solar absorption
Usually equals the space floor area. Override for:
- Sloped roofs (use actual roof area)
- Overhanging eaves
- Covered outdoor areas
Affects solar absorption:
- 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 Add Skylight
- Enter dimensions and count
- Assign a skylight type
Skylight Properties
Section titled “Skylight Properties”- Dimensions - Width and height
- U-value - Heat transfer coefficient
- SHGC - Solar heat gain coefficient
- Curb height - Height above roof surface
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
Section titled “Ceiling Plenums”For buildings with suspended ceilings:
Plenum Configuration
Section titled “Plenum Configuration”- Ceiling height - Height of occupied space
- Plenum height - Space between ceiling and roof
- Plenum type - Return air, supply, or unused
Plenum Effects
Section titled “Plenum Effects”Plenums affect thermal calculations:
- Insulation location (at roof or ceiling)
- Air temperature in plenum
- Return air interaction with envelope
Attic Spaces
Section titled “Attic Spaces”For buildings with attic spaces:
Attic Configuration
Section titled “Attic Configuration”- Attic ventilation rate
- Ceiling construction - Insulation at ceiling level
- Roof construction - Typically uninsulated
Calculation Method
Section titled “Calculation Method”Heat transfer through attics uses:
- Attic air temperature (between outdoor and indoor)
- Ceiling U-value for indoor-to-attic transfer
- Roof ventilation effects
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