Lightwell: How do I model?

Region: All States

Assessor Question:

I have a house that need I need to model that has a ‘lightwell’. Essentially, this lightwell is opening in the roof that extends down through upper floor to illuminate the courtyard below. So all zones that are adjacent to the lightwell will be to outside air. What is the correct way to model 1: the eaves & 2: the zones as the lightwell is in the middle of the dwelling. 

TechLink Response:

• The lightwell is an unroofed outdoor space and is therefore not a zone.
• Without seeing a section through the lightwell it is not possible to understand if any eave exists but the aperture in the roof appears to be approximately equal to the opening between the walls below.
• Accordingly, the sun will penetrate the opening in the roof and strike the walls around the lightwell at the upper level and the NatHERS model will take this into account to the extent possible given the shade obstruction of the wing walls and screens.
• The solar gain potential penetration through the small aperture to the lower level will  be negligible.
• This is the reason for ignoring the hole in the eave/shading caused by the upper level to the lower level.
• When TPA interpretation is required it is essential to adopt a conservative position to ensure that data entry does not anticipate an optimistic arrangement that would boost the performance assessment beyond the actual result.