Correct head height of windows after splitting a wall in FR5

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Assessor Question:

If you have a wall with high level windows already added and you split the wall so the wall above now has the high level windows, do you need to readjust the head height of the windows? For example I had a wall that was 3685mm high and was split at 3000mm. The wall above is now 685 mm high but the window head height is still 3685mm. Do I need to adjust this back to 685 or does the software know. I modelled both head height options and it does make a difference to the rating, so one head height is correct and the other is incorrect. Which is it? 

TechLink Response:

• The correct head height of window is 3685mm.
• Ensure that split wall of 685mm has a base height of 3000mm.