It looks like you are using a 'component' schedule rather than a 'surface' schedule.
When you look at how the walls trim you will see that the skins will trim each other as in the attached image.
So one skin length will include the width of the skin x 2 (6.09), 2 skin lengths will include the width of the skin x 1 (6.05) and only on skin length will not include any extra skin width (6.00).
Your skin width must be 0.045 and is being rounded up to 0.05 due to the number of decimal places.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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