Window-to-wall or roof ratio

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The standard 90.1 imposes a maximum percentage of glazed area of the gross
above grade wall and roof area of 40% and 5%, respectively, and I would like
to understand what was the groundwork/genesis for these percentages values
contribution, ore where they came from.

Vertical Fenestration

Vertical fenestration areas for new buildings and additions shall equal that
in the proposed design or 40% window-to-wall ratio of gross above-grade wall
area, whichever is smaller, and shall be distributed on each face of the
building in the same proportions in the proposed design

Skylights and Glazed Smoke Vents

Skylight area shall be equal to that in the proposed building design or 5%
of the gross roof area that is part of the building envelope, whichever is
smaller. If the skylight area of the proposed building design is greater
than 5% of the gross roof area, baseline skylight area shall be decreased by
an identical percentage in all roof components in which skylights are
located to reach the 5% skylight-to-roof ratio.

Thanks in advance for all your help

Joao Sousa

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Joined: 2010-10-07
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