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To surround or encircle something with glass. A noun or pronoun can be used between "glass" and "in." I think the architect plans to glass in the atrium.
glass something in
to enclose something, such as a porch, in glass. I want to glass this porch in, so we can use it in the winter. We glassed in our porch last year.
To surround or enclose something with glass: We glassed in the side porch to keep it warmer in winter.