Discover Windows / The Honest Trade Offs

Glass Is Generous and Glass Is Leaky

The material that gives you everything is also the weakest part of the wall.

Every opening is a negotiation with the wall it interrupts. A wall keeps heat where it is; glass lets it move. In cold weather a large glazed area is the part of the room shedding warmth, which is why people instinctively sit away from big openings on winter evenings even in rooms they otherwise love. In hot weather the same glass admits solar heat, and a room that felt luminous in one season can become uninhabitable in another. This is not a defect to be argued away. It is simply what glass is, and the reason openings were historically modest and considered.

The traditional answers were architectural rather than technical: shade the opening from outside so sun never reaches the glass, orient rooms so that the sun that does arrive is the sun you want, use the mass of the building to steady the swings, and provide something you can close. None of these require any product at all. They require thinking about the opening as part of a system rather than as a hole to be specified.

Anyone weighing changes to the fabric of a building needs a qualified professional, and this magazine will never pretend otherwise. What it will say is that the conversation goes better when you understand the trade. Every additional square of glass buys light and view and spends something in comfort and control. That exchange is legitimate. It is being unaware of it that produces the rooms nobody can sit in for half the year.