· Michael Blair
In Middle Tennessee the summer sun is high, and a sunroom roof faces it directly for most of the day. Glass walls admit morning and evening light; the roof admits noon. What the roof is made of decides how hot the room gets, how much light it has, how it sounds in a storm, and how it holds up to the hail that comes through most springs.
Glass
A glass roof gives the most light and the most sky, and it is the look most people picture. Left as plain double glazing it also turns the room into a greenhouse by mid-morning in summer. Making it work means insulated units with a low-E coating and a tint or solar-control layer, laminated for safety overhead, and usually some form of shading, either exterior blinds or interior cellular shades on tracks.
It is the heaviest roof, which affects the framing and the footings, and the most expensive. It is also the one hail concerns most, because while laminated glass rarely shatters, a large stone can crack an outer pane and the unit then needs replacing. For a conditioned four-season room a glass roof is a substantial heating and cooling load year round.
Solid roof
A solid insulated roof, usually foam-core panels with a finished ceiling, treats the room like the rest of the house. It blocks the overhead sun entirely, insulates as well as an ordinary roof, is quiet in rain and shrugs off hail. Light comes in through the walls and, if wanted, through skylights placed deliberately rather than everywhere.
This is what makes a true four-season room possible in this climate at a reasonable running cost. It gives up the sky view, and the room reads more as a family room with big windows than as a conservatory. For most Nashville houses, where the summer problem is worse than the winter one, it is the roof that gets used most.
- Glass: maximum light, maximum heat, highest cost, needs shading
- Solid: coolest, quietest, best insulated, no sky view
- Polycarbonate: light and heat in between, lightest, lowest cost
Polycarbonate
Multiwall polycarbonate panels are a translucent plastic with internal air channels. They admit diffused light without the direct glare of glass, weigh a fraction as much, resist hail well because they flex, and cost far less. Tinted and solar-control grades cut the heat considerably, though not to the level of a solid roof.
Their weaknesses are noise, which is a drumming in heavy rain, expansion, which needs to be allowed for in the framing or the panels buckle, and a life span that is shorter than glass, with the surface dulling over a couple of decades. They suit three-season rooms and screened porches being upgraded, and they suit budgets that a glass roof does not.
Choosing for the room you actually want
Start from how the room will be used and in which months. A room for spring and fall evenings can carry a polycarbonate or glass roof happily. A room meant to be an extra living room all year needs a solid roof and proper conditioning, and a glass roof on that room will cost money every month to fight.
Orientation matters too. A north-facing room can carry more glass overhead than a west-facing one, which gets the worst of the afternoon sun. Whatever the roof, the connection to the house wall is where leaks start, and the flashing there deserves more attention than the choice of panel.