Energy efficiency
Building Regulations require high levels of thermal efficiency and that can be hard to achieve with a substantially or completely glazed extension. More heat tends to be lost through glass than through a well insulated cavity wall. A typical house loses 10% of its heat through the windows around and around two-thirds of the energy loss occurs through the glass, says Green Spec. However, by specifying triple glazing or low-e (low-emissivity) glass or by topping up the insulation in cavity walls elsewhere in the house, you can make up the energy savings.
Hansen said: “Modern glazing has improved greatly. With the use of triple glazing and solar coatings, heat loss and gain can be kept to a minimum. New Building Regulations coming in June 2022 will mean formal calculations will be required on heat loss and gain when large expanses of glass are used, which is a prudent approach to ensuring the building remains comfortable.”
Design matters
If your home has great views, then floor to ceiling picture windows or glass walls can showcase them and truly enhance the indoors-outdoors connection. Using frameless glazing gives a minimal look and means the view is uninterrupted or panoramic. Meanwhile a glass box extension can flood a narrow or north-facing kitchen with light. Glass atrium additions are another way of bringing light in and adding wow factor
Planners often like glass link corridors that bridge connections between different buildings or architectural periods. Similarly, conservation officers favour glazed extensions to listed buildings as it shows a clear division between the historic structure and modern glass.
Frameless glass extensions can make a striking design statement, flooding an interior with light. Glass box extensions can be a separate room or an addition to an existing area for example, a kitchen, living or dining room. They can be used as a sunroom, extra sitting space or even home office.
Don’t forget the practicalities
While glass is strong and hard, it is also rigid and more difficult to install. Large sheets of glass are very heavy and often need to be lifted into position with cranes, adding to the cost. Consider too, the orientation of your home. A south-facing extension will receive more sun and so risk over-heating although there are solar control glass and specialist coatings to tackle this issue. If you have a solid roof above the glazing, it may overhang the glass and shade the room from too much sun.
Hansen said: “A little solar gain in the mornings is positive, but too much and the room will overheat. Solar gain isn’t usually an issue on north-facing facades, but external condensation is prevalent as there is no sunlight to heat the glass externally to burn off the morning dew. This is particularly an issue for triple glazing.”
Glass walls means nowhere to place electrical sockets (other than the floor) or fitted kitchen units which may need to be positioned centrally instead. Your new room may be more functional with only partially glazed walls and a solid roof concealing insulation.
How much does structural glazing cost?
Structural glazing is expensive, though prices vary greatly. A bespoke glass box extension will almost certainly cost more than a conventional build. Hansen said: “Glass is one of the most expensive construction materials around, hence the bigger price tag. As a rule, the bigger the span, the more structural load is going through the glass, which means thicker glass.”
