What is a conservatory?
A conservatory is an extension to a house whose walls, and usually roof, are mostly glass. In Dutch it is called a serre. Traditionally it is an unheated buffer space between house and garden; today the word is also used for a heated glass extension that is simply part of the living room.
Unheated or heated
That choice drives almost every other decision:
- Unheated conservatory (buffer space). Separated from the house by an insulated wall with an external-quality door. It collects solar heat in spring and autumn and is cold in winter. Simpler glazing will do, but expect condensation.
- Heated glass extension (living space). Open to the house, so it has to be built as a proper extension: insulated floor and foundations, low U-value double or triple glazing, thermally broken frames and heating that offsets the cold glass. Knocking through to an unheated conservatory without those upgrades gives a cold, damp room and high energy bills.
Application and points to watch
- Overheating. A south-facing glass roof quickly becomes unbearably hot in summer. Plan external shading from the start (internal blinds keep the heat inside), solar-control glass and ventilation through high-level vents or roof windows.
- Condensation. Warm, moist air condenses on cold glass and frames. Ventilate, choose thermally broken profiles and make sure condensate drains to the outside.
- Safety glass. Overhead glazing must hold together if it breaks, so laminated glass is used on the inner pane. Ask the supplier to confirm the glazing meets the local safety glazing rules.
- Foundations and junctions. A conservatory is not a shed: it needs foundations that will not settle differently from the house and a watertight, flexible junction with the wall.
- Roof pitch and cleaning. A glass roof that is too shallow holds dirt and water. Respect the minimum pitch of the system and think about how to clean it safely.
Permission
Rules differ by country and region. In England many rear conservatories fall under permitted development, and a single-storey, ground-level conservatory under 30 m² that is separated from the house by external-quality walls, doors or windows and has no heating from the main system is generally exempt from the Building Regulations, though its glazing must still be safe. Remove that separation and it becomes an extension that must comply in full. In the Netherlands a rear extension can often be built without a permit under conditions. Always check with your local planning and building control authority first.
Related terms
- Extension
- Condensation
- Thermal bridge
- Secondary glazed windows
- Roof extension
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