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Cross-market term

Conservatory and sunroom

A largely glazed room attached to a house, thermally separated from it, and exempt from some of the requirements a habitable extension would have to meet — an exemption that depends entirely on that separation.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Same word, different thing

    conservatory

    also sunroom, garden room, orangery, lean-to

    A regulatory category with conditions: a defined floor area, a proportion of glazing, thermal separation from the house, and independent heating controls. A glazed room failing those is an extension, not a conservatory.

  • Australia

    Close, not identical

    sunroom

    also enclosed verandah, conservatory, garden room

    Named by use rather than by a regulatory carve-out, with the NCC treating an enclosed sunroom as conditioned space if it is heated or cooled.

  • United Statesyours

    Same word, different thing

    sunroom

    also four-season room, three-season room, solarium, Florida room

    THREE-SEASON and FOUR-SEASON is the meaningful American split: three-season is unheated and outside the thermal envelope, four-season is inside it and must meet the energy code like any room.

  • Canada

    Close, not identical

    sunroom

    also four-season room, three-season room, solarium

    As the United States, with the three- and four-season distinction sharper because an unheated glazed room is unusable for much of the year.

The governing standard, by market

  • United Kingdom

    Approved Document L / The Building Regulations Schedule 2

    Conservation of fuel and power, and the exemptions for conservatories including the thermal separation condition.

  • United States

    IECC / AAMA 2100

    Energy code requirements for conditioned space, and voluntary specifications for sunroom products by category.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Window Wall Area-Weighted U-Factor Calculator →Window Heat Loss Savings Calculator →BTU Cooling / AC Sizing Calculator →

Frequently asked questions

What actually makes something a conservatory rather than an extension?
Conditions, not appearance, and the one that gets broken is the separation. British regulations exempt a conservatory from some energy requirements provided it is below a floor area limit, is substantially glazed in its walls and roof, is separated from the house by walls, doors and windows of the same standard as the external envelope, and has its own independent heating controls. Take out the doors to make an open-plan space, or extend the central heating into it, and it is no longer separated — it is now part of the conditioned building, and its glass has to meet the standards a habitable room's envelope would. That is the single most common regulatory problem with conservatories, and it is created after the build by an owner rather than by the installer.
Why is the separation a regulatory condition rather than a preference?
Because a conservatory is a very poor thermal envelope, and the exemption exists on the assumption that it is not being heated to living-room temperature all winter. A room with glass walls and a glass roof loses heat far faster per square metre than any compliant wall, and if it is brought inside the heated envelope the whole house's energy performance falls sharply. So the deal the regulations strike is: build it to a lower standard, and keep it separate so the house is not paying for it. Removing the separation takes the benefit of the exemption while removing the condition it was granted under — which is why building control treats it as a change requiring the glazing and the heating to be reconsidered, not as a decorating decision.
What is an orangery, and is it a different thing?
Traditionally yes, and in current usage it is mostly a marketing distinction with one real consequence. An orangery historically had substantial masonry piers and a solid roof with a glazed lantern in the middle, rather than a fully glazed roof — it was a building with large windows, not a glass box. That distinction matters because the proportion of GLAZING is one of the conditions for the conservatory exemption: a room with a largely solid roof may fall outside it and be treated as an extension, with the energy requirements that follow. So the word describes a look, and the thing it correlates with — how much of the envelope is glass — is a regulatory input. Anyone specifying one should establish which side of that line the design falls on before it is built rather than after.