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 thingloft
also roof space, attic
In British property usage a "loft apartment" is an American idea entirely — a converted industrial floor — while a British "loft conversion" is a room made in the roof space of a house.
Australia
Close, not identicalroof space
also attic, loft
Australian construction usage favours "roof space" for the void, with attic reserved for one converted to a habitable room.
United Statesyours
Same word, different thingattic
also roof space
"Loft" in American usage means either an open mezzanine within a room or a converted industrial apartment — not the roof void, which is the attic.
Canada
Close, not identicalattic
also roof space
As the United States, with attic the standard word for the void and loft carrying the mezzanine or apartment sense.
The governing standard, by market
United Kingdom
Approved Document B / L
Fire escape and thermal requirements for habitable rooms in a roof.
United States
IRC Chapter 8
Roof-ceiling construction, including attic ventilation and access.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Does a loft conversion mean the same thing everywhere?
- No, and the two meanings describe completely different projects. In Britain and Australia, converting the loft means making a habitable room in the roof space of an existing house: adding a stair, strengthening or replacing the floor, insulating at the roof slope, adding windows or dormers, and meeting fire escape and headroom requirements. In North America, a loft apartment means a dwelling made from an industrial or commercial floor plate, and a loft within a dwelling usually means an open mezzanine overlooking a room below. So a British article about loft conversions and an American one about loft living have almost nothing in common beyond the word.
- Why does insulating at the ceiling or at the slope change everything?
- Because it decides which side of the thermal envelope the roof space is on, and therefore how it must be ventilated. Insulate at the ceiling and the roof space is OUTSIDE the envelope: it is cold, it needs ventilating so moisture leaking up from the house can escape rather than condensing on the underside of the roof, and anything stored there is in an unheated space. Insulate at the slope and the space is INSIDE: it is warm, it is part of the heated volume, and the ventilation strategy changes completely — either a ventilated cavity above the insulation or a designed unventilated warm-roof build-up. Converting a loft moves the insulation line, which is why a conversion that adds insulation at the slope without removing it from the ceiling creates a cold pocket in between.
- What usually stops a roof space becoming a room?
- Headroom, the floor, and the escape route, roughly in that order. The existing ceiling joists are sized to carry a ceiling and light storage rather than a floor and its occupants, so they are normally strengthened or replaced — which eats headroom from below. A trussed roof has webs through the middle of the space that cannot simply be cut, so a conversion means a structural alteration rather than a fit-out. And a habitable room in a roof brings fire requirements: a protected escape route, often the whole stair enclosure upgraded, and window or means-of-escape provision. Each of those is normal and costed, and each is why the space that looks empty is not simply available.