What is the maximum pitch for loft conversion stairs?

42 degrees, for a private stair serving a single dwelling. This is the limit that most often forces the stair to run in a different direction from the one homeowners expect, because a steeper flight would fit in less floor space but is not permitted.

What headroom do loft conversion stairs need?

2.0 metres normally. Approved Document K contains a relaxation specifically for loft conversions where the full 2.0m is not achievable: 1.9m measured at the centre of the stair width, reducing to 1.8m at the side. This relaxation is often what makes a loft stair fit at all under a sloping ceiling.

Can I use a spiral or space-saver staircase for a loft conversion?

A space-saver (alternating tread) stair is only acceptable where it serves a single room and a conventional stair genuinely cannot be fitted — building control has to accept it, and many will not for a bedroom. Spiral stairs can comply but need care over going and headroom, and they are difficult to get furniture up. Neither is a shortcut around a stair that will not fit.

Does the loft stair have to be directly above the existing stair?

No, but it usually is, because that is where the headroom and the floor space exist. Stacking the new flight over the existing one also keeps the protected stairway continuous from the loft to the final exit, which is what Approved Document B requires.

Building Regulations

Loft conversion staircase rules

A loft stair must not pitch more than 42°, with a rise of 150–220mm, a going of at least 220mm, and twice the rise plus the going between 550mm and 700mm. Headroom is 2.0m, relaxed for loft conversions to 1.9m at the centre of the stair and 1.8m at the side. Landings are required top and bottom.

Last reviewed 1 September 2026

Why the stair decides the design

The stair is the constraint that reshapes the floor below. It has to land somewhere, it takes 2 to 3 square metres out of a first-floor room or landing, and its geometry is fixed by regulation rather than by preference. On a great many loft conversions the question is not “what will the loft room be like” but “which bedroom loses a corner”.

The numbers

Approved Document K, private stairs — a stair within a single dwelling.
Dimension	Requirement	Note
Maximum pitch	42°	Measured on the pitch line. No exceptions for lofts.
Rise (each step)	150–220mm	Every step in a flight must be equal.
Going (each step)	220mm minimum	Also equal throughout the flight.
2 × rise + going	550–700mm	The comfort relationship. A compliant rise and going can still fail this.
Headroom	2.0m; 1.9m centre / 1.8m side in a loft conversion	The relaxation applies only to loft conversions.
Width	No statutory minimum for a private stair	800mm is the practical minimum; below ~750mm getting furniture up becomes a problem.
Landings	Required at top and bottom	At least as long as the stair is wide, and clear of door swings.
Handrail	One side minimum; both sides if wider than 1m	900–1000mm above the pitch line.
Guarding	Required at the loft floor opening	Must not allow a 100mm sphere to pass through.

The loft conversion relaxation

The one concession Approved Document K makes to loft conversions is on headroom. Where the full 2.0m cannot be achieved — typically because the new flight rises into a sloping ceiling — Approved Document K accepts 1.9m measured at the centre of the stair width, reducing to 1.8m at the side.

The stair is also the escape route

Everything above is Approved Document K, which is about falling over. Approved Document B is about fire, and it treats the same stair as the protected escape route from the new third storey:

30-minute fire-resisting enclosure around the stairway, from the loft to a final exit
Fire doors onto the stair from every habitable room it passes on every floor
Interlinked mains smoke alarms on each storey
A final exit the route actually reaches — which is what makes an open-plan ground floor a design problem

See Building Regulations for loft conversions for how the fire strategy fits together.

When the stair will not fit

Turn it. A quarter or half landing changes where the headroom is needed and often solves the problem outright.
Run it under the ridge. Aligning the flight with the ridge line puts the head of the stair where the height is.
Dormer over the stairwell. A dormer placed over the head of the stair creates the headroom directly, at the cost of volume allowance.
Space-saver stairs. Alternating-tread stairs are acceptable only where the stair serves one room and a conforming stair genuinely cannot be fitted, and building control has to agree. Treat this as a last resort, not a plan.

Common questions

What is the maximum pitch for loft conversion stairs?: 42 degrees, for a private stair serving a single dwelling. This is the limit that most often forces the stair to run in a different direction from the one homeowners expect, because a steeper flight would fit in less floor space but is not permitted.
What headroom do loft conversion stairs need?: 2.0 metres normally. Approved Document K contains a relaxation specifically for loft conversions where the full 2.0m is not achievable: 1.9m measured at the centre of the stair width, reducing to 1.8m at the side. This relaxation is often what makes a loft stair fit at all under a sloping ceiling.
Can I use a spiral or space-saver staircase for a loft conversion?: A space-saver (alternating tread) stair is only acceptable where it serves a single room and a conventional stair genuinely cannot be fitted — building control has to accept it, and many will not for a bedroom. Spiral stairs can comply but need care over going and headroom, and they are difficult to get furniture up. Neither is a shortcut around a stair that will not fit.
Does the loft stair have to be directly above the existing stair?: No, but it usually is, because that is where the headroom and the floor space exist. Stacking the new flight over the existing one also keeps the protected stairway continuous from the loft to the final exit, which is what Approved Document B requires.

Sources

Approved Document K — stairs and headroom, including the loft-conversion relaxation
Approved Document B, Volume 1: Dwellings — fire safety — why a third storey changes what the staircase has to do

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Related guides

Building Regulations for loft conversions

Every loft conversion needs Building Regulations approval, whatever the planning position. Fire safety, stairs, structure and insulation — what each Approved Document requires.

Loft conversion head height

There is no legal minimum ceiling height for a loft room. 2.2m is a practical guideline, not a regulation — and the number that matters is the finished height after build-up.

Rear dormer loft conversion rules

The Permitted Development limits that shape a rear dormer: volume, ridge height, the 200mm eaves setback, highway frontage, matching materials and side windows.

Do I need planning permission for a loft conversion?

Most loft conversions in England need no planning permission — they are Permitted Development. Here are the six conditions that decide it, and the cases that fail.

Written by the LoftNow team from the legislation and Approved Documents cited above, and reviewed against the rules our assessment engine implements. It is general guidance for properties in England, not advice on your particular property — Permitted Development is self-assessed, and the definitive answer for a specific house comes from your local planning authority, normally via a Lawful Development Certificate.