A loft stair must be fixed and permanent, with a maximum rise of 220mm, a minimum going of 220mm, and 2m headroom over the pitch line — reduced to 1.9m at the centre and 1.8m at the edge where the roof slopes. That headroom requirement, not the roof, is what defeats most marginal lofts.
- A loft ladder or retractable stair cannot serve a habitable room. It has to be a fixed stair.
- The 2m headroom rule relaxes to 1.9m centre and 1.8m edge under a sloping roof. That concession saves many schemes.
- Space-saver stairs are allowed only to a single room, not where the loft has two.
- Count the bedrooms after the stair is drawn. Gaining one upstairs and losing one below is no gain.
The numbers you have to hit
A loft conversion creates a habitable storey, and the stair to it is covered by Part K of the Building Regulations. These are the figures that decide whether a scheme works.
Maximum rise 220mm — the height of each step.
Minimum going 220mm — the depth of each tread.
Maximum pitch 42 degrees for a private stair.
Twice the rise plus the going between 550mm and 700mm, which is the rule that keeps a stair comfortable rather than merely legal.
Minimum 2m headroom measured vertically from the pitch line — the imaginary line joining the nosings of the treads.
Consistent rise and going throughout the flight. You cannot make up a shortfall with one odd step.
A handrail at a height between 900mm and 1000mm, on at least one side, and both sides where the flight is wider than a metre.
There is no minimum width for a domestic stair in the regulations, which surprises people. In practice around 800mm is comfortable and below about 600mm becomes awkward to carry furniture up, but width is not what stops a loft scheme. Headroom is.
The headroom concession that saves schemes
This is the most useful thing on the page, and it is the detail most often missed by people measuring their own loft and concluding it cannot be done.
The general requirement is 2m of headroom above the pitch line for the whole stair. In a loft that is frequently impossible, because the stair arrives directly under a sloping roof.
So there is a specific relaxation for loft conversions: where the roof slope prevents full headroom, 1.9m at the centre of the stair width and 1.8m at the side is acceptable.
That 100 to 200mm makes a genuine difference. A great many conversions only work because of it, and a surveyor measuring against the flat 2m figure will write off lofts that are perfectly convertible.
Two practical points follow.
Measure at the right place. The constraint is where the stair meets the roof slope, which is usually at the top of the flight. Measure vertically from the nosing line to the underside of the rafters at that point.
A rooflight can create headroom. Putting a rooflight directly over the head of the stair raises the ceiling locally into the window reveal, and that is sometimes exactly enough. It also lights the stair, which is a requirement in its own right.
The four places it can go
| Position | What it costs you | When it works |
|---|---|---|
| Over the existing flight, off the half-landing | Usually nothing | The best outcome; needs a deep enough stairwell |
| Straight run over the existing stair | A little landing space | Where the landing is long enough |
| Into the smallest bedroom | That bedroom, or most of it | Last resort; check the bedroom count |
| Off the landing, turning | Landing circulation | Common; needs width on the landing |
| A new position entirely | Floor area below | Rarely worth it on a standard plan |
Row one is what you are hoping for and it is achievable in a great many houses, because the existing stairwell is already circulation space that the new flight can rise through. It is the first thing worth testing on any scheme.
Where the window on the half-landing goes
A detail that catches people out on the commonest arrangement.
On a typical semi or terrace the new flight rises over the existing one, turning off the half-landing. That half-landing usually has a window in it — and the new stair runs straight past or through where that window is.
The options:
Keep it and box around it, which works where the stair passes to one side and leaves the window readable.
Replace it with a smaller or higher window, keeping daylight on the stair.
Lose it and light the stair from above, with a rooflight at the top of the new flight. This is the usual answer and it works well, because a rooflight throws light down the whole stairwell.
Block it up entirely, which is the cheap option and leaves a dark stairwell and a blank patch on the elevation.
Worth raising early, because it affects the external appearance and, on a rendered or distinctive elevation, how the house looks from the side. It also affects whether the stairwell is a pleasant space or a dim shaft, and that is something you live with daily.
Space-savers, and what is not allowed
People reach for the compact options when the space is tight. Some are permitted and some are not.
Loft ladders and retractable stairs are not acceptable as access to a habitable room. If the loft is to be a bedroom, office or anything counted as a room, it needs a fixed stair. A loft with a ladder is storage, whatever it is furnished as.
Alternating tread stairs — the paddle-shaped treads that let a steeper pitch work — are permitted, but only in a loft conversion and only where there is insufficient space for a conventional stair, and only serving one habitable room. If the conversion creates a bedroom and a separate study, an alternating tread stair will not do.
Spiral and helical stairs are allowed and are governed by their own guidance. They look space-efficient and in practice a compliant spiral takes a surprisingly large circle, and moving furniture up one is difficult.
Winders — tapered treads at a turn — are permitted and are the single most useful tool for fitting a stair into a tight plan. The going is measured at the centre line of the flight, so a turn made with winders uses considerably less length than a half-landing.
The practical order is: try a straight flight, then a flight with winders, then a half-landing turn, and only then consider an alternating tread. Each step down that list costs some usability.
Fire, escape and the enclosure
- The stairway becomes a protected escape route. Adding a second storey above ground means the stair enclosure has to be fire-resisting all the way from the loft to a final exit.
- Fire doors onto the stairwell. Rooms opening onto the protected stair generally need fire doors with self-closers, which is a change on every floor and not just in the loft.
- Interlinked mains-powered smoke alarms on every storey.
- The loft room itself needs an escape window of adequate size and position, or in some arrangements a sprinkler system as an alternative route to compliance.
- Glazing in the stairwell may need to be fire-rated where it forms part of the enclosure.
- An open-plan ground floor complicates this considerably, because the protected route has to reach a final exit and an open stair into a living space does not provide one. The usual answers are enclosing the stair at ground level, or a sprinkler system.
The last point is the one that catches owners of knocked-through houses. A loft conversion in a house with an open-plan ground floor is entirely possible, but the fire strategy is a real design question with a real cost, and it needs settling before the drawings are finalised rather than discovered at inspection.
Count the bedrooms afterwards
A point worth making plainly, because it decides whether the project pays.
If the only workable stair position takes the third bedroom, you have converted a three-bedroom house into a three-bedroom house with an extra floor. The space is useful and the value added is much smaller, because buyers search and compare on bedroom count.
Before committing, draw the stair on the existing first-floor plan and count what is left. Then ask whether a different arrangement — winders instead of a half-landing, a turn the other way, taking a slice of the landing and a slice of the bedroom rather than the whole room — keeps the bedroom.
Often it can. A scheme that looked like it cost a bedroom frequently turns out to cost a wardrobe and a metre of landing instead, and that is the difference between a conversion that returns its cost and one that does not.
This is also the argument for getting the stair designed by someone who does it regularly. The difference between a workable arrangement and an unworkable one is often a few hundred millimetres and a turn in the right direction.
What it costs
These are the loft conversion figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Velux / rooflight conversion | £25,000–£35,000 | Simplest type |
| Dormer conversion | £35,000–£50,000 | Adds head height & space |
| Hip-to-gable | £45,000–£65,000 | End-of-terrace / semi |
| Average loft conversion | ~£35,371 | Type & extras dependent |
The stair is part of the conversion rather than a separate line, but the arrangement affects the total: a flight rising in the existing stairwell is far cheaper than one requiring structural alteration to the floor below, and fire-door upgrades throughout the house are a real cost that a thin quote may have left out.
It usually will. We check headroom against the loft concession rather than the flat 2m figure, which is what writes off lofts that are actually convertible.
Frequently asked questions
What are the stair regulations for a loft conversion?
Maximum rise 220mm, minimum going 220mm, maximum pitch 42 degrees, consistent throughout the flight, a handrail at 900 to 1000mm, and 2m headroom above the pitch line — relaxed to 1.9m at the centre and 1.8m at the side where a roof slope prevents it.
Can I use a loft ladder for a converted loft?
No. A habitable room needs a fixed, permanent staircase. A loft reached by a ladder or retractable stair is storage, whatever it is furnished as, and it cannot be signed off or marketed as a bedroom. This is one of the commonest reasons an unofficial loft room fails at sale.
How much headroom does a loft staircase need?
2m above the pitch line normally, but where a roof slope prevents it, 1.9m at the centre of the stair and 1.8m at the side is acceptable in a loft conversion. That concession saves a great many schemes, and measuring against the flat 2m figure writes off convertible lofts.
Are space-saver stairs allowed in a loft conversion?
Alternating tread stairs are permitted in a loft conversion, but only where there is insufficient room for a conventional stair and only where they serve a single habitable room. If the conversion creates a bedroom and a separate study, they are not acceptable.
Where does the staircase usually go?
Most often rising over the existing flight, turning off the half-landing, because that uses space which is already circulation. The alternatives are a straight run over the existing stair, a turning flight off the landing, or taking it from the smallest bedroom — which is the last resort.
Will a loft conversion mean fire doors throughout the house?
Usually, yes. The stairway becomes a protected escape route from the loft to a final exit, which generally means fire doors with self-closers to rooms opening onto it on every floor, plus interlinked mains smoke alarms. An open-plan ground floor complicates it further.
The stair decides the scheme
We draw the stair before the room, because that is the constraint. Free survey, and an honest answer about whether it keeps your bedroom count.