Advice
Is my loft big enough to convert?
Measure from the top of the ceiling joists to the underside of the ridge. About 2.2m or more is the usual rule of thumb. That figure is not in the building regulations, which set headroom over the new stairs instead: 2m, or 1.9m in the middle where space is tight.
How do I measure my loft's head height?
Take a tape up to the highest point. Measure from the top of a ceiling joist to the underside of the ridge timber.
That is the space you have now, not the room you will get. The new floor and the roof insulation both take some height.
The floor has to change because, as the Planning Portal says, in most homes the existing joists "will not have been designed to support a significant weight". How much? Warwick District Council's building control guide says "your new floor is likely to be around 200mm higher than your existing ceiling joists".
Sources: Planning Portal, is building regulations approval needed for a loft conversion, read 10 October 2026; Warwick District Council, loft conversions, read 22 October 2026.
How do I know if my loft is suitable for conversion?
Go up into the loft and run four checks. They come from a council building control guide.
Is there room to stand comfortably once the new floor sits about 200mm higher?
Is the loft large enough to give you a usable room?
Is anything passing through the space that would need moving?
Is there felt under the tiles, or is the roof fully weathertight?
If the answer to all four is yes, Warwick District Council says "your loft may well be suitable for conversion". Then check the roof timbers and where the stairs could go, below.
Source: Warwick District Council, loft conversions. Read 22 October 2026.Is 2.2m a building regulations rule?
No. It is a rule of thumb from guides. Approved Document K, the part of the regulations on stairs, sets headroom over the stair but no minimum room height.
Which? says: "The minimum height for loft conversions is 2.2 meters across at least 50% of the floor area." The Federation of Master Builders says: "Although the building regulations permit head heights of 2.2m, a far more comfortable height once a new floor covering has been laid and the ceiling finish has been applied is 2.4m." Neither points to a regulation that sets it.
What Approved Document K does set is headroom over the stair: 2m. For loft conversions it allows less where space is short: "Where there is not enough space to achieve the height shown in Diagram 1.3, provide the reduced headroom shown in Diagram 1.4." That diagram shows 1.9m at the centre of the stair and 1.8m at the side.
Sources: Which?, loft conversion building regulations and planning permission; Approved Document K, paragraph 1.13 and Diagram 1.4, both read 21 October 2026; Federation of Master Builders, loft conversions guide, read 10 October 2026.Is there room for the stairs?
Often this decides it. A tall loft still needs somewhere for a stair with enough headroom over it.
Approved Document K sets a limit on steepness too: "The maximum pitch for a private stair is 42°." Where a full stair will not fit, the Planning Portal says a space saving stair may be possible, and that retractable ladders or stairs are not normally acceptable.
Sources: Approved Document K, Table 1.1; Planning Portal, stairs in a loft conversion. Both read 10 October 2026.What type of loft cannot be converted?
Few are impossible. Many need the roof structure changed, and some need planning permission.
Trussed roofs are the hard ones. A 2025 guide from CNC Building Control, which covers Fenland, says: "Modern houses with trussed roof rafters are difficult to convert as the inner members of the truss cannot normally be removed."
Guides date the switch to trussed roofs anywhere from the 1960s to the 1970s, so the year your house was built is only a clue. Look up instead. A cut roof is open in the middle. A trussed roof has W shaped timbers across the space.
Flats are different. Permitted development for roof extensions does not cover a building containing flats, so a flat needs planning permission.
Sources: CNC Building Control, easy guide for loft conversions, 2025; Planning Portal, planning permission for a loft conversion. Both read 10 October 2026.Measured it and still not sure?
The survey is free and takes about twenty minutes. You get a written price before any work starts.
What if my loft is too low?
There are three usual ways round it, and one simpler choice.
The usual three are a dormer, lowering the ceilings below, or raising the roof. Raising the roof is the one that always needs planning permission, because it falls outside permitted development. That rules out work where "any part of the dwellinghouse would, as a result of the works, exceed the height of the highest part of the existing roof".
There is also a volume limit: 40 cubic metres on a terrace house and 50 on others, measured against the original roof. Earlier work counts. GOV.UK says: "Any previous enlargement to the original roof space in any part of the house must be included in this volume allowance."
Or keep it as storage, with loft boarding. Loft conversion or loft boarding explains the difference.
Sources: The General Permitted Development Order 2015, Schedule 2, Part 1, Class B; GOV.UK, permitted development rights for householders: technical guidance. Both read 10 October 2026.How many Cambridgeshire homes have a room in the roof?
Rooms in the roof are commonest in East Cambridgeshire, about 1 in 29 of the houses and bungalows with a certificate, and rarest in Fenland, about 1 in 68. Counts are from each home's most recent certificate, and a room in the roof is not always a converted loft.
About 1 in 36 (1,404 of 49,889).
About 1 in 40 (1,328 of 53,495).
About 1 in 55 (1,061 of 58,720).
About 1 in 29 (968 of 28,351).
About 1 in 38 (676 of 25,586).
About 1 in 68 (483 of 32,610).
Short answers
Is 2.4m better than 2.2m?
For comfort, yes. The Federation of Master Builders calls 2.4m "a far more comfortable height" once the floor and ceiling are finished. That is a guide's view, not a rule.
Can a loft conversion have a fixed ladder instead of stairs?
Only in a narrow case. Approved Document K allows one "only for access in a loft conversion that contains one habitable room", and only when a proper stair will not fit.
Can I use an alternating tread stair?
Sometimes. Approved Document K allows one only in a loft conversion, when a normal stair will not fit, and for access to one habitable room. It still needs "a minimum clear headroom of 2m". CNC Building Control, which covers Fenland, says these "will only be permitted in exceptional circumstances".
More advice
Find out if your loft can be converted
Take the measurement yourself, then book the free survey. It takes about twenty minutes. We check the joists, and you get a written price before any work starts. If the loft is too low for a room, boarding it for storage may be the better job. We do loft conversions too.
Complete Loft Services sorts out loft boarding and insulation across Cambridgeshire and the surrounding counties. The survey is free, and you get a written price before any work starts.
Written by Ben Criddle, who runs Complete Loft Services. Published . Facts checked on .