You are here: Loft Conversions: The Good, The Bad And The Downright Scary

1. What’s so good about loft conversions?

According to research from Nationwide Building Society loft conversions are the single most valuable home improvement:
- Average % value added
1. Loft conversion + 21%
2. Another bedroom + 12%
3. Central heating + 6.8%
4. Parking + 6.5%
5. An extra bathroom + 5.2%

Loft conversions also give you ‘more space for your money’

BUT not all roofs can be successfully or easily converted

AND there are many examples of poor quality loft conversions. Large box (mainly pre- 1988) dormers can detract from historic townscapes

2. Legislation


new rules from October 2008

  • Conversion of roof space to living accommodation is generally permitted if there is not a change to the plane of the roof fronting a highway (beware of corner sites!)
  • It must not exceed the height of the original roof.
  • It must not increase the volume of a terraced house by more than 40 cu. m. or 50 cu m. in other cases. Specifically - to count as ‘Permitted Development’:-
  • Dormers: must be set back at least 200mm from the eaves, as far as practicable.
  • Materials: should be similar in appearance to the existing house.
  • No balconies, verandas or raised platforms – including roof windows with ‘fold-out balconies’
  • Windows: side-facing windows to be obscure-glazed and non-opening unless the parts that can be opened are more than 1.7m above the floor of the room.

The Building Regs

from April 2007 - Key Changes to the Approved Documents

  • Escape from fire should be via a protected corridor / stairway (min 30 mins fire resistance) leading out to an external door.
  • Where open-plan room layouts exist at ground level, a new partition will be needed to enclose this escape route (or possible sprinkler protection + fire door)
  • Emergency escape windows now not essential (for floors over 4.5m above ground)
  • Fire doors are now required to the protected escape path
  • Self- closers no longer required

3. Key Design Options

Questions to ask - at the design stage

  • How much headroom is there in your existing loft?
  • Do you plan to install a large box dormer, traditional small dormers or just rooflight windows?
  • How will the new floor joists be supported?
  • What roof support is required at purlin & ridge level? 
  • How many new steels / beams will be required? 
  • Location of loft stairs?
  • Fire implications to the whole property?


Large dormers - type: full width, large box or mansard?

Small ‘cottage’ dormers: There’s a wide variety of traditional dormer and ‘halfdormer’ styles. Although they look good externally, they don’t add much space internally.


There’s also a wide variety of roof windows – not necessarily Velux !

4. What type of Roof?

5. Complying with fire

Typical 2 storey to 3 storey conversion, with loft floor more than 4.5m above external ground, but less than 7.5m. Compliance is more arduous for conversions above 7.5m where sprinkler systems and external fire exits may be required.

6. Loft Stairs

Where there’s not enough space to achieve 2m headroom, reduced headroom can be acceptable. Alternating tread ‘paddle’ stairs or a fixed ladder may be acceptable as a single flight + handrails both sides. Or spiral stairs, but only OK to a single loft room.

7. Designing the new structure

There are 3 main levels where new beams may be needed

- FLOORS A pair of new beams are installed across the ceiling joists, about ¼ distance in from front and rear. Supported in side walls.

- PURLINS When you remove the old purlins (or their struts), bang goes their support! Adding new steel or manufactured timber purlins is one way of compensating.

- RIDGE Normally required to support large dormer flat roof joists and to strengthen the existing ridge.


New Floor joists

- DIRECT support from internal walls Only suitable for some older properties. Main walls and spine must be able to support new loadings

- INDIRECT support from new beams Normally from one side wall or party wall to the other

1. Overslinging
New floor joists run above existing ceiling structure (where headroom isn’t an issue). Ends of the new floor joists slot into the side web of new beams.

2. Side-slinging (‘underslinging’)
New floor joists run alongside existing ceiling joists. Their ends hang down below new support beams, e.g. from long legged joist hangers.

3. Ceiling to floor conversions
New beams run under old ceiling allowing it to act as new floor – where headroom below permits.

4. Dropped ceilings
Demolish the old ceiling and build new floor/ceiling underneath – where head room below permits.

Extendable lightweight aluminium beams slide into roof space by removing just three rows of tiles on one side of the house

Minimises disruption – no need for heavy steels

LABC approved system, minimising loss of headroom

Spans up to 8.4m

Primarily for trussed rafter roofs

8. Loft Windows

Escape windows are no longer relied on as an escape route (for floors over 4.5m). To count as an ‘escape window’ a window must have a minimum clear opening of 0.33 sq m, with a minimum 450mm width and height).

Escape windows on roofs need to be set back with a max distance to the roof edge of 1.7m (sill to eaves).

Potential conflict between child safety and ease of escape, therefore sills should be no higher than 1.1m above floor level, but no lower than 600m (skylights) or 800mm (dormers). However ‘Juliet balconies’ with balustrades and French windows are fairly common.

The distance between dormer window sills and the existing roof should not normally exceed 225mm.

9. Loft Confusion

Comparing 3 quotes – are you comparing like with like?


Basic comparison

Detailed Comparison

10. Surveying Lofts

How should clients be advised where works do not comply with current Building Regs? What’s acceptable and what isn’t?

Q. Is it an original attic, or is it a conversion?
Clues in period properties include lathe & plaster to rafters, and old gable windows.

Q. Did the work require consent when it was carried out?
If so, what were the rules at the time of construction? e.g. open plan ground floor layouts? original doors to habitable rooms?

Q. Was consent obtained?
A completion certificate not just a ‘plans approved’ document. If not, advise a regularisation application (but likely effect on valuation?)

Q. Does it comply with current regs? (especially structure & fire safety)
Probably not – but is any non-compliance significant for the client?


The 2 most common customer complaints about new loft conversions are:-

1. Ceilings too low

2. Too hot in summer


Large dormers

  • Quality of coverings?
  • Access for maintenance?
  • Insulation ?

Openings for dormers and roof windows - are the rafters doubled up and trimmed?

11. Case Study

Existing rafters doubled up from ridge to new purlin wall with 50 x 100 timbers. New 50 x 100 collars bolted to rafters before cutting the original structure!

Insulation - complying with Part L.

Article written By Ian Rock MRICS