Cost of Loft Conversion in London:

The type of loft conversion depends on the amount of area present in the house followed by the actual cost in conversion involved simultaneously. Small companies charge around 10-15 % less than the big companies i.e. top companies. So there are several payable amounts like A Certificate of Lawfulness or planning fees cost £86 and £172 respectively are kept separated from the loft conversion company contract and are paid by the homeowner by his own. Building Control fees i.e. around £500 in addition with VAT is also paid by home owner to the local authority or government independent company.

• £1,150-£1,350 per square meter for a basic roof light conversion
• £1,250-£1,450 per square meter for a dormer conversion
• £1,350-£1,550 per square meter for some other complex options

For a two rooms and one bathroom loft conversion:

• Mansard Conversion- £35,000–£45,000
• Dormer Conversion- £30,000–£40,000
• Hip to gable conversion- £25,000–£30,000
• Roof Light Conversion- £20,000–£30,000

• When you want to install a new Loft Staircase the design may vary from a simple wooden one to a glass one and cost of it also depend on the scale and design of your staircase. For example, if you go for simple plain timber staircase it costs around £250 whereas a staircase made from glass panels and modern banister will cost £25,000.
• Bidvine, a best London Loft Conversion builders construct your loft room either renovating it or building a whole new room, the cost varies accordingly. The basic loft room conversion costs £11,000.
• Loft Dormer Extension on Bidvine for base costs around £2,000. It gradually increases from 10-20% if you are going to install a new dormer on your home because the amount of construction work increases with the labour cost too.

The quotes from https://builderinlondon.uk gives suggested costs of loft conversions depending upon the types of loft conversions by London Builders.

• Velux is the type of loft conversion that requires least cost ranging from £21,000-£41,000 involving fixing of 2 windows to roof.
• Dormer is the most common kind of loft extension today prevailing in UK, the standard dormer costs is from £31,000-£58,000 and the L-shaped Dormer is around £40,000-£60,000.
• Hip to Gable- In this loft conversion both the sloping ends of roof are replaced by gable wall and cost comes out to be £42,000-£65,000.
• Mansard is the most extensive option of London Loft Conversion where one side of the roof is converted into a straight wall and flat roof, which forms a whole together new storey. The cost of this is £45,000-£75,000.

All these loft conversions are subject to change depending upon the availability of space, design and architecture, builders involved and labour involved depending on the time period.