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Loft conversion quotes
A loft conversion turns unused roof space into a proper room, usually a bedroom, an office or a bathroom. It is often the cheapest way to add a real room, because you are building inside space you already have rather than extending into the garden.
There are four common types, and which you can have depends mostly on your roof. A rooflight conversion leaves the roof shape alone and fits windows into the existing slope, which makes it the simplest and cheapest. A dormer builds outwards to create full head height and usable floor area. A hip to gable conversion squares off a sloping side wall, and is what a hipped roof usually needs before it works at all. A mansard rebuilds most of the roof structure and is the most involved of the four.
Is your property suitable?
Head height decides this, and you can check it yourself before speaking to anybody. Stand in your loft and measure from the joists you are standing on up to the highest point of the roof. Two metres is the minimum, and around 2.4m is comfortable. Bear in mind that insulation and a new floor take some of what you measure today, so allow for it.
If you are short of that, a conversion is not impossible, but it means altering the roof rather than working inside it, which is a different job at a different price. A hipped roof often needs squaring off to a gable before there is usable space at all.
Beyond height, your existing roof structure and joists need assessing by a structural engineer. That is normal practice before anyone quotes properly, not an extra being added on.
Typical cost range
£31,625 – £86,250
Excludes VAT, and includes a 15% contingency allowance for the unexpected.
The loft conversion cost calculator gives a range scaled to your roof type and local labour costs.
Broadly, cost follows how much of the roof you are changing. A rooflight conversion is cheapest because the structure stays as it is. A dormer costs more. A hip to gable adds the cost of rebuilding a wall. A mansard is the most expensive, because it effectively rebuilds the roof.
The other thing that moves the figure a long way is an ensuite. Running plumbing up to a loft means drilling through structure and finding a route for supply and waste both, so it is rarely a small addition.
What to ask before hiring
Ask whether the staircase is included. It is sometimes quoted separately and it is not a small item, because it has to meet building regulations and it takes space from the floor below.
Ask who is doing the structural calculations and whether that cost is in the figure. Ask how building control sign off is being handled, and what the fire escape arrangement is, because both are mandatory for a habitable loft room rather than optional extras.
Ask what insulation standard is being worked to, whether the price is fixed, and whether you can pay in stages against work completed.
Red flags
A quote that never mentions building regulations or structural calculations. A loft room without proper sign off is a problem you meet years later, when you sell and the buyer's solicitor asks for a certificate you do not have.
A quote with no insulation standard in it. Anyone telling you planning permission is definitely not needed without having looked at your specific roof, your property type and whether you are in a conservation area. Anyone happy to skip the structural engineer.
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Loft conversion
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Common questions
Do I need planning permission for a loft conversion?
Many fall under permitted development, but altering the roof shape with a dormer or mansard has volume limits, and conservation areas are tighter. Check with your local council before you commit to a design.
How much head height do I need?
Two metres is the minimum, and around 2.4m is comfortable. Measure from the joists you are standing on up to the highest point of the roof, and bear in mind that insulation and a new floor will take some of what you measure today.
Which type of conversion is cheapest?
A rooflight conversion, because the roof structure stays as it is. A dormer costs more, a hip to gable more again, and a mansard is the most expensive because it effectively rebuilds the roof.
Does a loft conversion need building regulations approval?
Yes. A habitable loft room needs sign off, including the fire escape arrangement. Without it you will have a problem years later, when you sell and the buyer's solicitor asks for a certificate you do not have.