Dormer Loft Conversions by Giles, Architect on Design for Me

Image above: View Profile of Giles, architect of dormer loft conversions above


We frequently get asked for cost guidance by homeowners on Design for Me. We would always encourage you to discuss designs and budgets with your architect or designer and then get quotes from builders, but we know that a rough starting point can be useful!


Why a roof conversion?…

Roof conversions are one of the most common and widespread projects in the UK home renovation market. One of the main reasons is the value that loft conversions can add to your home (from 15% and up to 20% according to the Nationwide Building Society).

A roof conversions cost is often considerably less than the added value gained, and conversions are typically cheaper than extensions in relation to the additional floorspace. They can also quickly add space to your property without being too disruptive – you shouldn’t need to move out while the work is going on.

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What will it cost?

The price depends on:

  • The current condition and space/head height of your existing loft and;
  • What you are planning to do with the extra space!

If you just want to gain some storage space, it may cost nothing more than around £1,000. However, extending and converting your loft into bedrooms with en-suite bathrooms will cost much more due to the extra plumbing and construction work required. However, this additional cost could be offset in relation to value added to your property!

The other elements likely to influence your budget are the type of conversion chosen and the professionals (designers and contractors) you decide to hire. The price of your conversion is also subject to where you live in the UK, with London and the SE being notably higher. The prices given below relate to a UK average.


Types of loft conversion:


Basic Storage – £1000+ 

If you just want to gain some storage space, the cost of adding a hatch, pull down ladder and a basic floor can cost as little as £1000, and be done in less than a week.

Property website, Prime Location says that “even this kind of conversion can be worthwhile if you are planning to sell your property. Having more accessible storage space available means having more useable space – and space sells houses.”


Skylight Conversion: £15,000 – 25,000

Price estimate from the following sources: Prime Location ansimplyloft

OR £1,050 to £1,250 per square metre plus VAT (What Mortgage)

What is a skylight conversion? 

Creating a simple habitable space, including stairs and roof lights with no external projections from the existing roof shape. However, this option is only viable if you have the headroom (ideally no less than 7ft)! If not, you’ll perhaps need to consider the other options below.

Roof extension diagram


Prime Location also estimate the cost of these elements, which may be helpful in totting up your costs:

  • Loft stairs (manufactured and fitted) £500-£800 for a traditional straight flight or spiral £1000-£2000
  • Roof lights (supplied and fitted) £500-£750
  • Dormer window (built and glazed) £4000-£6000


Dormer Conversion: £25,000 – £35,000

Price estimate from the following sources: simplyloft (London usually cost between £30,000 and £50,000)

or £1,150 to £1,350 per square metre plus VAT (from What Mortgage)

What is a dormer conversion?

This is where the ridge height of the roof stays the same but a portion of the roof protrudes out often in a box-like shape. It can be a small section just containing a window (called a dormer window) or the width or length of the roof space.




Hip to Gable Conversion: £30,000 – £35,000 

Price estimate from the following sources: addaroomloftsmidwestroofing

What’s a hip to gable conversion? 

On a detached or semi-detached property, they sometimes have a sloping side (hipped roof). Replacing this sloping roof with a vertical wall (the gable) at the end to the same height as the ridge, and filling in the space in between is a hip to gable extension.

Hip to gable Roof extension


Mansard Roof Extension: £45,000+

Price estimate from the following sources: simplyloft

or £1,250 to £1,450 per square metre plus VAT (from What Mortgage)

What is a Mansard Roof Extension?

A mansard roof extension would involved raising the side walls and creating a new steep roof pitch to front and rear. The main advantage for this type is the additional head height achieved though raising the ridge height.


Mansard roof diagram

Roof conversion diagrams from


Managing your project costs

Ready to take the next steps in starting your loft conversion project?…

1. It pays to get professional advice from a good architect. They can help you realise the main ambitions for your loft conversion, whilst helping control your costs. They will work with you to make sure you get the most out of your budget; to recommend where your budget is best spent, and where costs would be unnecessary or could be minimised.

2. Make sure you get 3-5 quotes from recommended builders (your architect can help compile a tender list for you) to get a firm idea of the costs before starting work.

Your architect can also help you with your building contract, to prevent any nasty surprises down the line. They can also inspect the builder’s work to ensure it’s being carried out in accordance with the agreed design and specifications.

If you have any further questions about starting your loft conversion project, you can drop us an email on and we’ll see how we can help!


by Austin,  Design for Me

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6 Responses to “How much do roof conversions cost?”

  1. Lee Miles

    Hi I am buying a property with the outside part of a roof conversion complete but needs the inside finishing, it has the stairs completed but needs electrics plumbing and plaster boarding finishing including flooring and en suite. what rough costs would i be looking at for the remaining work. Many thanks

  2. farid khilji

    i need to build a dormer on my bunglow. need mansard roof extension. do i need to put whole new roof? or i can use existinig tiles and tussles?

  3. Bruce Rodger

    Hi I am thinking of having dormer extension and note advice on here about obtaining 3-5 quotes. However we have always been unlucky with contractors despite been very careful in our selection process. Problems range from negative attitude and poor workmanship, delays in completion, increase in costs and being unprepared to return to repair things that go wrong after money has been paid. It has always been a stressful experience however nice or angry we get. It simply seems that there is a general sneering, uncaring or patronising attitude from most contractors we have encountered. Does anyone know where we can find out how to find a reasonably priced builder with an appropriate attitude in the Sevenoaks area in Kent. I would be grateful for any recommendations or web links.


    Type of conversion: Dormer conversion
    Room(s) to be in the conversion: 1 x bathroom, 2 x bedrooms

    We are planning to start ASAP. Planning approved. 2 beds and a toilet with washroom

    Architectual plans have been drawn up for this job
    Planning Permission has been approved
    Building Regulations approval has not been applied for yet
    Style of property: Suburban

  5. Brendan Malkin

    Hi, I would like to find out the cost of installing a dormer in my property in London. If i email you the dimensions can you assist? Thanks. Brendan

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