Loft Conversion Cost and Price Guide | Average Costs in UK, London, etc

Dormer Loft Conversion Cost

The average cost of a loft conversion will also depend on what type of conversion you choose to have. One of the most popular options is the dormer loft conversion, which extends outwards from the back or side of the roof in a box shape. Dormers are sometimes referred to as kennel or box conversions and provide some additional space in the loft room. Dormer loft conversion prices vary depending on how many dormers you add and what else you do to the loft, but on average: 

1. 1. • Dormer Loft Conversion costs between £19,000 and £30,000

Get more information about dormer loft conversions and how much they cost.

Hip-to-Gable Loft Conversion Cost

Another popular option is to carry out a hip-to-gable loft conversion. This involves converting the hip (sloped) side of the roof into a flat edge which provides additional space inside the loft. The hip-to-gable loft conversion price will also vary depending on what else you have done to the loft, however:

1. 1. • Hip to Gable Loft Conversion costs between £30,000 and £35,000

Get more hip-to-gable loft conversion advice and prices.

Mansard Loft Conversion Cost

Mansard loft conversions are usually the most pricey options, but they also add maximum space.  A mansard conversion involves altering the entire roof slope to around 72 degrees, which means significant structural and building work needs to take place. On average:

1. 1. • Mansard Loft Conversion costs between £33,000 and £35,000

Find out more about mansard conversions and how much they cost.

Loft Conversion Planning Permission

As with any conversion or extension project, you’ll need to make sure that you don’t need to apply for planning permission when considering a loft conversion. Fortunately, loft conversions, including roof extensions, are classed as permitted developments in the UK, however, this may not apply if you live in:

1. 1. • A listed building
      • An Area of Outstanding National Beauty
      • A Conservation Area
      • A World Heritage Site
      • A National Park

In the above cases, you should consult your local building authority about whether you need planning permission for your loft conversion.  In all other cases, you won’t need to apply for planning permission for your loft conversion as long as you meet the following conditions:

1. 1. • You don’t extend your roof more than 40 cubic meters if you live in a terraced house of 50 cubic meters
      • If you live in a semi-detached house, roof extensions should be set back at least 20 cm from the eaves of the roof
      • If you’re installing side windows, they must be obscure-glazed and non-opening
      • You don’t extend beyond the plane of the existing roof slope if it’s facing a highway
      • All materials must be similar to the existing property
      • No part of the extension should be higher than the original roof height
      • Your loft conversion shouldn’t include any verandas, balconies or raised platforms

If you’re in any doubt about whether you need to apply for planning permission for your loft conversion, consult your local council; a loft conversion company or architect may also be able to offer advice.

DIY Loft Conversion Cost

It is possible to carry out loft conversions yourself to try and save cash. However, you should only attempt this if you have some experience and are absolutely sure you can carry out work safely and in accordance with both building regulations and planning permission guidelines. If your loft is already structurally sound, you have windows fitted and all the necessary electrical work completed and you’re only making cosmetic changes, it is possible to do this yourself. Prices will vary depending on what type of loft conversion you have; here’s a rough DIY loft conversion price guide to give you an idea:

1. 1. • DIY loft conversion could cost as little as £10,000

Get more advice about DIY loft conversions and information about prices.

The Party Wall Act and Loft Conversions

In addition to planning permission, if your house shares a wall with a neighbouring property under the Party Wall Act 1996 you need to inform your neighbours in writing that work is taking place; they have the right to contest this if they want to. To make sure your loft conversion goes smoothly, it’s best to talk to your neighbours beforehand.

Loft Conversion Building Regulations

All projects undertaken in the UK need to adhere to building regulations. Loft conversions need to comply with the following sections:

1. 1. • Part A – Structural Safety: this involves making sure that the loft walls, floors and joists are sturdy enough and that there’s sufficient headroom in the loft
      • Part B – Fire Safety: you will need to make sure that there’s an escape route in case of fire and that proper smoke alarms are installed
      • Part E – Resistance to Sound: there should be adequate sound proofing in your loft conversion
      • Part F – Ventilation: there must be adequate air vents and windows to adequately ventilate your loft conversion
      • Part L – Conservation of Fuel and Power: the loft will need to be insulated to conserve energy
      • Part P – Electrical Safety: any electrics in your loft must be installed by a qualified electrician
      • Part G – Sanitation, Hot Water Safety and Water Efficiency: if you’re planning  to install an en suite bathroom as part of your loft conversion then you’ll need to make sure plumbing is correctly and safely installed