A Guide to Loft Conversions

Table of contents

1. Is Your Loft Suitable for Conversion?
2. Types of Loft Conversion
3. Do You Need Planning Permission for a Loft Conversion?
4. Building Regulations for Loft Conversions
5. Loft Conversion Ideas by Room Type
6. How Long Does a Loft Conversion Take?
7. How Much Does a Loft Conversion Cost?
8. How to Find a Loft Conversion Specialist
9. FAQs: Loft Conversions

The conversion type that suits your property depends primarily on your roof shape - reading that section first will immediately narrow down your options before you get into costs and planning.

Is Your Loft Suitable for Conversion?

Not every loft can be converted economically, and a structural assessment by a builder or architect is the only definitive way to confirm viability. But there are specific indicators that give a strong signal before any professional is involved.

• Head height is the most important factor. The minimum ceiling height at the highest point of the roof space for a habitable room is generally considered to be 2.2 metres, though Building Regulations require 1.9m minimum in occupied areas. Measure from the floor to the highest point of the ridge. If you have less than 2.2m, the loft can only realistically be converted with structural roof alterations that add significant cost.

• Roof structure determines which conversion types are viable. Most UK homes built after the 1970s have trussed rafters - a web of timber triangles that fill the loft space. These can be converted but require a structural engineer's input to replace the trusses with new steel beams. Older properties with traditional cut roofs (individual rafters running up to a central ridge) have more open loft space and are generally more straightforward to convert.

• Roof pitch affects how much usable floor area can be created. A shallow pitch produces a limited floor area at adequate head height; a steeper pitch creates more usable space.

• Water tanks and services in the loft will need relocating as part of the conversion, the cost of moving a cold water tank and any associated pipework should be factored into the budget.

Find a loft conversion specialist near you

Types of Loft Conversion

The type of conversion that suits your property depends almost entirely on your roof shape and your property type. Each type has a different cost, planning status, and structural complexity.

Velux (Rooflight) Loft Conversion

The simplest and most affordable conversion type. Velux windows are installed into the existing roofline without changing the roof's shape or structure. No additional headroom is created - the conversion works by adding light and ventilation to an existing loft space that already has sufficient head height.

• Best for: Properties with adequate existing head height, homeowners on a tighter budget, and those who want to avoid the disruption of structural roof alterations.

• Planning status: Almost always permitted development, the most straightforward planning position of all conversion types.

• Typical cost: £22,500-£30,000.

• Not suitable for: Properties where head height is the limiting factor - a Velux conversion cannot add headroom.

Dormer Loft Conversion

The most popular conversion type in the UK. A dormer is a box-shaped structure that projects vertically from the existing roof slope, creating a flat-roofed extension that provides significant additional headroom and floor space. Dormers can be built at the rear, side, or front of the property, though rear dormers are by far the most common.

Dormers can range from a small single window dormer (primarily for light and access) to a full-width rear dormer that runs the entire width of the roof slope, maximising the usable floor area.

Best for: Most property types - terraced, semi-detached, and detached - where the rear dormer is the standard solution. A full-width rear dormer creates the largest possible room in most house types.

Planning status: A rear dormer on a standard residential property typically falls under permitted development. Front dormers, and any dormer in a conservation area or on a listed building, typically require planning permission.

Typical cost: £40,000-£60,000.

Hip to Gable Loft Conversion

A hip to gable conversion extends the sloping 'hip' end of the roof outward to create a vertical gable wall, significantly increasing the internal floor area and headroom at the end of the loft. The new gable wall is typically built to match the property's existing brickwork.

Hip to gable conversions are most commonly seen on semi-detached or end-of-terrace properties, where one end of the property has a hipped (sloping) roof. They are often combined with a rear dormer for maximum space, creating an L-shaped layout in the loft.

Best for: Semi-detached houses and end-of-terrace properties with hipped roofs where floor area is otherwise limited by the inward-sloping hip end.

Planning status: Because the roofline is altered, planning permission is more likely to be required than for a simple dormer. This varies by local authority — always confirm before starting work.

Typical cost: £50,000-£70,000.

Mansard Loft Conversion

The most extensive and most expensive conversion type. A mansard conversion replaces one or both sides of the roof with a near-vertical wall pitched at approximately 72 degrees, creating a large, square-profile room with maximum floor area and headroom throughout. The roof is typically finished with a flat felt or lead roof at the top.

Mansard conversions are most common on terraced properties in London, where local planning departments have historically been more receptive to them. They require the most structural work of any conversion type and typically need planning permission.

Best for: Terraced properties, particularly in urban areas, where maximising floor space is the priority and the existing roof structure limits what other conversion types can achieve.

Planning status: Almost always requires planning permission due to the significant changes to the roof profile.

Typical cost: £50,000–£80,000.

L-Shaped Dormer

An L-shaped dormer extends the roof of both the main rear slope and a rear addition or outrigger (the lower rear extension typical of Victorian and Edwardian terraces). This creates a larger overall loft space than a single-slope dormer, and is particularly effective on Victorian-era terraces where the outrigger otherwise limits the usable area.

Best for: Victorian and Edwardian terraced houses with a rear outrigger, where a standard rear dormer would miss the opportunity to convert the outrigger roof as well.

Planning status: Usually permitted development at the rear, subject to standard size limits - but confirm with your local authority.

Typical cost: £50,000-£70,000.

Compare loft conversion specialists near you

Do You Need Planning Permission for a Loft Conversion?

Many loft conversions fall under permitted development rights - meaning they don't require a planning application, provided specific conditions are met. Understanding these conditions is important because getting this wrong means retrospective application costs and potential enforcement action.

Permitted development applies if:

• The additional roof space created doesn't exceed 40 cubic metres for a terraced house, or 50 cubic metres for a detached or semi-detached house
• No extension is higher than the highest point of the existing roof
• No dormer extends beyond the plane of the existing roof slope at the front (facing a highway)
• The materials are similar in appearance to the existing house
• No verandas, balconies, or raised platforms are created
• The property is not in a conservation area or listed

Planning permission is required if:

• Any of the above conditions are not met
• The property is in a designated conservation area (in which case even small dormers on the front or side visible from the street need consent)
• The property is listed
• A mansard or hip to gable conversion is proposed (the significant roof alterations typically trigger the requirement)
• You're creating a self-contained annexe or flat within the converted space

Even where planning permission isn't required, it's worth applying for a Certificate of Lawful Development - formal confirmation from the council that no permission was needed. This avoids questions when the property is sold.

See our guide to building a conservatory for a comparison of how planning rules apply differently to different structure types - many of the same principles apply.

Building Regulations for Loft Conversions

Unlike planning permission, building regulations apply to virtually all loft conversions regardless of permitted development status. They exist to ensure the converted space is structurally safe and suitable for habitation.

Key areas building regs cover:

• Structural strength (Part A): The existing floor must be assessed and usually strengthened - loft floors are typically built to support only light storage loads, not the loads a habitable room generates. New steel beams may be required to support the additional weight and span of any dormers.

• Fire safety (Part B): All habitable rooms must have an adequate means of escape in the event of fire. For a top-floor conversion, this typically means a protected staircase with fire-resisting doors and walls, or an escape window (minimum 0.33m²) in the loft itself. This is one of the most commonly misunderstood requirements and one that significantly affects the design and cost.

• Insulation (Part L): The roof, walls, and floor of the converted space must meet current thermal performance requirements. This typically means rigid insulation between and beneath the rafters, or between the floor joists of the loft.

• Staircase (Part K): A permanent staircase must be provided. It must meet minimum headroom requirements (2m at the centre of the stair, reducing to 1.8m at the sides for loft staircases) and minimum width requirements.

• Electrics and plumbing (Parts P and G): Any new electrical installations must be certified by a qualified electrician. If a bathroom is included, drainage and ventilation requirements apply.

A Building Control officer will inspect the work at key stages and issue a completion certificate on sign-off. This certificate is what solicitors ask for when the property is sold. See the MyBuilder building regulations cost guide for typical approval fees.

Loft Conversion Ideas by Room Type

The most common uses for a converted loft space, and what each involves in practice. If you're comparing a loft conversion against other ways to add space, see our guide to garage conversions for how the two compare on cost, disruption, and usable space.

Master Bedroom with Ensuite

The most popular use for a converted loft, and typically the one that adds most value. A full-width rear dormer creates a room large enough for a double bed, built-in storage, and an ensuite. The ensuite requires drainage connections to the existing soil stack — typically straightforward where the soil stack runs close to the rear of the property, more complex where it doesn't.

Built-in eaves storage, making use of the low-headroom areas under the sloping roof sections, maximises usable space in rooms where the centre height is adequate but the edges are restricted.

Children's Bedroom or Guest Room

A more straightforward project than an ensuite conversion, since no plumbing is required. A single or double dormer typically provides sufficient room, and the slightly more quirky geometry of a loft room (sloping ceiling, eaves) tends to suit children's rooms well.

Home Office

The loft makes a practical home office location - separated from the main living areas, quiet, and benefiting from natural light through dormer or Velux windows. Acoustic insulation between the loft floor and the rooms below is worth including, particularly if video calls are a regular part of the working day.

Bathroom

A loft bathroom is less common as a standalone conversion but often added as an ensuite to a bedroom.

The critical consideration is drainage fall - the waste pipe must slope at sufficient gradient back to the soil stack. In some properties the geometry makes this straightforward; in others it requires a macerator pump, which adds cost and ongoing maintenance.

How Long Does a Loft Conversion Take?

Timescales vary considerably by conversion type, but the ranges are broadly consistent:

Conversion type	Typical build duration
Velux (rooflight)	4-6 weeks
Dormer	8-12 weeks
Hip to gable	10-12 weeks
Mansard	10-16 weeks

These figures cover the active build period once materials and permissions are in place. The pre-build phase - structural engineer's report, architect's drawings, planning application (if needed), and Building Control approval - typically adds 8-16 weeks to the overall timeline before work begins on site.

The most disruptive stage for the household is usually when the structural floor works are carried out and when the new staircase is fitted, both of these require access to the rooms below and involve significant dust and disruption.

How Much Does a Loft Conversion Cost?

Loft conversion costs vary significantly by type, location, and specification. London and the South East typically command a 20-30% premium on the national averages.

Conversion type	Typical cost range
Velux (rooflight)	£22,500-£30,000
Dormer	£40,000-£60,000
Hip to gable	£50,000-£70,000
L-shaped dormer	£50,000-£70,000
Mansard	£50,000-£80,000

The value uplift from a well-executed loft conversion is consistently quoted at 15-25% of property value. See the loft conversion cost guide](https://www.mybuilder.com/loft-conversion/price-guides/loft-conversion-cost) for a full breakdown by conversion type.

How to Find a Loft Conversion Specialist

A loft conversion spans structural work, carpentry, electrics, and plastering, and often plumbing. The most practical approach for most homeowners is a loft conversion company that manages the whole project, including the structural engineer's input, building control, and all trades, rather than hiring separately.

You can find and compare available loft conversion specialists near you on MyBuilder. Post your job with details of your property type, approximate loft dimensions, and what you want to use the space for — specialists in your area will respond with their initial recommendations and quotes.

All tradespeople on MyBuilder undergo checks at registration, such as ID documents, company details, certifications for regulated jobs and skill assessments, allowing you to hire with confidence.

Find a loft conversion specialist near you

FAQs: Loft Conversions

How Much Does a Loft Conversion Add to Property Value?

A well-executed loft conversion typically adds 15-25% to a property's value, according to widely cited UK estate agent surveys. The exact figure depends on the location, the quality of the finish, and what the conversion adds - a master bedroom with ensuite adding a bedroom count to the property (from two to three, or three to four) generates a stronger uplift than a conversion that doesn't change the headline bedroom count.

You can browse completed loft conversion projects on MyBuilder to see what different approaches and finishes look like.

Can I Stay in My House During a Loft Conversion?

Yes, in most cases. Loft conversions are generally possible to live through, the structural work is concentrated in the loft and roof space, the staircase installation is the most disruptive single stage, and the day-to-day disruption (noise, dust, contractors) is manageable for most households.

The main practical challenge is when the floor of the loft needs strengthening, which requires access from below through the ceiling of the rooms underneath.

Do I Need a Party Wall Agreement for a Loft Conversion?

If your property is semi-detached or terraced and the structural work involves the party wall, most commonly when the loft floor beams rest on or are fixed to the party wall, the Party Wall Act 1996 requires you to give your neighbour a formal notice before work begins.

The neighbour has the right to appoint a surveyor and may require a full party wall agreement. This is a legal process that takes time and has a cost, so it should be included in the project timeline from the start.

What Is the Minimum Height for a Loft Conversion?

Building Regulations require a minimum height of 1.9m in occupied areas of the converted space, though most designers aim for at least 2.2m to ensure the room feels spacious. If your loft measures less than 2.2m at its highest point, a structural conversion type that raises the roof height, such as a mansard or hip to gable, may be needed to create a practical room.

See the MyBuilder loft conversion cost guide for context on how minimum height affects which conversion types are viable and what each costs.

What Is the Best Type of Loft Conversion for a Terraced House?

A rear dormer or an L-shaped dormer (if the property has a rear outrigger) is typically the best choice for a standard terraced house. Dormers can usually be built under permitted development at the rear, maximise floor area and headroom, and work with most standard terraced roof structures.

In urban areas, a mansard conversion is sometimes preferred because local planning departments accept them, and they create more usable space than a dormer on a typical London terrace.