Dormer Loft Conversion Cost

Considering a dormer loft conversion?

This guide covers everything you need to know about the costs involved, from material and labour prices to average costs per square metre for different sizes and finish standards.

Even if you’re just exploring your options, getting several quotes early on will help you to set a realistic budget, compare like-for-like offers, and secure a reputable builder before schedules fill up.

It’s quick and easy to get free, no-obligation quotes from dormer loft conversion specialists near you using MyJobQuote.

Want to explore the details first? Scroll down to find costs, timelines, and everything else you need to plan your dormer loft conversion.

How Much Is a Dormer Loft Conversion?

On average cost of a dormer loft conversion is between £30,000 and £60,000 in 2025. The exact price you're quoted will depend on the size of the conversion, the quality of finish, the size of the property, the area of installation, and the ease of access.

However, prices may also vary as a result of labour fees - which can depend on how many tradesmen are required for the project. The labour cost also depend on your location, with London and the South East rates being more due to the higher cost of living.

Dormer loft conversions are a popular way that homeowners in the UK can add more liveable space to their homes. But it's a big project, which makes it essential to have a thorough understanding of loft conversion costs when you're planning it out.

Want are the costs made up of?

This overall cost is made up of many smaller fees that are essential to making sure your conversion is successful and completed to a high standard.

Usually, dormers are used for a new master bedroom and ensuite:

How much would that cost?

The cost for a master bedroom plus an ensuite will naturally sit at the higher end of the spectrum at around £35,000 to £45,000.

Dormer Loft Conversion Prices

Firstly, let's take a look at dormer conversion sizes:

• A small dormer loft conversion typically costs around £20,000 to £30,000.
• A medium dormer would be priced at £30,000 to £45,000.
• A larger-scale dormer loft conversion could cost anywhere from £45,000 to £60,000.

All these costs depend on the type of installation chosen, and other customisations (roof type, en-suite conversion, etc.) can change the cost accordingly.

For example, the small dormer cost is based on a basic conversion but the cost of a larger-scale project can easily result in being much higher than the above top-end, especially when looking at regional variations such as central London compared to the North of England or going for a more high-spec conversion.

The change in price is due to the materials needed and the additional time/labour required for the tradespeople to complete these additions.

Dormer loft conversions are a more common sight across the UK than mansard and hip-to-gable loft conversions.

They've continued to be a popular option over the years as they allow homeowners to get more headroom than a Velux loft conversion (which doesn't alter the roof) and make the most out of their property's available space.

Dormer loft conversions are generally more affordable. A hip-to-gable loft conversion cost usually requires a budget of about £45,000, whereas a mansard loft conversion typically costs around £57,500.

If you’re considering other loft conversion styles beyond dormers, such as hip-to-gable or Mansard conversions, See our full loft conversion cost guide for detailed pricing and breakdowns.

Dormer Loft Conversion Costs Breakdown

To give you a better understanding of where your budget goes, this table breaks down the average cost of a standard dormer loft conversion into its primary components. These figures cover the materials and labour for each specific trade or service involved in the project.

The total cost from these individual components gives you a clear baseline budget, which should then be increased by a contingency fund of 10-15% for unforeseen issues such as required foundation strengthening or unexpected material delivery problems. You can find a further breakdown of the material costs in the section below.

Dormer Loft Conversion Cost per m²

It can also help to understand prices on a per-square-metre basis. This gives a clearer picture of how costs scale with the size and specification of your project, especially if you’re comparing quotes or planning a larger loft conversion.

On average, a dormer loft conversion costs between £1,150 and £1,700 per m² depending on the complexity, materials, and location. A high-spec double dormer or conversions in London can reach £2,000+ per m².

These rates include the structure, insulation, windows, stairs, and internal finishes. Expect to pay toward the higher end for complex layouts, en-suites, or projects in London and the South East where labour rates are higher.

Prefabricated (Modular) Dormer Conversion Costs

A prefabricated dormer, sometimes called a modular loft conversion, is an increasingly popular alternative to traditional on-site construction. With this method, the entire dormer structure is manufactured off-site in a controlled factory environment, built to your exact specifications, and then transported to your property. A crane is used to lift it into place—often in a single day.

Prefabricated dormer typically cost a similar amount to traditionally build dormers, ranging from around £30,000 to £70,000 depending on the size and finish. The key advantages are not usually lower costs, but rather:

• Speed — On-site work can often be completed within days, significantly reducing the overall build time.
• Less Disruption — Since most of the work happens in a factory, your home experiences less noise, mess, and scaffolding.
• Cost Predictability — Factory-controlled pricing means fewer on-site labour fluctuations or unexpected delays.

The Main Consideration: Access

The main limitation of a prefabricated dormer is access. Your property needs clear space for a large crane to operate and safely position the dormer module on the roof. This makes modular construction ideal for detached or semi-detached homes, but less practical for terraced properties with restricted rear access.

What Is the Cost of Dormer Loft Conversion Materials?

This is the cost of your dormer loft conversion without the labour or installation costs.

We've compiled some tables below to illustrate the different costs, which should help you understand how the overall quote is deduced:

Loft Conversion Windows Cost

Loft Conversion Flooring Cost

Loft Conversion Insulation Cost

Loft Conversion Stairs Cost

General Building Materials Cost

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Labour Cost of Dormer Loft Conversion

During any large-scale project, there will usually be 2 or 3 people on-site at all times.

The variation in timescale will often depend on how easy it is to schedule all the different tradespeople and may also be affected by the weather.

Although the below provides an average cost for each labourer, be mindful this can also depend on the experience of the individual and can vary depending on the specific job.

While labour fees are often calculated by the hour, for larger jobs such as a loft conversion, it's likely you will be quoted for the day. Another factor to consider is your location, as labour fees tend to be higher in London and the South East than the National average.

Factors That Impact Dormer Loft Conversion Costs

Cost factors for your conversion can vary depending on multiple factors, including the size of your conversion and the property itself.

Often, it's feasible to convert to a one dormer in a 5x4 m2 loft for around £30,000 to £32,000 in total.

By comparison, a two dormer, two roof light conversion within a 5 x 6 m2 space can potentially cost between £43,000 and £45,000.

The cost can, of course, depend on the quality of the conversion and the materials you choose, as well as the price variation between different contractors and labourers.

Extra costs will also incur depending on the type of room you are converting your loft into. For example, if you want to add a full bathroom cost to your build, you will also need to pay out for plumbing and specialist fittings.

Other factors that will affect the final price of your conversion include:

• Size and Layout — The larger the loft, the more materials and labour are required. Complex layouts such as multiple dormers or unusual roof shapes increase structural work and can require additional scaffolding and planning considerations.
• Access & Roof Complexity — The ease of access to the property affects labour costs. Steep roofs, awkward angles, or homes with tight garden space may require hoists or cranes and additional scaffolding, increasing both time and expense.
• Location — Regional differences can add 20% to 30% to costs in high-demand areas such as London and the South East. Northern England and Scotland generally have lower labour and material rates, which can reduce overall project cost.
• Contractor Choice — Experienced, reputable contractors may charge more upfront but often deliver higher quality work, better project management, and fewer unexpected costs.
• Planning Permission & Regulations — While many dormers fall under permitted development, larger or front-facing dormers may require planning approval. Building regulations compliance (fire safety, insulation, stair design, structural support) is mandatory and can affect cost depending on inspections and approvals required.
• Timeframe & Seasonality — Projects scheduled during peak building seasons may cost more due to higher labour demand. Extended timelines also increase overheads such as scaffolding hire and project management fees.

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Additional Dormer Loft Conversion Costs

Beyond the main conversion costs, certain optional features or upgrades can increase your budget. These are not included in standard quotes and depend on your design choices.

• Bathrooms or En-Suites Upgrades — High-end fixtures, wet rooms, or larger bathrooms can add £5,000 to £12,000.
• Custom Joinery & Built-In Storage — Wardrobes, cupboards, and shelving tailored to your loft space may add £1,000 to £4,000.
• Premium Finishes — Luxury flooring, bespoke carpentry, or high-spec paint and decoration can increase costs by £1,000 to £3,000.
• Additional Rooflights or Velux Windows — Extra glazing improves light and ventilation but can cost £600 to £1,200 per window including installation.
• Optional Structural Enhancements — Extra beams, roof strengthening, or specialised insulation beyond standard requirements can add £2,000 to £5,000.

What's Involved in a Dormer Loft Conversion?

The average loft conversion can take between 6 to 8 weeks to complete, although this all depends on the size and quality of the project, plus the assumption there are no unforeseen circumstances along the way.

If you find a contractor to organise hiring labourers and tradespeople without any delays, and manage to keep good weather over the course of your project, then this will make the conversion run smoothly.

The below schedule is a rough guide to help you guage what's involved in each step, based on a minimum 6-week build and takes the assumption there aren't any unplanned delays.

• Week 1: Initial Setup and Roof Opening — The first step is to erect the scaffolding. The materials required for the job will be gathered on-site. The roof will be opened up during this week.
• Week 2: Adapting the Roof Structure — If the roof structure is changing, this will happen next. Extra supports may be installed if needed. For a rooflight conversion, the windows will go in now. For a dormer conversion, the dormer will be constructed.
• Week 3: Completing External Roof Work — External roof construction will be finished, and any tiling completed. Roof insulation will be installed, and internally, the space will be prepped for plumbing and electrics.
• Week 4: Fitting Windows and Internal Walls - Any windows that haven't gone in yet will be fitted. The floor will be laid with any ventilation as needed. The plasterboard will be fitted, and any internal walls will be built.
• Week 5: Staircase Installation, Electrics, and Fittings — The staircase will be installed, and bathroom fittings added if required. Electrics will be completed, and doors, plastering, and skirting wrapped up by the end of the week.
• Week 6: Wrapping Up — During this week, any unfinished jobs will be completed. If your contractor is responsible for the decorating, this will be one of the final jobs, along with a general clean-up and taking down any scaffolding.

Building Regulations & Planning Permission for a Dormer Loft Conversion

In the majority of cases you won't need to apply for planning permission in the UK as dormer loft conversions are considered a Permitted Development.

There are, exceptions to this rule. For example, if you live in a conservation area, listed building, or the conversion is likely to significantly change the appearance of your property. If you do require planning permission, application fees in the UK are usually around £258.

To qualify as a Permitted Development, the conversion must adhere to strict limits and conditions. The most critical rules relate to the size and placement of the dormer.

Permitted Development (PD) Size and Volume Limits

The additional roof space created by the conversion (including any previous roof additions) must not exceed the following volume allowances:

• 40 cubic metres (m3) for terraced houses.
• 50 cubic metres (m3) for detached and semi-detached houses.

If your proposed dormer exceeds these limits, you will need to submit a formal application for Planning Permission.

Even if you meet the volume limits, your dormer must also comply with the following design conditions to avoid needing Planning Permission:

• Materials — The materials used for the conversion must be of a similar appearance to the existing house.
• Windows —Side-facing windows must be obscure-glazed (e.g., frosted glass), and any opening part must be at least 1.7 metres above the floor.
• Height —The conversion must not extend above the highest part of the existing roof.
• Front —No part of the dormer or extension can extend beyond the plane of the existing roof slope on the principal elevation (the side facing the road).

Building Regulations

Even if you don't need planning permission, you do need to meet the required building regulations which generally cover the safety aspects of the build and materials used.

Building Regulation approval can be obtained by your local Building Control Department, with fees costing around £500 and £1,250 (depending on the scale of the project). You contractor will likely handle this for you, but do double check.

Party Walls

If you live in a terraced or semi-detached home, it's likely you share a wall with a neighbour. If so, you will need a surveyor and a legal professional to create what is known as a Party Wall Agreement. Surveyor rates can vary between £150 and £200 per hour with the final cost potentially amounting to around £1,000.

Types of Dormer Loft Conversions

There are several dormer loft conversion ideas, and the one most suited to your property will depend on the type of house (terraced, semi-detached, detached) and your existing roof shape.

Flat Roof Dormer Conversion

The flat roof dormer loft conversion is a simple structure that can be added to the front and/or rear of the loft.

It provides a fairly simple way to expand the usable space in the loft, increasing head height and providing lots of natural light afforded by the dormer windows.

The shed roof dormer loft conversion is similar to the flat roof option, but its roof slopes down at an angle slightly may be constructed with different materials and are usually more suited to homes with a gable roof.

Double or Twin Dormer Conversion

A double or twin dormer conversion features two smaller dormer structures instead of one large unit. These can either be built on opposite roof slopes (for example, one at the front and one at the rear) or side by side on the same slope in a “dog-house” style design. This layout is often chosen for its balanced look or to maximise usable space while keeping within planning limits.

Because you’re effectively constructing two separate dormers, the cost is higher than a standard single dormer. Each dormer requires its own framework, roofing, windows, and finishing work, which increases both material and labour expenses. Expect to pay £8,000 to £15,000 more than for a single dormer but generally less than for a large, full-width conversion that spans the entire roof.

Build times are also longer. A double dormer typically takes around 8 weeks to complete, compared to roughly 6 weeks for a single dormer conversion.

Gable-Fronted Dormer Conversion

The gable-fronted dormer loft conversion is sometimes also known as a dog-house dormer. This is a more complex solution consisting of a gable wall extension built upwards to meet the current ridgeline, with a new sloping roof section also built towards the new gable end.

Hipped Roof Dormer Conversion

A hipped roof dormer loft conversion is an extension where the roofs slope on all three sides of the structure. This is often an aesthetically pleasing look especially suited to larger properties. However, this type of dormer construction results in less usable space in the new loft than for example, a flat roof dormer.

L-Shaped Dormer Conversion

An L-shaped dormer loft conversion (also known as a dog leg dormer) consists of two dormers that are connected at right angles to each other.

If you have the right kind of property, this can be an excellent way to add as much space as possible, with good head height as well.

Usually, people use this type of loft conversion to create multiple rooms, helping you maximise the space within your home.

Benefits of a Dormer Loft Conversion

Whilst considering the costs of a loft conversion, be sure to also take into account the benefits that it can add to your home.

Add Value to Your House

It is widely agreed that a loft conversion is one of the very best ways to add value to your home, on average increasing property value by 22%.

If your aim is to increase your property's value, it is important to do some research before you start.

In most areas, there is a ceiling to the house prices. For example, in your area, houses might sell for a maximum of £350,000.

If you spent £320,000 on your home, there is no point in spending more than £30,000 on your loft conversion.

Spending more than that will not increase the value of your home further. So, make sure to do some research to help you fix your budget.

Avoid the Cost of Moving

If you have considered moving out of your current home due to lack of space, then first consider a loft conversion with a dormer.

They can offer you a way to get that extra space you need without the cost or the stress of having to relocate.

Adding Natural Light

Adding extra windows to your home, especially to the roof, is the perfect way to add more natural light into your home, often making it appear more spacious.

Energy Efficient

It is required by building regulations that insulation is included in your loft conversion.

This comes at an extra cost; however, it will benefit your home by making it more energy-efficient, and often, people benefit from a significant decrease in their heating bills.

Grow Without Losing Outdoor Space

When thinking of an extension, many people will assume that it will have to take up precious garden space.

However, with a loft conversion, your house becomes bigger, providing more space for your family without having to sacrifice your garden. This ideal for growing families and people with pets.

Can I Build a Dormer Loft Conversion Myself?

For a passionate DIY enthusiast, taking on a loft conversion can be tempting. However, it is essential to distinguish between simple internal finishing tasks and the structural work required for a dormer conversion.

A dormer loft conversion involves complex structural changes to the roof, which makes it unsuitable to be built entirely on a DIY basis.

The main structure of a dormer and the associated structural alterations inside the loft are critical tasks that require professional certification and expertise. You cannot bypass these:

• Structural Integrity — The dormer requires precise load-bearing calculations and reinforcement of the floor and roof to ensure the safety and stability of your entire home.
• Weatherproofing and Roofing — Making the dormer fully watertight and insulating it correctly is essential to prevent damp, mould, and leaks—issues that are costly to fix later.
• Building Regulations — All dormer conversions must pass strict Building Regulation inspections (covering fire safety, ventilation, stability, and access). Only work overseen and certified by a professional builder/inspector will receive the necessary sign-off, which is required for insurance and when selling your property.
• Access and Staircase — Installing a safe, compliant staircase that meets headroom and fire safety rules requires expert knowledge and often specialist cutting of structural joists.

If you plan on having a dormer, you will need to hire a loft conversion specialist to complete the main structural work and secure all necessary approvals.

That being said, you can still save a significant amount of money by handling the internal, non-structural finishing work yourself once the main build is complete and weatherproofed. These tasks are often called the 'second fix' and are perfect for a competent DIYer:

• Finishing Joinery — Installing internal door frames, hanging the final doors (which must be compliant fire doors), and fitting decorative elements like skirting boards and window architraves.
• Second-Fix Plumbing — If you are adding an en-suite, you can connect and fit the final fixtures like the toilet, basin, and shower (after the certified plumber has run the main pipework and drains).
• Flooring Installation — Laying the final floor covering, such as laminate, engineered wood, or carpet over the subfloor.
• Decorating — Painting, wallpapering, and applying other final decorative touches to the finished room.
• Tiling —Tiling bathrooms, floors, or other areas requiring a specialist finish.

Removing a Dormer Loft Conversion

Removing a dormer loft conversion is a big job, and with the value that it adds to your house, it is questionable whether it is worth doing, as the cost can be so high to safely remove all of the fittings.

If you were to remove your conversion, it would be best to get a contractor to give you a quote, and if walls shared with neighbours are to be affected, you may need another Party Wall Agreement.

Checklist: Hiring a Dormer Loft Conversion Specialist

• Get multiple estimates — Get quotes from multiple contractors and be wary of estimates that seem too high or too low.
• Hire locally — It is easier to contact local contractors, and they are likely to have much more knowledge of building codes in your area.
• Check their past work — Ask them to see pictures of work they have completed in the past. Consider if they have completed something similar to your project before and if you are happy with the standard to which it has been completed. You can also inquire about their reputation with the Better Business Bureau and look at their reviews online.
• Take your time making a decision — Take your time before signing a contract and be cautious when asked to pay a large deposit upfront. Make sure to read the fine print on all estimates and contracts.
• Check their insurance — Make sure the contractor is properly insured. You can ask any contractor for a certificate of insurance and even reach out to the insurance company to confirm that their policies are still in effect. If the contractor is not insured, you may be liable for accidents that occur on your property.
• Get everything in writing — Get your contract in writing, and make sure the contract is clear and well written. Consider having a lawyer review the contract, especially ones that include substantial costs.
• Don't pay upfront — Don't pay for the whole project before it is completed. It is common practice to pay one-third of the costs as an initial payment and to keep the rest as a retainer.
• Anticipate delays — Delays are common and are not necessarily anyone's fault, so don't panic if they occur. They can happen due to weather conditions or when waiting on labourers to become available.
• Keep a job file — Keep your contract and all other documents about the conversion in a file. This is your evidence should anything go wrong, so it is important to keep it all safe.

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