Piggyback Loft Conversion Cost

A piggyback loft conversion involves removing the existing roof, raising the perimeter walls and building a new roof above them to create extra head height and usable loft space.

This type of loft conversion is often set back from the front of the property to help preserve the original street view, while still giving homeowners more space than a standard dormer or Velux conversion may allow.

In this guide, we’ll look at piggyback loft conversion costs, what can affect the final price and what to expect when hiring a loft conversion specialist.

How Much is a Piggyback Loft Conversion?

A piggyback loft conversion is one of the most expensive due to the scale of structural alterations needed to create this extra space. Prices vary depending on the following factors:

• Property size: a bigger property will require more materials and a longer timescale.
• Complexity of build: complex designs or structural issues add to the cost.
• Planning permission required: the majority of piggyback loft conversions need planning permission, and this incurs extra fees.
• Level of interior finish: this varies hugely depending on individual needs, taste and budget.

Generally, a piggyback loft conversion costs between £60,000 and £85,000, which is considerably more than a standard rooflight or dormer conversion.

Variations in price are to be expected, depending on the location within the UK, as London and the surrounding areas are more expensive. Contractor experience will also influence how much you pay. Piggyback conversions are not the most common, so not all loft conversion specialists will have experience of building one.

Piggyback Loft Conversion Prices

As one of the more expensive styles of loft conversion, a piggyback extension is a substantial investment. Below are a range of prices for various jobs related to this type of home improvement.

Supply Costs

Supply costs vary depending on whether the piggyback loft conversion is a shell-only construction or fitted out as a fully habitable space. Below are some supply costs for the main materials used in a loft conversion.

Structural Steel

The cost of a structural steel beam for a loft conversion varies depending on the dimensions and weight of the beam. Costs range from £50 to £240 per linear metre.

Timber

Structural grade timber is required for a loft conversion, typically C24 - rated softwood. Sizes for floor joists and rafters vary from 47mm x 150mm to 47mm x 225mm, with average prices at around £15 - £23 per 4.8 metre length. Purlins and structural ridge beams of 75mm x 200mm cost around £9 to £13 per linear metre.

Roofing Materials

A piggyback conversion roof is pitched and typically takes tiles or slats. The cost of roof tiles varies depending on whether they are clay or concrete, the brand, profile and colour.

Concrete tiles range from £7.50 to £24 per square metre, while clay tiles cost £20-£60+ per square metre.

Slate tiles are either natural or synthetic. Spanish slate costs around £70-£100 per square metre, while synthetic slate, such as Eternit, costs £20-£45 per square metre.

Insulation

Rigid polyisocyanurate (PIR) insulation is typically used in roofs, walls and floors when building a loft conversion. Available in various thicknesses, the cost of this insulation ranges from £15 to £60 on average, but pallet quantities are often much cheaper.

Plasterboard

Standard 12.5mm plasterboard, as opposed to insulated plasterboard, costs from £10 to £14 per sheet. Each sheet is 2400mm x 1200mm or 8’ x 4’. As with insulation, buying plasterboard in larger quantities for a big project will usually result in a lower price.

Windows

The cost of windows for a piggyback loft conversion depends on the style and frame type you choose, as well as the size.

Rooflight windows, commonly known as Velux, cost from £350 to £750 for supply only. Prices vary depending on whether you have top hung or centre pivot styles, with the latter being more expensive.

Dormer windows come in a range of sizes and materials such as uPVC, timber or aluminium. uPVC is the most budget-friendly, with dormer windows costing between £800 and £1,500, while hardwood timber frames, like oak, cost between £3,500 and £5,000.

French windows for a Juliet balcony cost between £500 and £900 for uPVC and up to £2,500 for aluminium frames.

Staircase Material

The type of material used in a staircase determines how much it costs. Softwood stairs cost between £600 and £1,500 while hardwood stairs cost from £1,500 to £3,000. Metal or industrial style staircases can cost several thousand pounds and are usually manufactured off-site.

Flooring

Flooring materials for a loft conversion include the chosen finish, such as carpet, laminate or wooden flooring, but a subfloor is also needed. This is typically moisture-resistant chipboard, which costs £10-£20 depending on thickness. Sheets are usually 2400mm x 600mm.

Electrics

The average cost of supply-only first and second fix electrics for a piggyback loft conversion is around £700-£1,500. However, the choice of second fix items can significantly increase this price, with high-end fittings and fire-rated LED downlights adding to the cost.

Plumbing Materials

If a bathroom is included in the loft conversion, plumbing materials will add to the budget. Sanitary ware, pipework, fittings and heating elements such as towel rails or radiators can all add up to about £1,000 to £2,500 or more, depending on the quality of the items chosen.

Internal Finish

The level and quality of internal finish have a big impact on the average cost of a piggyback loft conversion. Whether you go basic or premium will increase your budget accordingly.

Additional Costs

In addition to the obvious costs, there are some fees and charges that you may not be immediately aware of when it comes to a loft conversion.

Architectural Drawings

The architect’s drawings are a scaled representation of the intended loft conversion. They are done to a technical specification and used to define their desired layout and structure.

The drawings ensure that all measurements are accurate for the construction and compliance of the loft conversion. They include a site plan, floor plan, elevations and sections which are used as a guide during construction, for material ordering and, in the initial stages, for planning approval. An architect's fees range from £2,500 to £7,500.

Structural Calculations

Working alongside the architect is the structural engineer. They create the structural calculations which verify that the house can withstand the extra weight of the loft conversion without compromising its structural integrity. Costs for a structural engineer are £750-£2,000.

Planning Application Fees

The cost of planning application fees for 2026 is £548 for a single dwelling. These fees tend to go up each year in April. You can check the Planning Portal for current charges.

Building Control Charges

Building control fees for a piggyback loft conversion are high, due to the significant structural alterations involved. As a result, more inspections are required, and this pushes the cost up. Prices vary by local authority, but an average cost is between £800 and £1,500.

Party Wall Surveyor Costs

If your home shares a party wall with a neighbour, a party wall notice is issued to alert them to works that will affect the wall. A party wall surveyor may inspect the wall, particularly if your neighbour requests a survey or fails to respond to the notice. The cost of the surveyor is between £900 and £2,500, depending on the area you live in and the complexity of the case.

Scaffolding

As a piggyback conversion involves removing the whole roof, scaffolding coverage is more extensive than for a standard rear or side dormer. Timescales are also longer for this type of loft conversion, so charges will be higher. Expect to pay £1,800 to £3,000+ for a full house wraparound for 12-14 weeks.

Skip Hire

Skip hire costs depend on the size of the skip, the duration of the hire and the location. A standard builder’s skip is 8 yards and costs £200-£350 per week. Larger skips, 12 - 16 yards, cost £350 to £600. If you need to put the skip on the public highway, you’ll have to pay for a permit. Prices vary by local authority but average around £30-£70.

Waste Removal

As a piggyback loft conversion requires the entire roof to be removed, the project will generate a lot of waste. You may need to swap your skip a few times during the course of the work, which adds to your budget.

Roof Alterations

The premise of a piggyback conversion is that the roof is removed and the replacement roof is raised to increase head height. These alterations are fundamental to the loft conversion and contribute significantly to the overall price, adding between £10,000 and £25,000.

Upgrading Insulation

As more than 25% of the roof is being changed, Building Regulations Part L applies to the required U value of the insulation, affecting your costs. The price for upgrading the insulation is £30-£35 per square metre for PIR rigid board on the roof slope and £10-£20 per square metre for mineral wool on the floor and walls.

Moving Water Tanks or Pipework

If a cold water tank in the loft needs to be removed, this costs around £200-£350. Moving pipework will cost extra depending on the extent and complexity of the work. Many homeowners use the occasion of a loft conversion to upgrade to an unvented hot water cylinder or combi boiler.

Electrical Upgrades

Electrical upgrades may be necessary as part of a loft conversion, particularly for older homes. Costs vary depending on specific needs and the size of the property, but you should budget between £1,000 and £3,500 for the work, particularly if a new consumer unit is required, which is usually the case.

Decorating

While you may decide to decorate your new loft conversion yourself, if you do want to hire a professional, expect to pay around £150 per square metre. This covers all walls, ceilings and woodwork. The day rate for a professional decorator is £120-£200.

Wall Strengthening

As the perimeter walls are raised by around 1.3 metres, the walls below may need to be reinforced to take the extra weight. Extra studs can be added to the lower walls, and larger floor joists can be installed between the existing ones.

Labour Costs and Timescales

Homeowners undertaking a loft conversion are typically concerned with the cost and how long the work will take. Let’s take a look at both elements of the project so you can plan ahead.

Labour Costs

Any loft conversion involves a myriad of trades from roofers to carpenters, plasterers to electricians, and a piggyback conversion is no exception. There will typically be numerous trades on site at any one time, so it’s clear that labour is a large part of the overall cost.

The following are national average daily rates for the different trades that will be involved in your loft conversion and some optional trades that you may need:

• Scaffolder: £280-£320
• Roofer: £280-£360
• Carpenter: £240-£360
• Bricklayer: £240-£320
• Plasterer: £150-£250
• Electrician: £300-£500
• Snagman: £180-£230
• Plumber (where needed): £320-£480
• Tiler (where needed): £200-£350
• Decorator (where needed): £250-£350

Labour rates vary depending on your location, but prices in London and the southeast will be higher in most cases.

Timescales

The timescale for piggyback loft conversions can vary depending on several factors, including:

• Size of the property: removing the roof, rebuilding the walls and fitting a new roof will take longer on larger homes
• Complexity of the project: design, structural and site issues can slow progress
• How much structural work is needed? The extent of necessary structural work adds to the timescale.
• Site access: restricted access or parking issues can disrupt deliveries of materials and limit machine entry to the site.
• Weather exposure during roof work: as the whole roof is off, the property is vulnerable to rain unless a ‘tin hat’ is erected or extensive tarpaulins laid out Whether a bathroom is included - the addition of a bathroom will extend the build timescale.

Factors that can delay a loft conversion include:

• Planning permission delays
• Party wall issues
• Unforeseen structural problems
• Material shortages
• Long lead times on materials
• Complex design changes

A shell-only project may take 6 - 8 weeks compared to a fully finished piggyback conversion, which often takes 12 - 14 weeks.

Cost Factors for a Piggyback Loft Conversion

When considering a project as large as a piggyback loft conversion, it’s important to understand all the cost factors. Below are the main things that will affect the price.

Property Size

Perhaps the most obvious cost contributor is the size of the property. A larger roof means more extensive work to remove and rebuild, increasing labour and material costs. Fitting out the newly created rooms is often something homeowners neglect to budget for.

Existing Roof Structure

The type of roof structure is a key determining factor in the cost and timescale of this type of conversion. A traditional cut roof with rafters and purlins takes less work to modify. However, a truss roof uses pre-fabricated triangular supports, which are far more complex to work with, adding weeks to the timescale and increasing the labour. Both of which add to costs.

Amount of Structural Alteration

As the roof ridge is being raised, the entire roof of the property is altered to create the new structure. New steel beams are installed, and the existing floor joists are strengthened or replaced. The amount of alteration depends on the existing roof structure and building needs.

Head Height

Head height for a loft conversion is measured from the existing floor joists to the ridge beam. Minimum requirements under Building Regulations are 2.2 metres. However, it’s necessary to allow for finished floor height, e.g., carpet, laminate, etc., as well as insulation and plasterboard in the ceiling.

A piggyback conversion requires around 2.4 - 2.5 metres of head height to meet this minimum. The need to increase the head height by lowering the ground floor ceilings can substantially add to the build cost.

Whether Planning Permission is Needed

Planning permission is almost always needed for a piggyback conversion, as the main purpose is to raise the ridge height. This is a common trigger for planning permission.

Unless the conversion adds less than 40 - 50 cubic metres of space, uses similar materials to the original dwelling and doesn’t go beyond the highest point of the original roof, it will need planning permission.

Steelwork Requirements

Steel beams or RSJs are needed for reinforcement in loft conversions. The requirements are determined by the structural engineer and are essential to prevent structural failure. Span, load and support conditions are all determined before ordering the steel beam.

Staircase Design

The staircase design can add to your costs. While a straight softwood staircase is cheapest, most conversions need a winder staircase, which costs slightly more. A hardwood or bespoke staircase will add significantly to the budget.

Number of Windows

The number of windows doesn’t just add to the material cost, it also adds to the labour charges. Each window requires an opening, flashing and specialised fitting.

Insulation Standards

To comply with Building Regulations, the insulation must be 270mm of mineral wool or 175mm of PIR board, underneath and between rafters. The pitched roof U-value must be 0.15 - 0.18 W/m2K.

Whether a Bathroom is Included

Adding a bathroom to a loft conversion can increase your budget by more than 10%. The necessary structural alterations, installation of pipework, tiling, sanitary ware and labour costs all add up.

Interior Finish Level

The standard of finish that you want for your interior has a direct impact on your loft conversion budget. A high specification or luxury finish will cost a lot more than a standard one.

Property Location

Labour rates and material costs vary widely across the country. The southeast of England and particularly London, are the most expensive for both. Larger cities also tend to be more expensive than more rural areas.

Ease of Site Access

Getting into and out of the site easily is important for workers, machinery and material deliveries. Any access problems or parking restrictions can add to the cost of the build. Considering this in advance can help to reduce any related costs.

Building Regulations Related to a Piggyback Loft Conversion

A piggyback loft conversion is not a regular project and requires detailed structural design and formal approval. As a result, it must comply with several Building Regulations.

Structural Safety

Part A of the Building Regulations deals with the structural safety of the dwelling. As the conversion involves significant structural alterations, compliance with this document of the Building Regulations is essential.

Fire Safety

Building Regulations Part B relates to fire safety and means of escape. It also concerns the use of materials to prevent fire spread both internally and externally, as well as access for firefighters.

Stairs

Part B also applies to the loft conversion stairs, along with Part K, which focuses on the safety of the stair design. This includes the pitch of the stairs, headroom and step dimensions. It also relates to the balustrade for a Juliet balcony.

Insulation

Part L of the Building Regulations relates to the performance of insulation in the loft conversion. This is to ensure that thermal U-values are achieved.

Ventilation

Part L also concerns ventilation, along with Part F, which is directly concerned with the air quality inside the property. It covers things like trickle vents, extractor fans and windows.

Sound Resistance

Part E of the Building Regulations requires minimum sound insulation in a loft conversion to reduce noise to the floors below and through party walls. It also concerns wall insulation, particularly new walls separating bedrooms and bathrooms.

Means of Escape

Approved Document B, relating to fire safety, concerns the means of escape from a loft conversion. The addition of a new storey often turns a two-floor home into a three-floor one; this means the stairway needs to be protected to allow escape in the event of a fire.

Mains-powered smoke alarms, 30-minute fire doors and the potential need for a sprinkler system for open plan spaces are also included in this part of the Building Regulations.

Party Wall

Where the property adjoins another, the neighbour must be served a party wall notice to inform them of the decision to raise the wall. This should be served 2 months before you commence work. Without agreement, a party wall surveyor is needed to deal with the issue.

Types of Piggyback Loft Conversion

While the main premise of a piggyback loft conversion is raising the external walls to increase head height internally, there are a few variations on the theme.

Standard Piggyback Conversion

The standard piggyback conversion is straightforward. The old roof is removed, the perimeter walls are raised by up to 1.3 metres, and a new roof is constructed. It may sound easy, but it involves a lot of structural alterations and requires formal approval from the local authority. This type of conversion achieves a full extra storey feel.

Set-back/Hidden Piggyback

A setback or hidden piggyback conversion is when the front portion of the roof remains at its original height, and the raised part is set back by around 4 metres. The intention is to retain the street view of the house as it was and to meet strict planning requirements. It’s a more visually interesting style for many homeowners.

Piggyback Conversion with Rear Dormer

A piggyback conversion that also incorporates a rear dormer is a major project and provides significantly increased habitable space within the home. It comprises a standard piggyback conversion with the addition of a dormer at the back of the property. This means extra head height and increased floor space.

Alternative Types of Piggyback Loft Conversion

Not all properties are suitable for a piggyback loft conversion, or you may not want the extra work of applying for planning permission. Luckily, there are alternatives.

Rooflight Loft Conversion

A rooflight loft conversion does not involve any significant changes to the roof other than installing a rooflight. The existing roofline remains intact, but the interior of the loft is converted into a habitable space, as long as head height allows.

The work can typically be done under permitted development rights and is the most affordable loft conversion, costing around £25,000 - £40,000. Disruption is minimal, and it’s a good choice for homes with steep roofs or those in conservation areas.

Dormer Loft Conversion

The most common type of loft conversion, a rear dormer, provides extra headroom in the loft space and fills it with lots of natural light. Most projects fall under permitted development unless the property is in a conservation area. Disruption to daily life can be significant as a large portion of the roof is removed and there is a lot of dust and noise.

Internally, it’s usually possible to fit a bedroom or two and an ensuite bathroom, depending on the available space. Dormer conversions suit most property types, and average costs are between £45,000 and £60,000.

Hip-to-gable Loft Conversion

A hip-to-gable conversion involves the formerly pitched gable-end roof being lifted vertically to come in line with the gable wall, adding extra headroom internally. The addition of a rear dormer further increases usable floor space. Disruption is worse in the first month of work, with a lot of noise and dust.

This type of conversion works for end-of-terrace, semi-detached and single-storey properties, costing around £45,000 to £70,000. Planning permission is not typically needed as long as the 50 cubic metre allowance is respected.

Mansard Loft Conversion

A mansard conversion is the closest alternative to building a piggyback loft conversion. The roof slope is replaced with a wall at 72 degrees, which is almost vertical. Costs average from £70,000 to £100,000, although London prices will be much higher.

As with a piggyback conversion, planning permission is almost always required. However, the work does produce a large living space and an aesthetically pleasing exterior. Properties suitable for this type of conversion are Victorian or Edwardian terraced houses and period homes.

This is a disruptive loft conversion as the entire roofline is altered, expect noise, dust and potential loss of services.

Full Home Extension

A full home extension involves adding liveable space through combining a loft conversion with a rear extension. This approach can significantly increase habitable space, although there are restrictions on the increased volume and planning permission is likely needed.

Terraced homes can add 40 cubic metres of new space, and semi-detached or detached properties can add up to 50 cubic metres. The average cost for a full home extension can be between £2,000 and £5,000 per square metre, depending on your location.

The extent of the works means that this is a highly disruptive project, and most homeowners move out for the duration of the works.

Hiring Contractors Checklist for a Piggyback Loft Conversion

For homeowners who have never hired a contractor before, knowing what to ask can remove a lot of uncertainty and stress.

Checking experience with major loft conversions and structural roof alterations It’s important to ensure that your chosen contractor has experience in doing a piggyback conversion. Loft conversion specialists are more likely to have worked on these projects, but even then, you should ask about previous jobs they’ve completed.

Asking to see previous similar projects

Most loft specialists are happy to provide details of previous similar projects and even arrange viewings with the client’s consent. This is an invaluable way to see what’s involved, inspecting the finished project and speaking to the homeowner about their experience with the contractor.

Confirming who handles drawings and calculations

Ask about the contractor’s use of an architect and structural engineer. Ideally, you will meet them and discuss the plans, design and any issues that may arise.

Checking whether planning and building control are included

Examine your quote and check that submitting planning applications and dealing with building control are included. Most contractors are well-versed in these processes and are happy to include them in the scheme of works.

Asking what is covered in the quote

If you’re not sure what is covered in the quote or the language is vague or overly technical, ask for clarification. There’s no shame in not understanding certain terms or technical language, as it’s not something you deal with daily. Most contractors are happy to discuss the details of the quote for clarity and to maintain a good relationship with the client.

Confirming the project timescale

A timescale is typically set at the beginning of the project and will be agreed with the contractor. However, it pays to bear in mind that the loft conversion is a complex process which needs to conform to many Building Regulations and planning conditions.

It’s also vulnerable for the first few weeks to the vagaries of the British weather. Therefore, it’s possible that delays will happen. In general, however, contractors try to stick to a schedule, for their sake as well as yours.

Checking Insurance

Make sure that your chosen loft conversion specialist has all the correct insurance cover, including public liability, employers' liability, professional indemnity and contractor’s all-risk insurance. Some will provide you with evidence as part of your quotation package, but if they don’t, ask for it.

Asking About Guarantees

Most loft conversion companies provide a 10-year structural warranty, which covers the major elements of the build. Ask if the warranty is transferable to any new owner. Some companies will have insurance-backed guarantees which cover any faults if the company ceases trading.

Comparing Several Detailed Quotes

For such a large and expensive project, you should get several detailed quotes. These can be compared, and you can gauge what the average cost of a piggyback loft conversion is for your area.

They also let you see any hidden costs that some contractors don’t include and identify the contractor who has specific experience in piggyback loft conversions.

Removing a Piggyback Loft Conversion

There are a few situations where all or part of a piggyback loft conversion needs to be removed.

Corrective Works

If an old conversion is defective and corrective works are required, it may be necessary to remove or alter all or part of the build. This always needs to be done by an experienced roofer or specialist loft conversion company to ensure structural stability.

Unauthorised Conversion

An unauthorised conversion, one without the proper planning consent, can be removed. Homeowners can apply for retrospective planning permission, but if the local authority refuses, the structure must be removed.

Leaking Roof

Extensive leaking may be due to structural defects, and these may necessitate partial or complete removal of the roof.

Structurally Unsound

A structurally unsound loft conversion may need to be removed if it poses a danger to life or property. For example, older conversions may not conform to current Building Regulations and safety standards. DIY or unprofessional alterations to the roof may have introduced weaknesses.

Removal costs can be high, due to the amount of waste generated, the specialist labour required to safely demolish the structure, and the work required to reinstate or alter the roof. Exact prices will depend on the size of the structure. The work is also highly disruptive, generating a lot of noise and dust.

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