Interior, Exterior, or Both

When looking at renovation costs, it's helpful to distinguish between interior and exterior renovation.

Interior refurbishment

A complete interior renovation, also called interior refurbishment, typically involves replacing all surfaces (floors, walls, ceilings), renovating bathrooms and kitchen, installing new plumbing, and updating the electrical system.

An interior refurbishment is more comprehensive than simple redecoration or a cosmetic renovation.

Based on industry data and completed projects, the simplest and smallest interior renovation projects cost around £650 per square metre, while larger projects can cost up to £2,000 per square metre. The average price is approximately £1,100 per square metre.

These prices include all project costs, including materials purchased directly by the client. Final prices vary significantly depending on choices made during the project.

Exterior renovation

An exterior renovation can include work such as:

• Drainage
• Insulation
• Re-pointing brickwork
• Re-rendering
• Re-cladding
• Roof replacement
• New windows and doors

Prices here can vary greatly depending on materials, size, number of storeys, location, any repairs needed and more. In total, we see that an exterior renovation usually costs about £400–£700 per m² per square metre wall area.

In the lower range, the cost might be closer to £250–£400 per m² per sqm, whereas higher complexity and more expensive materials could lead to a higher price range running about £700–£1,200+ per m² per square metre. 

Both interior and exterior

When renovating both interior and exterior, prices naturally increase substantially. A combined external and internal renovation typically starts at £1,500 per square metre for smaller projects. Prices can quickly rise to around £3,500 per square metre for more complex projects.

As a general rule, it's usually somewhat less expensive to completely renovate than to build new, as parts of the building (foundations, structural elements) remain during renovation. The average price for new build construction in the UK is around £2,600 per square metre including VAT and all costs, according to BCIS data.

What Drives the Cost in a Complete Renovation?

The square metre prices from the cost database provide a good indication of what to expect in terms of renovation project costs. However, this is an area with considerable variations.

Within the price ranges mentioned above, many factors can pull costs in either direction.

Size

The size of the property is naturally one of the determining factors. Even though prices are quoted per square metre, the total size matters significantly. Generally speaking, the price per square metre becomes somewhat lower for a large building than for a small building.

This is due to the contractor benefiting from economies of scale with a larger building, including material purchases, more efficient work processes, and so on.

Complexity

The complexity of the building also significantly affects your final costs. This includes, for example, the number of bathrooms included in the total project.

Number of bathrooms

Bathrooms or wet rooms are consistently much more expensive to renovate than any other room in the home. According to the Federation of Master Builders, the price for a complete bathroom renovation (all inclusive) typically ranges between £20,000 and £32,000, depending on size and standard.

The more bathrooms your property has, the higher the price per square metre. Kitchens also increase the price compared to simpler rooms like bedrooms and living rooms.

Structural modifications

If the contractor needs to make changes to the building's load-bearing structures, the price is significantly higher than changes to partition walls. Structural changes usually require planning permission from the local council and professional design work, which increases the cost.

Materials

Material choices are one of the areas where you as a property owner have considerable influence. Here you can determine the finish and quality you desire, which naturally affects the price. While there might not be enormous savings on standard building materials, when it comes to bathroom and kitchen fittings, there are substantial differences between the cheapest and most expensive options.

Choice of contractor

Finally, there's the question of who you end up hiring to do the work. Here too, there are significant differences, and this is something you should spend time on. The right choice of contractor ensures both a fair price and quality assurance. Through organisations like the Federation of Master Builders or TrustMark, you can find accredited contractors. TrustedBuilders will also help you find the right contractor for your specific project.

What's Included in the Contractor's Quote?

This is an important question to clarify early on. The contractor's quote includes all work to be done in connection with the complete renovation. This means all trades that need to be involved. Building materials are usually included in the contractor's bid.

However, what we typically refer to as "finishing materials" are usually excluded and might be something you need to arrange yourself.

By finishing materials, we mean things like kitchen units, bathroom fixtures, taps, toilets, flooring, and tiles. As mentioned earlier, this is one of the areas where there are large price differences and where the property owner's choices have significant consequences for the total price.

For example, you can choose to buy a basic kitchen for £5,000, or a custom-designed kitchen for tens of thousands of pounds. Kitchen installation is usually not included in the contractor's quote, as this is typically arranged through the kitchen supplier. Kitchen installation usually costs between £1,000 and £3,000, depending on the supplier and size.

Tiles and flooring also fall under the category of "finishing materials". As a homeowner, you can make great savings by following various suppliers' promotional campaigns. Many contractors can offer good prices in cooperation with their suppliers, but it's worth shopping around before deciding. Tiles and parquet flooring typically range from £20 per square metre up to several hundred pounds.

Finally, there's bathroom fixtures. Like kitchens, there are huge price differences depending on what you want. Here too, the contractor can assist with good offers from suppliers, but you should still look around and consider if alternatives give you a better price.

A small bathroom can be furnished for as little as £1,000, but most end up spending considerably more. Installation of bathroom fixtures should be included in the contractor's quote.

Cost Breakdown for Individual Elements

Earlier in the article, we discussed the square metre price for the entire renovation. But when evaluating quotes from individual contractors, it's good to keep in mind what the individual elements of the renovation might cost.

Below is a specific example of the price for an internal and external complete renovation of a 230 square metre detached house. Note that these prices vary significantly from project to project, so use this only as an example to understand roughly where the different items might fall.

Price from contractor, including labour and materials:

• Windows (including replacement and delivery) 20 windows: £27,000 
• Installing new window in facade: £3,200 
• Replace external cladding, including insulation: £33,000 
• New roof: £21,500 
• Drainage: £12,800 
• Bathroom excluding tiles and fixtures, including plumber: £19,000 
• WC room 1, including plumber: £3,600 
• WC room 2, including plumber: £3,600 
• Utility room, including plumber: £10,800 
• New plumbing: £18,400 
• External door and patio door: £4,800 
• Balanced ventilation: £9,600 
• Surfaces (floor, walls, ceiling): £41,600 
• Internal doors: £6,000 
• Architraves, linings, transition strips: £2,000 
• Electrician (for whole house): £29,600 
• Single garage attached to house: £14,400 
• Waste management: £4,800 
• Demolition, site setup, scaffolding: £24,000 
• Interior designer: £6,000 
• Architect: £4,000 

Total, contractor's quote: £300,800

Client's own purchases:

• Tiles for bathroom, WC, utility room, hallway: £4,800 
• Bathroom fixtures, 1 bathroom and 2 WC rooms: £6,400 
• Kitchen units: £24,000 Flooring: £10,000 
• Total, own purchases: £45,200

Total contractor + own purchases: £346,000

In total, this project ended up at approximately £1,500 per square metre, which is somewhat below average for this type of project (internal and external complete renovation of a detached house).

Building Regulations for a Complete Home Renovation (UK)

A complete home renovation in the UK must comply with Building Regulations to ensure safety, energy efficiency, and legal compliance. Always check with local Building Control before starting.

When Do You Need Building Regulations Approval?

Here are some of work that may require building regulations approval.

Structural alterations – Removing or altering load-bearing walls, chimney breasts, or cutting new openings for doors/windows requires approval (Part A – Structure). A structural engineer’s design is usually needed.

Bathrooms and plumbing – Adding a new bathroom or moving plumbing requires compliance with drainage (Part H) and ventilation (Part F) regulations.

Electrical work – Rewiring, adding circuits, or electrical work in bathrooms must comply with Part P (Electrical Safety). It should be certified by a registered electrician or approved by Building Control.

Heating systems – Installing or replacing boilers, radiators, or fireplaces requires compliance with Part J (combustion safety) and Part L (energy efficiency). Gas boilers must be installed by a Gas Safe engineer.

Windows and doors – Replacement windows/doors must meet thermal efficiency (Part L) and safety glazing (Part K) requirements. Using FENSA or CERTASS registered installers avoids needing separate Building Control approval.

Garage and basement conversions – Converting a garage, loft, or basement into living space always requires Building Regulations approval, ensuring proper insulation, fire safety, damp-proofing, ventilation, and emergency exits.

To ensure compliance, you can submit either a Full Plans application (detailed approval before work starts) or a Building Notice (for simpler projects). A completion certificate is issued once work passes inspections.

Do I Need Planning Permission?

Planning permission is separate from Building Regulations. Most internal renovations do not require planning permission unless they involve:

Listed buildings – Any work affecting the character of a listed property (internal or external) requires Listed Building Consent.

Structural changes that impact the external appearance – Cutting new windows, doors, re-roofing or changing cladding materials may require permission, especially in conservation areas. Cladding or re-roofing, often doesn’t require permission provided certain conditions are met - be careful to check these carefully. 

Change of use – If converting a house into flats or altering its function (e.g., from residential to business use), permission is required.

Extensions or loft conversions – Internal work is fine, but if you extend outward, raise the roof, or add dormers, planning may be needed.

For standard internal layout changes, bathroom/kitchen upgrades, or redecoration, planning permission is not required. However, in conservation areas, Article 4 directions may restrict even minor exterior work. Always check with your local planning authority before proceeding.

How to Find the Right Professionals

Choosing the right professionals is the key to a successful renovation project. Unfortunately, the construction industry has attracted some unreliable operators who can cause both frustration and significant financial problems for homeowners. There are stories of families who have had bad experiences after choosing the wrong tradesperson.

Fortunately, there are many construction companies that are reliable and skilled, with many successful complete renovations behind them. In the UK, organisations like TrustMark and the Federation of Master Builders that check and accredit contractors and tradespeople. 

At TrustedBuilders we check credit ratings, accreditations, and references, and connect you with contractors who are well qualified for your project.

How you choose to organise the work depends entirely on you and your expertise. You can select professionals for individual elements of the job and tailor your own package. However, most choose to give the job to a main contractor.

This way, you'll always have one company to deal with and often a project manager with whom you can communicate directly and continuously. The main contractor works closely with subcontractors and ensures all work is carried out to regulations and professional standards. If you choose to split the job, you must take responsibility as the project manager and be much more closely involved with the project.

Checklist for home renovation

1. Take your time planning the project and what you’d like to do
2. Look at financing
3. Set up a budget, making allowances for unexpected expenses
4. Find out what kind of building regulation approvals you need
5. Find out if you need planning permission
6. Get multiple quotes on the job, at least three
7. Check references, credit rating and accreditations
8. Hire reliable tradespeople
9. Agree on a realistic schedule
10. Keep communicating with your contractor(s) throughout the project

Regardless of which solution you choose, it's important to request quotes from multiple contractors. Get quotes from 3 different contractors and compare prices and other important factors. Through TrustedBuilders, you can get help connecting with quality-assured contractors who have good references and fair prices.