The Ultimate Guide to Single and Double Storey Extensions in the UK: Planning, Costs, and Regulations

Understanding Single and Double Storey Extensions

If you’re planning to expand your home in the UK, it’s essential to understand the key differences between single and double storey extensions. Choosing the right type can impact your property’s value, the amount of space you gain, and how much you’ll spend on the project. Below, we’ll break down what each option offers, complete with practical examples and a pros & cons comparison tailored for British homes.

Single Storey Extensions

Single storey extensions involve adding new space at ground level only—think of a rear kitchen extension or a side return that broadens your living room. These are popular among homeowners looking to create open-plan spaces or larger kitchens without altering the upper levels of their property.

Example:

A classic single storey extension in a Victorian terrace might see the kitchen extended into the garden, using bi-fold doors to seamlessly blend indoor and outdoor living—a great option for entertaining during those rare sunny UK afternoons!

Double Storey Extensions

Double storey extensions add extra space across two floors—often expanding both ground floor living areas and upstairs bedrooms or bathrooms. This is ideal for growing families who need more space but want to maximise their investment by increasing square footage on both levels.

Example:

Semi-detached houses in suburban London often feature double storey side extensions, providing a larger kitchen-diner below and an additional bedroom or home office above.

Comparison Table: Single vs Double Storey Extensions

Pros & Cons Summary for UK Homes:

• Single Storey Pros: Cheaper, easier planning process, less disruption.
  Cons: Limited space gain; may not meet long-term needs.
• Double Storey Pros: Maximises living space and property value; ideal for families.
  Cons: Higher cost, more complex planning and building regulations.

This overview should help you start thinking about which type of extension suits your needs best as you plan your next DIY project—without breaking the bank!

Planning Permission and Building Regulations

If youre thinking about adding a single or double storey extension to your UK home, understanding planning permission and building regulations is absolutely crucial. Getting this right from the start can save you both time and money, while helping you avoid costly mistakes down the line.

Do You Need Planning Permission?

Many extensions fall under what’s called “permitted development rights,” meaning you may not need to apply for full planning permission if certain conditions are met. However, it’s always best to check with your local council before starting any work. Here’s a quick overview:

The Basics of Building Regulations

No matter whether your project falls under permitted development or requires planning permission, all extensions must comply with UK Building Regulations. These cover structural integrity, fire safety, energy efficiency, ventilation, and accessibility. Typically, you’ll need to submit plans for approval and arrange inspections at key stages of the build.

Key Areas Covered by Building Regs:

• Foundations & Structure: Safe and stable construction is a must.
• Insulation: Adequate thermal performance to meet energy standards.
• Electrics & Plumbing: All installations must meet current codes for safety.
• Fire Safety: Escape routes, alarms, and fire-resistant materials required.
• Drainage: Proper waste and surface water management.

BUDGET TIP: Submit a “building notice” instead of full plans for smaller projects – it’s usually quicker and cheaper!

If in doubt, consult your local authority or a qualified architect to ensure compliance at every step. Investing a bit of time in proper planning can help you avoid headaches—and unexpected expenses—later on.

3. Cost Breakdown and Budgeting Tips

When planning a single or double storey extension in the UK, understanding the cost structure is essential for keeping your project on budget. Extension costs can vary widely based on location, size, materials, and finishes. Below, we’ll break down the main expenses you need to consider and share some savvy DIY-inspired tips to help you save money without sacrificing quality.

Main Cost Components

Sneaky Hidden Fees to Watch Out For:

• Party Wall Agreements: If your extension affects a shared wall with neighbours.
• Site Access: Tight access may require specialist equipment or extra labour.
• Upgrades to Existing Services: Old electrics or plumbing may need upgrading to meet regulations.
• VAT: Most building work is subject to 20% VAT unless zero-rated for special circumstances.

Practical Budget-Saving Tips for UK Households

Tackle Some DIY Tasks Yourself

If you’re handy with a paintbrush or up for laying your own flooring, you can save hundreds—sometimes thousands—by doing finishing touches yourself. Just be sure any gas or electrical work is done by qualified professionals for safety and compliance.

Reuse and Recycle Where Possible

Sourcing reclaimed bricks or timber from local salvage yards not only cuts costs but also adds character and sustainability points to your home. Check out community groups or online marketplaces for deals on leftover building materials.

Compare Quotes and Negotiate Wisely

Always get at least three quotes from reputable builders and don’t be afraid to negotiate. Make sure each quote lists everything included so there are no nasty surprises later on.

Avoid Over-Specifying Finishes Early On

You can choose mid-range fixtures during the build and upgrade them later as your budget allows. Focus on getting the structure right first.

Bespoke vs Off-the-Shelf Solutions

Bespoke glazing or joinery looks fantastic but can eat into your budget fast. Opt for standard-sized windows and doors where possible—they’re more affordable and quicker to install.

4. Design Inspiration and Involving Architects

When it comes to extending your home in the UK, whether its a single or double storey extension, the design is where your vision truly takes shape. This stage can be both exciting and daunting, especially if youre aiming for that perfect blend of practicality, style, and British architectural charm. Here’s how you can get inspired, consider some DIY design elements, and know when it’s time to call in a professional architect.

DIY Design Tips for Your Extension

• Research Local Styles: Take a stroll around your neighbourhood to spot common features—think bay windows, brickwork patterns, sash windows, or even coloured front doors. Matching these details helps your extension blend seamlessly into its surroundings.
• Maximise Natural Light: Consider adding skylights, bi-fold doors, or large windows to make your space feel airy and connected to the outdoors—a favourite in many British homes.
• Space Planning: Before calling an architect, sketch out your ideal floorplan on graph paper or use free online tools. Think about traffic flow between rooms and how you’ll use the new space day-to-day.
• Reuse & Upcycle: Salvage original materials where possible—reclaimed bricks or timber beams can save money and maintain character.

When Should You Hire an Architect?

The Benefits of Working with an Architect in the UK

• Navigating Planning Permission: An architect is familiar with local council requirements and building regulations across England, Scotland, Wales, and Northern Ireland.
• Bespoke Solutions: If you want something unique or need clever ways to maximise space on a tricky plot, architects bring creative expertise that off-the-shelf plans lack.
• Add Value: Professionally designed extensions often add more long-term value to your home—ideal if you’re thinking about resale down the line.
• Sustainability: Architects are up-to-date on eco-friendly materials and energy efficiency standards now expected in modern British builds.

British Architectural Styles to Consider for Your Extension

• Victorian: Ornate cornices, high ceilings, sash windows. Extensions can feature matching brickwork and period-appropriate details.
• Edwardian: Large bay windows and simple yet elegant proportions. Choose classic timber frames and muted colours for harmony.
• Cottage Style: Exposed beams, stone cladding, cosy layouts. Use reclaimed materials for authenticity.
• Contemporary British: Clean lines, open-plan living, lots of glass. Perfect for blending traditional exteriors with modern interiors.

The right approach is often a mix of DIY research and professional support. By drawing on local inspiration and involving an architect when needed, you can ensure your extension fits perfectly with both your needs and the character of your British home.

5. DIY vs Professional: What You Can Do Yourself

When planning a single or double storey extension in the UK, one of the biggest budget decisions is whether to tackle tasks yourself or hire a professional. While the British love a good bit of DIY, not every job is suitable for even the most enthusiastic homeowner. Here’s a breakdown of common extension tasks, highlighting what you can safely do yourself and what’s best left to qualified tradespeople.

DIY-Friendly Tasks

If you’re keen to get hands-on and save some pounds, these jobs are generally safe for confident UK homeowners:

• Painting & Decorating: Once the structure is up, painting walls, ceilings and woodwork is an excellent way to add your personal touch without much risk.
• Laying Laminate Flooring: Modern click-together systems make this a realistic weekend project with a big visual impact.
• Basic Landscaping: Laying turf or planting borders around your new extension can be tackled with basic tools and some elbow grease.
• Flat-Pack Furniture Assembly: Furnishing your new space often just requires patience and an Allen key.

Tasks Best Left to the Pros

Some aspects of an extension require specialist knowledge and compliance with UK regulations. Attempting these yourself could be dangerous and may invalidate insurance or building control approval:

• Structural Work (e.g., knocking through walls, roof construction)
• Electrical Installations: Must comply with Part P of Building Regulations; certified electricians only.
• Plumbing (especially gas work): Gas Safe registered engineers are legally required for all gas installations.
• Window & Door Installation: FENSA-registered fitters ensure compliance with energy and safety standards.
• Foundations & Drainage

Risk & Cost Comparison Table

*All savings are rough estimates based on typical UK labour costs as of 2024. Actual savings depend on project scope and region.

The Bottom Line: When in Doubt, Get Advice!

A practical approach is to mix-and-match: tackle cosmetic jobs yourself if you’re confident, but always bring in professionals for anything structural or involving regulations. If unsure about any task—especially where safety or legal compliance is concerned—consult your local council or a qualified tradesperson before proceeding. It might cost a bit more upfront but could save you thousands in the long run (not to mention peace of mind!).

6. Choosing Builders and Avoiding Cowboy Contractors

Finding the right builder is crucial for a successful single or double storey extension in the UK. Unfortunately, cowboy contractors—those who offer shoddy work or disappear with your deposit—are still a risk. Here’s how you can find reputable local builders, check their credentials, and spot red flags to avoid costly mistakes.

How to Find Reputable Local Builders

Start by asking neighbours, friends, or family for recommendations—word of mouth is powerful in the UK. You can also use trusted trade websites like Checkatrade, TrustMark, or the Federation of Master Builders (FMB). Local Facebook groups or community noticeboards often feature real experiences from homeowners in your area.

Key Platforms for Finding Trusted Builders

Checking Builder Credentials and Insurance

Always ask to see proof of public liability insurance and check if your builder belongs to a recognised trade association such as FMB or TrustMark. Don’t be shy about requesting references from previous clients—ideally those who’ve had similar extensions completed recently. If possible, visit completed projects to inspect workmanship first-hand.

Essential Checks Before Signing a Contract:

• ID Verification: Confirm registered business address and Companies House registration (if Ltd company).
• Insurance: Public liability & employer’s liability cover are must-haves.
• Qualifications: NVQ/SVQ certificates or equivalent construction qualifications.
• References: Speak directly with at least two past clients.
• Written Quotation: Insist on a detailed quote with breakdowns for labour and materials.
• Warranty/Guarantee: Clarify what post-completion guarantees are included.

Cowboy Contractor Red Flags to Watch Out For

• No Written Contract: Verbal agreements leave you unprotected if issues arise.
• Lack of Address or Landline: Only providing a mobile number or no fixed address is suspicious.
• Poor Online Presence: No reviews, website, or verified social profiles can be a warning sign.
• Pushing for Large Cash Deposits Upfront: Most reputable builders only require small deposits; large upfront payments are risky.
• No Proper Paperwork: Skipping invoices, insurance papers, or certificates is never acceptable.
• Tight “Too Good To Be True” Deadlines: Promising impossibly fast completion often means corners will be cut.
• Lack of Proper Safety Measures On-Site: Genuine professionals adhere to Health & Safety regulations at all times.

The Bottom Line: Protect Yourself and Your Budget

Avoiding cowboy contractors isn’t just about saving money—it’s about ensuring your home extension is safe, legal, and built to last. Take your time during the selection process and don’t be pressured into making quick decisions. With the right checks in place, you’ll have peace of mind as your project moves forward.

7. Project Timeline and Managing Disruption

When planning a single or double storey extension in the UK, understanding the typical project timeline and preparing for potential disruption can make the process much smoother. Below, we break down average timelines for each type of extension, highlight key phases, and share practical tips to keep your home life running with minimal fuss.

Typical Timelines for UK Home Extensions

*If planning permission is required; permitted development rights may shorten this stage.

Main Phases Explained

• Planning & Design: Engage an architect or designer to draw up plans tailored to your needs and budget.
• Permissions & Approvals: Submit plans to your local council for planning permission and/or building regulations approval.
• Construction: Includes site preparation, groundwork, structure build, roofing, internal works, and finishing touches.

Tips to Minimise Disruption During Your Extension Project

1. Create a Clear Schedule: Work closely with your builder to agree a realistic timetable. Ask for weekly updates so you know what to expect and when.
2. Zone Off Construction Areas: Use dust sheets, temporary walls, or even zip doors to separate living spaces from building zones – especially important if you have children or pets.
3. Plan Utilities Carefully: If possible, schedule major utility interruptions (water, electricity) during times when household impact will be lowest, such as weekdays when most people are out.
4. Consider Temporary Kitchen or Bathroom Setups: For larger projects that affect these spaces, set up temporary solutions in another room or even the garage.
5. Tidy Up Daily: Request that builders clean up at the end of each day – it makes a big difference to comfort and safety.
6. Liaise with Neighbours: Give your neighbours advance notice about noisy works or deliveries. A little consideration goes a long way in keeping relations friendly throughout your project.
7. Sensible Storage Solutions: Move valuables and fragile items out of harm’s way before work begins; consider hiring short-term storage if space is tight.
8. Clever Scheduling: Plan holidays or remote working days during the noisiest or most disruptive phases if possible.

The Budget-Savvy Approach: DIY Where Possible

If you’re handy, taking on simple DIY tasks like painting or basic landscaping after builders finish can save on labour costs and let you add a personal touch. Just be sure not to take on anything beyond your skillset – leave electrics and plumbing to the professionals for safety and compliance reasons.

Your Extension Journey – With Less Stress!

The key to minimising disruption is all in the planning. By understanding the timeline, communicating clearly with your contractor, and preparing your home in advance, you’ll be well on your way to enjoying your new space without unnecessary hassle or overspending.