Before any building work begins, you may need to pay for planning permission depending on the scale and nature of your extension.
Planning application fees in the UK typically range from £200 to £500 for a single-storey extension, but additional drawings or revisions from your architect may increase costs. Always factor in these charges at the start of your budgeting process.
Some extensions fall under Permitted Development rights, but larger builds, certain roof alterations, or work on listed buildings or in conservation areas usually require full planning permission. It’s best to confirm with your local planning authority early on.
Even if you don’t need planning permission, all home extensions must comply with Building Regulations to ensure structural safety and energy efficiency.
Building regulations cover foundations, structural integrity, fire safety, insulation, drainage, ventilation, and more. They ensure that the work meets minimum safety and performance standards.
Your local authority or approved inspector will charge for plan assessments and on-site inspections throughout the build. These charges vary but often range from £300 to over £1,000 depending on project size and complexity.
Home extensions can sometimes require moving or upgrading essential services like water, gas, electricity or drainage — often at significant cost.
If your extension interferes with mains drainage, gas meters, or incoming cables, you’ll likely need to pay utility companies for rerouting or extending connections. Costs can escalate if external digging or permissions from highways authorities are involved.
A larger home may require higher-capacity boilers, updated fuse boards, or additional sockets and circuits. These upgrades are often not included in builders’ estimates and can add hundreds or even thousands to your overall spend.
Before your extension begins to take shape above ground, considerable time and cost may go into preparing what lies beneath.
Uneven terrain, hidden rubble, tree roots, or clay-heavy soil can all complicate groundwork. These conditions often require more excavation, drainage solutions, or foundation adjustments that increase both time and expense.
If your site is difficult to access or requires mechanical digging, mini-diggers or skips may be brought in. This additional equipment and the operators needed can quickly inflate your budget.
Some homeowners overlook the need to vacate or relocate items during major works, which can come at an added cost.
If your extension significantly disrupts the use of key areas like the kitchen or bathroom, you may need to stay elsewhere. Hotel stays, short-term lets, or staying with relatives all carry varying financial implications.
Dust, debris and limited space during the build might mean hiring storage for valuable items. Whether using a self-storage unit or removal company, the cost adds up over weeks or months.
It’s not just your builder who contributes to your extension project – other professionals play vital roles and charge accordingly.
Design, structural safety, and feasibility checks often require input from qualified professionals. Their fees vary, but it’s common to spend several hundred to a few thousand pounds depending on the project's scope.
If your extension affects shared walls or neighbouring boundaries, you may need a formal Party Wall Agreement. Legal advice or planning consultants may also be required for complex applications.
The build might be complete, but the final details – often left out of quotes – can catch you by surprise.
Painting, tiling, flooring, and other finishes are frequently excluded from initial estimates. These ‘finishing touches’ are essential for liveability and aesthetics but can cost thousands if not budgeted for.
Lighting, taps, cabinetry, and other fixtures vary greatly in price and quality. Skilled decorators or finishers may be needed for a polished result, and it’s wise to allocate funds for this stage to avoid cutting corners.
Planning a home extension is exciting, but it's easy to underestimate the true cost. By accounting for these seven often-overlooked expenses, you’ll be better prepared financially and avoid nasty surprises as your project unfolds.
At CATH Services, we help homeowners navigate every stage of their extension — from initial planning to final finishes — with clear, transparent advice and experienced project management. If you’re considering extending your property, contact us today for a consultation and let’s bring your vision to life with no hidden costs.
At CATH Services, we provide a complete range of building and property improvement solutions for homeowners across Surrey, Hampshire and West Sussex. Our experienced team is committed to delivering exceptional craftsmanship, reliable service and results that transform your home. Here’s an overview of the services we offer.
There are countless reasons to choose CATH Services, but most importantly is our customer-focused approached that combines excellent workmanship with honesty and integrity
Public liability insurance up to 5 million pounds.
We have no hidden costs, so the price you're quoted is the price you'll pay.
We pride ourselves on ensuring that every client is left happy.
We use the very latest in equipment and have a fully trained team.
“CATH Services did an amazing job on our home extension. The team was professional, communicative, and delivered exactly what we envisioned. The attention to detail was outstanding, and they left everything spotless. Highly recommend!”
— Mark E
“We had our kitchen completely renovated, and the results are fantastic. The workmanship is top-notch, and the project was completed on time and within budget. It’s clear they take great pride in their work. Will definitely use them again!”
— Samantha F
“Excellent service from start to finish. The team transformed our outdated bathroom into a modern space that looks incredible. They were polite, efficient, and kept disruption to a minimum. I wouldn’t hesitate to recommend them!”
— David S
“CATH Services recently renovated our entire ground floor, and we couldn't be happier. They provided expert advice, used high-quality materials, and finished ahead of schedule.”
— Elaine R
“Peter and Gary are conscientious and thorough. They have done a number of jobs for us over the last 18 months, all of which have been completed to a high standard. They always leave the place clean and tidy. I can definitely recommend them.”
— Gill Lowe
“I know my ratings seem too good to be true, but we genuinely cannot fault Cath Services work. Peter and Gary have been brilliant, it doesn't matter what challenge you throw at them, they seem to be able to handle it and produce an excellent result. I would recommend them to anyone and everyone.”
— Caryn C
“I have used Cath Services for different jobs during a couple of years, such as fencing, cleaning roof and paving, new paving, clear out overgrown part of garden, etc. They are always in time, work very hard and finish with the best quality and neatness. Would never ask someone else to help me around my house and will highly recommend them to family and friends.”
— Agneta
“This is the second time I’ve used Cath Services. The first was for internal alterations and a bathroom at a previous property. Peter and Adam have done another beautiful job with my two bathrooms this time. Their attention to detail, ideas for a better finish, and how they think through the job to ensure the best outcome is outstanding…”
— Emma E
“I'm based in Witley, and have now used Peter and the team at Cath Services Ltd for several years. They quickly became my trusted company for any work around the house or garden. They have done projects including a driveway, bathroom refurbishment, wooden flooring, decking, paving, gate installation, and more. The quality is outstanding and I've always been delighted with the outcome…”
— Garth H
“I highly recommend Peter and his team for all job inside and outside the house. The quality of their performance is matching with the highest expectations. They are creative and helpful, having excellent ideas and don't know impossible. Do not hesitate to contact them if you need a professional help.”
— Melinda
“Peter and the team are our go-to for any outdoor work needed, be it fencing, landscaping, window or gutter cleaning. They do it all with the highest attention to detail, professionalism and skill. We’ll be seeing you soon again I’m sure guys!”
— Julia B
“Excellent company and delighted to recommend them. They arrive when they say they will and they get on with the job. Quality workmanship and attention to detail as well as being tidy.”
— Martin H
“They always do a great job, come on time and do windows. Often other little jobs too. Gutters and solar panels…”
— Jane DFind answers to common questions about our building and renovation services, how we work, and what to expect when you choose CATH Services. We’re here to help you plan your project with confidence and make informed decisions for your home.
We pride ourselves on reliability, fair pricing, and delivering every project with care and attention to your safety and satisfaction.
CATH Services supports homeowners and businesses across Surrey, Hampshire, and West Sussex. Whether you’re planning a renovation, extension, or general building work, we’re here to help – get in touch today.
Phone: 01483 663463
Email: info@cathservices.co.uk
Address: 25 Waverleigh Rd, Cranleigh GU6 8BZ
