We frequently receive inquiries from homeowners looking to extend their existing properties. The core question is always: “How much does an extension cost?”
1. Estimated Build Costs Per Square Meter (Excluding VAT)
To help you budget, we recommend the following allowances for extensions on existing residential properties. These prices are based on the total build area (external dimensions), not the internal floor plan, as current building regulations typically require walls to be up to 35cm deep.
- Lower Range: £2,000 per square meter
- Specification: Very basic finish and simple design.
- Mid Range: £2,500 per square meter
- Specification: Includes quality features like underfloor heating and tiled floors.
- Top Range: £3,000+ per square meter
- Specification: For high-end designs, such as large open-plan areas, large bi-fold doors, and integrated home automation systems.
2. Essential “Soft Costs” and Regulations
Beyond the physical build, you must budget for necessary professional and regulatory fees:
- Architectural Services: An architect or architectural technician is normally required for drawings and plans, costing in the region of £1,000–£2,000. A professional builder, like us, will have trusted partners we can recommend.
- Building Control: Required for any structural changes or the addition of sanitary facilities (like a toilet). Building Control ensures all work complies with minimum legal standards for safety, health, and energy efficiency.1
- VAT: Most established builders, including ourselves, are VAT registered and legally required to add VAT to the final price.
- Planning Permission: If you are wondering if you need planning permission for an extension, the government runs a very useful section clarifying when permission is needed on the official planning portal.
3. What Factors Push the Price Up?
Certain design choices or structural requirements will inevitably increase your overall expenditure:
- Large Steel Beams: These tend to require vertical steel supports to bear the load. Going above 4 meters often necessitates installing a pad stone (a large concrete base) beneath the existing property footings. Allow approximately £1,000 per meter once you exceed 4 meters.
- Roof Lanterns: These are highly sought after for natural light and are not as expensive as many people think. They typically start from about £3,500 installed.
- New Kitchens: A high-quality kitchen, including quartz worktops and appliances, generally starts at about £25,000.
- Unexpected Work (The Contingency): When working on any existing house—especially older properties—unforeseen issues can be uncovered once demolition or excavation begins. This can strain the builder-client relationship. It is always prudent to include a 5–10% contingency fund at the start of your project to cover these necessary surprises.2
4. When to Pay the Builder
Understanding the payment structure is critical for protecting both parties:
- Deposit: Most reputable builders will ask for a small deposit to secure your slot in their diary. We would caution against paying more than 10% of the project value upfront as a deposit. Paying a large amount in advance might signal that the builder is using your funds to cover other jobs.
- Payment Schedule: We typically ask for weekly or monthly payments to ensure consistent financial flow. On our projects, we provide a weekly tracker so both the client and Swallow Hill Homes can see precisely what work has been authorised and completed.
- Contract: A formal contract is strongly recommended for all larger projects. This clarifies payment terms and establishes a clear process should the relationship encounter difficulties.3
5. Should I Choose the Lowest Quote?
While bu
dgets are often tight, be cautious about accepting the lowest quote. If one quote is substantially cheaper than all others, you must ask how that contractor intends to maintain the quality you desire for your home. We are members of the Federation of Master Builders (FMB), a seal of quality.
For larger jobs, we highly advise checking customer references of previous jobs or arranging to see their completed work. Remember: if something feels too good to be true, it usually is.
6. Do I Need a Warranty?
The level of assurance depends on your trust in your chosen builder. Building Control is legally there to ensure all construction projects comply with minimum legal standards for safety and quality. They check plans and inspect key work stages (like foundations and fire safety) for compliance with Building Regulations.1
7. Where to Go for Ideas
- Shows like Grand Designs live are great for getting ideas.
- The Federation of Master Builders has a list of approved builders (like ourselves!).
- Magazines, such as Kitchens, Bedrooms and Bathrooms Magazine, are useful for flicking through to get design ideas.
- YouTube and the internet offer a wealth of information and inspiration.
Interested in getting a quote for your project?
We serve Beeston, Nottingham, Bramcote, Wollaton, Eastwood, Kimberley, Ilkeston, West Bridgford, Edwalton, and Wilford.
Contact Rob Bailey, Director, at 07737 988 243 or email rob.bailey@swallowhillhomes.com to discuss your project.
Beeston, Nottingham, Bramcote, Wollaton, Eastwood, Kimberley, ilkeston, West Bridgford, Edwalton, Wilford, FMB