DIY vs Professional Extensions: What Can You Do Yourself?
Which extension tasks you can legally tackle yourself, which require professionals, and how to save money without cutting corners.
TL;DR - The Quick Answer
London homeowners can save 20-40% on finishing work by doing decorating, landscaping, tiling, and skirting themselves - potentially £5,000-£12,000. However, gas work (Gas Safe registered), most electrical circuits (Part P), structural elements, and drainage connections are legally off-limits for DIY. Self-managing your project instead of using a main contractor can save a further 10-20%, typically £10,000-£25,000, but requires 20+ hours a week on site.
Many homeowners want to reduce extension costs by doing some work themselves. While this can save significant money, some tasks legally require qualified professionals. Getting the balance right protects your investment and keeps your family safe.
Work That Must Be Done by Professionals
Gas Work (Gas Safe Registered)
All gas work must be done by Gas Safe registered engineers. Includes boiler installation, gas pipe work, and appliance connections. Illegal and dangerous to DIY.
Most Electrical Work (Part P)
New circuits, consumer unit changes, bathroom/kitchen electrics, and outdoor wiring must be done by qualified electricians or self-certified with building control.
Structural Work
Foundations, load-bearing walls, steel beams, and roof structures should be done by experienced builders following structural engineer designs.
Drainage Connections
Connecting to main drains typically requires qualified groundworkers. Building control must inspect before backfilling.
DIY Suitability by Task
| Task | DIY? | Potential Savings |
|---|---|---|
| Painting & decorating | Yes | £2,000 - £5,000 |
| Landscaping & paving | Yes | £1,500 - £4,000 |
| Floor tiling | Yes (with care) | £1,000 - £2,500 |
| Kitchen fitting | Partially | £1,000 - £3,000 |
| Skirting & architraves | Yes | £500 - £1,500 |
| Electrical (circuits) | No | - |
| Gas work | No | - |
| Plumbing (basics) | Maybe | £500 - £1,500 |
| Task | DIY? | Potential Savings |
|---|---|---|
| Painting & decorating | Yes | £2,000 - £5,000 |
| Landscaping & paving | Yes | £1,500 - £4,000 |
| Floor tiling | Yes (with care) | £1,000 - £2,500 |
| Kitchen fitting | Partially | £1,000 - £3,000 |
| Skirting & architraves | Yes | £500 - £1,500 |
| Electrical (circuits) | No - Part P required | - |
| Gas work | No - Gas Safe required | - |
| Plumbing (basics) | Maybe | £500 - £1,500 |
Source: Mayfair Studio project data • Data as of 2025
Project Management Option
Rather than doing physical work, you can save by project managing your extension yourself. This means hiring individual trades rather than a main contractor.
Potential Savings
10-20% by cutting out main contractor markup.
Typical saving: £10,000-£25,000
Requirements
Time (20+ hours/week), confidence dealing with trades, understanding of construction sequence, ability to handle problems.
Risks of DIY
Insurance Issues
Poor DIY work that causes damage may not be covered by home insurance. Some insurers require professional certification for certain work.
Building Control Problems
Substandard work may fail inspection. Remedial work to fix DIY mistakes often costs more than hiring professionals initially.
Future Sale Issues
Buyers' solicitors check for certificates. Missing electrical or gas certificates can delay or derail sales.
Frequently Asked Questions
London homeowners can save 20-40% on an extension by DIYing finishing work - decorating, tiling, landscaping, and skirting save £5,000-£12,000 combined. Gas and electrical circuits must use certified tradespeople by law. Self-managing trades instead of a main contractor saves a further 10-20%, typically £10,000-£25,000.
Frequently Asked Questions
Can I do my own plumbing?
Basic plumbing like fitting taps, connecting washing machines, or installing toilets-yes. Anything involving gas, or new hot/cold supply runs should be done by qualified plumbers.
What electrical work can I do myself?
Minor work like changing light fittings, adding sockets to existing circuits (outside kitchens/bathrooms), and replacing like-for-like. New circuits and bathroom work need Part P certification.
Is it worth doing my own decorating?
Usually yes-it's low risk and can save significant money. However, if you have high ceilings, complex features, or want a perfect finish, professionals may be worthwhile.