There is a version of DIY that saves you thousands of pounds, teaches you your home, and produces results you're genuinely proud of. There is another version that voids your insurance, fails a building inspection, and costs more to fix than the original job would have. The difference, almost always, comes down to knowing which jobs belong in which category.
This guide gives you a clear framework: what the law actually requires, a decision table for 20+ common jobs, and a plain-English explanation of when cutting corners has consequences you won't see until it's too late.
The Golden Rule: What Legally Requires a Certified Tradesperson
Before anything else, understand that some domestic work is not a matter of personal choice — it is regulated by law, and carrying it out incorrectly (or without the right certification) is either a criminal offence, invalidates your insurance, or creates a legal liability when you come to sell.
The main regulated categories in the UK are:
- Gas work (Gas Safe Register) — Any work on gas boilers, gas appliances, gas pipework, or flues must be carried out by a Gas Safe registered engineer. This includes boiler servicing, installation, and replacement. It is illegal to carry out gas work without registration. If you do and there is an incident, you face criminal prosecution, and your home insurance will not pay out.
- Electrical work (Part P / NICEIC / NAPIT) — Most significant electrical work in a home falls under Part P of the Building Regulations. This includes installing new circuits, consumer unit replacement, work in kitchens, bathrooms, and outdoors. Work must be carried out by a registered competent person (NICEIC, NAPIT, ELECSA, etc.) who can self-certify — or, if you do it yourself, you must notify your local authority building control, pay a fee, and have the work inspected.
- Window and door replacement (FENSA / Certass) — Replacement windows and doors must comply with building regulations for thermal performance and safety glazing. A registered FENSA or Certass installer can self-certify. If you use an unregistered installer or do it yourself, you must apply for building regulations approval from your local authority. Without a certificate, you will have to declare this at sale, and buyers' solicitors will flag it.
- Oil heating (OFTEC) — Oil boiler work requires an OFTEC-registered engineer.
- Electrical installation condition reports (EICR) — An EICR (now required for all rental properties and increasingly expected on residential sales) must be issued by a qualified, registered electrician.
Skill Level Assessment Framework
Before deciding whether to DIY a job, be honest about your skill level:
| Level | Description | Appropriate jobs |
|---|---|---|
| Beginner | Little or no experience; comfortable with basic tools | Painting, simple garden work, assembling flat-pack furniture |
| Competent DIYer | Completed several successful projects; can work from instructions; knows when to stop | Tiling, basic plastering, laminate flooring, decking, flat-pack kitchens |
| Experienced | Trade-level skills; understands building regulations; familiar with structural principles | First-fix carpentry, timber framing, drainage, stonework, lime mortaring |
Be honest. Most home improvement disasters come not from genuine incompetence but from overestimating skill level and underestimating complexity.
Decision Table: 20+ Common Jobs
| Job | DIY Difficulty | Safety Risk | Legal Requirement | Typical Saving if DIY |
|---|---|---|---|---|
| Interior painting & decorating | Easy | Low | None | £200–£500 |
| Wallpaper hanging | Easy–Medium | Low | None | £150–£400 |
| Laminate / engineered floor fitting | Medium | Low | None | £500–£1,200 |
| Garden landscaping / decking | Medium | Low | None | £1,000–£3,000 |
| Flat-pack kitchen fitting | Medium | Low | None (new circuits need Part P) | £800–£2,500 |
| Tiling (walls and floors) | Medium | Low | None | £400–£1,000 |
| Plastering (small areas) | Medium–Hard | Low | None | £300–£800 |
| Bathroom refurbishment (like-for-like) | Medium–Hard | Low | None (unless moving electrics) | £500–£1,500 |
| Replacing internal doors | Easy–Medium | Low | None | £200–£600 |
| Fitting a bathroom fan | Medium | Medium | Part P (notifiable) | £100–£250 |
| Installing a new circuit | Hard | High | Part P — notifiable or certified | £200–£500 |
| Consumer unit replacement | Hard | High | Part P — must be certified | £300–£600 |
| Full rewire | Expert | High | Part P — must be certified | £2,000–£6,000 |
| Boiler replacement | Illegal to DIY | Extreme | Gas Safe — legally required | No saving possible |
| Gas appliance installation | Illegal to DIY | Extreme | Gas Safe — legally required | No saving possible |
| Window/door replacement | Medium | Low | FENSA/Certass or building regs approval | £200–£800 |
| Structural wall removal | Hard | Extreme | Building regs + structural engineer | £500–£1,500 (risky) |
| Roof repair (minor) | Hard | High | None (but insurer may query) | £200–£500 |
| Loft insulation top-up | Easy | Low | None | £300–£800 |
| Asbestos removal | Illegal to DIY | Extreme | Licensed contractor only | No saving possible |
The Hidden Cost of Bad DIY
Even when a job is technically legal to DIY, a poor-quality outcome can be extremely expensive:
- Insurance voidance — Some insurers include clauses that allow them to reduce or refuse payouts if unqualified work contributed to the loss. If a DIY electrical job causes a fire, expect scrutiny.
- Building regulations non-compliance — Unpermitted structural work, unnotified electrical work, or a missing FENSA certificate must be declared to buyers. You may need to apply for retrospective approval (not always possible), take out indemnity insurance, or reduce your asking price.
- EICR and Gas Safety Certificate on sale — Mortgage lenders and buyers' solicitors increasingly require these on residential sales, not just rentals. If your electrics or boiler were replaced by an unregistered person, you may have no valid certificate and will need remedial work before you can sell.
- Structural consequences — An incorrectly positioned RSJ, a load-bearing wall removed without proper calculation, or inadequate drainage can create problems that cost ten times the original saving to fix.
Jobs You Should Never DIY
- Gas work of any kind — boilers, appliances, pipework, flues. Always Gas Safe.
- Structural work without engineering sign-off — any beam, chimney breast removal, new opening, or underpinning needs structural calculations.
- Full electrical rewire or consumer unit replacement — must be a registered competent person.
- Asbestos removal — any asbestos-containing material (ACM) disturbed during renovation must be assessed. Friable asbestos (sprayed coatings, lagging) requires a licensed contractor.
- Flat roof or chimney work with significant fall risk — not a regulation matter, but a safety one.
Jobs Perfect for a Competent DIYer
- Tiling — walls and floors. With the right adhesive, spacers, and patience, results are often indistinguishable from professional work.
- Plastering small areas — patch plastering and skim coats over boarding take practice, but are learnable.
- Flat-pack kitchen installation — the kitchen itself is DIY-able; the plumbing for appliances and any new electrical circuits are not.
- Decking and garden structures — most fall under permitted development; no electrical or gas risk.
- Interior decorating — the single biggest spend a competent DIYer can reclaim.
- Laminate and engineered wood flooring — floating floors are forgiving and satisfying.
How to DIY Legally
If you want to carry out notifiable work yourself:
- Building regulations application — contact your local authority building control (LABC) or an approved inspector. Pay the fee (typically £200–£600 depending on work scope). A building inspector will visit at key stages.
- Self-certification schemes — some work can be self-certified via competent person schemes if you are qualified. Most DIYers are not, so the local authority route applies.
- Keep records — retain all receipts, plans, test certificates, and building control completion certificates. These are required documents on sale.
When to Get a Quote Even If You Plan to DIY
Getting a professional quote before you start has two functions: a reality check on complexity, and a baseline for what you're actually saving.
A quote forces a tradesperson to look at your specific situation and tell you what's involved. You may discover that the "straightforward" bathroom job involves moving a soil stack, rewiring the ceiling light, and boxing in a complex pipe run — and that the saving is now much smaller than you thought. Better to find out before you've bought the tiles.
For guidance on what to expect when you do hire a professional, see our checklist of questions to ask a builder before you commit.
- Renovation Cost Contingency: How Much to Budget and Why — whether you DIY or hire, set aside the right contingency; this guide breaks down the bands by project type
- When to Use a Project Manager vs Manage Your Own Renovation — if you decide to hire rather than DIY, the next question is whether to self-manage the trades or bring in a PM