Most extension problems are predictable. Here are ten of the most common mistakes and how to avoid them.
1. Setting a budget without a contingency
Costs rise when you open up an old house. Keep 10–15% in reserve and more for older properties. See the extension cost guide.
2. Hiring on price alone
A very low quote may exclude items or lead to extras later. Compare scope, not just totals: how to compare builder quotes.
3. Starting without approvals
Check planning, building regulations and party wall requirements before building. Unauthorised work can be expensive to put right and can derail a sale.
4. Changing your mind mid-build
Design changes during construction cause delays and extra cost. Finalise layout, sockets, lighting and finishes before work starts.
5. No written contract
Handshake deals lead to disputes. Use a written contract with a clear scope, price, programme and payment schedule: builder contracts and stage payments.
6. Paying too much too early
Pay for completed stages, not in advance. Keep a retention if agreed.
7. Ignoring the structure
Opening up walls, beams and foundations need an engineer's design. See removing a load-bearing wall.
8. Forgetting long lead times
Windows, bi-fold doors, kitchens and bespoke items can take weeks. Order early so the programme is not held up. See how long an extension takes.
9. Not planning for disruption
You will have dust, noise and possibly no kitchen. Arrange a temporary kitchen, protect furniture and tell neighbours in advance.
10. Overlooking light, heating and ventilation
A big extension can be dark, cold or overheat. Think about rooflights, orientation, insulation and ventilation at design stage. See kitchen extension ideas.
A simple checklist
- Budget with contingency
- Drawings and specification complete
- Approvals in place
- Itemised quotes compared
- Written contract and stage payments
- Realistic programme
Get it right first time
Abron Contracting builds extensions in Newport and can advise on your plans before you commit. Request a quote or call 01633379170.
Frequently asked questions
What is the most common extension mistake?
Underestimating the total budget, including fees, fit-out and contingency.
How can I avoid going over budget?
Fix the design, get itemised quotes, agree variations in writing and keep a contingency.
Do I need an architect or designer?
You need good drawings. For many projects, an architectural designer or design and build contractor is enough.
What if I want to change something during the build?
Agree the cost and time in writing before the change goes ahead.
How early should I order materials?
As soon as the design is fixed, especially long-lead items such as windows and bespoke doors.
