Building Advice & Cost Guides by DKM Builders Oxford Ltd

Find out how much a house extension costs in Oxfordshire in 2025. Learn average prices per m², planning rules, and money-saving tips from DKM Builders Oxford Ltd – Oxford’s trusted extension specialists.

How Much Does a House Extension Cost in Oxfordshire in 2025?

If you’re running out of space and considering an extension, understanding realistic costs helps you plan your budget confidently.

At DKM Builders Oxford Ltd, we’ve completed hundreds of single-storey, double-storey, and rear extensions across Oxfordshire – from Headington and Summertown to Abingdon and Witney.

Here’s our transparent 2025 cost guide, based on real Oxford projects.

Average Cost per m² 

Single-storey rear extension £2,100 m²

Double-storey extension £2,300 m²

Side extension £2,100 m²

Wrap-around extension £2,400 m²

Garage conversion £950 m²

What Affects the Final Price

• Ground conditions and foundation depth
• Access & parking permits (Oxford’s Controlled Zones)
• Structural steelwork and roof type
• Internal finishes (client-supplied or builder-supplied)
• Building Control & design fees

We always provide a detailed written estimate separating builder’s works, client allowances, and optional extras – so you know exactly what’s included.

Planning Permission & Building Control

Most small extensions in Oxfordshire fall under Permitted Development, but we handle both planning and Building Control on your behalf.

Our team prepare and submit architectural drawings, liaise with inspectors, and ensure compliance with UK Building Regulations.

How to Save Money on Your Extension

Combine works – refurbishing your interior during the extension stage reduces separate labour costs.

Client-supplied items – you can choose your own windows, doors, and tiles to suit your budget.

Transform Your Oxford Home with a Loft Conversion

Adding a loft conversion is one of the smartest ways to increase living space and property value in Oxford. Whether you’re planning a dormer, Velux, or full attic conversion, a well-designed loft can create an extra bedroom, home office, or en-suite master suite without extending the footprint of your home.

At DKM Builders Oxford Ltd, we manage every stage of your loft conversion – from initial drawings and planning permission through to construction and final Building Control sign-off.

Do You Need Planning Permission?

Most loft conversions in Oxford fall under Permitted Development, meaning you won’t need full planning permission provided.

However, if your property is:

• In a Conservation Area (e.g. North Oxford, Jericho, or Summertown)
• A listed building, or
• Includes a dormer facing the road

then full planning approval may be required.

Our design team handles all drawings and submissions to Oxford City Council, so you can relax knowing your project meets every regulation.

Building Control & Structural Design

Every loft conversion in Oxfordshire must comply with UK Building Regulations.

We work with local approved inspectors to ensure:

• Correct insulation and fire safety
• Structural steelwork (RSJs) designed and certified by an engineer
• Proper stairs access, ventilation, and emergency egress

This ensures your new space is safe, compliant, and built to last.

Typical Loft Conversion Costs in Oxford

As of 2025, most loft conversions in Oxford range between £45,000 – £75,000, depending on:

• Roof type (hip-to-gable, dormer, or Velux)
• Internal finishes and en-suite fittings
• Structural complexity and access

We always provide a fixed-price quote after site survey, including all design, labour, and materials with no hidden extras later on.