The Complete Guide to House Extensions: Costs, Timeline, and Process

Deciding to extend your home is a major investment in both your lifestyle and your property’s value. In the current 2026 market, the South West remains a popular area for development, with homeowners in Newton Abbot, Exeter, and Torbay looking to maximize their existing footprint.

This guide provides a transparent breakdown of what to expect in terms of financial investment, time, and the logistical steps required to get your project across the finish line.

1. Cost Breakdown: What to Budget in 2026

In the South West, building costs have stabilized slightly but remain influenced by material prices and labor demand. For 2026, you should budget based on the following square-metre rates (excluding VAT and professional fees):

Single Storey Extension: £1,900 – £3,300 per $m^2$

Double Storey Extension: £2,000 – £3,200 per $m^2$ (Often better value per $m^2$ as foundations and roofing costs are shared).

Basic vs. Premium Finish

Basic: £1,900/m² (Standard uPVC, laminate, basic lighting).

Standard: £2,500/m² (Aluminium bi-folds, engineered wood, mid-range kitchen).

Premium: £3,300/m²+ (Bespoke joinery, natural stone, smart home integration).

Typical Project Totals (Including VAT)

Small Rear Extension (20m²): £45,000 – £70,000

Medium Kitchen/Diner (30m²): £75,000 – £110,000

Large Double Storey (60m² total): £145,000 – £220,000

Note: Professional fees (Architects, Structural Engineers, Planning) typically add another 12% to 15% to your total budget.

2. The Timeline: From Concept to Completion

A realistic timeline for a house extension in 2026 is 9 to 15 months. While the build itself might only take 4 months, the “invisible” preparation takes up a significant portion of the schedule.

Pre-Construction (4 – 7 Months)

Design & Survey: 4 – 6 weeks.

Planning Permission: 8 – 12 weeks (Statutory council period).

Technical Drawings & Building Regs: 4 – 8 weeks.

Tendering & Contractor Booking: 4 weeks.

Construction Phase (3 – 6 Months)

Groundworks & Foundations: 2 – 3 weeks.

Shell & Roof (Watertight): 4 – 8 weeks.

First Fix (Plumbing/Electric): 2 weeks.

Plastering & Drying: 2 weeks.

Second Fix & Finishes: 4 – 6 weeks.

3. The Step-by-Step Process

Step 1: Feasibility and Briefing

Before hiring an architect, define your “must-haves.” Are you looking for a quiet home office or a social kitchen-diner? Establish a firm upper limit for your budget, including a 15% contingency fund for unforeseen groundworks or structural surprises.

Step 2: Design and Planning

Your architect will produce initial concepts. In Newton Abbot and the surrounding Teignbridge area, many rear extensions can be built under Permitted Development (PD), which avoids a full planning application. However, larger extensions or those in Conservation Areas will require a formal Householder Planning Application.

Step 3: Technical Design and Structural Engineering

Once planning is approved (or confirmed via a Lawful Development Certificate), a Structural Engineer must provide calculations for steel beams and foundations. These drawings ensure the building is safe and are required for Building Control approval.

Step 4: The Tender Process

Issue your technical package to at least three reputable builders. At V3 Build, we recommend comparing “apples with apples”—ensure every quote includes the same specifications for windows, flooring, and electrical points to avoid hidden extras later.

Step 5: The Build and Inspections

During construction, a Building Control officer will visit at key milestones: foundations (before pouring concrete), damp proof course (DPC), structural steels, insulation and drainage, and finally, completion.

Step 6: Completion and Handover

Once the work is finished and the final inspection is passed, you will receive a Completion Certificate. Keep this document safe; you will need it if you ever sell your property.

Partner with V3 Build

With over 25 years of experience serving Newton Abbot, Exeter, and the wider Devon area, we specialize in taking the stress out of this complex process. We provide a start-to-finish service that ensures your extension is delivered on time, within budget, and to an exceptional standard.