Building & Extensions
House Extensions in
Bishop's Stortford & Hertfordshire
Single, double-storey, side return and wrap-around extensions managed end-to-end by an owner-led team — from foundations through to plastered, ready-to-decorate finish.
Overview
Extensions Done Properly, From Foundations to Finish
An extension is the largest building project most homeowners ever commission. The two things that decide whether it goes well — beyond design — are quality of trade and quality of project management. We provide both under one roof: groundworkers, brickies, carpenters, roofers, plasterers, electricians and plumbers all coordinated by Jamie personally.
Most of our extension work falls into single-storey rear additions (kitchen-diner schemes), double-storey side and rear extensions (adding bedroom plus reception), wrap-around L-shaped extensions, and side returns on Victorian/Edwardian terraces. We handle planning coordination, Building Control, structural engineer input and full delivery — you have one number to call.
Why It Matters
Why Extension Projects Go Wrong
The two consistent failure modes on residential extensions are poor sequencing of trades and open-ended pricing. Poor sequencing means you wait three weeks for a plasterer because nobody booked them in time. Open-ended pricing means a £55,000 quote becomes a £78,000 actual cost because every variation gets billed at day rates without prior approval.
We address both directly. Trades are sequenced and locked in writing before we start. Materials are ordered to a programme. Variations are costed and approved before they happen. Cost certainty is the single most important thing we deliver — alongside the build itself.
Our Process
How We Deliver Building & Extensions
Initial Consultation
Free site visit, brief discussion, early flag of any planning, structural or budget issues. No commitment.
Detailed Itemised Quote
Fully written quote covering materials, labour, sub-contractors, skip hire, Building Control fees. Fixed price.
Programme & Scheduling
Trades sequenced, materials ordered, weekly programme agreed in writing before we break ground.
Build & Updates
Owner-led site management, daily clean-down, regular updates, all variations approved in writing before action.
Handover & Guarantee
Final walk-round, snagging completed, written insurance-backed workmanship guarantee on completion.
Benefits
What You Get with J&Co
Fixed Written Quotes
Every project itemised and fixed before we start — no creeping extras, no day-rate drift.
All Trades In-House
Groundworkers, brickies, roofers, plasterers, electricians coordinated by us, not subbed out and forgotten.
Owner-Led Management
Jamie runs every site personally — you speak to the decision-maker, not an account handler.
Insurance-Backed Guarantee
Workmanship cover backed by insurance on every extension we deliver.
Technical Detail
Single-Storey, Double-Storey or Wrap-Around — What's Right?
Single-storey rear extensions are the most common — typically extending the kitchen and creating a kitchen-diner-living space with bifold or sliding doors to the garden. Cost-effective per square metre, often achievable under permitted development rights, and the highest impact for most family homes.
Double-storey extensions add a bedroom (and often an en-suite) above a reconfigured ground-floor space. Cost per square metre is significantly lower than single-storey because you're sharing foundations, roof and external walls between two floors. Almost always requires planning permission and a structural engineer involved from day one.
Side returns on Victorian and Edwardian terraces are a specialism — filling in the awkward L-shape created by the original side passage to dramatically widen the kitchen. Common across Bishop's Stortford and Sawbridgeworth on period properties. Requires careful work where the new structure ties into existing walls.
Wrap-around extensions combine a rear and side extension into one project. Big-impact, big-cost, and the most complex of the four. Worth doing when the kitchen needs full reconfiguring rather than just enlarging.
For loft space adjustments at the same time see our loft conversion service. For full-house refurbishment scope see renovations and refurbishments.
Honest Pricing
How Much Does a House Extension Cost in Hertfordshire?
Honest 2026 ranges for our area. Every project quoted individually after a site visit and brief discussion of what you actually want.
Single-storey rear
£40,000–£90,000
Typical 4m × 5m rear extension including kitchen relocation, bifold doors and finishes.
Double-storey rear
£75,000–£140,000
Adds bedroom plus en-suite above reconfigured ground floor — better £/m² than single-storey.
Wrap-around
£100,000–£200,000+
Rear plus side return combined — highest impact, highest cost, fully bespoke quote.
What affects the price
- Footprint size (m²)
- Single vs double storey
- Glazing specification (bifold, slider, lantern)
- Kitchen relocation and finish
- Ground conditions and foundations
- Planning vs permitted development route
Service Area
Areas We Cover for Building & Extensions
We deliver this service across our full Hertfordshire and Essex catchment. Regular projects in Bishop's Stortford, Sawbridgeworth, Harlow, Saffron Walden, Stansted Mountfitchet, Great Dunmow, Epping, Ware, Hoddesdon, Broxbourne, Cheshunt, Welwyn Garden City and Stevenage.
Outside this list? Call us with your postcode — we frequently work the wider London fringe and across the rest of Hertfordshire.
Recent Work
Recent Building & Extensions Projects
FAQs
Building & Extensions — Frequently Asked Questions
Get a Free Extension Quote
Owner-led consultation, fixed itemised quote, fully managed build. Across Hertfordshire and Essex.
Page last updated: May 2026 · J&Co Builders Ltd · 1 Ugley Hall Cottages, Bishop's Stortford CM22 6JB