Picking the wrong builder costs months of stress before it costs money. Picking the right one is worth the time it takes. We work with one local builder across Barnet and the Hertfordshire border who handles extensions, garage conversions, structural work and full renovations.
What we cover
Areas We Cover
- High BarnetEN5
- East BarnetEN4
- New BarnetEN4
- WhetstoneN20
- FinchleyN3
- Mill HillNW7
- TotteridgeN20
- BorehamwoodWD6
- ElstreeWD6
- Potters BarEN6
- Hadley WoodEN4
- ArkleyEN5
Why Use Herts Build for Building Work
The single biggest building-project risk is the builder. Once work has started, you're tied to whoever you've chosen for months. Getting the right person matters more than getting the lowest quote.
The builders in the specialist we work with are checked: trading history checked, insurance verified, reference jobs visited where appropriate. They work locally — Barnet borough or the Hertfordshire border — and they specialise in domestic residential work. They're not a roofing company who'll quote your extension as a sideline.
Common Barnet Building Projects
The single-storey rear extension. The most-asked-for Barnet building project. 4–6m rear extension off the back of a 1930s semi or Edwardian terrace, opening the kitchen into a single dining/living space. Typical cost: £45,000–£75,000 for a 4m × 6m extension on a standard plot, with kitchen, flooring and decoration on top.
The side-return extension. Specific to Victorian/Edwardian terraces with the original side passage between the back addition and the boundary. Filling in the side return adds 1.5–2m of width to the kitchen and transforms the ground-floor flow. £35,000–£55,000.
The two-storey rear extension. Adds kitchen/dining downstairs plus an extra bedroom upstairs. More complex and expensive than single-storey (£75,000–£130,000+) but delivers significantly more space — often the right answer for growing families.
The garage conversion. Common in Borehamwood, Mill Hill, parts of East Barnet — particularly where the original garage is now too narrow for modern cars. Convert to a study, playroom or annex. £15,000–£25,000 for a basic conversion; £30,000–£45,000 if structural changes and a new opening to the house are involved.
Planning & Building Regulations
Most single-storey rear extensions in Barnet fall under permitted development (up to 4m for semi-detached, 3m for terraced, or 6m/8m respectively under prior approval). Two-storey rear extensions need planning permission. All extensions need Building Regs sign-off regardless.
Frequently Asked Questions
How long does a single-storey rear extension take?
Typically 12–16 weeks on site, plus 6–10 weeks of pre-construction (design, planning if required, structural calcs, Building Control).
Will I need to move out during the build?
For a rear extension you'll be without your kitchen for 4–6 weeks while the new floor goes in and the back wall comes out. Most families set up a temporary kitchen in the lounge or dining room. Whole-house renovations usually mean moving out completely.
Do you handle architectural drawings?
Yes — the builders in the specialist we work with either employ in-house architectural technicians or partner with local architects. Drawings are typically included in the design phase before construction starts.
What guarantees do I get?
Building work is typically warranted for 10 years (structural) under the contractor's standard terms. New-build elements (boiler, MVHR, electricals) come with manufacturer warranties. Ask each specialist about their warranty position during the quote stage.
How are payments structured?
Most builders work to a staged payment schedule — deposit on contract sign, then stage payments at agreed milestones (foundations complete, weathertight, second-fix complete, snagging-complete). Never pay the full amount upfront.