House Extensions Stevenage

An extension in Stevenage is judged against a written design guidance document with numbers in it. Knowing those numbers early keeps a scheme out of trouble later. We build to a structural engineer's calculations, coordinate building control applications and inspections, and work alongside your architect or designer on the drawings.

For Stevenage, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Hertfordshire work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Stevenage: the structural engineer we appoint designs the structure, we build it, and building control signs it off.

The design guidance sets the projection and height limits

Principle HD8 of Stevenage's Design Guidance SPD limits a single storey rear extension to 3.5 metres of projection where it would be within 1 metre of a shared boundary. Elsewhere the limit is 4 metres. The same principle sets heights of no more than 3 metres to the eaves and 4 metres to the ridge.

A two storey rear extension should project no more than 2.5 metres where it would be within 1 metre of a shared boundary, and should not exceed the eaves or ridge heights of the original property. Those figures decide roof pitch, beam depth and floor build up, so they belong in the first conversation.

Housing in Stevenage

About 38,430 homes are listed for Stevenage, and the mix is 76% houses to 24% flats, with 96% built after 1945, 1% in 1919 to 1939 and 2% earlier. 52% of homes here are terraced; a rear extension on a terrace in Stevenage digs foundations close to both neighbours, so notices to both are normal.

Daylight to the neighbours is tested with numbers too

Stevenage assesses loss of daylight using a 45 degree test in plan and elevation, and a 25 degree test where a proposal sits opposite a neighbouring window. A proposal complies with the 45 degree rule if it passes either the plan test or the elevation test.

Table 1 of the same document sets a minimum back to back separation distance of 25 metres between existing and new two storey dwellings, and 15 metres back to side. Where a scheme sits close to those thresholds, it is worth resolving the design before an application goes in.

Foundations depend on which part of town you are in

Across the Old Town High Street, the Town Square area, Bedwell, Shephall Green, Symonds Green, Poplars, Great Ashby and the Gunnels Wood Road area, the mapped superficial deposit is the Lowestoft Formation, recorded as diamicton. The British Geological Survey describes it as an extensive sheet of chalky till with outwash sands and gravels, silts and clays, of extremely variable thickness, reaching up to 60 metres locally in buried valleys.

At Martins Wood and at Bragbury End the mapped deposit is Anglian glaciofluvial sand and gravel rather than clay till, and the Broadwater area at Marymead sits on mapped Alluvium of clay, silt, sand and gravel. Foundation depth and type follow trial holes on your plot, not a rule of thumb for the town.

Building control route and the levy

Hertfordshire Building Control rules out the Building Notice route where you are building over a public sewer or within 3 metres of one. Where the notice route is open, work can start on site 48 hours after the notice is given.

Stevenage's Community Infrastructure Levy is payable on development creating 100 square metres or more of net additional floorspace, or on development of any size that results in a new house or flat. An extension below that threshold does not pay it, so the floor area is worth checking against the drawings before submission.

Kitchen extensions in Stevenage

68% of the houses in Stevenage are terraced. On a terrace the kitchen extension is built out from the back, into the side return where the house has one or across the full rear width, and a steel beam takes the old back wall so the kitchen and the new room become one space. The fit-out is priced on its own page, kitchen renovation in Stevenage; the build figures are in the table above.

Side return extensions in Stevenage

Side returns belong to Victorian and Edwardian terraces, and only 2% of homes in Stevenage predate 1919, so they are the exception here; most extensions run across the full rear width instead. Our side return extension page covers the build in detail, with build rates of £2,400 to £3,200 per m².

Double storey extensions in Stevenage

Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Stevenage often needs planning permission from Stevenage Borough Council. On the 52% of homes that are terraced, the neighbours' windows usually decide the depth. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.

• Drainage diversion and build-over agreements with the water authority
• Building control inspections at foundation, damp course and steel stages
• Flat and pitched roofs with rooflights or lanterns

VOA Council Tax stock of properties, March 2025, for all 12 statistical areas in Stevenage. Counts rounded by the VOA.

Two or three things usually come up alongside house extensions on a Stevenage job: RSJ and steel beam installation in Stevenage, house extensions in Hitchin, basement extensions, the Party Wall Act process for extensions, house extensions anywhere in London and Double Storey Extension Cost.

Why Stevenage Homeowners Choose GS Renovation

Extensions in Stevenage are measured against written figures: 3.5 or 4 metres of rear projection, 3 metres to the eaves, and daylight tested at 45 and 25 degrees. We work to those from the first site visit, alongside whoever is preparing your drawings, so the build and the consent do not pull in different directions. We build to a structural engineer's calculations rather than producing them, and building control applications and inspections are coordinated for you. Fully insured, free no obligation quotations, one point of contact.

• Dust screens and floor protection in occupied homes
• Weathertight shell reached before the fit-out begins
• Drainage diverted or built over with the right approval in place

Reviewed jobs near Stevenage

1 MyBuilder review from Stevenage, with each customer's own job title:

• Kitchen worktops, Stevenage, 24 Jun 2021 (5 out of 5)

Read all 31 on our reviews page.

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.