Three and a half metres on a terrace, four on a semi
Barnsley Council puts actual numbers on paper, which plenty of councils won't. Its House Extensions and Other Domestic Alterations guide, adopted in March 2024, says a single storey back addition to a terraced house should project no more than 3.5 metres. On a semi the figure is 4 metres. Go past 3 metres on either and the eaves should stay at or under 2.5 metres.
Two storeys get less. The guide asks for under 3.5 metres on a semi and 2.5 metres on a terrace, with room to argue for more if next door has already built out or there's a solid boundary wall. On a sloping plot the council may want it shorter. Detached houses are judged on design.
Those figures only matter if you're making a planning application. Build within permitted development and the guide never comes into it. Still, they tell you roughly where an officer will draw the line, and they sit alongside a 45 degree test taken from the middle of your neighbour's nearest window.
Two other numbers catch people out. At least half the garden should be left after any building, and there should be 10 metres between first floor back windows and the rear boundary. On the tight pre-1919 terraces of South Barnsley and Worsbrough, that second one can rule out a two storey addition before anyone draws it.
Semis, side gaps and the half metre step back
Semis made up 32.5% of occupied homes in the council's 2020 household survey, and the obvious way to grow one is sideways. Planners are wary of that. Their guide calls closing the gap between semis "a detrimental change to the character of the street scene".
So a two storey side addition here should step back at least 500mm from the front wall, carry a lower ridge, copy the pitch of the main roof and, where it can, stand a metre off the boundary. Width is capped at two thirds of the original house. On squared stone the step back may need to be deeper, because the joint between old and new stone is hard to hide.
Flat roofs get short shrift too. The guide calls them "an ugly and inferior form of construction" and won't normally accept a flat or shallow roofed porch. A flat roofed kitchen at the back isn't banned, but expect questions if it's visible from the road.
Which extension suits a Barnsley house
In rough order of how often they come up here. Each one links to a fuller guide.
Single storey at the back. Under national permitted development a semi or terrace can go 3 metres back, or up to 6 with prior approval, and the council's own depth limits don't apply to either route. Outside the 18 conservation areas, that covers most jobs.
Kitchen. The usual brief on a three bed semi. If your neighbour's kitchen window is close to the shared boundary, the 45 degree line from it will set your depth before the budget does.
Two storey. Usually an application, since permitted development needs 7 metres to the back boundary. The 10 metre rear window rule plus the 500mm side step back shape most designs. Ask your designer to show both on the first sketch.
Open plan. Knocking through a stone back wall on an older terrace means a steel, and steel beams are a building control inspection stage in Barnsley. Get the engineer's calculations done before the builder prices it.
Downstairs bedroom. Darton and Barugh, along with Hoyland, Wombwell and Darfield, have a high share of bungalows, which are the easiest homes to give a level access bedroom. A side addition to a bungalow can't have rooms in its roof under the guide.
Side return. Suits a pre-1919 terrace with a rear wing and a passage alongside. Permitted development allows it single storey, up to 4 metres high and half the original width, and not at all in a conservation area.
Wrap-around. This counts as a side extension too, so it needs permission in any conservation area. On a corner plot the council caps the side part at half the gap to the road.
Home office. Attached usually wins on a Barnsley plot, since the half garden rule counts outbuildings and extensions together.
Planning. Barnsley planners don't offer free chats before an application. If you're relying on permitted development, a lawful development certificate is cheap insurance when you come to sell.
Cost. No Barnsley figure from us. Foundations are the unknown on old mining ground, so get the mining check done before asking for prices.
What's under the footings
An extension means digging, and in Barnsley that brings the coal question straight in. The British Geological Survey says mines in the west of the district tend to be older and shallower, so subsidence is likely worse there. Its memoir also warns that colliery spoil can carry sulphates that attack concrete, and that infilled ground can settle unevenly.
The Mining Remediation Authority says that if your home is in a development high risk area you must check for mining risks, and you may need its permit before digging foundations or laying new drains. It also advises against building over or close to a mine entry. Its free map shows the risk areas.
Water is the other check. The Dearne and the Dove did the damage in June 2007, when 352 properties flooded across the borough. The council's flood strategy names Darton, Lundwood, Darfield Bridge and Bolton on Dearne on the Dearne, and Low Valley and Aldham Bridge on the Dove. If your plot is in Flood Zone 2 or 3, any planning application needs a flood risk assessment with it.
Then there's the Green Belt, which covered 77% of the borough in the council's 2014 review. Out there, the guide says all your extensions added together shouldn't be bigger than the original house. Cawthorne, Penistone and the other village conservation areas lose the side and two storey rear permitted development rights as well.
Where these facts come from
- Barnsley Council: House Extensions and Other Domestic Alterations SPD (2024)
- GOV.UK: Permitted development rights for householders, technical guidance
- GOV.UK: home extensions in former coal mining areas
- BGS: geology of the Barnsley district
- Barnsley Council: Local Flood Risk Management Strategy appendices (2017)
- GOV.UK: flood risk assessments for planning applications
- Environment Agency: flood risk standing advice
- Barnsley Council: Green Belt Review method report (2014)
- Barnsley SHMA 2021
- Barnsley Council: conservation areas
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Questions people in Barnsley ask
Can I build a 4 metre kitchen on the back of my Barnsley terrace without planning permission?
Not under the standard rights, which stop at 3 metres for a terrace. You can go to 6 metres through prior approval, where the council notifies your neighbours and has 42 days to decide. If you apply for full permission instead, its guide expects a terrace to stop at 3.5 metres.
My semi in Darton is near the Dearne. What extra do I need?
Check the government flood map for planning first. If the plot is in Flood Zone 2 or 3, a planning application must include a flood risk assessment, and the Environment Agency has standing advice for minor extensions that covers floor levels and flood resistant materials.
Do I need a Coal Authority permit to extend my house?
Only if you're in a development high risk area and the digging could reach coal seams, old workings or a mine entry. The body is now called the Mining Remediation Authority. Check its map before the foundations are designed, and ring its hazard line if the excavation turns up anything that looks like a shaft.
How big can I extend a house in the Green Belt near Penistone?
Barnsley's guide doesn't use a percentage. It says the original house must stay the dominant part, and the total of all extensions, past and proposed, shouldn't exceed its original size. The council can also remove permitted development rights to hold you to that.