What Could This House Actually Become?

You're stood in the kitchen with a cup of tea going cold, staring at the back wall, trying to picture it gone. Maybe you've just picked up the keys and you're working out if this 1930s semi could ever have the open-plan kitchen-diner you saw on someone else's Instagram. Maybe you've lived here fifteen years and the kids need a fourth bedroom that doesn't exist yet. Either way, the question is the same: what's the potential to extend, STPP (subject to planning permission), and how do you find out without paying an architect just to be told "no"?

This is the bit most people skip. They either assume everything needs full planning (it usually doesn't) or assume permitted development means a free-for-all (it really doesn't). The truth sits in the middle, and it's more generous than most homeowners expect, as long as you know which version of your house you've got and where its boundaries sit.

Let's walk through what's actually possible.

The kitchen-diner everyone wants

Picture the back of a typical semi. Original kitchen, maybe 3 metres wide, a door out to a scrappy bit of garden. Now picture that wall gone, replaced with a run of bifold doors, a kitchen island where the back step used to be, and six extra metres of floor. That's not a fantasy render. That's a standard single-storey rear extension, and for a huge number of houses in England it's achievable without planning permission at all.

Here's the number that surprises people: a detached house can go back up to 8 metres from the original rear wall under permitted development. Every other house type, semi-detached and terraced included, can go up to 6 metres. Height is capped at 4 metres. That's enough for a proper kitchen-diner, a utility, even a snug, built in one go.

There's a catch worth knowing before you get attached to the full 8 or 6 metres. Anything beyond 4 metres (detached) or 3 metres (everything else) triggers something called the neighbour consultation scheme. You don't need planning permission as such, but you do need to notify the council, who tell your neighbours, who get a window to object. No shovel goes in the ground until the council confirms you're clear, grants approval, or 42 days pass with nobody raising a hand. It's not a rejection risk in the way full planning is; it's a pause button. Build that six-week gap into your plan from day one and it never catches you out.

"I've just bought the house, what can I actually do with it?"

New owners ask a different question to people who've lived somewhere for years. You're not just wondering what's possible, you're wondering what's already been used up. Somebody built that side return in 2004. Does that count against you now?

It does, and this is where people get caught. Permitted development rights are tied to what was there on the day the house was first built, not what's there now. If a previous owner already extended to the maximum rear depth, you don't get to start again with a fresh allowance. Whatever's been built already eats into what you're allowed.

There's also a quieter limit that catches people out even more often: the 50% rule. Across the whole curtilage, excluding the footprint of the original house itself, the total area covered by buildings, extensions, outbuildings, garages, sheds, the lot, cannot exceed half the plot. It doesn't matter if that shed has been there since the 1960s. It counts. If there's already a garage, a summer house and a lean-to greenhouse out there, do the maths before you fall in love with a two-storey side extension, because you might have less room than you think.

If you're buying with extension plans already in mind, ask the seller or their agent for anything that shows what's been added and when. It's a five-minute conversation that can save you a wasted architect's fee.

Could you go up instead of out?

Some houses don't have the garden to extend backwards, but they've got roofline to spare. This is where adding a full storey on top comes in, properly adding a floor, not a loft conversion with a couple of dormer windows.

Done well, this turns a cramped 1960s bungalow into a four-bedroom house with a proper landing and a bathroom that isn't squeezed under the eaves. Since 2020 there's been a specific permitted development route for exactly this: houses with a single storey can add one more, and houses with two or more storeys can add up to two more.

It comes with real conditions, though, and they're worth knowing before you get attached to the idea. The house needs to have been built between 1 July 1948 and 28 October 2018, so Victorian terraces and brand-new builds are both out of scope for this particular route. The finished height can't exceed 18 metres overall, and each new storey can add no more than 3.5 metres. If your house isn't detached, the new roofline can't sit more than 3.5 metres above next door's, which stops you towering over a terrace. And critically, even though this sits under permitted development, it's never automatic: you must get prior approval from the council first, covering things like how it looks from outside, the effect on neighbours' light, and general impact on the street. Think of prior approval as a lighter-touch version of planning permission, not the absence of one.

One more thing worth saying out loud: none of this applies in a conservation area. If your street is protected, upward extensions under this route are off the table entirely, whatever your neighbours further down the road have done.

What if your street is a conservation area?

This is the conversation nobody wants to have, but better now than after you've commissioned drawings. If your house sits on article 2(3) land (conservation areas, National Parks, AONBs, the Broads, or World Heritage Sites), several of the generous allowances above simply don't apply to you.

No side extensions under permitted development, full stop. No two-storey rear extensions under permitted development, only single storey. And no cladding the outside in render, timber, tile hanging, pebble dash, stone or artificial stone without permission, even if you're not changing the shape of the house at all, just its surface.

This doesn't mean nothing is possible. It means the single-storey rear route is often still your best friend, but the larger 8m/6m allowances described earlier don't apply on this land either, so you're working to the standard limits, and anything beyond that genuinely needs planning permission. It also means a conversation with a planning consultant who knows your specific conservation area is worth having early, because conservation area character varies a lot street to street, and what got approved two doors down might reflect something specific to that property, not a blanket rule for the road.

The extension that needs almost no permission at all

Not every improvement is a six-figure kitchen project. Sometimes it's the front door. A porch, done properly, is one of the simplest permitted development wins available: up to 3 square metres of external ground area, no part higher than 3 metres, and positioned at least 2 metres back from any boundary facing the road. Stay inside those numbers and you don't need to ask anyone. Go bigger, taller, or closer to the pavement, and you're back into planning permission territory for what might otherwise feel like a small job.

It's a useful illustration of the general shape of permitted development: small, sensible, set-back changes tend to sail through without anyone's say-so. Big, visible, forward-facing changes get more scrutiny, because they change how the street looks, not just how the house works.

The wall you can't touch: extending to the front

This trips up more people than almost anything else. Homeowners assume if they can extend the back and the side, the front must be fair game too, especially on a generous plot with a long driveway.

It isn't, in almost every case. Permitted development does not allow you to extend beyond the wall that forms the principal elevation of the house (generally the front, facing the road), or beyond a side wall that itself fronts a highway. That restriction isn't just about the wall itself either: it covers the whole area in front of an imaginary line drawn from the end of that wall out to the property boundary. On a corner plot, where a side wall also faces a road, there's an extra layer of restriction on that side too.

Translate that into practical terms: if you're picturing a bigger porch-come-office at the front, or bringing the side of the house forward to meet the building line of a wider plot, that's planning permission territory, not permitted development. It doesn't mean refusal. It means a different process, with design and streetscene considerations the council will want to see addressed properly.

So what could your house actually become?

Put it all together and most houses have more than one route to more space, not just one. A 1930s semi with an unextended rear might manage a 6-metre kitchen-diner under permitted development, with the neighbour consultation scheme kicking in only past the 3-metre mark. A detached 1990s house with room on the roofline might add a whole storey, done properly via prior approval, turning a three-bed into a five-bed without touching the garden. A Victorian terrace in a conservation area has fewer shortcuts but still has the standard single-storey rear option, assuming nobody's already used it up.

None of these routes tell you what your specific house, on your specific street, with whatever's already been built in that garden, can actually take. That's not a guessing game you should play with a tape measure and a hopeful attitude. It's a quick, specific check against what's already there and what the rules actually allow for that plot, and the real answer to "potential to extend, STPP" always lives at that level of detail, not in a general rule of thumb.

Does adding an extension actually add value?

It's the question underneath all the others. Generally, yes, well-executed extensions that add genuine usable space, particularly an extra bedroom or a proper kitchen-diner that improves how the whole ground floor flows, tend to add real value, often more than the build cost if done thoughtfully and finished well. Badly judged extensions, the kind that leave a house looking lopsided from the street or eat the entire garden, can do the opposite. The value isn't in the square footage alone. It's in whether the finished house makes sense as a whole, inside and from the pavement.

What's next

Somewhere between the cup of tea going cold and the finished kitchen-diner with light pouring in, there's a real answer about what your specific house can become, and it's usually more than you'd guess sitting at the table imagining it. The fastest way to find out isn't a phone call or a guess based on what the house two doors down managed. Put your address into the box on the homepage and see what the planning history and the permitted development picture actually say about your plot, your garden, and your roofline. That's the fun part: finding out the house you're already in might have more left in it than you thought.