Most loft conversions on houses don’t need loft conversion planning permission. Rear dormers, hip-to-gable conversions and rooflight lofts usually fall under Permitted Development, as long as they stay within size and design limits. You will normally need full planning permission for a mansard, a front dormer, any loft on a flat, or a house in a conservation area. Every loft conversion needs Building Regulations approval, whatever the planning route.
This guide explains the rules for England, which loft types need consent, what it costs, and what our own test applications showed about adding extra storeys.
The four planning routes at a glance:
| Route | When it applies | Council fee (England, from April 2026) | Typical decision time |
|---|---|---|---|
| Permitted Development, no application | Your loft meets all the Permitted Development limits | None | None |
| Lawful Development Certificate | Confirms in writing that your loft is Permitted Development. Strongly recommended | £274 | Around 8 weeks |
| Householder planning application | Mansards, front dormers, conservation areas, or anything over the limits | £548 | 8 weeks |
| Prior approval for additional storeys (Class AA) | Adding one or two whole storeys to a post-1948 house | Prior approval fee | 8 weeks |
When is a loft conversion Permitted Development?
A loft conversion on a house is Permitted Development, so it needs no planning application, if it meets all of these limits:
- Volume: the extra roof space is no more than 40 cubic metres on a terraced house, or 50 cubic metres on a semi-detached or detached house. Earlier roof extensions count towards this.
- Height: nothing is higher than the highest part of the existing roof.
- Front roof: nothing extends beyond the existing roof slope on the side of the house facing the road.
- Materials: the outside looks similar to the rest of the house.
- No outdoor space: no balconies, verandas or raised platforms.
- Side windows: obscure-glazed, and fixed shut unless the opening part is more than 1.7 metres above the floor.
- Eaves: the dormer is set back at least 20 centimetres from the original eaves where possible. This doesn’t apply to a hip-to-gable conversion.
- Rooflights: they stick out no more than 15 centimetres from the roof slope.
When Permitted Development doesn’t apply
You will need a full planning application, whatever the size, if:
- The property is a flat or maisonette. Flats have no Permitted Development rights for roof extensions.
- The house is in a conservation area, a National Park, an Area of Outstanding Natural Beauty or a World Heritage Site.
- The house is listed. You will also need listed building consent.
- Your council has an Article 4 direction that removes Permitted Development rights in your street. Many London boroughs have these, so always check.
- Permitted Development rights were removed by a condition on an earlier planning permission, which is common on newer estates.
If you are unsure, a loft specialist or your council can check before you spend money on drawings. For homes in conservation areas, see our conservation areas guide.
Which loft conversions need planning permission?
The type of loft makes the biggest difference. This is the usual position for a house outside a conservation area:
| Loft type | Usually needs planning permission? | Why |
|---|---|---|
| Rooflight (Velux) | No | No change to the roof shape |
| Rear dormer | No, if within the volume limit | Sits on the back roof slope |
| Hip-to-gable | No, if within the volume limit | Changes the side roof, not the front |
| L-shaped dormer | Often no, but check the volume | Large dormers on bigger terraces can exceed 40 cubic metres |
| Front dormer | Yes | Extends the roof slope facing the road |
| Mansard | Yes, in most cases | Rebuilds the roof slope almost vertically and usually exceeds the limits |
| Raising the ridge | Yes | Goes higher than the existing roof |
Mansards are common in London, and many councils have design guides that support them, especially on terraces where neighbours already have one. A refusal on the first application is not always the end: a revised design can often be approved. See our comparison of mansard and dormer loft conversions.
Can I add an extra storey without planning permission?
In theory, yes. Since 2020, a Permitted Development right known as Class AA lets some homeowners add whole new storeys to their house without a full planning application. In practice, it rarely works for London homes.
The Class AA rules
- Up to two extra storeys on a house of two or more storeys, or one on a bungalow.
- Only houses built between 1 July 1948 and 28 October 2018. Most Victorian and Edwardian London terraces are excluded.
- Not in conservation areas or other protected areas, and not if the house has already been extended upwards.
- Height limits: the finished house can be no more than 18 metres high. On a terraced or semi-detached house, it can’t be more than 3.5 metres taller than the neighbouring roofs.
- Design: new storeys must go on the main part of the house, use similar materials and keep the same roof pitch.
- Prior approval is required. The council still judges the design, the effect on neighbours’ light and privacy, and how it looks in the street.
These rights should not be confused with the similar-sounding 2020 rights for adding new flats on top of blocks of flats and commercial buildings. Those are for developers, not for extending your own home.
For the full official rules, see the Planning Portal’s guide to adding storeys and the government’s key facts on building upwards.
What our own test applications showed
When the rights were introduced, we tested them straight away. We submitted applications to add storeys to mid-terraced houses in Newham, Lambeth and Hounslow. All three were refused.
Planners in Hackney and Camden were more open to the idea when we discussed it with them. So whether adding storeys can work depends heavily on your council and your street.
Our advice: for most London houses, a mansard or dormer loft conversion is a far more reliable way to add a floor. If you want to explore adding storeys, talk to us first. We can tell you what we learned from our applications and whether your house is likely to qualify.
Other approvals your loft conversion needs
Lawful Development Certificate
Even if your loft is Permitted Development, a Lawful Development Certificate from your council confirms it in writing. It costs £274 in England and usually takes around eight weeks. It is optional, but we recommend it. Buyers’ solicitors will ask for proof when you sell, and it protects you if a neighbour complains.
Building Regulations approval
Planning permission is about how the loft looks and affects the area. Building Regulations are about whether it is safe and built properly, and every loft conversion needs them, including Permitted Development ones. They cover:
- the structure, including new floor joists and steel beams
- fire safety and a protected escape route down the stairs
- the staircase and headroom
- insulation, ventilation and sound insulation
A building control inspector checks the work in stages and issues a completion certificate at the end. Without it, you may have problems selling or remortgaging. See our guide to Building Regulations and fire safety.
Party wall agreements
If you share a wall with a neighbour, the Party Wall etc. Act 1996 almost always applies, because loft steel beams are usually set into the party wall. You must serve notice at least two months before that work starts. Your neighbour can agree, or appoint a surveyor to agree a party wall award. The Act doesn’t let them block the loft, but late notice can delay your start. See our party wall guide.
Planning a loft conversion? We can check your house, tell you which planning route applies, and handle the applications for you.
Loft conversion planning permission: frequently asked questions
How long does loft conversion planning permission take?
A householder planning application usually takes eight weeks from when the council registers it. A Lawful Development Certificate usually takes a similar time. Allow extra time for drawings beforehand, and for any changes the council asks for.
How much does loft conversion planning permission cost?
In England, from April 2026, a householder planning application costs £548 and a Lawful Development Certificate costs £274. Architect drawings, a structural engineer and any party wall surveyor are extra.
What happens if I build a loft without planning permission when I needed it?
The council can issue an enforcement notice requiring you to change or remove the work, at your own cost. You can apply for retrospective permission, but there is no guarantee it will be granted, and it can cause problems when you sell.
Do I need planning permission for a loft conversion in a terraced house?
Usually not, if it is a rear dormer or rooflight conversion within 40 cubic metres and the house is not in a conservation area. A mansard or any front-facing change will need permission.
Can my neighbours stop my loft conversion?
If your loft is Permitted Development, neighbours have no say in the planning decision. If you apply for planning permission, they can comment, and the council will take their views into account. Under the Party Wall Act they can’t stop the work, but they can appoint a surveyor.
Do I need planning permission for a loft conversion in a flat?
Yes. Flats and maisonettes have no Permitted Development rights for roof extensions, so any change to the roof needs a full planning application. You will usually need the freeholder’s permission too. See our guide to loft conversions in flats.
Get loft conversion planning permission right first time
The planning route decides your design, your timeline and your costs, so it is worth getting it right before anything else. We can visit, check your house against the rules and your council’s policies, and tell you whether you need loft conversion planning permission, with no obligation.
