House Extension Granville: A 2026 Planning Guide for Homeowners

If you own a period terrace, Victorian semi, or a 1970s detached house on or around a Granville Road, Granville Street or Granville Avenue (street names that crop up in dozens of towns across England and Wales), you have almost certainly wondered how far you can extend before you need to involve the council. This guide sets out, in plain English, exactly what permitted development rights allow, when you need full planning permission, and how the process actually works in 2026 for a typical house extension Granville project, whether that is a single-storey rear kitchen extension, a loft conversion, or an upward extension adding a whole new storey.

Streets like these tend to have a mix of housing stock: Victorian and Edwardian terraces with narrow rear gardens, inter-war semis with generous side returns, and pockets of post-war detached housing. Each type has slightly different extension potential, and the rules change again if your property sits within a conservation area. We will walk through all of it.

Why Location on the Street Matters as Much as the Rules

Before you sketch a single wall, establish two things about your specific plot:

1. Is your house on article 2(3) land? This covers conservation areas, National Parks, Areas of Outstanding Natural Beauty, the Broads, and World Heritage Sites. Many older residential streets, including plenty of "Granville" style Victorian terraces, sit inside a designated conservation area even if the rest of the town does not. Check your council's conservation area map before assuming anything is permitted development.
2. What is the "original house"? For planning purposes, this means the house as it was built, or as it stood on 1 July 1948 if it was built before that date. If a previous owner already added a rear extension or loft dormer, your remaining permitted development allowance is measured against that original footprint, not the current one. Many homeowners discover their PD rights have already been partly or fully used up by a previous extension.

Both of these checks take five minutes on your council's website and can save you weeks of wasted design work later.

Permitted Development: What You Can Build Without Planning Permission

Single-Storey Rear Extensions

This is the most common route for a house extension Granville project, typically a kitchen-diner or family room addition.

Under standard permitted development rules, a single-storey rear extension must not:

• Extend beyond the rear wall of the original house by more than 4 metres for a detached house, or 3 metres for a semi-detached or terraced house
• Exceed 4 metres in height

Measurement runs from the base of the original rear wall to the outer face of the new extension wall, excluding guttering overhang. Get this measurement wrong and you risk a retrospective planning application, or worse, an enforcement notice.

The Larger Extension Route (Neighbour Consultation Scheme)

If you want to go bigger, there is a well-established larger home extension allowance, provided your house is not on article 2(3) land and not on a site of special scientific interest:

• Up to 8 metres beyond the original rear wall for a detached house
• Up to 6 metres for any other house type
• Still capped at 4 metres in height

Anything beyond the standard limits (over 4m for detached, over 3m for others) triggers the neighbour consultation scheme. In practice this means:

1. You submit a written notice to the council describing the extension.
2. The council notifies your adjoining neighbours.
3. Neighbours have 21 days to raise objections.
4. If objections are received, the council must decide whether the extension's impact on neighbouring amenity is acceptable.
5. Work cannot legally start until the council confirms no prior approval is needed, grants approval, or 42 days pass with no decision issued.

Budget for this timeline in your build schedule. Contractors are frequently booked and rebooked because homeowners assume they can start digging foundations the week after submitting notice.

What You Cannot Do Under Class A, Regardless of Size

No permitted development rear or side extension can go beyond a wall that forms the principal elevation of the house, and the same restriction applies to a side elevation that fronts a highway. This is why front extensions almost always require a full planning application; the "principal elevation" rule effectively blocks them under permitted development in nearly every case. On corner plots, where a side wall faces a road, there is an additional restriction on side extensions too. If your Granville-area property sits on a corner, get this checked early; corner plots are one of the most common sources of enforcement action because homeowners assume side-facing walls are treated like any other side wall.

Loft Conversions: What Class B Actually Allows

A loft conversion is often the cheapest way to add a bedroom or home office without touching the footprint of the house, but there are two restrictions worth knowing before you commission drawings:

• Balconies are excluded. Permitted development rights for roof extensions do not cover a roof balcony or terrace. If your loft conversion design includes a Juliet balcony or a walk-out terrace, that element needs a planning application even if the rest of the loft works fits within permitted development.
• Article 2(3) land blocks the whole thing. In a conservation area, National Park, AONB or World Heritage Site, dormer loft conversions and roof enlargements are not permitted development at all. Every loft dormer on these streets needs a full planning application, regardless of size.

This second point catches out a surprising number of homeowners on older residential roads, because loft conversions on similar-looking houses two streets away might have gone ahead without planning permission simply because that street falls outside the conservation area boundary.

Adding a Whole New Storey: The Upward Extension Route

Since 2020, permitted development has allowed some houses to add entire additional storeys rather than just a rear or roof extension. This is a genuinely useful option for a detached, semi-detached or terraced house that has run out of garden to build into.

Key conditions:

• The house must have been built between 1 July 1948 and 28 October 2018. Anything older or newer does not qualify.
• You can add up to 2 additional storeys if the house already has 2 or more storeys, or 1 additional storey if it is currently single-storey.
• The new storeys must sit on the principal part of the house, not on a side or rear wing.
• The finished building must not exceed 18 metres in total height.
• Each new storey must add no more than 3.5 metres to the height of the house.
• For semis and terraces, the new roof height must not exceed the neighbouring property's roofline by more than 3.5 metres.

Crucially, this route is never automatic. Even where a house meets every condition above, you must apply for prior approval from the local planning authority before starting work. The council will assess matters such as external appearance, the impact on neighbouring amenity, and effects on natural light to adjoining properties. And like loft dormers, this route is completely unavailable on article 2(3) land or for listed buildings, so if your street is in a conservation area, upward extension under permitted development is off the table entirely; you would need a full planning application instead.

Conservation Areas: The Extra Layer of Restriction

A significant proportion of period housing on older residential roads sits inside a conservation area, and this changes the rules substantially. If your street is affected, Class A permitted development rights are cut back in three specific ways:

1. No exterior cladding as permitted development. Rendering, pebble dash, stone cladding, timber or plastic cladding, and tiling to the exterior are all excluded. If your extension design includes a render finish to match a modern kitchen extension, that finish itself may need consent even if the extension's size is otherwise compliant.
2. No side extensions. Any extension beyond a side wall is not permitted development in a conservation area, full stop, regardless of how modest it is.
3. No two-storey rear extensions. A rear extension of more than a single storey is not permitted development. Anything beyond single-storey at the rear needs a full application.

Combine this with the loft conversion restriction above and the picture becomes clear: conservation area properties have meaningfully reduced permitted development rights across the board. If you are house-hunting with extension plans in mind, checking conservation area status before you make an offer is not optional, it is essential due diligence.

The Council Process, Step by Step

Whether you are relying on permitted development or need a full application, the practical process looks like this:

1. Pre-application check. Contact the council's planning department (many offer a lawful development certificate service) to confirm whether your proposal is permitted development. This typically costs a modest fee and takes 4 to 8 weeks, but it gives you a legally binding answer rather than a guess.
2. Design and drawings. Even PD extensions benefit from proper measured drawings, both for building control purposes and to avoid disputes with neighbours or future buyers.
3. Building regulations approval. This is separate from planning permission and applies regardless of PD status. Structural work, insulation, fire safety and drainage all need sign-off. Budget 4 to 6 weeks for building control approval to run alongside your build.
4. Full planning application (if required). Standard determination periods are 8 weeks for householder applications, extending to 13 weeks for larger or more complex schemes. In practice, expect the council to come back with clarification requests that add several weeks.
5. Neighbour consultation scheme (larger single-storey rear extensions only). As above, budget up to 42 days beyond your notice submission.
6. Party wall matters. If your extension sits on or near a boundary shared with a neighbour, you may need a party wall agreement under separate legislation. This runs alongside, not instead of, the planning process.

Typical Costs and Timescales in 2026

Costs vary by region and finish specification, but as a rough guide for 2026:

• Single-storey rear extension (standard PD size): £1,800 to £2,800 per square metre for a good quality finish, with a typical 20 to 25 square metre kitchen extension costing £45,000 to £70,000 all-in.
• Larger rear extension via neighbour consultation: costs scale similarly per square metre, but add £500 to £1,500 in council fees and consultant time for the notification process itself.
• Loft conversion: £45,000 to £65,000 for a dormer conversion with an en-suite, more if a planning application is required due to conservation area status or a balcony feature.
• Upward extension (additional storey): significantly more involved structurally, often £80,000 upwards, reflecting the need for foundation checks, structural engineering, and prior approval fees.
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