If you’re running out of space, building an extension is much less disruptive than moving house. One stumbling block for many is planning permission – namely the rules of what you can and can’t build.You also need to brush up on the Party Wall Act and the neighbourhood consultation scheme. These pieces of legislation regulate construction activities affecting neighbouring properties to maintain harmonious relationships and avoid legal disputes between property owners.

The below guidance doesn’t apply to listed buildings, which are subject to stricter planning rules. The rules are also different if you live in an area of outstanding natural beauty. Where appropriate, consult with your local planning office.

The Original House Rule

In development guidelines, you’ll often see the term “original house”. This refers to the property as it stood on the 1st of July 1948 or on the date it was built after.

So, if the property already has an extension, you have to factor this into any future development. For example, one planning stipulation is:

You need planning permission if more than half the land around the “original house” is to be covered.

So, in this context, you need to exclude any previous developments from your calculations.

Types Of Planning Permission

There are two main types of planning applications: full planning permission and outline planning permission.

• Full planning permission is when detailed plans are submitted for all aspects of the development, which provides certainty for construction; it’s suitable for complex projects with defined details.
• Outline planning permission is preliminary approval based on concepts; detailed designs aren’t required at this stage, and this allows flexibility in design exploration, with reserved matters needing approval later.

Do I Need To Submit A Planning Application For An Extension?

Understanding where you require planning permission for an extension isn’t black and white. Not all extensions are built to the same specification, and the requirements differ depending on whether it’s a side, rear, front, or double- or single-storey extension.

All extensions

You need planning permission if any of the following are applicable to your extension:

• It’s forward of the front or side of the “original house” that faces onto a highway
• Over half the land around the “original house” will be covered
• Materials used aren’t similar to the existing house (except conservatories)
• The building will be higher than the highest point of the house
• Eaves and ridge height are higher than the existing house (single- and two-storey)
• Eaves height is more than three metres (if within two metres of the boundary)
• The building includes the addition of verandas and balconies.

Side extension

You need planning permission if any of the following are applicable to your side extension:

• Higher than four metres
• More than one storey
• Wider than half the width of the “original house”.

Single-storey rear extension

You need planning permission if any of the following are applicable to your single-storey rear extension:

• Higher than four metres
• A semi-detached house that extends beyond the rear of the “original house” by more than six metres
• A detached house that extends beyond the rear of the “original house” by more than eight metres.

Two-storey rear extension

You need planning permission if any of the following are applicable to your two-storey rear extension:

• Extends more than three metres beyond the rear of the “original house”
• Within seven metres of the boundary opposite rear wall
• Pitch of the roof pitch doesn’t match the existing property
• Side-facing windows are not obscure-glazed and can open.

Understanding The Party Wall Act

The Party Wall Act 1996 exists to prevent and mitigate disputes between neighbours. The law requires that you give notice to a neighbour if you are:

• Building near the boundary of a neighbour
• Working on a wall that separates your property from a neighbour’s.

It’s strongly recommended that you familiarise yourself with the Party Wall Act 1996 here.

The Neighbour Consultation Scheme Explained

If you’re planning to build a large single-storey rear extension, you’ll need to contact your local planning authority through a Prior Approval application.

Important! Your extension is classed as “larger” if it’s between 4–8 metres for a detached house or 3–6 metres for a semi-detached house.

Neighbours can object to your home extension, which can be investigated by your local council.

It allows neighbours to be informed about larger extensions, and it gives them an opportunity to express concerns or object to the development.

Generally, if the extension falls within the permitted guidelines, no action will be taken that results in you needing to apply for planning permission or remove the extension. However, the power rests firmly with the local authority to assess whether the project’s impact on surrounding properties is acceptable.

After the application has been submitted, the determination period lasts for 42 days.

Lawful Development Certificate (LDC)

While your permitted development rights may mean that you can proceed with your extension without planning permission, if you’re concerned about neighbour disputes, you can apply to your local planning authority to obtain a lawful development certificate.

It’s not a legal requirement to obtain one, but it serves as proof that your development is lawful, meaning you can carry out your project with confidence.

The costs to obtain a certificate vary depending on your country:

• England – £103
• Scotland – £101
• Wales – £85

Important! The fee is double if you’re applying in retrospect, that is, for a construction that has already taken place.

If you decide to use your permitted development rights (without needing planning permission), you may jeopardise your project. If your extension deviates from the rules, you risk being fined or forced to demolish the work.

It’s also likely that you’ll need a lawful development certificate at some point, anyway. If you decide to sell your property, in the absence of legal documentation, many buyers will be dubious when purchasing a property that’s been extended.

The 45-Degree Rule Explained

Imagine you’re looking at your floor plans from a bird’s-eye view. Using the midpoint of your neighbour’s nearest window, draw a 45-degree angle away from the window.

If your extension is within this line, it’s deemed acceptable; if it intercepts, then it’s likely that overshadowing will occur (loss of daylight).

The “right to light” gives a landowner the right to receive light through defined apertures in buildings on their own land which neighbouring properties have to take into consideration.

Planning Permission For Extensions – Bottom Line

After assessing the guidelines within, you should have a stronger idea about whether you need planning permission for your extension.

Even if your extension falls under your permitted development rights, and if you proceed to build without planning permission, applying for a lawful development certificate will give you peace of mind before commencing construction.

For specialist projects or if you need any further advice, contact your local planning authority or a planning consultant. If you live in Wales, Planning Aid provides free expert advice.

Planning Permission FAQs

Are building regulations the same in England and Scotland?

Building regulations in England and Wales are set out in the Building Act 1984, and those in Scotland are set out in the Building Act 2003 (Scotland).

So if you’re a developer planning a project spanning multiple locations across the UK, you’ll need to factor in localised regulations. For example, in Scotland, sprinkler installations are mandatory in flatted accommodation, larger multi-occupancy dwellings, and places that deliver care.

What is the difference between building regulations and planning permission?

Building regulations determine the minimum standard for the design and construction of buildings. The regulations are primarily concerned with structural stability, safety, and technical compliance.

Planning permission relates more to the external appearance of the building and ensures any landscaping considerations are in keeping with the local environment to deter inappropriate developments.

What is the 4-year rule for planning permission in the UK?

The four-year rule (which applies to dwellings under class C3) states that local authorities can’t serve enforcement notices for unauthorised developments four years after the commencement of the development.

Despite the rule helping many homeowners gain retrospective planning permission, the four-year rule is set to be phased out in 2023 – thereby closing the loophole.

What is retrospective planning permission?

Retrospective planning permission is sought after building work has already been completed when the necessary permission hasn’t already been obtained. A council may request that you apply for this, for example, if you have constructed a house extension with different materials than what was originally granted.