Building an extension can be a fantastic way to add extra space and augment the appeal and value of a semi-detached home. Numerous homeowners have unused and unloved side returns that present a perfect opportunity to extend.

For many of the clients we speak with, planning permission is a concern—not because there is any particular reason to doubt that a planned extension would be approved, but because of the time, red tape and costs involved.

The good news is that a well-managed extension designed and constructed in accordance with permitted development rules may not need any formal consent, although compliance with building regulations remains crucial, and Pinnacle Works can certainly assist with this.

How Do Permitted Development Rules Apply to Semi-Detached Homes?

It’s always worth speaking with an experienced building firm since the permitted development rules can be complex and are often technically worded. This makes it more likely that some homeowners will assume they can proceed without realising that their extension plans breach the restrictions—such as being over the maximum height.

The thresholds for completing an extension under permitted development will also depend on whether you’d like to extend to the side, rear, or front of your home and whether the completed extension will incorporate one or two storeys.

While not an exhaustive list, the below summary gives you a good indication as to the maximum extension sizes for a semi-detached home:

• Up to half of the original land included in the deeds can be converted into buildings or extensions, which includes outbuildings such as sheds.
• Permitted development does not apply to any property extension work that involves building forward from the front of the main house.
• Side return extensions can be up to four metres in height and cannot be any more than half the width of the original house.
• If the semi-detached extension reaches within two metres of the boundary, the maximum height reduces to three metres.
• Single-storey extensions cannot extend past the original back wall by more than three metres without consent, with a maximum extension height of four metres in all scenarios.
• Two-storey extensions are allowed under permitted development rules as long as they don’t reach more than three metres beyond the original rear wall, get within seven metres of any boundary, and have a roof pitch that is consistent with the existing house.

Additional rules apply: Windows added to a side extension should be non-opening and obscured for privacy unless the window is over 1.7 metres from the floor. Building materials should be as close as those used within the existing home, and any installation of a balcony or veranda is not permitted.

When a Planning Permission-Approved Semi-Detached House Extension May Be Preferable

The outline of the permitted development rights above showcases how it is perfectly possible to construct a bespoke extension to expand your semi-detached home without needing to go through a planning application process.

However, there are circumstances where you might decide that, to achieve your dream home, you would be better off seeking consent or find that the nature of your home means that permitted development rules don’t apply.

Properties in a conservation area and those with historical listing status always require full planning permission. The likelihood of approval will depend on myriad factors, such as the impact of the extension on the aesthetic appearance of the home and whether this can be designed in sympathy with the character and style of the existing dwelling.

Other homeowners want to transform the size and usage of their property and wouldn’t be satisfied with the size limitations imposed by the permitted development criteria. This can mean that planning permission is worth applying for to ensure your extension fulfils all your objectives.

If you’d like to visualise what a semi-detached extension might look like either way, you are welcome to contact the Pinnacle Works team. We can mock up a digital representation of your planned extension or show you previous projects of a similar size to give you a better idea of which options are best suited to you.

The Importance of Building Regulations Compliance When Extending Your Home

Regardless of whether you opt for a semi-detached extension under permitted development rules or go for a more significant build and require consent, the work on your property must be compliant with the UK building regulations—a set of legal requirements that ensure structures are safe and built to the necessary standards.

For example, the regulations cover areas like fire protection and evacuation, energy efficiency, and gas safety, designed to ensure that every new home or modification is suitable for habitation and has the necessary structural integrity.

The easiest way for homeowners to be satisfied that their extension is 100% compliant is to work with a reputable, established contractor. We can verify compliance and provide certifications that confirm the extension has been assessed and properly constructed. Retaining that certificate is important, especially if you ever intend to sell your home.

Obtaining a Lawful Development Certificate for Your Extension

It might be worthwhile applying for a document called a Lawful Development Certificate (LDC), which attests that the extension was allowed under permitted development rules and did not require planning consent from the local authority.

There is a fee for an LDC, and you’ll need to submit plans and drawings explaining why you think the extension is compliant, but this offers the peace of mind that you have official documentation confirming that your extension is lawful.

Finally, we can also consult with homeowners who want to extend their semi-detached home with the work expected to impact a shared wall with a neighbour. In this case, the Party Wall Act 1996 applies, and although the process is typically straightforward, you’ll need to ensure your neighbour has no objections before we start work.

Should you need further information about anything discussed in this guide, from planning permission to permitted development, obtaining a party wall agreement, or adhering to building regulations, you can contact the knowledgeable extension team at Pinnacle Works to arrange a good time to talk.