Three Common Mistakes People Make When Planning Their House Extension

And how to avoid them

1. Assuming you don’t need permission

Many homeowners believe that an extension is automatically permitted without full planning permission and proceed on that assumption. But the reality is more nuanced.

Facts & context:

• In England, the rules known as “Permitted Development Rights” let homeowners extend their houses without full planning permission if the work meets specific criteria.
• For example, a single-storey rear extension may be covered under Permitted Development provided it stays within defined size limits and other conditions.
• However, Permitted Development rights do not apply in all cases: they may be removed for listed buildings, properties in conservation areas, flats/maisonettes, or where an Article 4 direction has been issued.
• Builders report that verifying eligibility for Permitted Development (or checking whether a full planning application is needed) prevents enforcement or costly redesigns later.

Builder’s Tip:

Always confirm with your local planning authority or experienced builder what is allowed. What might be permitted on one street may not be on the next if local restrictions apply. If in any doubt, applying for a Lawful Development Certificate (LDC) can give you formal assurance that your scheme meets the permitted rights.

2. Forgetting to notify neighbours (Party Wall & boundary matters)

Even when planning and building permissions are handled, overlooking obligations to neighbours and shared boundaries often causes delay and dispute.

Facts & context:

• Under the Party Wall etc. Act 1996, if you carry out work affecting a shared wall, boundary, or foundations close to a neighbouring building, you must serve notice and possibly obtain a formal agreement.
• The notice period is important: a “Party Structure Notice” usually requires at least two months’ notice; an “Adjacent Excavation Notice” requires at least one month.
• Failure to serve the correct notice or getting it wrong might lead to legal disputes, delays or the need to halt work.

Builder’s Tip:

Give neighbours early notice of your intentions, preferably in writing, and use the correct Notice under the Party Wall Act. If you’re working on a semi-detached, terraced or boundary shared site then treat the Party Wall process as part of the early design stage, not an afterthought.

3. Underestimating timelines and materials

Many projects fail or overrun because the build-up to the on-site work is under-planned: design, approvals, lead times, procurement and trades all take time.

Facts & context:

• Even if planning permission is granted, the design and building regulations work, procurement of bespoke materials (windows, glazing, structural steel) and scheduling of trades contribute heavily to overall timeline. Industry articles highlight how lead times for key materials are extending.
• Some sources show that single-storey extensions often take 4-6 months on site, but when you factor in pre-construction phases you may be looking at 9-12 months overall.
• Not planning for contingency or material lead times can lead to budget increases or delayed hand-over.

Builder’s Tip:

Start your project planning early. Budget at least three to six months before your build day for design development, planning/PD checks, building regulations submission and materials lead-in. Factor contingency into your schedule and budget to allow for things like delays in manufacturing or surveyor availability.

Why these matter & how Kingdom addresses them

At Kingdom we see the difference between smooth, well-managed builds and those that struggle often lies in attention to these early stages. By embedding checks on permission, neighbour notifications and realistic timelines into our process we minimise risk and maintain quality, budget and client satisfaction.

When you choose Kingdom you’re choosing a partner that:

• reviews planning status and Permitted Development eligibility for your site,
• manages neighbour/party wall obligations from day one,
• builds realistic project schedules including pre-build, build and post-build phases, and
• keeps you updated, so you always know what step comes next.

✉️ Want to avoid costly delays or disputes? From confirming planning requirements to managing neighbour notices and timelines, Kingdom handles the details that keep your project running smoothly. Get in touch and we’ll help you start your extension the right way, with clarity, compliance, and confidence.