In the UK, building a new house almost always requires both planning permission and building regulations approval. Planning permission must be obtained from your local council before construction if you’re putting up a new dwelling or significantly altering a site’s use or appearance​. Building regulations approval (sometimes called a building warrant or building control) is also mandatory; this ensures the new structure meets safety and quality standards for structure, fire, insulation, etc.​ In short, you’ll need to submit a planning application for the new build and get it approved, then have a building control body sign off on your plans and inspect the work. It’s wise to consult with an architect or your local planning authority early on to understand all required permits.

The cost of a new build can vary widely depending on size, design, and location. A rough benchmark for a detached house is around £1,800 – £3,000 per square metre of construction​ (excluding the land purchase). This means a 100 m² new home might cost on the order of £180,000 to £300,000 to construct, though final totals depend on your specifications. High-end materials or custom features will push costs toward the upper end of the range​. Keep in mind this is just construction – you’ll also need to budget for professional fees (architect, engineers), planning application fees, and site prep. Building a house is a significant investment, so getting detailed quotes and perhaps a fixed-price contract from a reputable builder is important for accurate budgeting.

In most cases, yes – you will need planning permission to knock down an existing house and build a new one in its place, because it’s treated as new construction. There is a relatively new exception: as of 2020, the government introduced a permitted development right (often called Class ZA) allowing certain vacant buildings to be demolished and rebuilt as homes without full planning permission​. However, this applies only in limited circumstances (for example, the existing building must have been vacant and not too large), and you’d still need to get prior approval from the local authority for the demolition and design. For the typical homeowner looking to replace their own occupied house, you should expect to go through the normal planning application process for the new build. Additionally, you must notify your local council’s building control before any demolition (per Section 80 of the Building Act) to ensure safe practices. It’s wise to consult your council and get professional advice so that both the teardown and the new build meet all legal requirements.

Demolishing and rebuilding is a major project, usually costing on the order of hundreds of thousands of pounds. The exact cost will depend on the size of the house and the design/quality of the new build. For example, one estimate for demolishing and rebuilding an average 3-bedroom house is around £180,000 to £250,000 in total​. This typically includes site surveys, demolition work (including clearing debris and possibly hazardous materials like asbestos), and constructing the new house from foundations up​. Given the high cost, homeowners often ask if it’s worth it. Rebuilding can be very worthwhile if the existing structure is in poor condition or can’t be easily extended to meet your needs – it allows you to create a brand-new, custom-designed home tailored to your preferences. In fact, many self-build enthusiasts choose this route because the long-term benefits (a home built to modern standards and exactly as desired) outweigh the drawbacks of cost and complexity​. That said, if your current house only needs some updating or adding space, consider alternatives like extensive renovations or a large extension​, which might be cheaper and less disruptive. Rebuilding is a big decision, so weigh the financial and practical factors carefully and consult professionals to explore what option makes the most sense for your situation.