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.

Many modest house extensions do not require full planning permission thanks to Permitted Development (PD) rights. Under PD rules, you can often build a small rear or side extension up to certain size limits without a planning application (for example, a single-storey rear addition that doesn’t extend too far out and isn’t too high)​. However, there are important caveats – if your proposed extension is large, two-storey, facing a highway, or your home is in a conservation area or listed, you will likely need to apply for planning permission. It’s best to check with your local planning authority or an architect: they can confirm if your plans fall within PD limits or if you must seek permission​. Regardless of planning, building regulations approval will always be needed for an extension to ensure it’s structurally sound and safe.

Extension costs depend on the size and spec, but a good rule of thumb is to budget about £1,800 – £3,000 per square metre for a standard extension build​. For example, a 20 m² extension (around a modest single-room addition) might cost roughly £40–55k all-in​. Simpler finishes or builds outside London may be toward the lower end, while high-end kitchens or bathrooms in the extension push costs higher. Don’t forget to factor in design fees, planning or building control fees, and any VAT on labor/materials. Also consider that unexpected issues (like moving drains or addressing structural quirks) can add to the budget, so include a contingency (often ~10-15%). By getting detailed quotes from builders, you can get a more precise idea based on your specific plans.

Usually no – most loft conversions don’t require planning permission. Converting an attic into living space is generally allowed under Permitted Development as long as you don’t significantly alter the roof shape or exceed certain volume limits​. For instance, adding roof windows (Velux-style skylights) or a modest rear dormer often falls within PD rights. Exceptions are if your property is in a conservation area or is a listed building, or if the conversion involves extending beyond the existing roof height or adding a large dormer on the front elevation (facing the highway)​. In those cases, you would need to apply for planning permission. Even when planning isn’t needed, you must comply with building regulations for the loft (for insulation, floor strength, fire safety, staircase design, etc.), and your plans may need approval by Building Control.

The cost of a loft conversion can range quite a bit based on size and complexity. A basic loft conversion of ~20 m² (just adding a room in the existing loft space) might start around £20,000 to £30,000, whereas a larger or luxury conversion (for example, adding a dormer extension or an en-suite bathroom) could be £50,000 or more​. Costs include reinforcing the floor, adding insulation, skylights or dormer construction, stairs, electrics, and finishes. Despite the expense, loft conversions are popular because they tend to boost your home’s value significantly – often adding an estimated 20%–25% to the property’s value when done well​. Essentially, converting your loft can be a cost-effective way to gain an extra bedroom or usable space compared to moving house, and it usually pays off by increasing resale value​. Just be sure to get quotes from experienced loft specialists to budget correctly.

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.