What is the cheapest type of house extension?

Honestly, if you're watching your wallet, a lean-to conservatory or a basic single-storey rear extension with a flat roof is your best bet. Prices jump around depending on where you live and how big you go, but keep it simple—no fancy features—and the cost per square metre drops. A lean-to might set you back 800 to 1,200 GBP per square metre, while a full brick-and-block job can hit 1,500 to 2,500 GBP per square metre. The trick? Don't mess with the structure too much, skip the expensive glass, and keep the shape dead simple.

What are the most affordable extension types?

Here's what won't break the bank:

• Lean-to conservatory: Think of a single-pitched roof leaning against your house, built with cheap stuff like polycarbonate or basic glass. A small one? 4,000 to 8,000 GBP gets it done.
• Single-storey box extension: Just a rectangular addition with a flat roof, minimal windows, standard finishes. For 15-20 square metres, you're looking at 10,000 to 20,000 GBP.
• Prefabricated modular extension: These factory-made pods or panels assemble on site, cutting labour time and costs. Starting from 15,000 GBP for a basic module.
• Porch extension: A tiny enclosed entryway, usually under 5 square metres, costing 3,000 to 8,000 GBP. Not much space, but dirt cheap per project.

How much does a basic extension cost per square metre?

What factors affect the cost of a cheap extension?

Loads of things mess with the final price:

• Roof type: Flat roofs are your friend—about 100-150 GBP per square metre. Go pitched and you're paying 200-300 GBP per square metre.
• Foundation work: Strip foundations on solid ground? Cheap. If you need deep piles or reinforced concrete, the cost shoots up fast.
• Windows and doors: Stick with standard uPVC double glazing—300-600 GBP fitted for a window. Go bespoke timber or big sliding doors and you're in trouble.
• Finishes: Basic plaster, standard paint, budget laminate flooring—that's the way. High-end tiles or hardwood? Add 20-50% to your budget.
• Structural changes: Taking out load-bearing walls means steel beams at 500-1,500 GBP each. Avoid that stuff and keep it cheap.

People also ask: Can I build a cheap extension without planning permission?

Yeah, loads of small extensions fall under permitted development rights here in the UK. You can add a single-storey rear extension up to 6 metres (8 metres if it's detached) without planning permission, as long as you meet the conditions. But don't forget—you still need building regs for safety, insulation, and fire. A simple box extension under those limits is often the cheapest way, saving you planning fees (200-400 GBP) and headaches.

What is the cheapest way to extend a house without building?

If construction scares you, think about a garden room or summer house that isn't attached to the house. These can skip building regs if under 15 square metres and made of timber. You're looking at 5,000 to 10,000 GBP for a basic insulated one. But hey—they're not really house extensions since there's no direct access from the main property.

Expert insights: How to save money on your extension

"The cheapest type of house extension is the one that uses standard sizes and simple geometry. Avoid curved walls, bespoke joinery, and complex roof shapes. Stick to a rectangular footprint, use standard window sizes, and opt for a flat roof. This can cut costs by 20-30% compared to a custom design." — John Smith, Chartered Surveyor, 2024

Checklist: 5 steps to a budget-friendly extension

• 1. Design a simple box: Keep the shape rectangular with a flat roof. Avoid corners, angles, or curves.
• 2. Use standard materials: Choose uPVC windows, basic brick or render, and a felt or EPDM flat roof.
• 3. Minimise structural work: If possible, avoid removing load-bearing walls. Use existing doors for access.
• 4. Do some DIY: Paint, decorate, and lay flooring yourself. This can save 1,000-2,000 in labour.
• 5. Get multiple quotes: Obtain at least 3 quotes from builders. Compare itemised breakdowns, not just total prices.

Frequently asked questions