8 Smart Design Hacks to Keep Your Home Extension Costs Under Control (Without Compromising on Style)

Hi, I’m Frazer, Design Director at Plan It UK. We design hundreds of home extensions every year, and one of the questions we hear most often is:

“How can I get the look I want without blowing the budget?”

The good news? If you plan smart from the design stage, you can still achieve your dream space while keeping costs in check. Here are my top 8 hacks to help you do exactly that.

1. Large Panes of Glass – Done the Smart Way

Big glazing panels look incredible, bring in loads of natural light, and can even reduce brick and labour costs. The trick is in the sizing.

• Opt for smaller, more manageable sections that can be installed by hand rather than needing an expensive crane.

• Consider adding small sections of brickwork in carefully chosen spots — this allows us to hide steel columns inside and reduce the need for heavy-duty steel beams (and their plant hire costs).

2. Open-Plan Living Without the Price Tag

Taking out the entire back wall often means a lot of steel — and a lot of cost. But there’s a clever workaround.

• If you’re happy to have your steel columns sit about 40cm into the room, you can often avoid needing a costly steel ground beam.

• These columns can be neatly boxed in or hidden inside tall kitchen larder units, making them disappear into the design.

3. Bulkheads – Don’t Fear the Drop

Most people want steel beams hidden flush in the ceiling, but lowering them to create a bulkhead can be a big win.

• It’s cheaper and quicker to install.

• You can integrate bulkheads into the design — they’re perfect for zoning spaces, adding LED lighting, or creating a natural spot for curtain rails.

4. Soil Testing Saves Surprises

Before you start digging, soil testing tells you exactly how deep your foundations will need to go.

• Without it, your builder might dig 1 metre, then wait for Building Control to say “go deeper” — and that extra digging can blow your budget.

• With a soil test, you get accurate costs upfront and avoid delays.

5. Blockwork Over Brickwork

If you don’t need exposed brick as a feature, blockwork is a faster, cheaper option.

• Blocks are larger, so walls go up quicker, meaning the roof can go on sooner and trades can start inside earlier.

• You also skip the time-consuming process of pointing up every single brick.

6. Reuse What You’ve Got

Where possible, keep as much of the existing structure as you can.

• Less demolition means less propping, which keeps things moving faster and reduces labour costs.

• Sometimes it’s actually cheaper to extend out by another metre than to knock down internal walls — if planning rules allow it.

7. Plan Your Finishes From the Start

Builders usually price for the shell of the extension, not your final finishes.

• Having a full list of interior finishes ready from the outset helps you understand the true project cost.

• This avoids those “oh, we didn’t budget for that” moments later on.

8. Right-Size Your Skylights

Bigger skylights need bigger structural supports — which means more money.

• Think about where the sunlight will be at different times of day and design accordingly.

• A couple of well-placed smaller skylights, combined with a light-reflective paint colour, can bounce daylight beautifully through your home.

Final Thought:
Great design isn’t just about making your home look amazing — it’s about making it work smarter. By thinking ahead, tweaking certain details, and understanding how small design choices affect costs, you can create a stunning extension without overspending.

If you’re planning a home extension and want to explore clever, cost-effective design ideas, get in touch with us at Plan It UK — we’d love to help.