If you’re looking to maximise your home’s potential without moving, combining a loft conversion with a rear extension could be your smartest investment yet. In this guide, we’ll explain how to combine loft and rear extensions effectively, ensuring a seamless transformation that’s cost-efficient, fully compliant, and tailored to your lifestyle. At KT5 Construction, we’ve helped London and Surrey homeowners unlock space, value and functionality—often saving them thousands through early-stage planning and practical solutions.

Why Combine Loft and Rear Extensions?

Merging a loft conversion with a rear extension means you’re expanding both vertically and horizontally. It’s a powerful way to:

• • Add 2–4 new functional rooms, such as a master suite, office, utility room, or open-plan kitchen-diner

  • Future-proof your home for growing families or work-from-home needs

  • Improve energy efficiency with unified insulation and glazing upgrades

  • Avoid the repeat costs of phased projects by building everything in one go

KT5 Cost-Saving Tip: By coordinating both projects at once, KT5 can reduce duplicated costs in scaffolding, structural works, design fees, and project management—often saving clients up to 20%.

Key Considerations Before You Begin

1. Planning Permission & Permitted Development

Many homes in London fall under permitted development rights, which may allow both types of extensions without full planning permission. However, combining them can push the boundaries, so it’s essential to:

• • Check volume allowances (e.g., 40m3 for terraced homes, 50m3 for semis/detached)

  • Ensure rear extension depth and height fall within guidelines

  • Review restrictions if you’re in a conservation area

KT5 Expertise: We help homeowners navigate local planning requirements and secure approvals without unnecessary delays.

2. Structural Feasibility & Integration

A successful dual extension hinges on how well the structures connect:

• • Load-bearing assessments and steel beam placements

  • Staircase location and natural light flow

  • Floor levels alignment for smooth transitions

KT5 Solution: We work with trusted architects and engineers to develop a cohesive structural design that blends loft and rear spaces seamlessly.

Design Tips for a Cohesive Finish

• • Use consistent flooring and paint finishes between new and existing spaces

  • Match window styles and rooflights across loft and ground floor

  • Integrate open-plan concepts with zoned lighting and glazing

  • Consider a roof terrace or Juliet balcony for added appeal

KT5 Creative Approach: From bespoke Velux layouts to skylit kitchen diners, our design team ensures every detail works practically and aesthetically.

Why Homeowners Choose KT5 Construction

• • Budget-Minded from the Start: KT5 listens closely to your financial goals and helps tailor your project accordingly—without compromising on design.

  • Expert Guidance at Every Step: From planning permission to final fixtures, KT5 ensures the process is smooth and fully supported.

  • One Team, One Vision: As both designer and builder, KT5 eliminates delays, miscommunications, and hidden costs.

  • Value Engineering: KT5 helps cut non-essential spending while enhancing quality finishes.

  • Trust and Reputation: Homeowners choose KT5 because of our reputation for delivering results on time, on budget, and with minimum disruption.

Cost Breakdown and Budgeting Tips

Typical Cost Ranges (London-based projects):

• • Loft conversion: £45,000 to £70,000+

  • Rear extension: £55,000 to £90,000+

  • Combined project (with savings): £85,000 to £125,000

Factors Affecting Costs:

• • Roof type and pitch

  • Plumbing locations (especially if adding bathrooms)

  • Size and quality of finishes

KT5 Money-Saving Blueprint:

• • Value-engineer architectural plans before build

  • Phase finishes (e.g., shell out a future bathroom)

  • Use our trade discounts on materials

  • Leverage our project sequencing to avoid rework

Frequently Asked Questions (FAQs)

Q: Can I live in the property during the works?

A: In many cases, yes. KT5 plans build schedules to minimise disruption.

Q: Will I need separate planning permission for each extension?

A: Not always—KT5 will help assess and manage applications under combined permitted development rights.

Q: How long does a combined project take?

A: Typically 4–6 months, depending on size and finishes.

Ready to Maximise Your Home?

Contact KT5 Construction today for a free consultation or use our Extension Cost Calculator to get an instant quote in 60 seconds.

Let’s build smarter—up and out.