Planning and designing your new home extension is an exciting milestone—but before you dive into paint swatches and furniture layouts, there’s a crucial step you can’t afford to overlook: the design and planning stage.

Flawless architectural drawings are the foundation of your dream extension. Without precise plans and expert guidance, even the most stunning vision can fall short in execution.

In this guide, we’ll walk you through:

✅ The must-know types of house extension designs
✅ Why professional drawings make or break your project
✅ Cost insights and key considerations
✅ Everything else you need to turn your dream extension into reality

Several types of drawings are required when designing and constructing buildings and when applying for planning permission.  They include…

• Existing drawings
• Design floor plans
• Elevations
• Structural drawings
• Electrical drawings
• Plumbing and sanitary drawings

Existing Plan Drawings

These are the as-is blueprints of your home, capturing its current layout and structure. They reveal how your rooms connect and function today—serving as the critical foundation for your renovation or extension plans.

Proposed Floor Plans

The heart of your project, these drawings map out the new vision for your space. They detail room layouts, flow, and functionality—guiding builders in shaping your dream home during construction, remodelling, or demolition.

Proposed Elevations

Think of these as your home’s portrait from every angle. These 2D drawings showcase the exterior (and sometimes interior) façades, illustrating the north, south, east, and west views to ensure cohesive design and aesthetics.

Structural Drawings

The backbone of your build, these technical plans specify load-bearing elements, materials, and reinforcements. They ensure your home isn’t just beautiful—but safe, stable, and built to last.

Electrical Drawings

A wiring roadmap for electricians, these diagrams plot out circuits, outlets, and fixtures. They prevent guesswork, ensuring seamless installation of lighting, power, and smart systems.

Plumbing & Sanitary Drawings

These plans keep the water flowing and waste moving. They outline freshwater supply, drainage, irrigation, and stormwater systems—so every pipe and fixture is perfectly placed.

Why Proper Plans and Designs Are Essential for Your Project

1. They Ensure Project Success

A well-crafted design isn’t just the first step – it’s the foundation of your project’s success. Thoughtful planning saves you time, prevents costly surprises, and helps transform your vision into reality efficiently.

2. They’re Crucial for Planning Permission

For projects requiring full planning permission, professional drawings are non-negotiable. Even for permitted development projects, we strongly recommend obtaining a Lawful Development Certificate. This official documentation proves your build complies with regulations and protects your investment.

3. Many Are Legally Mandatory

Regardless of whether you opt for a full building regulations package, certain structural elements require certified engineering calculations. This isn’t just red tape – it’s vital protection ensuring your build is safe, compliant, and built to last.

The timeline for finalizing your extension plans depends on three key factors:

• The scale and complexity of your project
• Your architect’s current workload and availability
• Whether you can provide existing property drawings

Typical Timeframe:

For most residential projects, you can expect the design process to take approximately 2-5 weeks. This period allows your architect and building consultants to:

1. Carefully develop your concept
2. Refine all technical details
3. Create precise, regulation-compliant drawings
4. Ensure every element meets your requirements

Understanding Architectural Service Costs

Professional architectural fees typically range from 5% to 15% of your total construction budget. The exact percentage depends on the scope of services – architects providing full project management will be at the higher end of this scale, while design-only services typically cost less.

Several key factors influence the final price:

1. Project Scale: Larger developments require more detailed planning
2. Design Complexity: Unique architectural features increase planning time
3. Location Factors: London and Southeast projects often incur higher fees
4. Professional Expertise: More experienced practices command premium rates
5. Reputation Premium: Award-winning architects may charge additional 10-20%

It’s worth noting that chartered architects generally charge more than architectural technologists or designers, reflecting their:

• RIBA-accredited qualifications
• Comprehensive insurance coverage
• Legal authority to certify projects
• Greater design experience

For high-profile architects with competition wins or published projects, fees can increase significantly – sometimes 25-50% above standard rates – due to the perceived value of their design pedigree.

This investment often pays dividends through:

✓ More innovative use of space
✓ Higher quality finishes
✓ Better planning approval success rates
✓ Increased property value

Comprehensive Extension Services – All Under One Roof

While architectural designers lead your project, you’ll also need specialist support. Typical additional professional fees include:

• Structural engineers: £500-£1,000 (essential for safety calculations)
• Building surveyors: £500-1,500 (for detailed condition reports)

At House Plans UK, we simplify the process with:

✓ Transparent fixed fees – No surprise costs
✓ In-house design experts – Proven extension specialists
✓ End-to-end service covering:

• Planning applications
• Building Regulations packages
• Precise measured surveys
• Trusted contractor recommendations
• Financing guidance

Our integrated approach ensures seamless coordination between all specialists, saving you time and avoiding costly miscommunications. From initial sketches to final sign-off, we handle every detail to bring your vision to life.

While you can attempt an extension without professional help, working with an architectural designer (like us) ensures your project reaches its full potential. Here’s how we add value:

✅ Space-Smart Designs – We don’t just draft plans—we optimize your layout to make the most of light, flow, and functionality, often uncovering possibilities you hadn’t considered.

✅ Boosted Property Value – A well-designed extension doesn’t just look great—it increases your home’s worth, typically far outweighing the design fees.

✅ Smoother Approvals – Planning applications succeed on details. We know exactly what councils require, minimizing delays or rejections.

✅ Guidance You Can Trust – From material choices to builder coordination, we help you navigate pitfalls that could otherwise cost time and money.

The Reality Check:

You could manage without a design professional—but with your time, budget, and home’s future at stake, our expertise safeguards your investment. The right design doesn’t just look good—it works for years to come.

When to Submit Your Extension Plans to the Council

You must submit your extension drawings to the local council during the planning stage – whether you’re applying for:

• Full planning permission, or
• A Lawful Development Certificate (LDC)

Important: This submission must happen before any construction begins.

The Critical Path for Your Project:

1. Structural Drawings First :  Always commission these before builders start work. At House Plans UK, we strongly advise going beyond the basics with a complete Building Regulations package that includes:

• Detailed structural calculations
• Full technical specifications
• Compliance documentation

Why this matters: Without these professional drawings, you’re relying on contractors to interpret requirements – a risky approach that could lead to costly mistakes or non-compliance

2. Approval Options

With your Building Regulations package, you can either:

• Submit directly to local building control, or
• Work with an approved inspector who manages the entire inspection process

Understanding Your Drawing Options:

2D Drawings:

• Technical, scale plans showing layout and measurements
• Essential for planning approvals and construction
• Show length and height dimensions
• Often paired with 3D visuals

3D Drawings

• Photo realistic representations with depth and perspective
• Bring your design to life before building begins
• Display height, width and depth
• Help communicate your vision to builders and planners

Key Benefits of 3D Visualizations:

• Eliminate design misunderstandings
• Help spot potential issues early
• Make planning applications more persuasive
• Let you “walk through” your future space

At House Plans UK, we provide both 2D technical drawings and 3D visualizations, ensuring you have complete confidence in your project from concept to completion.