What Are the Rules for a Double Storey Side Extension?

by | 10th June 2025 | KT5 Construction News | 0 comments

Rules for a Double Storey Side Extension

Are you planning to expand your home and wondering what the rules for a double storey side extension are in 2025? At KT5 Construction, we help homeowners in Surrey and Greater London transform unused space into practical, beautiful living areas—without breaching planning laws or building regulations. Whether you’re thinking of adding a new bedroom above a garage or creating a full-width open-plan ground floor, understanding the legal framework is essential to avoid costly delays.

Why Choose a Double Storey Side Extension?

Maximise Living Space Without Losing Garden Area

    • Doubles the usable square footage

    • Ideal for narrow or unused side plots

    • Perfect for growing families or multigenerational homes

Add Significant Property Value

According to market data, a well-designed two-storey extension can increase property value by 10%–20%.

Flexible Design Opportunities

    • Create a large open-plan kitchen-diner

    • Add a new bedroom with an en-suite above

    • Combine with loft conversions for full-home Upgrades.

Planning Rules for Double Storey Side Extensions in 2025

1. Planning Permission Requirements

While some side extensions fall under Permitted Development (PD) rights, double storey side extensions generally require full planning permission.

Key Planning Rules:

    • Setback from Front Elevation: The upper floor must be set back from the front to avoid visual dominance.

    • Distance from Boundary: Should be at least 1 metre from the property boundary to avoid terracing effects.

    • Obscure Glazing: Side-facing upper windows must be obscure-glazed to preserve neighbour privacy.

    • Roof Pitch: Must match the original property for aesthetic consistency.

    • Designated Land Restrictions: Extensions on greenbelt, listed, or conservation areas will face stricter rules.

2. Permitted Development Limits (If Applicable)

If eligible, PD allows:

    • Side extension width up to half the width of the original house

    • Rearward projection of no more than 3 metres, or 6m with prior approval (for semi-detached homes)

    • Eaves height of no more than 3 metres, and total height not exceeding 4 metres

Building Regulations for Double Storey Side Extensions

You must comply with the UK Building Regulations regardless of planning permission. Key areas include:

1. Structural Integrity

A structural engineer may be required to assess whether your existing foundations (e.g., garage) can support the extra storey.

2. Fire Safety

    • Fire doors and escape routes required

    • Smoke alarms on each level

    • Fire-resistant materials mandatory

3. Energy Efficiency & Insulation

Compliance with Part L is required for thermal efficiency. Insulation standards must reduce heat loss effectively.

4. Ventilation & Drainage

Proper airflow, extractor fans in bathrooms, and adequate plumbing connections are essential.

5. Party Wall Act

If you’re building near a neighbour’s wall or boundary, you’ll likely need to serve notice under the Party Wall Act 1996.

Neighbour Considerations & Privacy Laws

KT5 Construction always advises:

    • Informing neighbours early about plans

    • Ensuring side windows use obscure glazing

    • Minimising overshadowing and respecting the 45-degree rule for light

This reduces objections during planning and fosters goodwill during construction.

Why Choose KT5 Construction?

As experienced builders, KT5 Construction specialises in period home extensions. We bring your vision to life through practical design, honest pricing, and expert delivery.

What sets us apart:

    • Free architectural or structural design if you appoint KT5

    • Transparent quotes and no hidden costs

    • Tailored designs for every family and layout

    • Coverage across Surrey and Greater London

    • Experience in wraparound, loft, and rear extensions

We’re not just builders—we’re your project partner.

Design & Layout Considerations

Your layout should maximise function and comfort. Our in-house designers recommend:

    • Ground Floor: Open-plan kitchen/living room with bi-fold doors

    • First Floor: Master bedroom with en-suite and walk-in wardrobe

    • Above-Garage Option: Turn the garage into a utility or office, bedroom above

Costs to Consider

Double storey side extensions in Surrey typically range between £100,000 – £250,000, depending on:

    • Size and finishes

    • Groundworks and structural reinforcements

    • Planning and regulation compliance

    • Internal customisation (e.g., kitchens, bathrooms)

💡 Tip: Use our free home extension cost calculator [coming soon] or book a site survey today.

FAQs – Rules for a Double Storey Side Extension

1. Do I always need planning permission for a double storey side extension?

In most cases, yes. Especially if your design impacts neighbouring views, light, or is on designated land.

2. Can I build over my garage?

Yes, provided the garage foundation can support a second storey. A structural survey is required.

3. How long does the project take?

Typically 16–24 weeks from planning to completion, depending on weather, materials, and complexity.

Start Your Extension Journey Today

Transform your unused side space into something exceptional. Contact KT5 Construction now for a free consultationor site visit. Call us at 0845 053 7224 or Book Online.