What Are Double Storey Rear House Extensions & Are They Worth It?

The Basics of a Double Storey Rear Extension

What Exactly Is a Double Storey Rear House Extension?

A double-storey rear extension is a two-storey addition built at the back of your existing house. Unlike a single-storey extension, it offers an upper and lower level, doubling your living space in one project.

Key Differences Between Single-Storey and Double-Storey

• Single-storey extensions only expand the ground floor.
• Double-storey extensions give you both an extended ground and upper floor.
• You get more value per square metre with a two-storey extension.

The Role of Existing House Structure

The structure of your existing building, including the existing roof and floor plan, plays a massive role in how smoothly your extension can be planned and executed.

Benefits of a Double Storey Rear House Extension

Doubling Your Space Without Doubling Your Footprint

One of the biggest perks? You keep your garden space intact. Unlike wider extensions, rear double-storey extensions grow upwards, not outwards.

Cost Effectiveness Compared to Moving Home

The extension cost per square metre is typically lower than the cost of moving, especially when you factor in:

• Stamp duty
• Estate agent fees
• Legal costs

Improving Home Value and Functionality

Many homeowners find they can add an extra bedroom, office, or en suite bathroom, which increases the resale value.

Considerations Before You Build

Planning Permission: Do You Need It?

You might be able to build under permitted development rights, meaning you won’t need full planning permission as long as:

• It doesn’t extend more than three metres from the rear wall
• It doesn’t exceed seven metres from the original house
• It’s not in a conservation area or an area of outstanding natural beauty

Always seek planning permission if unsure.

Building Regulations You Must Follow

Regardless of planning status, your extension must meet building regulations, covering:

• Structural integrity
• Insulation
• Fire safety
• Drainage

The Party Wall Agreement Explained

A party wall agreement may be needed to prevent disputes if your extension affects a shared wall (like in a terraced house).

Design Factors and Planning

Matching the Existing Roof and Ridge Height

The roof pitch, ridge height, and existing eaves must usually align with your existing house’s roof.

Roof Pitch, Eaves, and Windows

If your extension faces a neighbour’s garden or house, the upper floor window design must maintain privacy, potentially requiring frosted glass or limited openings.

Making Use of Existing Garage or Garden Space

Do you have an existing garage? You could integrate it into your new extension project or build over it for more space.

Costs and Budgeting

Average Double Storey Extension Cost in the UK

The cost of a double-storey extension varies depending on the region and finish, but averages between £1,500 and £2,500 per square metre.

Factors That Affect Extension Cost

• Quality of finishes
• Location
• Size (measured in square feet)
• Access to the site
• Whether you use a structural engineer

Building Control Fees and Additional Expenses

Expect to pay for:

• Building control fees
• Architectural drawings
• Planning submission costs
• Landscaping and decorating

How to Maximise the Space

Adding an Extra Bedroom or En Suite Bathroom

Use the upper storey for an extra bedroom or bathroom, which is ideal for growing families.

Designing Multi-Use Ground Floor Areas

Transform the ground floor into an open-plan kitchen, dining area, or family room that flows into your garden space.

Ideas for Upper Floor Window and Natural Light

Maximise light with skylights, bifold doors, and rear-facing windows overlooking the garden.

Is It Worth It?

When a Double Storey Rear Extension Makes Sense

It’s worth it when you:

• Need additional space
• Don’t want to lose garden space
• Want to stay in your current location

Comparing Value vs. Investment

You may recoup 50-80% of your investment in property value, sometimes even more in high-demand areas.

Real-Life Examples and Scenarios

• Detached house owners often gain multiple rooms.
• Terraced house dwellers find it’s a more innovative use of limited land.
• Those with existing single-storey extensions can build on top.

Conclusion

A double-storey rear house extension can be worth it if you’re after more space, better functionality, and long-term value. Whether you’re adding a bedroom, office, or open-plan kitchen, the benefits are hard to ignore, especially if your home is in a desirable location. Ensure you know planning permission, building regulations, and how to work with your existing property to maximise your investment.

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