Garage Extension & Building Over a Garage: Costs and Considerations
Building over an existing garage is a practical and cost-effective way to gain additional living space. Whether you’re considering a master suite, guest bedroom, or a home office, extending above your garage offers versatile options for maximizing your property’s potential. This approach works for both attached and detached garages, making it a flexible choice for homeowners.

Benefits of Building Over a Garage
One major advantage of building above an existing garage is cost reduction. By utilizing the existing structure, you can save on new foundations and reduce construction complexity. However, the feasibility of this extension depends on the garage’s current construction. Many garages are built with single-skin brickwork, which may not support the additional weight of a second floor. Similarly, the original foundations might need reinforcement or replacement to meet structural requirements. Other options include installing a steel frame to support the first floor structure or looking at building the first floor in timber and using cladding, render or brick slips.

In some cases, homeowners find it more efficient to rebuild the garage entirely. This option provides more freedom in design and ensures the new structure meets modern building standards.

Design Considerations and Planning Permissions
Most local authorities require the first-floor extension to be set back at least one meter from the side boundary to avoid creating a “terracing effect” with neighboring properties. If the garage is close to the boundary, structural steel beams may be necessary to support the new extension, increasing the complexity and cost of the project.

If space allows, you may be able to extend over the entire footprint of the garage. However, working with an experienced designer or architect can help you navigate these constraints and optimize the available space.

Estimated Costs for Garage Extensions

The cost of a garage extension varies based on size, complexity, and construction type. Average prices per square meter are:

  • Single-storey extension: £1,800-£2,500/m² (including foundations and roof).
  • First-floor extension (above an existing structure): Approx. £1,300/m².

For example, a typical semi-detached property measuring 8m in depth and 3m wide could result in a 24m² floor area per level.

  • Ground floor: £43,200–£60,000
  • First floor: £30,000–£40,000

When to Rebuild Instead of Extend

In some cases, the original garage’s structural limitations make rebuilding a better option. This approach offers design flexibility, allowing you to create an extension that perfectly suits your needs without compromising due to existing constraints.