Premium SIPs House Extensions Designed for Space, Comfort & Value

Comfortable and Energy-Efficient

SIPs (Structural Insulated Panels) create a highly insulated, airtight building envelope. That means a space that’s comfortable in winter and summer, with lower heating costs compared to many traditional build-ups.

Fast Build Programme

Because SIPs are supplied as a precision-cut panel system, the structure goes up quickly and accurately.

This usually means:

• Less time on site
• Less disruption around your home
• Fewer delays during construction
• A more predictable project schedule

Less Mess, Less Disruption

Shorter on-site time typically means fewer deliveries, less waste, and less disturbance — ideal if you’re living at home while the annex is being built.

Strong, Solid Structure

SIPs form a rigid structural shell that feels solid and permanent — not like a temporary outbuilding. The panels combine structure and insulation in one engineered system, creating a robust building envelope.

Minimal Waste

Panels are designed and cut specifically for your project, helping reduce offcuts and keeping the construction site tidier compared with many traditional building methods.

Typical Cost to Build an Annex (UK)

Annex costs vary depending on size, specification (basic shell vs fully finished), groundworks, and services such as water, drainage, and electrics.

As a rough guide:

• SIPs supply (panels or kit): depends on design, openings, roof type, and panel specification
• Typical fully finished annex build cost: often in the region of £1,800–£3,000+ per m²

For a 30 m² annex, the SIPs kit supply (panels/kit only) is typically £54,000–£90,000 + VAT, depending on openings and roof design. This excludes groundworks, doors/windows, finishes, services, and installation.

These figures are indicative. We’ll always quote the SIPs supply clearly, and we’re happy to talk through the wider build cost drivers so you can budget properly.

Typical Running Costs

Running costs depend on how you heat the space, how it’s used, and your energy tariff. SIPs are designed to reduce heat loss, so the space is typically cheaper to keep comfortable than many traditional constructions.

As a broad rule of thumb:

• A well-built, well-insulated annex can often be kept comfortable with low, steady background heat rather than turning heating on and off.
• Many customers choose electric heating (panel heaters or underfloor heating) or air source heat pump systems depending on the project.

If you share your annex size, intended use, and heating plan, we can help you estimate realistic running costs and recommend the best SIP panel specification.