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MODERN • ENERGY-EFFICIENT • BUILT TO LAST

Premium SIPs House Extensions Designed for Space, Comfort & Value

Create a warm, modern living space with a high-performance SIPs annex kit built for comfort, strength and long-lasting value — all fully compliant with UK building regulations.

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SIPs Annexes

Add a warm, solid extra space without the months-long build.
A SIPs annex is one of the quickest, cleanest ways to create a high-performance room that works all year round
— whether you’re planning Gust Suite, Home Office, Air BnB, Granny Annex, or Extra living space.

Why build an annex with SIPs?

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. Less time on site usually means less disruption, fewer delays, and a more predictable 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 “proper” and robust — not like a temporary outbuilding.
Minimal waste
Panels are designed and cut to suit your project, helping reduce offcuts and keep the site tidy.
Typical cost to build an annex (UK)
Annex costs vary a lot depending on size, specification (basic shell vs. fully finished), groundworks, and services (water, drainage, electrics). As a rough guide:
· SIPs supply (panels/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 example, a 30 m² annex is commonly £54,000–£90,000+ fully finished.
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 — but 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 blasting the heating on and off. – Many customers choose electric heating (panel heaters/underfloor) or air source heat pump solutions, depending on the project.
If you share your annex size, intended use, and heating plan, we can help you think through realistic running costs and the best panel specification