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 solid 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 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 example, a 30 m² annex is commonly around £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 or underfloor heating) 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.

Why Choose RD SIPs?

We’re a modern, family-run SIP supplier based in Herefordshire, set up to support annex projects properly — with certified panels, clear lead times, and straightforward technical guidance.

With RD SIPs, you get:

• Certified SIP panels and kits
• Clear, honest lead times
• Practical technical support throughout design and installation
• A supplier that’s responsive and easy to reach when questions come up

Typical SIPs Annex Projects

SIPs work brilliantly for annexes of all kinds, including:

• Guest bedroom with en-suite
• Home office or studio
• Garden annex or multi-use room
• Holiday let or Airbnb-style accommodation
• Extra living space for family

How It Works

1. Share your basics: location, intended use, and rough size (or drawings if you have them).
2. We confirm the panel specification and talk through key details like openings, roof type, and access.
3. You receive a clear quote for the SIP supply.
4. We manufacture and deliver your SIPs kit, with support available to help your build go smoothly.

Get a Quote for Your SIPs Annex

Send us your rough dimensions (or plans) and your build location, and we’ll help you choose the right SIP specification and provide a clear, straightforward quote.