Annex Kits – Landing Page - Structural Insulated Panels (SIPs) UK

rDSIPs Habitable annex kits

The RD SIPs Annex Kit — A Proper Habitable Annex. Built in Days. Certified for Building Regs.

26m² of certified SIP construction. Walls that meet building regs. A roof that outperforms most new builds. Everything you need in one order.

What Is the Annex Kit?

The Annex Kit is a 6.1m × 4.27m SIP annex kit — designed, fabricated, and dry-fitted in our Herefordshire workshop before it ever reaches your site. It comes with a generous 0.61m roof overhang for a practical, attractive finished appearance.

This isn’t a glorified garden room. It’s a certified, habitable structure built to full UK Building Regulations. That means it’s warm in winter, cool in summer, legally compliant, and — crucially — insurable, mortgageable, and signable by building control.

At approximately 26m² of floor area before allowing for wall thickness, it works as a home office, a self-contained annexe for family, a rental space, or an accessible guest suite. Whether you’re creating accommodation for relatives, guest space, or additional living space, this kit gives you a highly insulated, energy-efficient building shell — and the perfect starting point for creating extra space at your property.

Right now, the Annex Kit is on our Winter sale. Prices aren’t listed here because every project is slightly different — get in touch and we’ll give you a straight answer.

WHAT’S INCLUDED

Everything you need to build. One order. One delivery. Nothing left to source.

6.1m × 4.27m building footprint with a 0.61m roof overhang
SIP wall panels — 147mm PUR-bonded, fabricated to your design
SIP roof panels — 172mm, designed for the roof overhang specified
Rubber roof covering
Batten
Membrane
Adhesive / glue
Foam
Screws and fixings
Timber
Structural calculations — professionally prepared and included in the kit price
Technical drawings and plans — site-ready, clear, and yours to hand to your builder or building control
Declaration of Performance (DOP) — your official certification document proving panel compliance
Technical support and installation guidance — from us, by phone or email, throughout your build

That structural calculations point is worth stopping on. Most self-builders and contractors don’t realise they need them until building control asks — then it’s a wait of several weeks and a bill of several hundred pounds to get an engineer to produce them. They come with this kit, included in the price, from day one. No delays. No surprise costs. No engineer to chase.

This is a set-price, all-inclusive kit. The list above is what arrives. There is nothing left to source, specify, or pay extra for on the materials side. You order once, it arrives complete, and your team can get straight to work.

UK manufactured, UK-wide supply available.

COMPLIANCE: Built to Building Regulations — This Isn’t a Garden Room

Most people don’t realise how big the gap is between a garden room and a habitable structure. A garden room keeps the rain out. A habitable annex has to keep people warm, meet thermal standards, and satisfy your local building control officer.

The Annex Kit is designed from the ground up for habitable use. That means:

Full compliance with current UK Building Regulations — not just “suitable for use,” but properly certified
U-values that meet and exceed what the regs require — see the callout below
All the certifications your building control officer, insurer, and mortgage lender need to see
DOP included with every kit — no gaps in your compliance trail
Structural calculations included — ready for building control from day one

If you’re investing in an annex — for family, for rental income, for resale value — this is the structure that holds up under scrutiny. Not because we say so, but because the paperwork proves it.

WALL PANELS — 147mm SIP

0.18 W/m²K

Current Building Regulations require 0.18 or lower. The Annex Kit meets the standard exactly — and our PUR core consistently delivers it in the real world, not just on paper.

ROOF PANELS — 172mm SIP

0.15 W/m²K

Current Building Regulations require 0.18 or lower. Our roof panels beat the requirement by a significant margin — a genuine advantage in energy bills and comfort year-round.

In plain English: a U-value measures how much heat escapes through a material. Lower is better. Our wall panels hit the building reg limit. Our roof panels beat it — and our 147mm PUR-bonded panels are engineered to achieve a U-value of approximately 0.18 in practice, not just on a data sheet.

WHY THE ANNEX KIT SELLS OUT FAST

These are the reasons people order quickly when the Annex Kit goes on sale:

One order, nothing left to source — panels, roof covering, batten, membrane, adhesive, foam, fixings, timber, structural calcs, DOP, drawings, and support. That is the complete list. Nothing is missing.

Structural calculations included — worth hundreds of pounds and weeks of waiting if you had to arrange them yourself. They’re in the kit.

Builds in days, not weeks — SIP construction is fast, and because your kit is prepared before arriving on site, the main structure assembles far quicker than many traditional methods. An experienced team can have the structural frame up in two days.

Habitable all year round — this is a real room, not a shed with a desk in it. Warm in winter, comfortable in summer, with a highly insulated building envelope designed to retain heat and hold comfortable internal temperatures throughout the year.

Mortgageable and insurable — the certifications and DOP mean your build is covered where it counts: building control sign-off, insurance, and if you ever need to raise finance against your property.

Zero on-site waste — panels are cut and dry-fitted in our workshop. What arrives on your site is what goes up. No off-cuts, no skips.

Energy bills slashed — U-values that outperform most new builds mean lower heating costs from day one, year after year, and reduced ongoing energy demand for the life of the annexe.

Reduced disruption — less time on site means lower labour costs and fewer days of construction activity at your property. Ideal where building work is taking place alongside an occupied home.

Predictable quality, controlled conditions — panels are produced in a controlled manufacturing environment with full material and production traceability, then dry-fitted in the workshop to catch potential errors before they reach site. PUR auto-bonding helps prevent delamination and supports the integrity of the panel system.

UK-wide delivery — we arrange delivery wherever you are. Remote or access-tricky? Call us. We’ll sort it.

Family business, real people — you’ll speak to someone who actually knows SIPs. Regan started this company because he couldn’t find a decent supplier for his own extension. He’s not going to leave you without support.

WHAT YOU GET ON DELIVERY DAY

When the Annex Kit arrives, here’s what you’ll be working with:

Factory-fabricated SIP panels — cut accurately, labelled clearly, and dry-fitted in our workshop before leaving us. What arrives is what was designed.

A complete materials pack — roof covering, batten, membrane, adhesive, foam, screws, fixings, and timber. Everything is included. Nothing needs to be bought separately.

Structural calculations — in hand, ready for your building control submission. Produced by professionals, included in the kit price.

Your DOP document — ready for building control. Not chased, not “to follow.” With you from day one.

Technical drawings and plans — sized and annotated so your builder can get straight to work without a call to us. Though we’re here if they need one.

Delivery planning support — covering access and handling considerations, so installation is as straightforward as possible.

A phone number that gets answered — installation questions, site surprises, or just a second opinion. We’re a small team and we pick up.

The panels are fabricated to your specific design and dry-fitted in our workshop — so by the time they reach your site, we’ve already caught the problems that catch other builders out.

DESIGNED AROUND YOUR PROJECT

Every property and every annexe is different. Your SIP kit can be designed around the dimensions, layout and requirements of your project rather than forcing you into a one-size-fits-all structure.

Whether you’re planning accommodation for relatives, additional guest space, or a larger self-contained annexe, our team can help you develop the right SIP solution — and guide you through the design and planning stages.

Guidance through the design and planning stages
Advice on foundations, openings and roof design
Kits designed around your project requirements
Installation and best-practice fitting guidance

CLEAR LEAD TIMES, STRAIGHTFORWARD SUPPLY

Once the design is agreed, your annex kit is manufactured and prepared for delivery to site.

4–8 Weeks — Typical supply time. House and building projects are typically supplied within 4–8 weeks, subject to design and scheduling.

UK-Wide — Supply available, with delivery planning and communication throughout the design and manufacturing process.

The Annex Kit Is on Sale Now — But Not for Long

If you’re planning an annexe, this is the moment. The Annex Kit is certified, complete, and ready to order at a Winter sale price. These windows don’t stay open.

Tell us your project, your site, and your timeline. We’ll come back to you with a straight answer — no pressure, no waffle.

[Enquire About the Winter Sale →]

Or call us — we’re a family business and we answer our phones.