Flat Pack Annexe Kits

Sustainable and Cost-Effective Granny Annexes Built with SIPs; Manufactured by Us, Installed by You

SIPS Garden Buildings Annexes

Flat Pack Annexe Kits

Our range of one and two bedroom garden annexe kits have been designed to offer habitable space for family members, that’s as stylish on the outside as it is on the inside.

Our SIPs granny annexe kits are built using our pre-manufactured SIPs system; an innovative method of construction that delivers sustainable, time-efficient and cost-effective builds.

They’re ideal for homeowners who have sites where access is difficult, as the weight and size of panels having been carefully designed to make manual handling and assembly easy, even in areas where access is tight.

Utilising our pre-manufactured SIPs system, we supply structural and insulated flat pack annexe kits for a main contractor to install on site.

Installed Annexes
Flat Pack Annexes

Building with SIPs is a cost-effective and efficient solution to the need for additional space for a wide range of uses:

  • Homeowners
  • Architects
  • Builders
  • Schools
  • Educational Establishments
  • Sports Facilities
  • Leisure Buildings
  • Health and Medical Organisations
  • Self-Builders

The Benefits of Building with SIPs

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Faster Construction Speeds

The premanufactured nature of SIP panels offers a significantly reduced site installation time in comparison to traditional construction methods such as masonry or timber framing.

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Reduced Energy Costs

SIPs are very airtight in its construction and with less timber required than traditional timber frame construction, there is a vast reduction of cold bridges in the wall build up and less energy is needed to heat and cool rooms.

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Lower On-Site Costs

Due to the stringent, tried and tested design and manufacturing process, materials work harmoniously together, delivering a highly predictable and reliable product whilst minimising construction waste and labour costs.

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High Structural Performance

The composite construction of SIP panels offers enhanced structural performance, strength and stability in comparison to traditional construction methods.

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Lightweight Prefabricated Structure

SIPs construction is an incredibly strong, yet lightweight system. This can minimise disruption on site, utilising low impact footings (where conditions permit), requiring less labour and allowing for easier handling.

Granny Annexe UK

Our Service

Our panels are fabricated off-site to exacting standards, at our purpose-built manufacturing facility, using the highest quality closed cell EPS insulation and FSC certified and structurally graded orientated strand board.

Our garden annexe kits are delivered to the kerbside at your property and installed by your builder onsite to your desired specification.

Attention to detail, professionalism and customer service are at the heart of every project we deliver and we’re proud of our reputation for designing and manufacturing and installing stunning annexe kits.


What’s Included in Our Annexe Kits

All of our annexe kits include the following specification, as standard:

• Insulated Timber Frame Floor (200mm Insulation)
• Caber Deck Flooring Sheets
• SIP Panels for Walls (150mm Insulation)
• SIP Panels for Roof (175mm Insulation)
• Breather Membrane
• Cavity Batons
• Insect Mesh
• External Cladding (2 Sides British Cedar, 2 Sides Thermowood)*
• EPDM Rubber Roof Full Kit
• Guttering and Downpipes
• All SIP Joining Splines
• Stainless Steel Brad Nails
• UPVC Glazing Per Model**
• Vapour Barrier
• Metal Fascias
• Roof Light and Timber Upstand (1000 x 800)
• Full Technical Drawings and Instructions for Installation
• Full Fixing Kit (Foam, Screws, Timber Locks, Glues)


*Alternative claddings are available
**Upgrades to windows and doors are available

Annexe Models

Our Group Products

Technical Information


Our panels are constructed using enhanced grey EPS insulation.

EPS is an inert material that will not off-gas or degrade over time, unlike PIR and PUR insulations, resulting in thermal performance that will remain consistent over the lifetime of the building.

The enhanced grey EPS used in our panels is a closed cell structure and offers far superior thermal resistance values over standard EPS, with a water permeabilityof 0.015 to 0.030 mg(pa.h.m) and a thermal conductivity value of 0.032 W/mK

Structural Performance

Our wall and roof systems have been fully tested to British Standard and Eurocode loadings for domestic buildings.

Each bespoke project will have a full structural design and structural appraisal from a third-party engineer, using the structural load testing data.

Standard Details and U Values

We have a range of standard details to assist andguide clients, architects and builders in the understanding and application of our SIPs wall and roof systems.

Our thermal values are tailored towards ‘new thermal elements’ required for home extensions and ancillary building, including home annexes.

U values are calculated on the complete wall or roof build up and these can be enhanced further with additional internal insulation, if required.

Self Build Buildings

Information & Guidance

We have a range of technical data, installation guides and useful information on building with SIPs, to help guide clients, architects and builders.

Find out more
How to order SIPs

How to Order from Us

If you would like to find out more, discuss a project you’re planning or request a quote, please call us on 01452 840284 or email us at [email protected].

Alternatively, please complete the form to the right and we’ll be in touch.

If you’d like to visit us, our showroom in Gloucestershire is open from 10:00am until 4:00pm Monday to Friday and by appointment on Saturday, where we are on hand to discuss your plans for creating the additional space you’re looking for.

Case Studies


Really, really pleased with it

Really pleased with it all and enjoy sitting and taking in the view, glass of wine in hand of course! We did new decking immediately outside of it, in order to open the bi fold doors fully as an extension to the room. All in all, really, really pleased with it.

Such excellent service!

My wife and I just wanted to thank Richard, yourself and the rest of the team for all the support, ad hoc technical tips and advice that we got whilst building our Garden Room. I know that I visited the show room 2 or 3 times and Richard and the team, even though quite busy, showed us every courtesy and help. Such excellent service! I have finally completed the build of our 3 x 5m Garden Room, and we are very pleased with it.

The kit was fantastic!

Here are some pictures of my project I completed about 2 months ago, the kit was fantastic!

It’s such a good design!

We love the room and it was so easy to build. It’s such a good design!

It’s perfect and we love it!

We use it as a gym and use it most days, it’s perfect and we love it!

Great customer service and I’ll definitely be using you guys again.

Just wanted to email to thank you and your team. Great customer service and I’ll definitely be using you guys again. The driver was a really nice guy and very helpful. The build went really well and the customer was very happy.

I am very pleased with everything

I have completed the build of my DIY room that I purchased from you and I am very pleased with everything, looks really good.

Permitted Development, Planning Permission and Building Regulations Information

Permitted Development
Building Regulations
Planning Permission