Annexes for Home, Work, Education or Leisure

Sustainable and Cost-Effective Garden Annexes and Ancillary Accommodation Beautifully Built with SIPs

Granny Annexes UK

Annexes Efficiently Built with SIPs

If you’re looking for beautifully designed, habitable space for members of your family, our range of pre-fabricated one and two bedroom annexes offer stylish space, a range of features, a choice of finishes and reduced annual energy costs.

All of our annexes are architecturally designed and are built using our pre-manufactured SIPs system; an innovative method of construction that delivers sustainable, time-efficient and cost-effective builds.

Our annexes are designed to exceed BS3632 and comply to Part L of Building Regulations.

SIPs (structural insulated panels) are a modern and innovative method of construction, utilising off-site manufacture, and suitable for a wide variety of uses, ranging from small ancillary buildings through to large construction projects. 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.

As one of the leading suppliers of SIPs, we specialise in offering homeowners, businesses and organisations the opportunity to add the space they need and take advantage of the benefits of building with SIPs.

Annexe Kits
Granny Annexe UK

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.

SIPS Garden Buildings Annexes

Our Service

We offer a complete service, which includes groundworks^, full structural calculations, Certificate of Lawfulness^^, installation and finishing, based on one of our four annexe models.

Throughout your project, every stage will be managed by our experienced team, from discussing your requirements and suitable annexe models through to manufacturing at our purpose-built facility and installation and finishing on site.

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, manufacturing and installing stunning annexes built with SIPs.

On every one of our projects our work is carried out in accordance with Health and Safety Executive guidance and regulations for construction. All four of our garden annexe models can be adapted for different needs and optional extras can be specified.

^Groundworks up to 10m from the edge of the building. Additional distance priced separately.

^^If surveys and/or additional reports are required, these will be charged for in addition to our standard service. Should you wish to increase the size of your annexe, this will be subject to applying for full planning permission, which we can assist with, and may incur additional costs.

What's Included

Our dedicated in-house team offers a turnkey service, from planning to completion, and will take care of every stage of your project, ensuring that it’s delivered on time and on budget, to the highest of standards.

All of our annexes include the following specification, as standard:


  • Certificate of Lawfulness^^
  • Concrete Pads or Ground Screws
  • Services Installed up to 10m from edge of Annexe^
  • Main Construction in SIPs
  • Cedar Cladding to 2 Sides and 2 Sides Box Profile Metal Sheeting in Anthracite
  • UPVC Windows and Doors
  • SPC Flooring
  • Full Interior Decoration
  • One or Two Bedrooms
  • Bath/Shower Room
  • Kitchenette
  • Sockets and Switches
  • Electric Underfloor Heating
  • 120 Litre Immersion Tank
  • Smoke Detectors
  • Rooflight
  • External Decking
  • Internal and External Downlights
  • All Certifications (Building Regulations, Structural Calculations, U Value Calculation)

^Groundworks up to 10m from the edge of the building. Additional distance priced separately.

^^If surveys and/or additional reports are required, these will be charged for in addition to our standard service. Should you wish to increase the size of your annexe, this will be subject to applying for full planning permission, which we can assist with, and may incur additional costs.

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