Frameless Glass Box Extensions
Minimalist Modern Design, Maximum Light
Ultra-slim structural glazing creates a seamless connection between your home and garden. Floor-to-ceiling glass, stunning contemporary aesthetics and the potential to achieve an A++ thermal rating.
Call us anytime on 01243 538999 – David our digital assistant will take a few details so the right specialist can follow up personally.
What is a Glass Box Extension?
A Glass Box Extension represents the pinnacle of contemporary architectural design. Using structural glazing technology, these minimalist extensions create an almost invisible boundary between your living space and garden, maximising natural light and views.
At Room Outside, we specialise in bespoke Glass Box Extensions featuring floor-to-ceiling glass panels, flat structural glass roofs and large-format sliding or pivot doors. Each installation is precision-engineered to create a seamless indoor-outdoor living experience.
Constructed using structural safety glass with structural glass purlins sealed with structural silicone bonding using unique and specialist techniques. Alongside our Glass Box Extensions, we also design and install bespoke conservatories and orangery extensions across England — including West Sussex, East Sussex, Surrey, Hampshire, Kent, Essex, Greater London, Berkshire and Dorset — since 1973.
Key Benefits
Sleek Frameless Glass Extensions for Contemporary Homes
Four things we do differently that premium homeowners consistently value.
Precision Engineering
Every Glass Box Extension is individually engineered using structural glazing technology. We design around your architecture, your proportions and how you want to use the space.
New Generation Glass
Our advanced glazing option is designed to help block up to 80% of solar heat while maintaining natural light, with the potential to achieve an A++ thermal rating.
Insured Guarantees
Depending on product and location, we offer up to a 10-year structural guarantee backed by independent UK insurers.
Full Project Management
We handle everything — structural engineering, planning applications, building regulations, foundations, installation and finishing. Over 50 years of project experience across England.
Glass Box Extension Projects
A selection of recent Glass Box Extensions designed and installed by Room Outside across England. Click any image to view full size.
Glass Box Extension Features
Every Glass Box Extension is precision-engineered with premium structural glazing and the latest thermal technology.
Frameless Structural Glazing
Constructed using structural safety glass with structural glass purlins sealed with structural silicone bonding using unique and specialist techniques.
Floor-to-Ceiling Glass
Full-height glazing maximises views and floods your space with natural light. Creates a dramatic sense of openness.
New Generation Glass
Advanced thermal glazing designed to help block up to 80% of solar heat while maintaining natural light, with A++ ratings achievable.
Sliding and Pivot Doors
Choose from large-format sliding, pivot or bi-fold doors for dramatic openings.
Walk-On Glass Roofs
Optional structural glass roofs create stunning visual connections between floors.
Structural Engineering
Full structural engineering is included with every project. We manage calculations, building regulations and building control sign-off.
Door and Opening Options
Choose from a range of premium door systems to complete your Glass Box Extension.
Sliding Glass Doors
Pivot Doors
Bi-Fold Doors
Glass Box Extension vs Orangery
Both create stunning extensions, but they suit different architectural styles and priorities.
| Feature | Glass Box Extension | Orangery |
|---|---|---|
| Style | Contemporary, frameless, minimalist | Traditional with solid perimeter and lantern |
| Glazing | Structural glazing — near-invisible joints | Framed glazing with insulated perimeter |
| Thermal | A++ achievable with New Generation Glass | A++ achievable — enhanced insulation |
| Price from | £40,000 | £35,000 |
| Build time | 12–16 weeks | 10–14 weeks |
| Best for | Modern homes, maximum glass, clean lines | Period homes, warmth and built-in feel |
Not sure which suits your property? Our design consultants can recommend the best option during a free home visit. Learn more about our Orangeries →
Glass Box Extension vs Conservatory
Both maximise light, but a Glass Box Extension takes a fundamentally different architectural approach.
| Feature | Glass Box Extension | Conservatory |
|---|---|---|
| Design | Frameless structural glazing | Framed glazing with pitched or flat roof |
| Aesthetic | Ultra-contemporary, minimalist | Traditional or modern depending on style |
| Natural light | Maximum — structural glass on all sides | Excellent — fully glazed roof and walls |
| Thermal | A++ achievable with New Generation Glass | A+ achievable with New Generation Glass |
| Price from | £40,000 | £25,000 |
| Build time | 12–16 weeks | 8–12 weeks |
| Best for | Architectural statement, seamless views | Light-filled family rooms, garden connection |
Both add valuable living space — the right choice depends on your property style and how you want the room to feel. Learn more about our conservatories →
Not sure which Glass Extension is right for your home?
Book a free home consultation. We will visit, assess structural requirements, and show you exactly what is possible — with no obligation.
Call us anytime – David our digital assistant will take a few details so the right specialist can follow up personally.
How a Project Works
From first conversation to finished Glass Box Extension, here is what to expect at each stage.
Free Home Design Visit
A specialist visits your home to discuss your vision, assess structural requirements, take measurements and discuss glass specification options. No obligation.
Design and Engineering
We produce detailed architectural drawings and structural engineering plans. You will see exactly what the finished Glass Box Extension will look like before committing.
Build and Installation
Your Glass Box Extension is precision-built using structural glazing, then professionally installed. We manage the full project from foundations through to building control sign-off.
Handover and Aftercare
We do not consider a project complete until you are fully satisfied. Depending on product and location, your Glass Box Extension may be covered by up to a 10-year insured guarantee.
What Our Customers Say
Independently verified reviews from Google. Real homeowners sharing their experience — unedited and in their own words.
“Room Outside did an amazing job with our glass extension. The design is modern, the build quality is excellent, and the team was professional from start to finish. The space is bright, comfortable all year round, and has completely transformed our home. Highly recommended for anyone looking for a premium glass sunroom or extension.”
“We have always had a problem of our conservatory overheating as it faces the sun and was often unbearable during the summer. I was recommended to Room Outside and the special New Generation Glass which I have now had fitted. What a difference this has made! It’s now a room that we can use all the time. Matt who oversaw the team fitting it, went the extra mile to make sure everything was perfect. I am so impressed I have now recommended two more people to Room Outside!”
“Very happy with the work Matt did for us with our glass conservatory. Matt and Matthew were very professional and always tidied up the place at the end of each day before leaving. They arrived on time every day and checked everything with us and listened to our feedback. We are happy with our new glass roof and warm weather this week will hopefully demonstrate that the new generation glass protects us from the heat. We would recommend Matt and Room Outside. Many thanks.”
Glass Box Extension FAQs
Common questions about Glass Box Extension costs, planning and installation.
A Glass Box Extension is a minimalist architectural addition using structural glazing. It creates an almost invisible boundary between your living space and garden, maximising natural light and views.
A frameless Glass Box Extension typically costs from £40,000 to £100,000+ depending on size, glass specification, and complexity. Room Outside offers premium Glass Extensions from £40,000 fully installed with building control and up to 10-year guarantee. See our glass extension prices UK 2026 guide for a detailed breakdown.
Many Glass Extensions fall under Permitted Development Rights, but restrictions apply in conservation areas and for listed buildings. Room Outside provides full planning guidance with every project.
Yes. Our Glass Box Extensions feature New Generation Glass technology with advanced thermal breaks and low-e coatings, with the potential to achieve A++ energy ratings.
A typical Glass Box Extension takes 12–16 weeks from initial consultation to completion, including design, structural engineering, foundations, installation and finishing.
Depending on product and location, we offer up to a 10-year structural guarantee backed by independent UK insurers, alongside separate product-specific warranties.
Get Your Free Glass Extension Quote
Book a free home design consultation with our specialist team. We will discuss your vision, assess structural requirements and provide a detailed quotation.
Prefer to talk? Call us on 01243 538999 — David our digital assistant will take a few details so the right specialist can follow up personally.