We design and fit glass extensions in Clerkenwell for homeowners who want a bright, modern room that opens onto the garden. This page is for you if you want more light and space than a standard rear wall allows. You will learn about the types of glass extension, how they are built, the rules that apply, what sets the cost and how to care for one.
A glass extension is a room built mostly from glass, held by slim aluminium frames or by the glass itself. It often has a glass roof and wide sliding or bi-fold doors. The result is a space that feels part house and part garden. It suits a kitchen diner, a family room or a place to sit and watch the seasons change.
All our work is fitted by FENSA registered installers and backed by a 10-year guarantee. To compare every room style we offer, see our main conservatories page.
Types of Glass Extension
A glass extension can take many forms. The main types are:
- Glass box: a cube of glass with a flat glass roof and slim or hidden frames. It looks clean and modern next to brick.
- Lean-to glass room: a sloping glass roof against the house wall, with glass walls below. A good fit where the space under the eaves is low.
- Side return infill: a glass roof over the narrow strip down the side of a terrace house, which turns a dark kitchen into a bright one.
- Glass link: a short glass corridor that joins the house to a new wing or outbuilding.
- Glazed rear wall: a full width wall of sliding or bi-fold doors under a solid roof with roof lights.
If you want a softer, more classic look, a lean-to conservatory may suit you. If you want more solid wall and a roof lantern, an orangery is worth a look.
Frames, Glass and Doors
Most glass extensions use powder coated aluminium. It is strong enough to hold large panes with slim frames, so you see more garden and less frame. Frames come in any colour, with grey and black the most asked for. A thermal break in the frame stops heat leaking out through the metal.
The glass is the heart of the room, so we take care over the spec:
- Roof glass: toughened and laminated for safety, with solar control to cut heat and glare.
- Wall glass: double or triple glazed units with low-E coats and argon gas.
- Self-cleaning glass: a coat on the outer pane helps rain wash dirt away.
- Doors: sliding doors give big, unbroken views. Bi-fold doors open the full width.
For a solid roof with light from above, we can fit a roof lantern or a flat roof light. Every door has multi-point locks, so the room is as secure as the rest of your home.
How a Glass Extension Is Built
A glass extension needs a solid base and close work to fine limits. Large panes leave no room for error, so the base must be level and true. We dig and pour footings, lay the slab with insulation and a damp proof membrane, and set the frame on top.
Where the extension meets the house, we fit a steel beam or posts if walls are opened up. The roof glass is lifted into place, often with a small crane or glass lifter for big panes. Seals and flashings tie the glass to the house wall so it stays dry.
Our how we work page sets out the full journey, from the free survey to fitting and aftercare.
Planning and Building Regulations
Many single storey rear glass extensions fall under permitted development, so you may not need planning permission. Limits apply to depth, height and how close it is to the boundary. Rules are tighter for listed homes, flats and homes in conservation areas, and a side extension on some homes needs permission.
Building Regulations nearly always apply to a glass extension, unlike some conservatories. That is because it is often open to the house with no external door between. Part L limits how much glass an extension can have, unless the heat loss is made up in other ways. A heat loss calculation can show the design still meets the rules. We handle building control and the paperwork, so you get a sign-off at the end.
What Drives the Cost of Glass Extension
Each glass extension is built to order, so we do not list fixed prices. These are the main things that set the cost:
- Size: more floor area means more base, frame and glass.
- Glass spec: triple glazing, solar control and self-cleaning coats add to the total.
- Structure: frameless designs and opening up the rear wall with a steel beam cost more.
- Doors: large sliding panes and wide bi-folds cost more than French doors.
- Ground work: drains, a slope or poor soil can mean extra base work.
- Access: if big panes need a crane or a long carry, this adds time.
- Finish: heating, flooring, lights and blinds all add to the total.
After a free survey, you get a written, fixed quote with no hidden extras, with the payment stages set out. Ask for yours on our get a quote page.
Keeping a Glass Room Comfortable
The big worry with glass rooms is that they get too hot or too cold. Good design deals with both. Solar control roof glass reflects much of the sun's heat. Roof vents and opening doors let warm air out. Underfloor heating keeps the room warm in winter without bulky radiators. Blinds give shade and privacy on bright days. Face, size and glass type all play a part, and we plan these with you at the survey.
Choosing the Right Glass Extension
Start with how you want to use the room. A kitchen diner needs space for units and a table, plus good air flow. A family room needs shade for screens. Then think about the garden. A north facing room gets soft, even light all day. A south facing room gets lots of sun, so solar control glass and blinds matter more. Last, think about the house. A glass box can sit well next to old brick, but some homes suit a more classic room. We bring samples and drawings to the survey to help you decide.
Frequently Asked Questions
Can the design of a glass extension be made to suit your home?
Yes. Every glass extension is made to measure. You choose the shape, the size, the frame colour and the type of glass. You can pick sliding or bi-fold doors, a glass or solid roof, and add a roof lantern or roof vents. We match the look to your home, whether it is a period house or a new build, and plan it with you.
Does a glass extension add value to a property?
A well built extension adds living space and light, which buyers like. A bright kitchen diner that opens to the garden is a strong selling point. The added value depends on your home, your street and how well the room is built. A room that stays warm in winter and cool in summer will appeal far more. A local estate agent can give you a view.
Is planning permission needed for a glass extension?
Many single storey rear extensions fall under permitted development, so you may not need it. Limits apply to depth, height and distance from the boundary. Listed homes, flats and homes in conservation areas have tighter rules. Building Regulations nearly always apply to a glass extension, and we deal with building control for you. We check all of this at the survey.
What upkeep does a glass extension need?
Clean the glass inside and out every few months, or less with self-cleaning glass. Wash the aluminium frames with warm, soapy water. Clear gutters and check the roof seals once a year. Keep door tracks free of grit and oil the locks now and then. Open vents on warm days to let damp air out, which helps stop condensation.
Can a glass extension be built on uneven ground?
Yes, but it takes more planning. We check the soil and the slope at the survey. On sloping ground, we may need deeper footings, a raised base or a few steps down to the garden. Good drainage around the base is key so water runs away from the room. These extra steps are set out in your written quote.
To see the rest of our services, visit our home page.
