A louvred pergola gives adjustable shelter with open sides. A fixed-roof veranda gives permanent cover with open sides. A glass room encloses the space entirely. Choose by how you will actually use it: more evenings outdoors, reliable shelter from rain, or a heated room you can sit in during January.
Three structures get pitched at the same patio, and they are routinely described as if they were competing versions of the same thing. They are not. They sit at different points on one spectrum — how much weather you are shutting out, and how much of the garden you are willing to stop calling a garden. Get that decision right and the planning route, the building regulations, the spans and the winter running costs all follow from it.
What is the difference between a pergola, a veranda and a glass room?
The roof decides the shelter. The sides decide whether you have built a room.
A louvred pergola has a roof of rotating aluminium blades. Open them and you have an open structure with sky overhead. Close them and the blades seal against each other to form a solid, water-shedding roof. The sides stay open unless you add infills.
A fixed-roof veranda — what the glazing trade usually calls a lean-to roof — is a permanent glazed or solid roof fixed against the house wall and carried on posts at the front. It is always covered. You cannot open it to the sky, and you never have to remember to close it.
A glass room encloses the space: glazed roof, glazed walls, doors that shut. At that point you have made a room, and it is treated like one — by the weather, by the building regulations, and by your heating bill.
| Louvred pergola | Fixed-roof veranda | Glass room | |
|---|---|---|---|
| Roof | Rotating aluminium blades | Fixed glazed or solid panels | Fixed glazed panels |
| Sides | Open, infills optional | Open | Fully glazed and sealed |
| Shelter from rain | Yes, once closed | Yes, always | Yes, always |
| Shelter from wind | Only with side infills | Limited | Complete |
| Open sky on demand | Yes | No | No |
| Usable in winter | With heating and side infills | Marginally, with heating | Yes, if heated |
| Counts as an extension | No | No | Usually yes |
| Typical consent question | Outbuilding rules | Outbuilding or extension rules | Extension rules |
The last two rows are where most of the real difference lives, and they are the two nobody asks about until the drawings are finished.
Do you need planning permission for a pergola, a veranda or a glass room?
A freestanding pergola usually falls under permitted development for outbuildings in England, provided it is no more than 2.5 metres high within two metres of a boundary, sits behind the principal elevation, and keeps total building coverage under half the land around the original house. A glass room is treated as an extension, with its own separate limits.
Permitted development for outbuildings allows “a maximum height of 2.5 metres in the case of a building, enclosure or container within two metres of a boundary of the curtilage of the dwellinghouse”, with no more than half the land around the original house covered by additions or other buildings, and nothing forward of the wall forming the principal elevation. That sits comfortably within the proportions of a typical louvred pergola on a rear terrace.
A glass room attached to the house follows the extension rules instead. A single-storey rear extension cannot extend beyond the rear wall of the original house by more than four metres on a detached house or three metres on any other house, cannot exceed four metres in height, and where it comes within two metres of the boundary the eaves height cannot exceed three metres.
The word “veranda” is a planning trap
Here is the detail that catches people out. Both sets of permitted development rights — outbuildings and extensions — explicitly exclude “verandas, balconies or raised platforms”. The Order sets a numeric test for a raised platform, which must not exceed 0.3 metres in height. It does not define a veranda at all.
In practice the exclusion is aimed at overlooking: structures that let people stand or sit above ground level and see into a neighbour’s garden. A covered patio at ground level is a very different proposition from a raised veranda. But because the term is undefined, whether your particular structure is caught is a question for your local planning authority, not for a supplier — and it is worth asking them before anyone orders anything.
Two constraints override all of the above. Within the curtilage of a listed building, any outbuilding requires planning permission. And on designated land — conservation areas, national parks, Areas of Outstanding Natural Beauty and World Heritage Sites — buildings at the side of a property require permission, with tighter area limits further from the house. A good share of our own work sits in exactly those areas, which is why we treat consent as the first conversation rather than the last.
Which of them triggers building regulations?
Open structures usually escape building regulations; enclosed ones usually do not. Schedule 2 of the Building Regulations 2010 exempts a detached single-storey building under 30 square metres containing no sleeping accommodation, and exempts a conservatory, covered yard or covered way, or a carport open on at least two sides, at ground level and under 30 square metres.
Class 6 covers detached single-storey buildings with a floor area not exceeding 30 square metres and no sleeping accommodation. The condition attached is the interesting one: the building must either stand at least one metre from the boundary, or be constructed substantially of non-combustible material. Aluminium is a non-combustible material. Timber is not. A freestanding aluminium structure tight against a boundary therefore sits on the right side of that condition in a way an equivalent timber one does not — a genuinely practical difference on a narrow urban plot.
Class 7 covers ground-level extensions, exempting “a conservatory, porch, covered yard or covered way” and “a carport open on at least two sides”, again up to 30 square metres. An attached pergola or veranda open on at least two sides falls naturally into that shape.
A glass room can also be exempt, but only if it meets every condition: built at ground level, under 30 square metres, single storey, separated from the house by external-quality walls, doors or windows, with an independent heating system on separate temperature and on/off controls, and with glazing and fixed electrical installations that comply. Remove the doors between house and glass room — the very thing most people want to do — and you have created a structural opening that requires building regulations approval regardless of whether the room itself is exempt.
Do louvred pergola roofs actually keep the rain out?
Yes — when the roof is engineered as a drainage system rather than as a set of blades. The blades seal against rubber gaskets when closed, and the water they shed has to be caught and taken away, which is what the perimeter beams and the hollow posts are for. On the systems we supply, the gutter is integrated into the frame and the downpipes run inside the posts, so there is no external plumbing bolted onto a structure you chose for its clean lines.
The volumes are easy to underestimate. One millimetre of rain falling on one square metre of roof is one litre of water. A 6 metre by 4 metre pergola is 24 square metres, so every millimetre of rainfall puts 24 litres onto that roof. A wet afternoon is measured in hundreds of litres, and all of it arrives at the posts. That is the part cheaper structures get wrong — not the blades, the water.
A rain sensor closes the roof automatically when the first drops land, which matters more than it sounds: the failure mode for a manual structure is not that it cannot shed water, it is that nobody was home to close it. A fixed glazed roof has no such failure mode. It is always closed, it always sheds to a gutter, and there is nothing to remember — which is the whole argument for a glazed lean-to roof over an adjustable one.
How far can each one span without a post in the middle?
Span is where these structures separate. Our louvred pergola runs to a single bay of 6 metres by 4 metres with no mid-post, and our Sheerline S3 lean-to roof reaches a 4,500mm projection without a bolster on 135mm by 50mm rafters. Kit-market pergolas typically stop between 3 and 3.6 metres deep.
Depth is the number that decides whether the space is usable. At 3 metres deep you can put a table under cover, but not a table plus the room to walk around it. At 4 metres you get a dining setting and a seating area under one roof, which is the difference between a covered patio and an outdoor room. Mid-posts are the other quiet compromise: a post in the middle of a 6 metre run lands exactly where you want to walk, or exactly where the table wants to go.
For a glass room, span becomes a glazing question rather than a structural one, and that is where a manufacturer’s range starts to matter: the aluminium conservatory and orangery roof systems we fabricate take heavy-duty rafter and beam profiles for large spans, and the glazed walls beneath them can be slim-framed sliding doors rather than conventional frames.
Which one can you actually use in January?
An open pergola with the roof closed keeps rain and frost off you, but the air around you is outdoor air. Add side infills on the exposed elevations — sliding glass panels, zip screens or louvred panels — and a radiant heater, and it becomes usable on a cold clear evening. It does not become a room, and it should not be sold as one.
A fixed-roof veranda with open sides is a similar proposition with less flexibility: permanent cover, outdoor air, and no way to close down the windward side unless you add infills.
A glass room is the only one of the three that is genuinely a room in winter, and it earns that by being sealed and glazed properly. The glazing specification decides whether it is pleasant or punishing. Across the roof systems we supply, a standard 24mm double-glazed unit sits at approximately 1.4 W/m²K, an enhanced 28mm unit at approximately 1.1 W/m²K, and a high-performance 30mm unit at approximately 1.0 W/m²K. Solar-control and self-cleaning roof glass address the other half of the problem: a glazed roof that is comfortable in February can be unbearable in July if the glass was only specified for one of them.
A pergola extends the season. A glass room changes it, and takes on a room’s running costs and a room’s regulations in order to do so.
Can you start with a pergola and add glass later?
Yes, and for a lot of gardens it is the most sensible sequence — provided the structure was specified for it from the start. Adding glass to a frame engineered for it is straightforward; adding it to one that was not means starting again.
Side infills are made to measure per elevation: frameless sliding glass panels, motorised or manual zip screens, or louvred side panels that slide, fold, swing or stay fixed. Enclose one or two elevations and you have a sheltered outdoor room. Enclose the lot in glass and you have something very close to a garden room, without the foundations and the permanence of an extension.
The catch is that most pergola suppliers are not glazing companies. They will sell you a structure and a screen; the frameless sliding glass is somebody else’s product, fitted by somebody else and warranted by somebody else. We fabricate aluminium glazing in Slough and install it ourselves, which is why the glass-sided version of a louvred aluminium pergola is one job with one accountable party rather than a relay.
Where we install garden glazing
We have resolved 968 completed orders to a postcode district. The districts below are where that work is most concentrated. These are glazing installations across the whole product range rather than pergolas specifically — the louvred pergola range launched in September 2026. Coverage is nationwide; the clusters simply reflect where the density sits.
Maidenhead and Bray (SL6) — 21 installs
Our largest single district. The factory is in Slough, minutes away, which shortens every survey, remake and snagging visit. The Fisheries Estate at Bray is the premium riverside pocket here, and riverside plots bring their own constraints on where a structure can sit.
Windsor (SL4) — 19 installs
The Royal Borough applies unusual heritage rigour to anything within the Castle’s setting. In the rear gardens of listed and near-listed properties here, a new structure is a consent conversation before it is a design conversation.
Wimbledon (SW19) — 15 installs
Victorian and Edwardian villas under Merton’s conservation control. The dominant project shape is the side-return and rear extension, which is precisely where a covered terrace or a glazed room ends up competing with the extension itself for the same patch of garden.
Streatham Hill and Brixton (SW2) — 14 installs
Period London stock on relatively narrow plots. On most of these gardens the binding constraint is the 2.5 metre height limit within two metres of a boundary, not the floor area.
East Finchley, Finchley and Whetstone (N2, N20) — 12 and 7 installs
Inter-war and Edwardian family houses. The load-bearing local fact: in N2, Hampstead Garden Suburb Trust consent is statutory and separate from council planning. A homeowner needs both, and a supplier who does not know that will cost you months.
Esher, Cobham, Walton and Weybridge (KT10 to KT13) — 24 installs
Large individual houses, often on private estates with their own hours of restriction, gate protocols and vehicle-access rules. We work to those routinely, and for an estate manager that is the part that matters.
So which one should you choose?
- You want to use the garden more often, and still want it to feel like a garden. A louvred pergola: open overhead when it is fine, sealed when it is not, with the option to add glass sides later.
- You want reliable cover over one specific spot — a dining terrace, an outdoor kitchen, a route between doors — and never want to think about it again. A fixed-roof veranda or lean-to roof.
- You want another room, and are prepared for it to be one. A glass room, specified properly for both winter and summer, with the building regulations settled at the start.
The three are not really in competition. They answer three different questions, and almost everyone arrives already knowing which of the three they want — they have simply not been asked in those terms yet.
Tell us about your garden and we will tell you which one fits
Survey, design, manufacture and installation as one job, from our factory in Slough, with nationwide coverage. Send drawings or photographs and we will come back with a considered proposal.
